Recent advances in high-throughput quantitative bioanalysis by LC–MS/MS

Simultaneous determination of cyclophosphamide and carboxyethylphosphoramide mustard in human plasma using online extraction and electrospray tandem mass spectrometry (HTLC-ESI-MS/MS)

A rapid and selective method for simultaneous determination of cyclophosphamide and its metabolite carboxyethylphosphoramide mustard (CEPM) was developed using online sample preparation and separation with tandem mass spectrometric detection. Diluted plasma was injected onto an extraction column (Cyclone MAX 0.5 mm x 50 mm, >30 microm), the sample matrix was washed with an aqueous solution, and retained analytes were transferred to an analytical column (Gemini 3 microm C18 110A, 100 mm x 2.0 mm) using a gradient mobile phase prior to detection by MS/MS. Analytes were detected in an API-3000 LC-MS/MS system using positive multiple-reaction monitoring mode (m/z 261/140 and 293/221 for CTX and CEPM, respectively). Online extraction recoveries were 76% and 72% for cyclophosphamide and CEPM. Within-day and between-day variabilities were <3.0%, and accuracies were between -6.9% and 5.2%. This method has been used to measure plasma cyclophosphamide and CEPM concentrations in an ongoing Phase II study in children with newly diagnosed medulloblastoma.

Rapid quantification of levosulpiride in human plasma using RP-HPLC-MS/MS for pharmacokinetic and bioequivalence study

A rapid and validated method for analysis of levosulpiride in human plasma using liquid chromatography coupled to tandem mass spectrometry was developed. Levosulpiride and tiapride (IS, internal standard) were extracted from alkalized plasma samples with ethylacetate and separation by RP-HPLC. Detection was performed by positive ion electrospray ionization in multiple-reaction monitoring mode, monitoring the transitions m/z 342.1 --> m/z 112.2 and m/z 329.1 --> m/z 213.2, for quantification of levosulpiride and IS, respectively. The standard calibration curves showed good linearity within the range of 2-200 ng/mL (r(2) > or = 0.9990). The lower limit of quantitation was 2 ng/mL. The retention times of levosulpiride (0.63 min) and IS (0.66 min) presented a significant time saving benefit of the proposed method. No significant metabolic compounds were found to interfere with the analysis. This method offered good precision and accuracy and was successfully applied for the pharmacokinetic and bioequivalence study of a 25 mg of levosulpiride tablet in 24 healthy Korean volunteers.

Restricted-access media supports for direct high-throughput analysis of biological fluid samples: review of recent applications

This review presents an update on the use of restricted-access materials (RAMs) for direct injection of biological samples. The fundamental improvements in the preparation of tailored RAMs and the diversity of applications with these phases are presented. Insights into diminishing the matrix effect by the use of RAM supports in methods by LC–MS and into the low number of methods for enantiomeric separations by direct injections of biological samples are addressed. The diversity of systems that incorporate RAMs for selective sample clean-up or fractionation in proteome and peptidome analysis is also covered.

Comparison of fused-core and conventional particle size columns by LC-MS/MS and UV: application to pharmacokinetic study

The chromatographic performance of fused-core (superficially porous) HPLC packing materials was compared with conventional fully porous particle materials for LC-MS/MS analysis of two pharmaceuticals in rat plasma. Two commercially available antidepressants, imipramine and desipramine, were assayed using a conventional analytical C(18) column (5 microm, 2.0 mm x 30 mm) and a fused-core C(18) column (2.7 microm, 2.1 mm x 30 mm). Retention time, column efficiency, pressure drop, resolution, and loading capacity were compared under the same operating conditions. The fused-core column demonstrated reduced assay time by 34% and 2-3-fold increased efficiency (N). Loading capacity up to 25 microl of extract injected on column showed no peak distortion. The registered back-pressure from a flow rate of 1.0 ml/min did not exceed 3400 psi making it compatible with standard HPLC equipment (typically rated to 6000 psi). Two mobile phases were examined, and morpholine as an organic base modifier yielded a 2-5-fold increase in S/N near the limit of detection over triethylamine. The 2.7 microm fused-core column was applied to the analysis of imipramine and desipramine in extracted, protein precipitated rat plasma by LC-MS/MS. The calibration curves were linear in the concentration range of 0.5-1000 ng/ml for both imipramine and desipramine. Intra-run precisions (%CV) and accuracies (%bias) were within +/-7.8% and +/-7.3% at three QC levels and within 14.7% and 14.4% at the LOQ level for both analytes. Following a single method qualification run, the method was applied to the quantitation of pharmacokinetic study samples after oral administration of imipramine to male rats.

