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

The corona discharge used to generate positive and negative ions under conventional atmospheric pressure chemical ionization conditions also provides a source of 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. This technique, which has been named electron capture atmospheric pressure chemical ionization/mass spectrometry, provided an increase in sensitivity of 2 orders of magnitude when compared with conventional atmospheric pressure chemical ionization methodology. It is a simple procedure to tag many biomolecules and drugs with an electron-capturing group such as the pentafluorobenzyl moiety before analysis. Pentafluorobenzyl 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 pentafluorobenzyl radical. A similar process was found to occur under electron capture atmospheric pressure chemical ionization conditions. By monitoring the negative ions that were formed, it was possible to obtain attomole sensitivity for pentafluorobenzyl derivatives of a representative steroid, steroid metabolite, prostaglandin, thromboxane, amino acid, and DNA-adduct.

High throughput liquid chromatography/mass spectrometry bioanalysis using 96-well disk solid phase extraction plate for the sample preparation

The 96 well solid phase extraction (SPE) operated by robot in the LC/MS/MS bioanalysis offered rapid sample preparation for drugs and metabolites in biological matrices, based on simultaneous extraction of 96 samples. The use of a disk as sorbent in the 96 well plate further improved the performance of SPE and allowed for small elution volumes, making it possible to 'dilute and shoot" after SPE elution. In this study, a 96 well plate (Empore) was developed, characterized and optimized for several pharmaceutical compounds. In addition, a robot (MultiProbe) was modified to automate the 96 well plate operation. Examples were given to illustrate the major differences of using 96 well disk plate SPE in the method development as compared to the traditional SPE. This technology has been successfully used to support many clinical studies. Typically, a batch of 96 samples were prepared in 1-1.5 hours unattended (except for the replacement of a collection plate). Considerable savings in disposable supplies were also noted.

Analysis of five HMG-CoA reductase inhibitors-- atorvastatin, lovastatin, pravastatin, rosuvastatin and simvastatin: pharmacological, pharmacokinetic and analytical overview and development of a new method for use in pharmaceutical formulations analysis and in vitro metabolism studies

A specific, accurate, precise and reproducible high-performance liquid chromatographic (HPLC) method was developed and validated for the simultaneous quantitation of five 3-hydroxy-3-methyglutaryl coenzyme A (HMG-CoA) reductase inhibitors, viz. atorvastatin, lovastatin, pravastatin, rosuvastatin and simvastatin, in pharmaceutical formulations and extended the application to in vitro metabolism studies of these statins. Ternary gradient elution at a flow rate of 1 mL/min was employed on an Intertisl ODS 3V column (4.6 x 250 mm, 5 microm) at ambient temperature. The mobile phase consisted of 0.01 m ammonium acetate (pH 5.0), acetonitrile and methanol. Theophylline was used as an internal standard (IS). The HMG-CoA reductase inhibitors and their metabolites were monitored at a wavelength of 237 nm. Drugs were found to be 89.6-105.6% of their label's claim in the pharmaceutical formulations. For in vitro metabolism studies the reaction mixtures were extracted with simple liquid-liquid extraction using ethyl acetate. Baseline separation of statins and their metabolites along with IS free from endogenous interferences was achieved. Nominal retention times of IS, atorvastatin, lovastatin, pravastatin, rosuvastatin and simvastatin were 7.5, 17.2, 21.6, 28.5, 33.5 and 35.5 min, respectively. The proposed method is simple, selective and could be applicable for routine analysis of HMG-CoA reductase inhibitors in pharmaceutical preparations as well as in vitro metabolism studies.

Increased serotonin 2A receptor availability in the orbitofrontal cortex of physically aggressive personality disordered patients

BACKGROUND

Impulsive physical aggression is a common and problematic feature of many personality disorders. The serotonergic system is known to be involved in the pathophysiology of aggression, and multiple lines of evidence have implicated the serotonin 2A receptor (5-HT(2A)R). We sought to examine the role of the 5-HT(2A)R in impulsive aggression specifically in the orbitofrontal cortex (OFC), given that our own studies and an extensive literature indicate that serotonergic disturbances in the OFC are linked to aggression. We have previously hypothesized that increased 5-HT(2A)R function in the OFC is a state phenomenon that promotes impulsive aggression.

