Liquid chromatography/electron capture atmospheric pressure chemical ionization/mass spectrometry: analysis of pentafluorobenzyl derivatives of biomolecules and drugs in the attomole range

Liquid chromatography-tandem mass spectrometry applications in endocrinology

Liquid chromatography-tandem mass spectrometry (LC-MS/MS) has been recognized as a primary methodology for the accurate analysis of endogenous steroid hormones in biological samples. This review focuses on the use of LC-MS/MS in clinical laboratories to assist with the diagnosis of diverse groups of endocrine and metabolic diseases. Described analytical methods use on-line and off-line sample preparation and analytical derivatization to enhance analytical sensitivity, specificity, and clinical utility. Advantages of LC-MS/MS as an analytical technique include high specificity, possibility to simultaneously measure multiple analytes, and the ability to assess the specificity of the analysis in every sample. All described analytical methods were extensively validated, utilized in routine diagnostic practice, and were applied in a number of clinical and epidemiological studies, including a study of the steroidogenesis in ovarian follicles.

Analysis of estrogens in serum and plasma from postmenopausal women: past present, and future

Previous studies have shown that the selection of women who are at high breast cancer risk for treatment with chemoprevention agents leads to an enhanced benefit/risk ratio. However, further efforts to implement this strategy will require the development of new models to predict the breast cancer risk of particular individuals. Postmenopausal women with elevated plasma or serum estrogens are at increased risk for breast cancer. Therefore, the roles of various enzymes involved in the biosynthesis of estrogens in postmenopausal women have been reviewed in detail. In addition, the potential genotoxic and/or proliferative effects of the different estrogen metabolites as risk factors in the etiology of breast cancer have been examined. Unfortunately, much of the current bioanalytical methodology employed for the analysis of plasma and serum estrogens has proved to be problematic. Major advances in risk assessment would be possible if reliable methodology were available to quantify estradiol and its major metabolites in the plasma or serum of postmenopausal women. High performance liquid chromatography (HPLC) coupled with radioimmunoassay (RIA) currently provides the most sensitive and best validated immunoassay method for the analysis of estrone and estradiol in serum samples from postmenopausal women. However, inter-individual differences in specificity observed with many other immunoassays have caused significant problems when interpreting epidemiologic studies of breast cancer. It is almost impossible to overcome the inherent assay problems involved in using RIA-based methodology, particularly for multiple estrogens. For reliable measurements of multiple estrogens in plasma or serum, it will be necessary to employ stable isotope dilution methodology in combination with liquid chromatography-tandem mass spectrometry (LC-MS/MS). Extremely high sensitivity can be obtained with pre-ionized estrogen derivatives when employed in combination with a modern triple quadrupole mass spectrometer and nanoflow LC. Using [(13)C(6)]-estrone as the internal standard it has proved possible to analyze estrone as its pre-ionized Girard T (GT) derivative in sub-fg (low amol) amounts on column. This suggests that in the future it will be possible to routinely conduct LC-MS assays of multiple estrogen metabolites in serum and plasma at even lower concentrations than the current lower limit of quantitation of 0.4pg/mL (1.6pmol/L). The ease with which the pre-ionization derivatization strategy can be implemented will make it possible to readily introduce high sensitivity stable isotope dilution methodology in laboratories that are currently employing LC-MS/MS methodology. This will help conserve important plasma and serum samples as it will be possible to conduct high sensitivity analyses using low sample volumes.

Stable-isotope dilution LC–MS for quantitative biomarker analysis

The ability to conduct validated analyses of biomarkers is critically important in order to establish the sensitivity and selectivity of the biomarker in identifying a particular disease. The use of stable-isotope dilution (SID) methodology in combination with LC–MS/MS provides the highest possible analytical specificity for quantitative determinations. This methodology is now widely used in the discovery and validation of putative exposure and disease biomarkers. This review will describe the application of SID LC–MS methodology for the analysis of small-molecule and protein biomarkers. It will also discuss potential future directions for the use of this methodology for rigorous biomarker analysis.

Steroid assays in paediatric endocrinology

Most steroid disorders of the adrenal cortex come to clinical attention in childhood and in order to investigate these problems, there are many challenges to the laboratory which need to be appreciated to a certain extent by clinicians. The analysis of sex steroids in biological fluids from neonates, over adrenarche and puberty present challenges of specificities and concentrations often in small sample sizes. Different reference ranges are also needed for interpretations. For around 40 years, quantitative assays for the steroids and their regulatory peptide hormones have been possible using immunoassay techniques. Problems are recognised and this review aims to summarise the benefits and failings of immunoassays and introduce where tandem mass spectrometry is anticipated to meet the clinical needs for steroid analysis in paediatric endocrine investigations. It is important to keep a dialogue between clinicians and the laboratory, especially when any laboratory result does not make sense in the clinical investigation.

Comparison of electron capture-atmospheric pressure chemical ionization and electrospray ionization for the analysis of gambogic acid and its main circulating metabolite in dog plasma

Gambogic acid (GA), a promising anticancer candidate, is a polyprenylated xanthone abundant in the resin of Garcinia morella and Garcinia hanburyi. Electron capture-atmospheric pressure chemical ionization (EC- APCI) and electrospray ionization (ESI) techniques, both in the negative ion mode, were evaluated regarding ionization, fragmentation patterns and sensitivity for simultaneous liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis of GA and its main circulating metabolite, 10-hydroxygambogic acid (10-OHGA) in dog plasma. Both analytes underwent extensive in-source fragmentation in EC-APCI, which was not desirable for reliable quantification of these analytes, whereas the substitution of ESI for EC-APCI almost eliminated the source instability of both analytes. Negative ion ESI was, therefore, chosen for the development of an LC-MS/MS method for simultaneous determination of these analytes. After protein precipitation by acetonitrile, all analytes were separated on a Luna C18 HST column (50 x 2.0 mm i.d., 2.5 microm) with a mobile phase of 20 mmol L(-1) ammonium acetate water solution containing 0.2% acetic acid:acetonitrile (18:82, v/v). The detection was performed on a tandem mass spectrometer using selective reaction monitoring mode. Calibration curves were linear over the range of 10-6000 ng mL(-1) for GA and 3-2000 ng mL(-1) for 10-OHGA. The method was successfully applied to the pharmacokinetics study of GA injection in six beagle dogs.

Atmospheric pressure ion sources

This review of atmospheric pressure ion sources discusses major developments that have occurred since 1991. Advances in the instrumentation and understanding of the key physical principles are the primary focus. Developments with electrospray and atmospheric pressure chemical ionization and variations encompassing adaptations for surface analysis, ambient air analysis, high throughput, and modification of the ionization mechanism are covered. An important and limiting consequence of atmospheric pressure chemical ionization, chemical noise, is discussed as is techniques being employed to ameliorate the problem. Ion transfer and transport from atmospheric pressure into deep vacuum is an area undergoing constant improvement and refinement so is given considerable consideration in this review.