Sample preparation and separation techniques for bioanalysis of morphine and related substances

In present time the use or misuse of morphine and its derivatives are monitored by assaying the presence of the drug and its metabolites in biofluids. In the present review, focus is placed on the sample preparation and on the separation techniques used in the current best practices of bioanalysis of morphine and its major metabolites. However, as methods for testing the misuse of heroin, a morphine derivative, often involve bioanalytical methods that cover a number of other illicit drug substances, such methods are also included in the review. Furthermore, the review also includes bioanalysis in a broader perspective as analysis of plant materials, cell cultures and environmental samples. The review is not intended to cover all publications that include bioanalysis of morphine but is more to be considered a view into the current best practices of bioanalysis of morphine, its metabolites and other related substances.

Quantification of polar drugs in human plasma with liquid chromatography–tandem mass spectrometry

Liquid chromatography–tandem mass spectrometry (LC–MS/MS) has played an important role in quantitative bioanalytical assays. This review summarizes the recent progress on quantification of polar drugs in plasma with LC–MS/MS. Various types of polar analytes were extracted using protein precipitation or solid-phase extraction and precolumn derivatization was utilized in some cases. The analytes were then separated using different types of chromatographic method, which included reversed-phase chromatography, aqueous normal-phase chromatography, hydrophilic interaction liquid chromatography and ion-pairing chromatography. Stationary phases of mixed mode and porous graphitic carbon materials are gaining acceptance in bioanalytical applications. These technologies can be valuable supplements in the quantification of polar drugs in human plasma with LC–MS/MS. Matrix effects have also been discussed in this review.

Bioanalytical hydrophilic interaction chromatography: recent challenges, solutions and applications

Hydrophilic interaction chromatography (HILIC) has, in recent years, been shown to be an important supplement to reversed-phase liquid chromatography for polar analytes. HILIC, in conjunction with tandem mass spectrometry (MS/MS), has been steadily gaining acceptance in the analysis of polar compounds from complex biological matrices. This hyphenated technique offers the advantages of improved sensitivity by employing high organic content in the mobile phase, shortened sample preparation time with direct injection of the organic-solvent extracts of biological samples and the potential for ultra-fast analysis because of low-column backpressure. This article reviews recent challenges presented by HILIC, advancements in the better understanding of retention characteristics of analytes with different mobile- and stationary-phase compositions and solutions to ion suppression and interference problems encountered in HILIC–MS/MS assays. Applications of HILIC–MS/MS are summarized, including those for pharmacokinetic studies, metabolic studies, therapeutic drug monitoring and clinical diagnostics.

Steroid measurement with LC-MS/MS in pediatric endocrinology

The liquid chromatography-tandem mass spectrometry (LC-MS/MS) is an increasingly common tool in the clinical laboratory. Established applications include routine assays for detecting inborn errors of metabolism and for monitoring therapeutic drugs and steroids. Steroid profiling is a very effective method for distinguishing almost all steroid related disorders. It allows accurate diagnosis and is very useful in many clinical situations. Most methods for the determination of steroid hormones are based on immunoassays, which are rapid and easy to perform. However, the reliability of steroid immunoassays has been shown to be doubtful because of the lack of specificity and of matrix effects. Immunological methods, especially direct assays, often overestimate true steroid values. This is of particular importance in the newborn period and in early infancy. Problems with steroid immunoassays have further been reported for female patients or when analysing different media, e.g. saliva. Patient follow-up over time or between laboratories, as well as longitudinal studies are extremely difficult. In contrast to immunoassays, which allow the measurement of only a single steroid at a time, LC-MS/MS has the advantage that a wide spectrum of steroid hormones can be measured simultaneously. The applicability for clinical samples and problems in pediatric endocrinology will be discussed.