METHODS

Serotonin 2A receptor availability was measured with positron emission tomography and the selective 5-HT(2A)R antagonist radioligand [(11)C]MDL100907 in two groups of impulsively aggressive personality disordered patients-14 with current physical aggression, and 15 without current physical aggression-and 25 healthy control subjects. Clinical ratings of various symptom dimensions were also obtained.

RESULTS

Orbitofrontal 5-HT(2A)R availability was greater in patients with current physical aggression compared with patients without current physical aggression and healthy control subjects; no differences in OFC 5-HT(2A)R availability were observed between patients without current physical aggression and healthy control subjects. No significant differences in 5-HT(2A)R availability were observed in other brain regions examined. Among both groups of impulsively aggressive personality disordered patients combined, OFC 5-HT(2A)R availability was correlated, specifically, with a state measure of impulsive aggression.

CONCLUSIONS

These findings are consistent with our previously described model in which impulsive aggression is related to dynamic changes in 5-HT(2A)R function in the OFC.

Determination of free fatty acids as pentafluorobenzyl esters by electron capture gas chromatography

A method for the determination of free fatty acids in minute serum samples has been developed. The acids are esterified by extractive alkylation, using tetrabutylammonium as a counter ion and pentafluorobenzyl bromide as alkylating reagent. The derivatization of palmitic acid required a reaction time of 25 min. The excess of pentafluorobenzyl bromide is removed by coupling it with a phenoalkylamine and extraction of the product into an acidic aqueous phase. Quantitation is carried out by gas chromatography with electron capture detection. The precision achieved in the determination of 6.2 mug of palmitic acid in 50 mul of mouse serum was 6.1% (S.D.).

Simultaneous determination of rosuvastatin and fenofibric acid in human plasma by LC-MS/MS with electrospray ionization: assay development, validation and application to a clinical study

A simple, sensitive and specific LC-MS/MS method for simultaneous determination of rosuvastatin (RST) and fenofibric acid (FFA) was developed and validated with 500 microL human plasma using carbamazepine as an internal standard (IS). The assay procedure involved a simple one-step liquid/liquid extraction of RST and FFA and IS from plasma into ethyl acetate. The organic layer was separated and evaporated under a gentle stream of nitrogen at 40 degrees C. The residue was reconstituted in the mobile phase and injected onto X-Terra MS C-18 column (4.6 mm x 50 mm, 5.0 microm). Separation of RST, FFA and IS was achieved with a mobile phase consisting of 0.05 M formic acid:acetonitrile (45:55, v/v) at a flow rate of 0.40 ml/min. The API-3000LC-MS/MS was operated under the multiple reaction-monitoring mode (MRM) using the electrospray ionization technique. Positive ion acquisition chromatographic run was used in the present method. Nominal retention times of RST, FFA and IS were 2.35, 4.70 and 2.32 min, respectively. Absolute recovery of RST, FFA and IS was 74, 61 and 69%, respectively. The lower limit of quantification (LLOQ) of RST and FFA was 1.00 ng/ml and 0.50 microg/ml, respectively. Response function was established for the range of concentrations 1.00-50.0 ng/ml and 0.50-20.0 microg/ml for RST and FFA, respectively, with a coefficient of determination (r2) of 0.999 for both the compounds. The inter- and intra-day precision in the measurement of RST quality control (QC) samples 5, 15, 400 and 800 ng/ml, were in the range 8.93-9.37% relative standard deviation (R.S.D.) and 1.74-16.1% R.S.D., respectively. Similarly, the inter- and intra-day precision in the measurement of FFA quality control (QC) samples 0.5, 1.5, 8.0 and 15.0 microg/ml, were in the range 9.78-11.6% relative standard deviation (R.S.D.) and 0.22-17.4% R.S.D., respectively. Accuracy in the measurement of QC samples for RST and FFA were in the range 88.1-108 and 87-115%, respectively, of the nominal values. RST and FFA were stable in the battery of stability studies, viz., bench-top, auto-sampler and freeze/thaw cycles. Stability of RST and FFA was established for 1 month at -80 degrees C. The application of the assay to a clinical study confirmed the utility of the assay.