Quantification of F2-isoprostanes as a reliable index of oxidative stress in vivo using gas chromatography-mass spectrometry (GC-MS) method

Free radical-induced lipid peroxidation has been implicated in a number of human diseases including atherosclerosis, cancer, and neurodegenerative diseases. F(2)-Isoprostanes (IsoPs) are isomers of prostaglandin PGF(2alpha) that are generated in vivo from the free radical-initiated peroxidation of arachidonic acid independent of cyclooxygenase enzymes. Since the discovery of the IsoPs in the early 1990s, a large body of evidence has been accumulated to indicate that quantification of these F(2)-IsoPs represents the most reliable biomarker to assess oxidative stress in vivo. A variety of analytical approaches have been developed for the quantification of these novel compounds; these methods include mass spectrometry (MS) detection coupled to gas chromatography (GC) or liquid chromatography (LC) separation, and detection using immunological approaches. This article summarizes our current methodology to quantify F(2)-IsoPs in biological fluids and tissues using GC-MS. This method includes solid-phase extraction (SPE), thin-layer chromatography (TLC) purification, chemical derivatization, and MS detection using negative ion chemical ionization (NICI) coupled with GC. The protocol described herein has been optimized and validated to provide the best sensitivity and selectivity for quantification of F(2)-IsoPs from a variety of biological sources.

Targeted quantitative analysis of eicosanoid lipids in biological samples using liquid chromatography-tandem mass spectrometry

The eicosanoids are a large family of arachidonic acid oxidation products that contain 20 carbon atoms. Cyclooxygenase (COX)-derived eicosanoids have important roles as autacoids involved in the regulation of cardiovascular function and tumor progression. Lipoxygenase (LO)-derived eicosanoids have been implicated as important mediators of inflammation, asthma, cardiovascular disease and cancer. Cytochrome P-450 (P450)-derived eicosanoids are both vasodilators and vasoconstrictors. There is intense interest in the analysis of reactive oxygen species (ROS)-derived isoprostanes (isoPs) because of their utility as biomarkers of oxidative stress. Enzymatic pathways of eicosanoid formation are regioselective and enantioselective, whereas ROS-mediated eicosanoid formation proceeds with no stereoselectivity. Many of the eicosanoids are also present in only pM concentrations in biological fluids. This presents a formidable analytical challenge because methodology is required that can separate enantiomers and diastereomers with high sensitivity and specificity. However, the discovery of atmospheric pressure ionization (API)/MS methodology of electrospray ionization (ESI), atmospheric pressure chemical ionization (APCI), and electron capture (EC) APCI has revolutionized our ability to analyze endogenous eicosanoids. LC separations of eicosanoids can now be readily coupled with API ionization, collision induced dissociation (CID) and tandem MS (MS/MS). This makes it possible to efficiently conduct targeted eicosanoid analyses using LC-multiple reaction motoring (MRM)/MS. Several examples of targeted eicosanoid lipid analysis using conventional LC-ESI/MS have been discussed and some new data on the analysis of eicosanoids using chiral LC-ECAPCI/MS has been presented.

Targeted chiral lipidomics analysis of bioactive eicosanoid lipids in cellular systems

We have developed a targeted lipidomics approach that makes it possible to directly analyze chiral eicosanoid lipids generated in cellular systems. The eicosanoids, including prostaglandins (PGs), thromboxanes (TXs), leukotrienes (LTs) and alcohols (HETEs), have been implicated as potent lipid mediators of various biological processes. Enzymatic formations of eicosanoids are regioselective and enantioselective, whereas reactive oxygen species (ROS)-mediated formation proceeds with no stereoselectivity. To distinguish between enzymatic and non-enzymatic pathways of eicosanoid formation, it is necessary to resolve enantiomeric forms as well as regioisomers. High sensitivity is also required to analyze the eicosanoid lipids that are usually present as trace amounts (pM level) in biological fluids. A discovery of liquid chromatography-electron capture atmospheric pressure chemical ionization/mass spectrometry (LCECAPCI/MS) allows us to couple normal phase chiral chromatography without loss of sensitivity. Analytical specificity was obtained by the use of collision-induced dissociation (CID) and tandem MS (MS/MS). With combination of stable isotope dilution methodology, complex mixtures of regioisomeric and enantiomeric eicosanoids have been resolved and quantified in biological samples with high sensitivity and specificity. Targeted chiral lipidomics profiles of bioactive eicosanoid lipids obtained from various cell systems and their biological implications have been discussed.

Mapping DNA adducts of mitomycin C and decarbamoyl mitomycin C in cell lines using liquid chromatography/ electrospray tandem mass spectrometry

The antitumor antibiotic and cancer chemotherapeutic agent mitomycin C (MC) alkylates and crosslinks DNA, forming six major MC-deoxyguanosine adducts of known structures in vitro and in vivo. Two of these adducts are derived from 2,7-diaminomitosene (2,7-DAM), a nontoxic reductive metabolite of MC formed in cells in situ. Several methods have been used for the analysis of MC-DNA adducts in the past; however, a need exists for a safer, more comprehensive and direct assay of the six-adduct complex. Development of an assay, based on mass spectrometry, is described. DNA from EMT6 mouse mammary tumor cells, Fanconi Anemia-A fibroblasts, normal human fibroblasts, and MCF-7 human breast cancer cells was isolated after MC or 10-decarbamoyl mitomycin C (DMC) treatment of the cells, digested to nucleosides, and submitted to liquid chromatography electrospray-tandem mass spectrometry. Two fragments of each parent ion were monitored ("multiple reaction monitoring"). Identification and quantitative analysis were based on a standard mixture of six adducts, the preparation of which is described here in detail. The lower limit of detection of adducts is estimated as 0.25 pmol. Three initial applications of this method are reported as follows: (i) differential kinetics of adduct repair in EMT6 cells, (ii) analysis of adducts in MC- or DMC-treated Fanconi Anemia cells, and (iii) comparison of the adducts generated by treatment of MCF-7 breast cancer cells with MC and DMC. Notable results are the following: Repair removal of the DNA interstrand cross-link and of the two adducts of 2,7-DAM is relatively slow; both MC and DMC generate DNA interstrand cross-links in human fibroblasts, Fanconi Anemia-A fibroblasts, and MCF-7 cells as well as EMT6 cells; and DMC shows a stereochemical preference of linkage to the guanine-2-amino group opposite from that of MC.