SPE and large-volume sample stacking in MEKC for determination of doxycycline in biological fluids: comparison of direct injection to SPE-MEKC

A novel and simple method has been developed for the determination of doxycycline (DOX) in biological fluids. The method is based on SPE, large-volume sample stacking (LVSS) and MEKC with UV-DAD detection. Six SPE cartridges have been used in investigation for sample clean up and pre-concentration (Supelco LC-8, LC-18, LC-SCX, and LC-WCX, as well as Strata-X and X-C). DOX was determined on a 56 cm (effective length 50 cm) x 50 microm id fused-silica capillary. The BGE was 20 mM borate buffer, pH 9.3, containing 80 mM SDS and 7.5% v/v of methanol (30 sx50 mbar), and the temperature and voltage were 25 degrees C and 30 kV, respectively. The analytical wavelength was set at 210 nm. Under optimized conditions it is possible to determine DOX in human serum, urine, semen, tears and saliva with recovery of 97.5% (RSD 2.5%). The method was shown to be sensitive (LOD is 1 microg/L) and precise (intra-day RSD 0.2 and 2.4%; inter-days 0.4 and 3.5% for migration time and peak area, respectively). Results for developed SPE-LVSS-MEKC were compared with LVSS-MEKC method with direct sample injection. The new LVSS-MEKC method is presented as a useful technique for rapid determination without extraction procedure of DOX in human urine and serum, using 80 mM of SDS, 10% v/v of methanol and 40 mM borate buffer (pH 9.3; 30 s x 50 mbar; 25 degrees C; 30 kV; 350 nm), but not for the other biological fluids, according to lower sensitivity of the method and because of the sample composition.

Pre-study and in-study validation of an ultra-high pressure LC method coupled to tandem mass spectrometry for off-line determination of oxytetracycline in nasal secretions of healthy pigs

In order to quantify oxytetracycline (OTC) in nasal secretions of healthy pigs after intramuscular injection of OTC at doses of 10, 20 and 40 mg/kg bodyweight, an original method based on ultra-high pressure liquid chromatography coupled to tandem mass spectrometry (UPLC-MS/MS) was developed and fully validated. Sample preparation consisted in protein precipitation preceded by the addition of a releasing protein reagent. Metacycline (MTC) was used as internal standard. Separation was carried out at 65 degrees C in the gradient elution mode on a short analytical column filled with Acquity BEH C(18) stationary phase. The mobile phase consisted in a mixture of water and acetonitrile containing 1 mM of oxalic acid and 0.1% (v/v) of formic acid. The triple quadrupole mass spectrometer operated in the positive electrospray ionization mode; OTC and MTC were detected using multiple reaction monitoring. The pre-study and in-study validation of this bioanalytical method was performed by applying a novel strategy based on total measurement error and accuracy profiles. The maximum risk of observing future measurements falling outside the acceptance limits during routine as well as the measurements uncertainty were also estimated.

High-performance liquid chromatography-tandem mass spectrometry in the identification and determination of phase I and phase II drug metabolites