Determination of important odor-active aldehydes of wine through gas chromatography–mass spectrometry of their O-(2,3,4,5,6-pentafluorobenzyl)oximes formed directly in the solid phase extraction cartridge used for selective isolation

A method for the quantitative determination of octanal, nonanal, decanal, (E)-2-nonenal and (E, Z)-2,6-nonadienal in wine has been developed. In the proposed method, 200 ml of wine percolate through a solid phase extraction (SPE) cartridge packed with 200 mg of LiChrolut EN resins. The interferences are eluted with 60 ml of an aqueous solution containing 40% of methanol and 1% of NaHCO3. In the same SPE cartridge, the corresponding O-(2,3,4,5,6-pentafluorobenzyl)oximes are formed by letting percolate 2 ml of the reagent solution (5 mg ml(-1)). At room temperature the derivatization goes to completion in 15 min. The derivatives are eluted with 2 ml of dichloromethane, and the extract is concentrated and then analyzed by gas chromatography-mass spectrometry (GC-MS). The percentage of recovery in the isolation process is better than 90% in all cases with the exception of octanal, and is independent of the wine studied. In the cases of octanal, nonanal and decanal, the detection limits of the method are determined by the contamination levels of the reagent itself, and vary between 160 and 380 ng l(-1). For (E)-2-nonenal and (E, Z)-2,6-nonadienal, the detection limits were 12 and 20 and ng l(-1), respectively. The linearity of the method upheld until 10 microg l(-1) and was satisfactory in all cases. The reproducibility of the method is independent of the concentration and ranges from 30 to 190 ng (l(-1). The method has been applied to the analysis of these components in several wine samples. With the exception of (E, Z)-2,6-nonadienal, all the components can reach concentrations above their corresponding odor threshold values.

Assay methods for the measurement of total homocyst(e)ine in plasma

Analytical methods to measure plasma total homocyst(e)ine (tHcy) concentrations are reviewed. High-pressure liquid chromatography (HPLC) with fluorometric detection is the most widely used method to determine plasma tHcy concentrations. Both monobromobimane and ammonium 7-fluorobenzo-2-oxa-1,3-diazole-4-sulphonate (SBD-F) are popular thiol-specific fluorogenic agents suitable for tHcy analysis. Monobromobimane has the advantage that it is highly reactive towards thiols, but its hydrolysis products are also fluorogenic, thus necessitating complex chromatography to obtain satisfactory separation between the compounds of interest and interferents. SBD-F does not show fluorescence, thus allowing isocratic separation of SBD-F derivatized thiols. SBD-thiol adducts are light sensitive and require protection against light to ensure reliable results. HPLC with electrochemical detection is also often used and has the advantage that no derivatization of thiols is required prior to detection. A recently reported liquid chromatography electrospray tandem mass spectrometric assay has the potential to become the reference method for plasma tHcy analysis. Other methods to measure plasma tHcy concentrations include gas-liquid chromatography, capillary electrophoresis, and immunoassays. Fluorescence polarization immunoassay compares well with gas chromatography-mass spectrometry and may become the method of choice in routine diagnostic clinical chemistry laboratories. Instability of tHcy in whole blood as well as postprandial and orthostatic variation are preanalytical factors that should be accounted for in plasma tHcy analysis. Between-method and between-laboratory variations in serum tHcy analysis are not yet satisfactory; certified reference material and standardization of the plasma tHcy assay will be essential to reduce between-laboratory bias.

Occurrence and fate of rosuvastatin, rosuvastatin lactone, and atorvastatin in Canadian sewage and surface water samples

Rosuvastatin (RST) and atorvastatin (ATO) are prescription drugs and members in the statin family used for the treatment of elevated cholesterol levels. A method using solid-phase extraction and liquid chromatography-tandem mass spectrometry (LC-MS/MS) for the determination of ATO, RST and its metabolite rosuvastatin lactone (RSTL) in sewage and surface water samples has been developed. In the influent and effluent samples collected from 11 sewage treatment plants located in Ontario, Canada, ATO, RST, and RSTL were detected in all samples with median concentrations of 166 ng L(-1) (influent) and 77 ng L(-1) (effluent) for ATO, 448 ng L(-1) (influent) and 324 ng L(-1) (effluent) for RST, as well as 158 ng L(-1) (influent) and 41 ng L(-1) (effluent) for RSTL. Due to the inter-conversion between RST and RSTL, the total concentration of RST and RSTL in a sewage sample should be reported. The median removal rate by wastewater treatment was 66% for ATO and 22% for RST and RSTL combined. These statins were quite persistent in sewage. After a storage period of 21 and 62 days, there was only a slight decrease in ATO concentration and no change in the total RST concentrations. These three compounds were also detected in a number of surface water samples at low ng L(-1) concentrations. This is the first reported occurrence and fate of RST and RSTL in the Canadian aquatic environment.