Simultaneous determination of tetrahydrocortisol, allotetrahydrocortisol and tetrahydrocortisone in human urine by liquid chromatography-electrospray ionization tandem mass spectrometry

Simultaneous quantification method of three major metabolites of cortisone and cortisol, tetrahydrocortisol, allotetrahydrocortisol and tetrahydrocortisone by liquid chromatography-electrospray ionization tandem mass spectrometry (LC-ESI-MS/MS) was investigated in a positive mode using a recently developed picolinyl derivatization. Conversion of each steroid into the corresponding picolinyl derivatives (1b, 2b or 3b) was performed by mixed anhydride method using picolinic acids and 2-methyl-6-nitrobenzoic anhydride. Derivatization proceeded smoothly to afford the corresponding 3, 21-dipicolinyl derivatives. Positive ion-ESI mass spectra of the picolinyl derivatives were dominated by an appearance of [M+H](+) as base peaks in all cases. The picolinyl derivatives provided 15 to 80-fold higher ESI response in the LC-ESI-MS/MS (selected reaction monitoring: SRM) when compared to those of underivatized molecules in a positive LC-ESI mode. The use of the picolinyl ester, solid-phase extraction, and deuterium labeled internal standards enabled the concentrations of these metabolites in human urine to be determined simultaneously by LC-ESI-MS/MS (SRM) with a small sample volume of less than 1microl urine.

Stable isotope-coded quaternization for comparative quantification of estrogen metabolites by high-performance liquid chromatography-electrospray ionization mass spectrometry

A fast and sensitive LC-ESI-MS method is described for the comparative quantification of 16 estrogen metabolites based on the derivatization of estrogens with a novel derivatizing reagent, N-methyl-nicotinic acid N-hydroxysuccinimide ester (C1-NA-NHS). The process introduces a quaternary amine to the analytes, making the analytes permanently charged regardless of the pH of the high-performance liquid chromatography (HPLC) mobile phase. This quaternization resulted in a highly efficient separation of 16 estrogen metabolites in 7 min at a detection level below 1 ng/mL. By using a deuterated derivatizing reagent (C1-d(3)-NA-NHS), a complete set of deuterated standards was utilized and used as internal standards in a comparative quantification and recovery study, demonstrating acceptable results over a wide concentration range. A pooled breast cancer serum sample was analyzed using the described method, and 15 estrogens were detected in the range of 80-530 pg/mL.

Determination of serum methylmalonic acid by alkylative extraction and liquid chromatography coupled to tandem mass spectrometry

Despite the new advances in bioanalytical techniques, the analysis of low-molecular-weight organic acids in complex matrices is still a challenge. Although new strategies applying liquid chromatography-tandem mass spectrometry (LC-MS/MS) seem to be promising, sample preparation methodologies hamper its application in most clinical laboratories. The quantitation of methylmalonic acid (MMA) in biological matrices is an emblematic example due to its low concentration, the need for derivatization to increase its molecular weight, and the presence of the physiologically more abundant isomer succinic acid. Here we present a new strategy for rapid and sensitive MMA quantitation by combining alkylative extraction and LC-MS/MS. Alkylative extraction conditions were optimized to allow endogenous detection of MMA using only 50 microL of serum with a short sample preparation procedure. The formation of a unique ion from the MMA dipentafluorobenzyl derivative in negative atmospheric pressure chemical ionization (APCI) allowed its detection with high sensitivity and with no interference from succinic acid, a more abundant physiologically present isomer.

Analysis of steroidal estrogens as pyridine-3-sulfonyl derivatives by liquid chromatography electrospray tandem mass spectrometry

Sulfonyl chlorides substituted with functional groups having high proton affinity can serve as derivatization reagents to enhance the sensitivity for steroidal estrogens in liquid chromatography electrospray ionization tandem mass spectrometry (LC-ESI-MS/MS). The most commonly used reagent for derivatization of estrogens for LC-ESI-MS/MS is dansyl chloride. In this study, we compared dansyl chloride, 1,2-dimethylimidazole-4-sulfonyl (DMIS) chloride, pyridine-3-sulfonyl (PS) chloride, and 4-(1H-pyrazol-1-yl)benzenesulfonyl (PBS) chloride for derivatization of 17beta-estradiol (E2) prior to LC-ESI-MS/MS. The product ion spectra of the dansyl and DMIS derivatives were dominated by ions representing derivatization reagent moieties. In contrast, the product ion spectrum of the PS derivative of E2 and, to a lesser extent, the PBS derivative, showed analyte-specific fragment ions. Derivatization with PS chloride was therefore chosen for further investigation. The product ion spectrum of the PS derivative of E2 showed intense ions at m/z 272, assigned to the radical E2 cation, and at m/z 350, attributed to the loss of SO(2) from the [M+H](+) ion. Third-stage mass spectrometry of the PS derivative of E2 with isolation and collisional activation of the m/z 272 ion resulted in steroid C and D ring cleavages analogous to those observed in electron ionization mass spectrometry. The product ion spectra of the PS derivatives of estrone, 17alpha-ethinylestradiol, equilin, and equilenin showed similar estrogen-specific ions. Using derivatization with PS chloride, we developed an LC-ESI-MS/MS method with multiple reaction monitoring of primary and confirmatory precursor-to-product ion transitions for the determination of E2 in serum.

Chemical analysis of atherosclerotic plaque cholesterol combined with histology of the same tissue

Sensitive method for chemical analysis of free cholesterol (FC) and cholesterol esters (CE) was developed. Mouse arteries were dissected and placed in chloroform-methanol without tissue grinding. Extracts underwent hydrolysis of cholesteryl esters and derivatization of cholesterol followed by liquid chromatography/mass spectrometry (LC/MS/MS) analysis. We demonstrated that FC and CE could be quantitatively extracted without tissue grinding and that lipid extraction simultaneously worked for tissue fixation. Delipidated tissues can be embedded in paraffin, sectioned, and stained. Microscopic images obtained from delipidated arteries have not revealed any structural alterations. Delipidation was associated with excellent antigen preservation compatible with traditional immunohistochemical procedures. In ApoE(-/-) mice, LC/MS/MS revealed early antiatherosclerotic effects of dual PPARalpha,gamma agonist LY465606 in brachiocephalic arteries of mice treated for 4 weeks and in ligated carotid arteries of animals treated for 2 weeks. Reduction in CE and FC accumulation in atherosclerotic lesions was associated with the reduction of lesion size. Thus, a combination of LC/MS/MS measurements of CE and FC followed by histology and immunohistochemistry of the same tissue provides novel methodology for sensitive and comprehensive analysis of experimental atherosclerotic lesions.

Targeted chiral lipidomics analysis by liquid chromatography electron capture atmospheric pressure chemical ionization mass spectrometry (LC-ECAPCI/MS)

The corona discharge used to generate positive and negative ions under conventional atmospheric pressure chemical ionization (APCI) conditions also provides a source of low-energy gas-phase electrons. This is thought to occur by displacement of electrons from the nitrogen sheath gas. Therefore, suitable analytes can undergo electron capture in the gas phase in a manner similar to that observed for gas chromatography/electron capture negative chemical ionization/mass spectrometry (MS). This technique, which has been named electron-capture APCI (ECAPCI)/MS, mass spectrometry provides an increase in sensitivity of two orders of magnitude when compared with conventional APCI methodology. It is a simple procedure to tag arachidonic acid- and linoleic acid-derived oxidized lipids with an electron-capturing group such as the pentafluorobenzyl (PFB) moiety before analysis. PFB derivatives have previously been used as electron-capturing derivatives because they undergo dissociative electron capture in the gas phase to generate negative ions through the loss of a PFB radical. A similar process occurs under ECAPCI conditions. By monitoring the negative ions that are formed, it is possible to obtain extremely high sensitivity for PFB derivatives of oxidized lipids derived from arachidonic and linoleic acid. A combination of stable isotope dilution methodology and chiral liquid chromatography-ECAPCI/MS makes it possible to resolve and quantify complex mixtures of regioisomeric and enantiomeric oxidized lipids.