Applications of tandem mass spectrometry (MS/MS) techniques coupled with high-performance liquid chromatography (HPLC) in the identification and determination of phase I and phase II drug metabolites are reviewed with an emphasis on recent papers published predominantly within the last 6 years (2002–2007) reporting the employment of atmospheric pressure ionization techniques as the most promising approach for a sensitive detection, positive identification and quantitation of metabolites in complex biological matrices. This review is devoted to in vitro and in vivo drug biotransformation in humans and animals. The first step preceding an HPLC-MS bioanalysis consists in the choice of suitable sample preparation procedures (biomatrix sampling, homogenization, internal standard addition, deproteination, centrifugation, extraction). The subsequent step is the right optimization of chromatographic conditions providing the required separation selectivity, analysis time and also good compatibility with the MS detection. This is usually not accessible without the employment of the parent drug and synthesized or isolated chemical standards of expected phase I and sometimes also phase II metabolites. The incorporation of additional detectors (photodiode-array UV, fluorescence, polarimetric and others) between the HPLC and MS instruments can result in valuable analytical information supplementing MS results. The relation among the structural changes caused by metabolic reactions and corresponding shifts in the retention behavior in reversed-phase systems is discussed as supporting information for identification of the metabolite. The first and basic step in the interpretation of mass spectra is always the molecular weight (MW) determination based on the presence of protonated molecules [M+H]⁺ and sometimes adducts with ammonium or alkali-metal ions, observed in the positive-ion full-scan mass spectra. The MW determination can be confirmed by the [M-H]^- ion for metabolites providing a signal in negative-ion mass spectra. MS/MS is a worthy tool for further structural characterization because of the occurrence of characteristic fragment ions, either MSⁿ analysis for studying the fragmentation patterns using trap-based analyzers or high mass accuracy measurements for elemental composition determination using time of flight based or Fourier transform mass analyzers. The correlation between typical functional groups found in phase I and phase II drug metabolites and corresponding neutral losses is generalized and illustrated for selected examples. The choice of a suitable ionization technique and polarity mode in relation to the metabolite structure is discussed as well.

Development of capillary electrochromatography with poly(styrene-divinylbenzene-vinylbenzenesulfonic acid) monolith as the stationary phase

A new polystyrene-based monolithic stationary phase, which was prepared by single step in situ copolymerization of styrene, divinylbenzene and vinylbenzenesulfonic acid (VBSA), was developed as a separation column for capillary electrochromatography, in which VBSA was employed as the charge-bearing monomer. Polymerization time of the polystyrene-based monolith had slightly influenced the separation time of the tested analytes, but it effectively altered their separation resolutions. Furthermore, baseline separation for a wider range of acetonitrile levels of mobile phase was achieved when a monolithic column prepared by a longer polymerization time was used. This novel polystyrene-based monolithic column provided an adequate electroosmotic flow either in basic or acidic mobile phase when VBSA level was maintained at 2.6% (w/w). Finally, this proposed polystyrene-based column allowed seven tested analytes to achieve a reproducible baseline separation within 2.2 min with theoretical plate numbers higher than 164 000 plates/m.

Type 2 diabetes: Gaining insight into the disease process using proteomics

The incidence of diabetes mellitus is growing rapidly, with an increasing disease related morbidity and mortality. This is caused by macro- and microvascular complications, as a consequence of the often late diagnosis of type 2 diabetes (T2D), but especially by the difficulties to control glucose homeostasis due to the progressive nature of the disease. T2D is moreover a dual disease, with components of beta-cell failure and components of insulin resistance in peripheral organs, such as liver, fat, and muscle. Understanding the pathogenesis of the disease by gaining insight into the molecular pathways involved in both phenomena is one of the major assets of proteomic approaches. Moreover, proteomics and peptidomics may provide us with robust biomarkers for beta-cell failure, insulin resistance in pheripheral organs, but also for the development of diabetic complications. This review focuses on the knowledge gained by use of proteomic and peptidomic techniques in the study of the pathophysiology of T2D and in the attempts to discover new therapeutic targets.