Determination of the enantiomer of a cholesterol-lowering drug by cyclodextrin-modified micellar electrokinetic chromatography

The development, optimization and application of a chiral CE (capillary electrophoresis) method for the determination of the enantiomer content of a new cholesterol-lowering drug (BMS-180431-09) is discussed. The chiral CE technique, cyclodextrin-modified micellar electrokinetic chromatography (CD-MEKC), was employed with hydroxypropyl beta-cyclodextrin as the chiral selector in the run buffer. The detection limit of the unwanted enantiomer was about 0.06% w/w. The effect of various parameters on the separation, validation data and examples of the application of the chiral CE method are included.

Critical aspects of the determination of pentafluorobenzyl derivatives of aldehydes by gas chromatography with electron-capture or mass spectrometric detection

This work presents a thorough study of some aspects critical to the quantitative performance of methods for the determination of volatile aldehydes previously derivatized to pentafluorobenzyl hydroxylamine oximes. The conclusions of the study are further applied to the validation of an optimized procedure for the determination of oxidation-related aldehydes from wine. Aspects studied include the chromatographic injection, the analytical performance of electron-capture detection (ECD) or MS detection, and the way in which the derivatization is carried out. Different injection techniques have been optimized and compared (classical splitless-hot injection; cold splitless; and large volume solvent split injection). All of them were carried out in a programmed temperature vaporization (PTV) injector, with a 350 microL internal volume liner (3.4 mm internal diameter). Classical splitless injection of hexane extracts is troublesome and requires large carrier gas flows (>10 mL min(-1)). Cold splitless injection was clearly superior. Large volume solvent split injection has been also optimized. ECD has been found to lack the necessary selectivity for the determination of unsaturated aldehydes in wine, although the quantitation of several minor aldehydes is possible. MS detection has proven to be superior for the determination of these compounds in wine. The way in which the reagent is applied is also critical and for the case of wine is important to ensure that the reagent is applied after some of the major wine aldehydes have been eliminated. The finally proposed method is extremely sensitive. Method detection limits ranged from 0.002 microg L(-1) (for unsaturated aldehydes) to 0.73 microg L(-1) (for phenylacetaldehyde) and precision (measured as relative standard deviation) is < or =6% in all cases. The method makes it possible to determine quantitatively in a single run the wine aldehydes with sensory significance (isobutyraldehyde, 2-methylbutanal, isovaleraldehyde, (E)-2-hexenal, (E)-2-heptenal, (E)-2-octenal, (E)-2-nonenal, methional and phenylacetaldehyde).

Gas chromatography-mass spectrometry method for determination of phospholipid peroxides; II. Transesterification to form pentafluorobenzyl esters and detection with picogram sensitivity

The purpose of this study is to develop a higher sensitivity method to detect phospholipid peroxides in tissues to more effectively investigate the role of lipid peroxidation in pathology. We recently presented a gas chromatography-mass spectrometry (GC-MS) method for identification and measurement of phospholipid peroxides at the 10 ng level (van Kuijk, et al. J. Free Rad. Biol. Med., 1:215-225, 1985) based on transesterification to form fatty acid methyl ester derivatives. While this method is quite useful under some circumstances, more sensitivity was desirable to analyse trace amounts of lipid peroxidation products in small samples of various tissues. We present a method to prepare pentafluorobenzyl esters of fatty acids and hydroxy fatty acids directly from phospholipids by transesterification at room temperature or from triglycerides at 60 degrees C. Oxidized lipids are extracted into dichloromethane and peroxide functions are reduced with sodium borohydride. Transesterification of phospholipids is carried out in dichloromethane with 20% (v/v) pentafluorobenzyl alcohol, 1% (w/v) potassium tert-butoxide and 0.2 N (m-trifluoromethyl phenyl) trimethyl ammonium hydroxide at room temperature for 30 min. Pentafluorobenzyl esters are purified on open silica columns, O-trimethyl silyl derivatives of the alcohol functions are formed, and GC-MS is carried out with negative ion chemical ionization detection. The single or double oxidation products of oleate, linoleate, arachidonate, and docosahexaenoate were detected with 10 pg sensitivity in oxidized rat retina phospholipids or synthetic phospholipids, by negative ion chemical ionization with specific ion monitoring of carboxylate anions.