New techniques to detect oxidative stress markers: mass spectrometry-based methods to detect isoprostanes as the gold standard for oxidative stress in vivo

Free radical-induced lipid oxidation under oxidative stress has been implicated in a number of human diseases. Isoprostanes (IsoPs), isomers of prostaglandins, are one of the major classes of oxidation products derived from this oxidation process. Measurement of the levels of IsoPs by Mass Spectrometry-based methods has become the "gold standard" biomarker of oxidative stress in vivo. Significant advances have been made in understanding this important pathway of lipid peroxidation since the discovery of IsoP formation in vivo 18 years ago. Studies from our laboratory and others are discussed that have provided insights into the mechanism of formation. Furthermore, new independent studies have demonstrated that IsoPs are the most reliable available marker of lipid peroxidation in vivo, and recent work examining IsoP formation has provided valuable information about the pathogenesis of numerous human diseases. Thus, the complexity of the IsoP pathway has expanded, providing novel insights into mechanisms of lipid peroxidation in vivo and allowing investigators to explore the role of oxidative stress in human disease.

Use of novel picolinoyl derivatization for simultaneous quantification of six corticosteroids by liquid chromatography-electrospray ionization tandem mass spectrometry

Simultaneous quantification method of six corticosteroids, cortisone, cortisol, cortexolone, corticosterone, dehydrocorticosterone and deoxycorticosterone, by LC-electrospray ionization (ESI)-MS in a positive mode using novel picolinoyl derivatization was investigated. Conversion of each corticosteroid into the corresponding picolinoyl derivative was performed by mixed anhydride method using picolinic acids and 2-methyl-6-nitrobenzoic anhydride. Derivatization proceeded smoothly to afford the corresponding 21-monopicolinoyl derivatives. Positive ion-ESI mass spectra of the picolinoyl derivatives were dominated by the appearance of [M+H](+) as base peaks. The picolinoyl derivatives provided 5-10 times higher ESI response in the LC-ESI-MS-selected reaction monitoring (SRM) when compared to those of underivatized molecules in a positive LC-ESI-MS mode. The use of the picolinoyl ester, solid-phase extraction, and deuterium labeled internal standards enabled to determine the concentrations of these corticosteroids in human saliva simultaneously by LC-ESI-MS-SRM.

Cyclooxygenase-2-mediated metabolism of arachidonic acid to 15-oxo-eicosatetraenoic acid by rat intestinal epithelial cells

Rat intestinal epithelial cells that permanently express the cyclooxygenase-2 (COX-2) gene (RIES cells) were used to investigate COX-2-mediated arachidonic acid (AA) metabolism. A targeted chiral lipidomics approach was employed to quantify AA metabolites that were secreted by the cells into the culture media. When intact RIES cells were treated with calcium ionophore A-23187 (1 microM) for 1 h, 11-(R)-hydroxyeicosatetraenoic acid (HETE) was the most abundant metabolite, followed by prostaglandin (PG) E 2, 15-(S)-HETE, 15-oxo-eicosatetraenoic acid (ETE), and 15-(R)-HETE. Incubation for a further 23 h after the calcium ionophore was removed resulted in a substantial increase in PGE 2 concentrations while HETE and 15-oxo-ETE concentrations decreased to almost undetectable levels. A similar metabolic profile was observed when RIES cells were treated with increasing concentrations of AA for 24 h. Incubation of the RIES cells with 10 microM AA revealed that maximal concentrations of 11-(R)-HETE, 15-(S)-HETE, and 15-oxo-ETE occurred after 10 min of incubation when the 15-( S)-HETE concentrations were approximately twice that of PGE 2. There was a gradual decrease in the concentrations of HETE and 15-oxo-ETE over time, whereas PGE 2 concentrations increased steadily until they reached a maximum after 24 h of incubation. The ratio of PGE 2 to 15-(S)-HETE was then approximately 20:1. 15-(S)-HETE and 15-oxo-ETE concentrations declined in the cell media during prolonged incubations with pseudo-first-order rate constants of 0.0121 and 0.0073 min(-1), respectively. 15-(S)-HETE was shown to undergo metabolism primarily to 15-oxo-ETE, which was further metabolized to a glutathione (GSH) adduct. The GSH adduct of 15-oxo-ETE was further metabolized in the extracellular milieu to a cysteinylglycine adduct. Thus, we have established for the first time that 15-oxo-ETE can be formed biosynthetically from AA, that 15-(S)-HETE is its immediate precursor, and that 15-oxo-ETE forms a GSH adduct. For ionophore-A-23187-stimulated cells and at early time points for AA-stimulated cells, 11-(R)-HETE was the major eicosanoid to be secreted into the media. Adding increasing concentrations of AA to cells in culture made it possible to estimate with surprising accuracy endogenous eicosanoid production using regression analyses. Thus, after 24 h in the absence of added AA, 11-(R)-HETE and 15-(R)-HETE were estimated to be present at concentrations close to the detection limit of our very sensitive assay. These data further highlight the importance of endogenous COX-2-mediated lipid peroxidation and illustrate the necessity to monitor eicosanoid formation from endogenous stores of AA in cell culture experiments.

Identification of the Peroxidation Products of 13-Hydroxy-γ-linolenate and 15-Hydroxyarachidonate: Mechanistic Studies on the Formation of Leukotriene-like Diols

Monohydroxy-gamma-linolenates and arachidonates were oxidized in the presence of alpha-tocopherol and free radical initiators at 37 degrees C. The dihydroxylinolenate products were analyzed and identified by use of a combination of liquid chromatography, mass spectrometry, and NMR techniques. A mechanism for the formation of the dihydroxylinolenates is proposed based on product analysis of oxidations using varied concentrations of alpha-tocopherol. The mechanism for monohydroxyarachidonate oxidation is the same as that of monohydroxylinolenates. However, arachidonate diol analysis is more complicated because of the formation of additional regioisomers that are a result of the parent arachidonate possessing multiple bisallylic hydrogens.