Metabolism and bioavailability of flavonoids in chemoprevention: current analytical strategies and future prospectus

Flavonoids are structurally diverse and among the most ubiquitous groups of dietary polyphenols distributed in various fruits and vegetables. Many have been proposed to be bioactive compounds in the diet that are responsible for lowering the risk of cancer and have been used in chemoprevention studies using animal models of this disease. As for any xenobiotic, to evaluate the potential risks and benefits of bioflavonoids to human health, an understanding of the physiological behavior of these compounds following oral ingestion is needed as well as their absorption, distribution, metabolism, and excretion (ADME). The study on metabolism and bioavailability is very important in defining the pharmacological and toxicological profile of these compounds. Due to great structural diversity among flavonoids, these profiles differ greatly from one compound to another, so that the most abundant polyphenols in our diet are not necessarily the ones that reach target tissues. Therefore, careful analysis of flavonoids and their metabolites in biological systems is critical. Mass spectrometry in various combinations with chromatographic methods has been a mainstay in applications that involve profiling and quantification of metabolites in complex biological samples. Because of its speed, sensitivity and specificity, liquid chromatography-tandem mass spectrometry (LC-MS/MS) has become the technology of choice for sample analysis. This review describes the chemistry of polyphenols and flavonoids, their ADME, and the various mass spectrometry-based strategies used in the analysis of flavonoids, including future trends in this field.

Hydrophilic interaction liquid chromatography (HILIC) in proteomics

In proteomics, nanoflow multidimensional chromatography is now the gold standard for the separation of complex mixtures of peptides as generated by in-solution digestion of whole-cell lysates. Ideally, the different stationary phases used in multidimensional chromatography should provide orthogonal separation characteristics. For this reason, the combination of strong cation exchange chromatography (SCX) and reversed-phase (RP) chromatography is the most widely used combination for the separation of peptides. Here, we review the potential of hydrophilic interaction liquid chromatography (HILIC) as a separation tool in the multidimensional separation of peptides in proteomics applications. Recent work has revealed that HILIC may provide an excellent alternative to SCX, possessing several advantages in the area of separation power and targeted analysis of protein post-translational modifications. [figure: see text]

Current applications of liquid chromatography/mass spectrometry in pharmaceutical discovery after a decade of innovation

Current drug discovery involves a highly iterative process pertaining to three core disciplines: biology, chemistry, and drug disposition. For most pharmaceutical companies the path to a drug candidate comprises similar stages: target identification, biological screening, lead generation, lead optimization, and candidate selection. Over the past decade, the overall efficiency of drug discovery has been greatly improved by a single instrumental technique, liquid chromatography/mass spectrometry (LC/MS). Transformed by the commercial introduction of the atmospheric pressure ionization interface in the mid-1990s, LC/MS has expanded into almost every area of drug discovery. In many cases, drug discovery workflow has been changed owing to vastly improved efficiency. This review examines recent trends for these three core disciplines and presents seminal examples where LC/MS has altered the current approach to drug discovery.

Methanol-Associated Matrix Effects in Electrospray Ionization Tandem Mass Spectrometry

Background: Matrix effects can profoundly reduce the performance of electrospray ionization mass spectrometry. Preliminary observations indicated that the methanol used in the mobile phase could be a source of differential ionization or ion suppression.

Methods: Drug stability studies, analysis of biological extracts, mixing experiments, and postcolumn infusions were used to test 9 commercial methanols for ionization differences in liquid chromatography-tandem mass spectrometry assays for immunosuppressants. Area responses for the drugs and internal standards were compared for mobile phases prepared with each selected methanol. Postcolumn infusion experiments were performed to confirm the degree of ionization differences occurring at the ion source, and to evaluate the proportions of ammonium, sodium, and potassium adducts.

Results: The decrease in signal for the immunosuppressant drugs was shown to result from differential ionization associated with the selected methanols. Product ion intensity varied by 10-fold among the methanols tested. For sirolimus, tacrolimus, and mycophenolic acid, the percentage change in ionization was the same for the drug and its corresponding internal standard. Postcolumn sirolimus infusion evaluation revealed that a 1000-fold analyte concentration difference did not affect ionization. The proportions of ammonium, sodium, and potassium adducts of sirolimus precursor ions differed in relation to the source of methanol.

Conclusions: Organic solvents used in mobile phases and extract preparation of biological samples may be associated with ion suppression, affecting adduct formation and assay sensitivity.