Monitoring of allethrin, deltamethrin, esbiothrin, prallethrin and transfluthrin in air during the use of household mosquito repellents

Three types of mosquito repellent [two different mosquito coils containing allethrin 0.1% w/w and transfluthrin 0.03% w/w, an aerosol sample containing a combination of two pyrethroid molecules (deltamethrin 0.02% w/w + allethrin 0.13% w/w) and two different mosquito mats containing esbiothrin 2.0% w/w and prallethrin 1.5% w/w as active ingredients] were individually subjected to use in a closed room. Air samples from the room were drawn at different time intervals (15, 30 and 45 min, and 1, 2, 4, 6 and 8 h) uniformly from three different positions in the room (top, middle and bottom) with the pyrethroid contents analysed using gas chromatography-electron capture detection (GC-ECD). Analysis of air samples showed maximum concentrations of the pyrethroid residues allethrin (0.0120 ppm), transfluthrin (0.0134 ppm), deltamethrin (0.0057 ppm), allethrin (0.080 ppm), esbiothrin (0.015 ppm) and prallethrin (0.0138 ppm) within 30-45 min of use. The drop in residue content was significant with time. At the end of a 6 h period, most of the residues had dissipated to below 0.0001 ppm. Further significant differences were observed in the residue contents tested at different points within the room. Studies were compared with the experimental results obtained when the mosquito repellents were tested with air circulation in the room.

Gas chromatography-mass spectrometry characteristics of methylated perfluoroacyl derivatives of cytosine and 5-methylcytosine

Pentafluorobenzoyl and heptafluorobutyryl derivatives of cytosine and pentafluorobenzoyl-5-methylcytosine have been examined by mass spectrometry following permethylation. Electron impact mass spectra were used to confirm the structures of the derivatives. The permethylated pentafluorobenzoyl derivatives of cytosine and 5-methylcytosine are sensitive for quantitative analysis by capillary gas chromatography-mass spectrometry. Under negative ion chemical ionization conditions 1 femtogram of each is detected.

Determination of 19-nortestosterone, testosterone and trenbolone by gas chromatography-negative-ion mass spectrometry after formation of the pentafluorobenzylcarboxymethoxime-trimethylsilyl derivatives

The known reaction of 3-ketosteroids with carboxymethoxylamine (to form the corresponding carboxymethoximes), followed by esterification of the carboxyl group with pentafluorobenzyl bromide, has been used to obtain derivatives of 19-nortestosterone, testosterone and trenbolone suitable for high-sensitivity detection with gas chromatography-negative-ion chemical ionization mass spectrometry. These derivatives, after further silylation of the alcoholic groups of the steroids, showed excellent chromatographic and spectrometric characteristics and were detectable in the low picogram range. The derivatization gave rise to the formation of two isomers which were distinguishable by gas chromatography. The existence of the two isomers was also confirmed by high-performance liquid chromatography. Examples of the usefulness of this derivatization procedure are given for the analysis of 19-nortestosterone, testosterone and trenbolone in meat and urine samples. By the use of immunoaffinity extraction and addition of deuterated internal standards (synthesized by isotopic exchange), the new derivatization procedure allowed a correct identification and quantitation of the steroids and reached very low detection limits [0.02 ppb (10(9] for 19-nortestosterone and testosterone, 0.06 ppb for trenbolone].