Negative ion-atmospheric pressure photoionization: electron capture, dissociative electron capture, proton transfer, and anion attachment

To better guide the development of liquid chromatography/electron capture-atmospheric pressure photoionization-mass spectrometry (LC/EC-APPI-MS) in analysis of low polarity compounds, the ionization mechanism of 19 compounds was studied using dopant assisted negative ion-APPI. Four ionization mechanisms, i.e., EC, dissociative EC, proton transfer, and anion attachment, were identified as being responsible for the ionization of the studied compounds. The mechanisms were found to sometimes compete with each other, resulting in multiple ionization products from the same molecule. However, dissociative EC and proton transfer could also combine to generate the same [M - H](-) ions. Experimental evidence suggests that O(2)(-*), which was directly observed in the APPI source, plays a key role in the formation of [M - H](-) ions by way of proton transfer. Introduction of anions more basic than O(2)(-*), i.e., C(6)H(5)CH(2)(-), into the APPI source, via addition of di-tert-butyl peroxide in the solvent and/or dopant, i.e., toluene, enhanced the deprotonation ability of negative ion-APPI. Although the use of halogenated solvents could hinder efficient EC, dissociative EC, and proton transfer of negative ion-APPI due to their EC ability, the subsequently generated halide anions promoted halide attachment to compounds that otherwise could not be efficiently ionized. With the four available ionization mechanisms, it becomes obvious that negative ion-APPI is capable of ionizing a wider range of compounds than negative ion chemical ionization (NICI), negative ion-atmospheric pressure chemical ionization (negative ion-APCI) or negative ion-electrospray ionization (negative ion-ESI).

Highly sensitive determination of estrone and estradiol in human serum by liquid chromatography-electrospray ionization tandem mass spectrometry

A highly sensitive and specific quantification method of estrone and estradiol in human serum was described based upon the use of picolinoyl derivatization and liquid chromatography-electrospray ionization mass spectrometry (LC-ESI-MS) in a positive mode. Estrogens were treated with picolinoyl chloride hydrochloride or picolinic acid and 2-methyl-6-nitrobenzoic anhydride followed by a solid-phase extraction with ODS cartridge. Picolinoyl derivatization proceeded quantitatively even in a microscale, and the picolinoyl esters provided simple positive ESI-mass spectra showing [M+H](+) as base peaks for these estrogens. The picolinoyl derivatives of these estrogens showed 100-fold higher detection response compared to underivatized intact molecules by LC-ESI-MS (selected reaction monitoring). Using this derivatization, estrogens spiked in the charcoal treated human serum samples were analyzed with limit of quantification (LOQ), intra-day accuracy and precision of 1.0pg/ml, 96.0% and 9.9% for estrone, and 0.5pg/ml, 84.4% and 12.8% for estradiol, respectively. Estrone and estradiol added to the crude serum samples were recovered with comparable LOQ and accuracy obtained for the charcoal treated serum samples as well.

Surface desorption atmospheric pressure chemical ionization mass spectrometry for direct ambient sample analysis without toxic chemical contamination

Ambient mass spectrometry, pioneered with desorption electrospray ionization (DESI) technique, is of increasing interest in recent years. In this study, a corona discharge ionization source is adapted for direct surface desorption chemical ionization of compounds on various surfaces at atmospheric pressure. Ambient air, with about 60% relative humidity, is used as a reagent to generate primary ions such as H(3)O(+), which is then directed to impact the sample surface for desorption and ionization. Under experimental conditions, protonated or deprotonated molecules of analytes present on various samples are observed using positive or negative corona discharge. Fast detection of trace amounts of analytes present in pharmaceutical preparations, viz foods, skins and clothes has been demonstrated without any sample pretreatment. Taking the advantage of the gasless setup, powder samples such as amino acids and mixtures of pharmaceutical preparations are rapidly analyzed. Impurities such as sudan dyes in tomato sauce are detected semiquantitatively. Molecular markers (e.g. putrescine) for meat spoilage are successfully identified from an artificially spoiled fish sample. Chemical warfare agent stimulants, explosives and herbicides are directly detected from the skin samples and clothing exposed to these compounds. This provides a detection limit of sub-pg (S/N > or = 3) range in MS2. Metabolites and consumed chemicals such as glucose are detected successfully from human skins. Conclusively, surface desorption atmospheric pressure chemical ionization (DAPCI) mass spectrometry, without toxic chemical contamination, detects various compounds in complex matrices, showing promising applications for analyses of human related samples.

Highly sensitive assay of HMG-CoA reductase activity by LC-ESI-MS/MS

We have developed a new sensitive and specific nonradioisotope assay method to measure the activity of HMG-CoA reductase, the rate-controlling enzyme in the cholesterol biosynthetic pathway. This method was based upon a stable isotope dilution technique by liquid chromatography-tandem mass spectrometry using electrospray ionization in positive mode. Mevalonic acid, the product of HMG-CoA reductase, was converted to mevalonolactone (MVL) in an incubation mixture, extracted by a salting-out procedure, derivatized into the mevalonyl-(2-pyrrolidin-1-yl-ethyl)-amide, and then purified using a disposable silica cartridge. The resulting mevalonylamide was quantified by selected reaction monitoring using the positive electrospray ionization mode. The detection limit of this mevalonylamide was found to be 240 amol (signal-to-noise ratio=3), approximately 833 times more sensitive than that of MVL measured by a conventional radioisotope (RI) method (200 fmol). The variances between sample preparations and between measurements by this method were analyzed by one-way layout and calculated to be 3.2% and 1.8%, respectively. The recovery experiments were performed using incubation mixtures spiked with 0.77-2.31 nmol MVL/mg protein and were validated by a polynomial equation. These results showed that the estimated concentration within a 95% confidence limit was 0.47+/-0.07 nmol/mg protein, which coincided completely with the observed X0 nmol/mg protein with a mean recovery of 94.6%. This method made it possible to measure HMG-CoA reductase activity with a high degree of reproducibility and reliability, and especially with sensitivity superior to that of the conventional RI method.

Liquid chromatography-tandem mass spectrometry analysis of the DNA adducts of aristolochic acids

Electrophilic attack of aristolactam-nitrenium ion by the C7 position to the exocyclic amino group in the DNA bases led to the formation of the major adducts. In this study, liquid chromatography coupled with electrospray ionization tandem mass spectrometry was applied to the study of DNA adducts of aristolochic acid (AA). When DNA (bases and CT-DNA) was incubated with AA, dG-AAI, dG-AAII, dA-AAI, dA-AAII, dC-AAI, and dC-AAII were detected and characterized. The dC adducts of AA were identified for the first time. The soft ionization technology allowed detection of the intact DNA adducts. High-resolution MS and MS-MS capabilities of a quadrupole time-of-flight mass spectrometer were shown to be efficient for DNA adducts analysis. DNA-AA adducts showed characteristic fragmentation patterns in MS-MS analysis. The dissociative loss of 116 Da from the DNA-AA adducts, which resulted from internal hydrogen transfer and cleavage at the C-N glycosidic bond, provided a characteristic fragment for the structural elucidation.

Trace determination of steroids causing age-related diseases using LC/MS combined with detection-oriented derivatization

With the rapid shift to an aging society in Japan, age-related diseases, such as osteoporosis, dementia and cancer, are sharply increasing. The measurement of steroids related to these diseases in biological fluids and tissues is useful for elucidation of the nature, diagnosis and treatment of such diseases. LC/MS is considered to be the most promising method for this purpose due to its specificity and versatility, but it sometimes does not demonstrate the required sensitivity for trace amounts of steroids, because steroids have a rather low response using either electrospray ionization (ESI) or atmospheric pressure chemical ionization (APCI). To overcome this problem, the author developed detection-oriented derivatization procedures for steroids in LC/MS. For ESI-MS, introduction of a permanently charged moiety is effective. Based on this, 2-hydrazino-1-methylpyridine was developed and used in monitoring prostatic 5alpha-dihydrotestosterone, a good index for the follow-up of patients affected by prostate cancer under androgen deprivation therapy and salivary dehydroepiandrosterone, which is now often designated as an anti-aging hormone. A proton-affinitive Cookson-type reagent, 4-[2-(6,7-dimethoxy-4-methyl-3-oxo-3,4-dihydroquinoxalyl)ethyl]-1,2,4-triazoline-3,5-dione, was used for the determination of 1alpha-hydroxyvitamin D3 [1alpha(OH)D3], a synthetic prodrug of the active form of vitamin D3, in human plasma, and this new LC/positive-APCI-MS method enabled the pharmacokinetic study of 1alpha(OH)D3 in humans. Electron-capture APCI-MS based on derivatization with 2-nitro-4-trifluoromethylphenylhydrazine was used for the analysis of neurosteroids, which affect brain excitability through action at the neurotransmitter receptors. With this method, the stress-induced rapid biosynthesis of pregnane-type neurosteroids in rat brains was demonstrated.

Analysis of steroid estrogens in water using liquid chromatography/tandem mass spectrometry with chemical derivatizations

Even in trace amounts, estrogens such as 17beta-estradiol (E2), estrone (E1), estriol (E3), and 17alpha-ethinyl estradiol (EE2) may have adverse effects on humans and the aquatic ecosystem. Therefore, it is essential to be able to measure trace amounts of steroid estrogens in water. To date, most instruments are not sensitive enough to detect these chemicals in small samples of water. Sensitivity, however, may be improved by using appropriate derivatization reagents to modify the structures of these estrogens so that their ionization efficiency is increased, making them more detectable by liquid chromatography/mass spectrometry (LC/MS). This study uses dansyl chloride, 2-fluoro-1-methylpyridinium p-toluenesulfonate (FMPTS), and pentafluorobenzyl bromide (PFBBr) as derivatization reagents to react with the phenolic estrogens to make them more detectable in water. We also test how environmental matrices (wastewater effluent, river water, and drinking water) influence the detectability of these estrogens. Both qualitative and semi-quantitative comparisons of these derivatization methods were made. We found that dansyl chloride derivatives created signal intensities one or two orders of magnitude greater than those normally found in underivatized estrogen standards. The signals derived by FMPTS were analyte-dependent, and the products derived from E1, E2, and EE2 produced 2.19 to 12.1 times the signal intensity of underivatized E1, E2, and EE2. The product derived from E3 produced weaker signals than that produced by underivatized E3. The PFBBr derivatives produced signals that were as much as 5.8 times those found in the underivatized estrogens. When these derivatization methods were applied to river water, drinking water and effluents from a sewage treatment plant (STP), the different matrices were found to significantly suppress the signals if we used electrospray ionization, though this influence became less significant if we used atmospheric pressure chemical ionization. This study suggests that PFBBr derivatization can best be used for the detection of these estrogens in complex environmental matrices such as river water and STP effluents and that the dansyl chloride derivatization is best used for clean samples such as drinking water.

Electron capture atmospheric pressure photoionization mass spectrometry: analysis of fullerenes, perfluorinated compounds, and pentafluorobenzyl derivatives

An electron capture (EC) ionization mechanism has been found to be highly efficient in negative-ion atmospheric pressure photoionization (APPI) for the analysis of compounds with positive electron affinity (EA). Using negative-ion APPI, we first report the sensitive detection of natural electrophores with limited polarity, such as fullerenes and perfluorinated compounds, by mass spectrometry (MS). Using direct infusion on a quadrupole time-of-flight (QTOF) mass spectrometer, the limits of detection (LODs) for C(60) and perfluoromethylcyclohexane were determined to be 0.15 pg (0.2 fmol) and 1 femtoliter (fL) ( approximately 1.5 pg or 4.3 fmol), respectively. As the EA of the analyte increases, the detection sensitivity is enhanced. Making use of the accurate mass measurement capability of the QTOF mass spectrometer, we were able to investigate the elemental composition of the ions in each spectrum and attribute the observed high sensitivity to an EC-initiated ionization process. The proposed EC ionization mechanism is further supported by the observation of a dissociative EC reaction of pentafluorobenzyl (PFB)-derivatized phenols. The analysis of phenols by EC-APPI of their PFB derivatives resulted in very high sensitivity, with the lowest reported LOD of approximately 0.17 pg (0.5 fmol) being for 2,4-dinitrophenol. For future LC/EC-APPI-MS applications, the effect of additives and solvents on sensitivity was also tested and reported.

Synthesis of pyridine-carboxylate derivatives of hydroxysteroids for liquid chromatography-electrospray ionization-mass spectrometry

Synthesis and liquid chromatography-electrospray ionization-mass spectrometric (LC-ESI-MS) behaviors of the picolinoyl, 6-methylpicolinoyl, nicotinoyl, 2-methoxynicotinoyl and isonicotinoyl derivatives of the hydroxysteroids estrone, estradiol, 3beta-hydroxyandrost-5-en-17-one (dehydroepiandrosterone) and testosterone in positive mode were investigated. Each steroid was converted to the corresponding pyridine-carboxylate derivative by the acyl chloride method or the mixed anhydride method using the corresponding free acids and 2-methyl-6-nitrobenzoic anhydride; in each case, the latter method principally gave a better yield. The pyridine-carboxylate derivative of each steroid exhibited a clear single peak in liquid chromatography with a reversed phase column and CH(3)CN-0.1% CH(3)COOH as a mobile phase. The positive-ESI-mass spectra of the picolinoyl, 6-methylpicolinoyl and 2-methoxynicotinoyl derivatives showed a predominance of [M+H](+), whereas [M+H+CH(3)CN](+) was observed with high intensity in the nicotinoyl and isonicotinoyl derivatives. Even in the case of estradiol, with its two hydroxyl groups, a single charged ion of [M+H](+) or [M+H+CH(3)CN](+) was observed in the positive-ESI-mass spectrum of each derivative. The results revealed that picolinoyl derivatization is a simple and versatile method suitable for the sensitive and specific determination of hydroxysteroids by LC-ESI-MS (selected reaction monitoring).