Application of the extractive alkylation technique to the pentafluorobenzylation of morphine (a heroin metabolite) and surrogates, with special reference to the quantitative determination of plasma morphine levels using mass fragmentography

The pentafluorobenzylation of morphine and related phenolic alkaloids by extractive alkylation is described. The alkylation is performed using tetrabutylammonium as counter ion and ethyl acetate as solvent. Optimum reaction conditions are presented together with the gas chromatographic properties of the derivatives formed. The technique is applied to the quantitation of plasma morphine levels. Using morphine-d3 as internal standard mass fragmentographic analysis of morphine as its pentafluorobenzyl- and pentafluorobenzyl, mono-trifluoroacetyl derivatives is demonstrated, and a case report is presented. Quantitation to a plasma morphine level of 5 ng/ml is readily attainable.

Gas chromatographic and spectral properties of pentafluorobenzyl derivatives of 2,4-dichlorophenoxyacetic acid and phenolic pesticides and metabolites

Eleven phenols and 2,4-dichlorophenoxyacetic acid, compounds that may be found in body fluids of humans exposed to pesticides, are derivatized with pentafluorobenzyl bromide and characterized by gas chromatography with electron capture detection. These derivatives are further characterized by positive and negative chemical ionization mass spectrometry, nuclear magnetic resonance spectroscopy, and gas chromatography-Fourier transform infrared spectroscopy. Negative chemical ionization mass spectra of all derivatives have an anionic base peak derived from the parent analyte. In the positive mode the nonchlorinated derivatives have base peaks indicative of the analyte, while chlorinated derivatives are cleaved to give the pentafluorobenzyl cation as base peak. The possibility is explored that ortho-substituted phenols might be formed as byproducts in these derivatizations.

From Spill to Sequestration: The Molecular Journey of Contamination via Comprehensive Multiphase NMR

Comprehensive multiphase NMR is a novel NMR technique that permits all components (solutions, gels, and solids) to be studied in unaltered natural samples. In this study a wide range of CMP-NMR interaction and editing-based experiments are combined to follow contaminants (pentafluorophenol (PFP) and perfluorooctanoic acid (PFOA)) from the solution state (after a spill) through the gel-state and finally into the true solid-state (sequestered) in an intact water-swollen soil. Kinetics experiments monitoring each phase illustrate PFOA rapidly transfers from solution to the solid phase while for PFP the process is slower with longer residence times in the solution and gel phase. Interaction-based experiments reveal that PFOA enters the soil via its hydrophobic tails and selectively binds to soil microbial protein. PFP sorption shows less specificity exhibiting interactions with a range of gel and solid soil components with a preference toward aromatics (mainly lignin). The results indicate that in addition to more traditional measurements such as Koc, other factors including the influence of the contaminant on the soil-water interface, specific biological interactions, soil composition (content of lignin, protein, etc.) and physical accessibility/swellability of soil organic components will likely be central to better explaining and predicting the true behavior of contaminants in soil.

Analysis of trace levels of pesticides in rainwater by SPME and GC-tandem mass spectrometry after derivatisation with PFBBr

Solid-phase microextraction (SPME) was used for the analysis of some pesticides (bromoxynil, chlorotoluron, diuron, isoproturon, 2,4-MCPA, MCPP and 2,4-D) in rainwater after derivatisation with PFBBr and gas chromatography-ion trap mass spectrometry. The derivatisation procedure was optimized by testing different methods: direct derivatisation in the aqueous phase followed by SPME extraction, on-fibre derivatisation and derivatisation in the injector. The best result was obtained by headspace coating the PDMS/DVB fibre with PFBBr for 10 min followed by direct SPME extraction for 60 min at 68 degrees C (pH 2 and 75% NaCl). Good detection limits were obtained for all the compounds: these ranged between 10 and 1,000 ng L-1 with a relatively high uncertainty due to the combination of derivatisation and SPME extraction steps. The optimized procedure was applied to the analysis of pesticides in rainwater and results obtained shows that this method is a fast and simple technique to assess the spatial and temporal variations of concentrations of pesticides in rainwater.