Rapid measurement of deuterium-labeled long-chain fatty acids in plasma by HPLC-ESI-MS

Imbalanced fatty acid metabolism contributes significantly to the increased incidence of metabolic disorders. Isotope-labeled fatty acids (2H, 13C) provide efficient means to trace fatty acid metabolism in vivo. This study reports a new and rapid method for the quantification of deuterium-labeled fatty acids in plasma by HPLC-MS. The sample preparation protocol developed required only hydrolysis, neutralization, and quenching steps followed by high-performance liquid chromatography-electrospray ionization-mass spectrometry analysis in negative ion mode using single ion monitoring. Deuterium-labeled stearic acid (d7-C18:0) was synthesized to reduce matrix interference observed with d5 analog, which improved the limit of detection (LOD) significantly, depending on the products analyzed. Linearity > 0.999 between the LOD (100 nM) and 30 microM, accuracy > 90%, precision > 88%, and adequate recovery in the dynamic range were obtained for d7-C18:0 and d7-oleic acid (C18:1). Upon oral dosing of d7-C18:0 in rats, the parent compound and its desaturation and beta-oxidation products, d7-C18:1 and d7-C16:0, were circulating with a maximal concentration ranging from 0.6 to 2.2 microM, with significant levels of d7-fatty acids detected for up to 72 h.

Targeted quantitative analysis of fatty acids in atherosclerotic plaques by high sensitivity liquid chromatography/tandem mass spectrometry

The quantitative analysis of fatty acid composition in atherosclerotic plaques provides a way to monitor the underlying etiology of atherosclerosis. Previously, the method of choice for analyzing fatty acids in biological samples was gas chromatography/mass spectrometry (GC/MS); however, recent developments in electrospray ionization (ESI)/liquid chromatography (LC)/tandem mass spectrometry have made it a superior alternative. Previous research has largely focused on global analyses of intact lipids rather than more targeted analysis of the fatty acids themselves. We have now developed a targeted, stable isotope dilution LC-electrospray ionization/multiple reaction monitoring/MS method for the quantitative analysis of 10 fatty acids (myristic, palmitic, stearic, oleic, linoleic, alpha-linolenic, gamma-linolenic, arachidonic, eicosapentaenoic, and docosahexaenoic acids) using their trimethylaminoethyl ester (TMAE) derivatives to improve sensitivity. The method was validated, had a detection limit in the fmol range, and was used in the analysis of fatty acids in atherosclerotic plaques from carotid arteries.

Characterisation of a series of acetals/ketals of bis(2-nitrophenyl) ethanediol and bis(4,5-dimethoxy-2-nitrophenyl) ethanediol under APCI mass spectrometric conditions

A series acetals/ketals of aldehydes and ketones formed by the reaction of two photolabile protecting groups, bis(2-nitrophenyl) ethanediol and bis(4,5-dimethoxy-2-nitrophenyl) ethanediol (I and II, respectively), were analysed under EI, LSIMS, ESI and APCI conditions to obtain molecular weights as well as structural information. The EI and LSIMS techniques failed to give molecular weight information. The positive ESI yielded [M + H](+) ions only for I; however, with added Na(+) both I and II formed [M + Na](+) adducts. But upon decomposition, the [M + Na](+) ions yielded Na(+) ion as the only product ion. Similarly, under negative ion ESI conditions both I and II gave molecular weight information by forming adduct ions with halide anions (F(-), Cl(-), Br(-) and I(-)); however, they did not give structural information as they resulted in only the halide anion as the abundant fragment ion upon dissociation. All the compounds formed abundant M(-*) ions under negative ion APCI conditions, and their MS/MS spectra showed characteristic fragment ions; hence the acetals/ketals of I and II could be successfully characterized under negative ion APCI conditions.

Liquid chromatography-mass spectrometric assay of androstenediol in prostatic tissue: influence of androgen deprivation therapy on its level

Androstenediol (Adiol, androst-5-ene-3beta,17beta-diol) is suspected of being an endogenous proliferation agent of prostate cancer (PCa) even after androgen deprivation therapy (ADT). A liquid chromatography-electron capture atmospheric pressure chemical ionization-mass spectrometric (LC-ECAPCI-MS) method for the determination of Adiol in prostatic tissue was developed and validated for evaluating the influence of ADT on the prostatic Adiol level. After derivatization of Adiol with 4-nitrobenzoyl chloride, the detection response of the derivative was increased 150 times more than that of intact Adiol. The LC-MS method was specific and reliable for the measurement of a trace amount of Adiol in 30 mg of tissue. The clinical study using the developed method showed that the prostatic Adiol level was not changed by ADT. That is, the prostatic Adiol levels of PCa patients with ADT (n = 12), benign prostate hypertrophy patients without ADT (n = 8) and bladder cancer patients (without prostatic disease) (n = 6) were 0.83 +/- 0.28, 0.62 +/- 0.31 and 0.71 +/- 0.28 ng g(-1)tissue, respectively, and there was no significant difference between these groups.

Studies on neurosteroids XVIII LC-MS analysis of changes in rat brain and serum testosterone levels induced by immobilization stress and ethanol administration

The liquid chromatography-mass spectrometry (LC-MS) methods were developed and validated for the determination of testosterone (T) in the brain and serum of rats and of 5alpha-androstane-3alpha,17beta-diol (ADIOL), a metabolite of T, in the brain of rats. After derivatization of T with 2-hydrazino-1-methylpyridine and of ADIOL with p-nitrobenzoyl chloride, the detection sensitivities of T and ADIOL using LC-MS were increased 70- and 400-times superior to those of intact T and intact ADIOL, respectively. Those LC-MS methods are specific and reliable for the analysis of trace amounts of T and ADIOL in small amounts of samples. The animal studies using the developed methods showed that the brain and serum levels of T and the brain levels of ADIOL were not changed by stress or ethanol administration but the concentration ratio of the brain T to serum T in the stressed rats was higher than that in untreated rats. The low levels of endogenous AIDOL in brain of stressed and unrestrained rats found in this study demonstrated that the contribution to anesthetic and anxiolytic effects of ADIOL via gamma-aminobutyric acid type A receptors may be negligible.

Analysis of veterinary drug residues in shrimp: A multi-class method by liquid chromatography–quadrupole ion trap mass spectrometry

A liquid chromatography-mass spectrometry (LC-MS) method was developed to screen and confirm veterinary drug residues in raw shrimp meat. This method simultaneously monitors 18 drugs of different classes, including oxytetracycline (OTC), sulfonamides, quinolones, cationic dyes, and toltrazuril sulfone (TOLS). The homogenized shrimp meat is extracted with 5% trichloroacetic acid. The extract is further cleaned using polymer-based SPE. A 50 mm phenyl column separates the analytes, prior to analysis with an ion trap mass spectrometer interfaced with an atmospheric pressure chemical ionization source. This method is able to confirm oxytetracycline residues at 200 ng/g, toltrazuril sulfone at 50 ng/g, sulfaquinoxaline at 20 ng/g, and the other 15 drugs at 10 ng/g or lower levels. An estimate of the level of residues can also be made so that only confirmed samples above action levels will be sent for quantitation. The method is validated with both fortified and incurred samples, using multiple shrimp species as well. This multi-class method can provide a means to simultaneously monitor for a wide range of illegal drug residues in shrimp.

Procedure for increasing the detection responses of estrogens in LC-MS based on introduction of a nitrobenzene moiety followed by electron capture atmospheric pressure chemical ionization

A practical procedure for determining estrogens in biological fluids has been studied using liquid chromatography-electron capture atmospheric pressure chemical ionization-mass spectrometry combined with derivatization. Among the commercially available reagents (4-nitrobenzoyl chloride, 2,4-dinitrofluorobenzene, 4-nitrobenzenesulfonyl chloride and 4-nitrobenzyl bromide), 4-nitrobenzenesulfonyl chloride was of the most practical use; it rapidly and quantitatively reacted with estrogens and increased the detection responses by 8-23 times. The derivatization method allowed the reproducible and accurate quantification of serum and urine estrone and estradiol of a pregnant woman, which is useful for diagnosis of the fetoplacental function, with small amounts (10 mul) of sample and a simple pretreatment procedure. Tatsuya Higashiis Associate Professor of the Laboratory of Clinical Analytical Sciences (Professor Kazutake Shimada's research group) at the Graduate School of Natural Science and Technology of Kanazawa University. He received the Japan Society for Analytical Chemistry Award for Young Scientists in 2003 and the Pharmaceutical Society of Japan Award for Young Scientists in 2006. His current research interests are the development of methods for increasing sensitivity in LC-MS to detect and characterize trace amounts of biologically active steroids, such as estrogens, androgens and neuroactive steroids.

Use of flow injection atmospheric pressure photoionization quadrupole time-of-flight mass spectrometry for fast olive oil fingerprinting

The recently introduced technique of an atmospheric pressure photoionization (APPI) source coupled to quadrupole time-of-flight mass spectrometry (QqTOFMS) has been applied to fast olive oil fingerprinting on the basis of the accurate mass measurements obtained with this instrumentation. The key compounds can be characterized as [M+H]+ (produced by proton transfer) or as [M]+* (by charge transfer) ions in the mass spectra. [M+H]+ ions, however, show higher abundance, especially for triacylglycerols. Other ions present in APPI-MS are the acylium ion [RiCO]+ and [RiCO-H2O]+. This latter ion is absent in the electrospray ionization (ESI)-MS spectra, and this represents valuable complementary information. Several critical parameters in the APPI source were optimized such as LC eluent composition, ion spray voltage and, especially, declustering potential. APPI-QqTOFMS allows easy discrimination among different edible oils: olive, extra virgin olive, olive-pomace, hazelnut, sunflower, corn and several mixed oils, with high throughput (approximately 1 min per sample). Cluster analysis was applied to obtain the best experimental conditions for oil discrimination on the basis of declustering potential. Principal components analyses of these APPI-MS spectra show that the approach can be used for studies of olive oil adulteration with other oils, even in the case of hazelnut oil that exhibits a high chemical similarity with olive oil.

Derivatization in mass spectrometry--8. Soft ionization mass spectrometry of small molecules

This is the first of two reviews devoted to derivatization approaches for "soft" ionization mass spectrometry (FAB, MALDI, ESI, APCI) and deals, in particular, with small molecules. The principles of the main "soft" ionization mass spectrometric methods as well as the reasons for derivatizing small molecules are briefly described. Derivatization methods for modification of amines, carboxylic acids, amino acids, alcohols, carbonyl compounds, monosaccharides, thiols, unsaturated and aromatic compounds etc. to improve their ionizability and to enhance structure information content are discussed. The use of "fixed"-charge bearing derivatization reagents is especially emphasized. Chemical aspects of derivatization and "soft" ionization mass spectrometric properties of derivatives are considered.

Matrix-assisted laser desorption/ionization high-energy collision-induced dissociation of steroids: analysis of oxysterols in rat brain

Neutral steroids have traditionally been analyzed by gas chromatography/mass spectrometry (GC/MS) after necessary derivatization reactions. However, GC/MS is unsuitable for the analysis of many conjugated steroids and those with unsuspected functional groups. Here we describe an alternative analytical method specifically designed for the analysis of oxosteroids and those with a 3beta-hydroxy-delta5 or 5alpha-hydrogen-3beta-hydroxy structure. Steroids were derivatized with Girard P (GP) hydrazine to give GP hydrazones, which are charged species and readily analyzed by matrix-assisted laser desorption/ionization mass spectrometry. The resulting [M]+ ions were then subjected to high-energy collision-induced dissociation on a tandem time-of-flight instrument. The product ion spectra give structurally informative fragment ion patterns. The sensitivity of the analytical method is such that steroid structures can be determined from low-picogram (low-femtomole) amounts of sample. The utility of the method has been demonstrated by the analysis of oxysterols extracted from rat brain.

Targeted chiral lipidomics analysis

Genomics, transcriptomics, and proteomics are proving to be very useful techniques, which have impacted significantly on our understanding mechanisms of human disease. However, this systems biology approach has several drawbacks than can be overcome by the integration of metabonomics and lipidomics. We have developed a targeted lipidomics approach that makes it possible to directly analyze chiral lipids generated in cellular systems. Bioactive lipids are usually present in trace amounts as enanatiomers and regioisomers that require separation before they can be analyzed by mass spectrometry. Normal phase chiral chromatography is generally used to resolve bioactive lipid enanatiomers. However, conventional electrospray and atmospheric pressure chemical ionization/tandem mass spectrometry have limited sensitivity when normal phase solvents are used, which makes it difficult to conduct studies when only trace amounts of the bioactive lipids are present. The use of electron capture atmospheric pressure chemical ionization/tandem mass spectrometry overcomes this problem. Enantiomers and regioisomers of targeted bioactive lipids can be quantified using stable isotope dilution methodology coupled with normal phase chiral chromatography and electron capture atmospheric chemical ionization/tandem mass spectrometry. A targeted lipidomics profile from rat epithelial cells transfected with cyclooxygenase-2 and maintained in culture was obtained. Inhibition with the non-selective cyclooxygenase inhibitor aspirin increased the formation of 15(R)-hydroxyeicosatetraenoic acid in the cells although it completely inhibited formation of the 15(S)-enantiomer and prostaglandin E2. New mass spectrometry instrumentation with an improved atmospheric pressure chemical ionization source was found to be an order of magnitude more sensitive than existing instruments for analysis of bioactive lipids using electron capture methodology. This type of mass spectrometer will permit a more detailed analysis of cellular bioactive lipid production than has been possible previously. It will also permit in vivo targeted lipidomics studies to be conducted using biological fluids derived from animal models and human subjects.