Development of a simple liquid chromatographic method for the separation of mixtures of positional isomers and anomers of synthetic 2-, 3- and 4-fluorobenzoic acid glucuronides formed via acyl migration reactions

Many drugs containing carboxylate groups form beta-1-O-acyl glucuronides as their major phase II metabolites in vivo. These ester glucuronides are potentially reactive due to the susceptibility of the acyl group to nucleophilic reactions resulting in hydrolysis, acyl migration or covalent adduct formation. In the present study, a number of synthetic fluorobenzoic acid glucuronide conjugates were chosen as models for chromatographic studies. A high-performance liquid chromatography method is presented for the simultaneous determination of the 1-, 2-, 3- and 4-positional isomers of the acyl glucuronides, and their alpha- and beta-anomers for the 2-, 3- and 4-fluorobenzoic acids as well as each aglycone formed as a result of hydrolysis. The same elution order was found for the acyl migrated glucuronide isomers of the three fluorobenzoic acids in their equilibrium mixtures. The alpha-4-O-acyl isomer eluted first followed by the beta-4-O-acyl isomer, then the beta-1-O-acyl, the beta-3-O-acyl, the alpha-3-O-acyl, the alpha-2-O-acyl and finally the beta-2-O-acyl isomer eluted. The method was used to determine the overall degradation rates, the acyl migration rates and the hydrolysis rates of 1-O-(2-fluorobenzoyl)-beta-D-glucopyranuronic acid 1-O-(3-fluorobenzoyl)-beta-D-glucopyranuronic acid and 1-O-(4-flurobenzoyl)-beta-D-glucopyranuronic acid in a buffer system pH 7.4 at 25 degrees C. It was found that the order of beta-1-glucuronide acyl migration rates was 2-fluorobenzoyl > 3-fluorobenzoyl > 4-fluorobenzoyl. Both the acyl migration rates and the elution order were interpreted in terms of electronic effect of the fluorine substituent on the carbonyl carbon.

Determination of cyflufenamid residues in 12 foodstuffs by QuEChERS-HPLC-MS/MS

Agricultural products are often contaminated with trace amounts of pesticide residues. To ensure food safety, a reliable, sensitive, and efficient method that accurately identifies pesticide residues in a wide variety of foodstuffs is needed. This study applied a modified QuEChERS extraction technique, coupled with high performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) to optimize the identification of the cyflufenamid, a new broad-spectrum fungicide with unclear mode of action in toxicity, in 12 foodstuffs. The method has been validated according to the European Union SANTE/12682/2017 guidelines for its linearity, limit of detection (LOD), and limit of quantification (LOQ), indicating an excellent performance. The recovery of cyfluenamid in all matrix were ranged between 70.8% and 117.8%, with relative standard deviation (RSD) <15% which is much lower compared to other methods. The method has been used for determine cyfluenamid in foodstuffs followed the ISO17025:2017 measurement technical note, which demonstrated it is suitable for routine quantitative analysis of cyflufenamid in most of the popular commercial agricultural products.

Atmospheric pressure chemical ionization of fluorinated phenols in atmospheric pressure chemical ionization mass spectrometry, tandem mass spectrometry, and ion mobility spectrometry

Atmospheric pressure chemical ionization (APCI)-mass spectrometry (MS) for fluorinated phenols (C6H5-xFxOH Where x = 0-5) in nitrogen with Cl- as the reagent ion yielded product ions of M Cl- through ion associations or (M-H)- through proton abstractions. Proton abstraction was controllable by potentials on the orifice and first lens, suggesting that some proton abstraction occurs through collision induced dissociation (CID) in the interface region. This was proven using CID of adduct ions (M Cl-) with Q2 studies where adduct ions were dissociated to Cl- or proton abstracted to (M-H)-. The extent of proton abstraction depended upon ion energy and structure in order of calculated acidities: pentafluorophenol > tetrafluorophenol > trifluorophenol > difluorophenol. Little or no proton abstraction occurred for fluorophenol, phenol, or benzyl alcohol analogs. Ion mobility spectrometry was used to determine if proton abstraction reactions passed through an adduct intermediate with thermalized ions and mobility spectra for all chemicals were obtained from 25 to 200 degrees C. Proton abstraction from M Cl- was not observed at any temperature for phenol, monofluorophenol, or difluorophenol. Mobility spectra for trifluorophenol revealed the kinetic transformations to (M-H)- either from M Cl- or from M2 Cl- directly. Proton abstraction was the predominant reaction for tetra- and penta-fluorophenols. Consequently, the evidence suggests that proton abstraction occurs from an adduct ion where the reaction barrier is reduced with increasing acidity of the O-H bond in C6H5-xFxOH.