Improved procedure for preparation of pentafluorobenzyl derivatives of carboxylic acids for analysis by gas chromatography with electron-capture detection

Simultaneous determination of allantoin and glycolic acid in snail mucus and cosmetic creams with high performance liquid chromatography and ultraviolet detection

A new methodology for simultaneous quantitative analysis of allantoin and glycolic acid in snail mucus and cosmetic creams was developed. HPLC separation was achieved a Synergi-Hydro RP column within 7min using isocratic elution with potassium phosphate (pH 2.7; 10mM) at a flow rate of 0.7mL/min at 30°C. Sample pretreatment was performed by dilution of mucus or cosmetic cream in the elution buffer, heating at 60°C for 20min, adjusting the pH to 2.9 and purification with hexane extraction. Linearity was determined with spiked samples and the LLOQ values of 0.0125 and 0.2500mg/mL were determined for allantoin and glycolic acid, respectively. Accuracy and intra- and inter-day repeatability were studied at three levels of concentrations (0.04, 0.08 and 0.16mg/mL for allantoin and 0.1, 1.5 and 4.0mg/mL for glycolic acid) using spiked mucus and cream base samples; mean values of recovery were in the range of 96.81-102.42% in all matrices tested, whereas the respective RSDs (%Relative Standard Deviation) were less than 3.04% in all cases. Spiked mucus and cream samples were stable (RSD<4.16 and relative error<4.34%) at room temperature and at 4°C for 1 week and at -18°C for 6 months; samples were also stable after three freeze-thaw cycles. The method was applied to the analysis of different lots of snail mucus, and of three commercial creams containing snail mucus.

Measurement of bisphenol A levels in human urine

We report a new approach for assessing human exposure to bisphenol A (BPA) by measuring BPA in urine after enzymatic deglucuronidation. This method involves addition of (13)C(12)-labeled BPA, enzymatic deconjugation, solid-phase extraction, and derivatization with pentafluorobenzyl bromide. The product of the derivatization is separated by gas chromatography followed by mass spectrometric detection using negative chemical ionization and selected ion monitoring. Using this analysis method, urine samples fortified with both a constant level of labeled BPA and a range of unlabeled BPA levels (0.27-10.6 ng/ml) demonstrated constant percentage recovery. In addition, a range of urine sample volumes (0.25-10.0 ml) with constant amounts of added internal standard produced a linear response (r(2)=0.99). The method limit of detection was 0.12 ng/ml. This method was validated by duplicate analyses using gas chromatography coupled to a high-resolution mass spectrometer.

Determination of glycolic acid in cosmetic products by solid-phase extraction and reversed-phase ion-pair high-performance liquid chromatography

A procedure has been developed for the assay of glycolic acid in cosmetic products by reversed-phase high-performance liquid chromatography using an ion-pairing method. After dissolution in tetrahydrofuran-water (90:10, v/v), samples were purified by solid-phase extraction using silica-based strong anion-exchange cartridges and analysed directly on an Ultrasphere ODS column with UV detection at 210 nm and methanol-phosphate buffer (2:98, v/v), containing tetrabutylammonium iodide, as the mobile phase. Recovery of glycolic acid from different cosmetic matrices was between 92.4 and 96.2% and the precision of the method was better than 5.4% relative standard deviation. The procedure is rapid, simple, selective and it is suitable for routine analyses of commercial cosmetics.

Quantitative determination of oxalate and other organic acids in drinking water at low microgram/1 concentrations

In this research, a recently developed ion chromatography method for organic acids was expanded to include oxalate. A major challenge was that oxalate elutes between inorganic anions such as sulfate, phosphate, bromide and nitrate, which are often present in much higher concentrations than oxalate. Optimization of the previously reported method made it possible to determine oxalate in these matrices. However, for those samples in which higher inorganic anion concentrations caused the oxalate peak to be obscured, a "heart-cut" column switching technique was used as an alternative. The method detection limit for oxalate was 9 micrograms/l with the direct approach and 6 micrograms/l for the "heat-cut" technique. These modifications represent a valuable supplement to a recently developed method for monitoring ozonation by-products in drinking water.

Methods to reduce background interferences in electron-capture gas chromatographic analysis of valproic acid and its unsaturated metabolites after derivatization with pentafluorobenzyl bromide

Analysis of the branched, medium-chain fatty acid anticonvulsant, valproic acid, and its unsaturated metabolites by gas chromatography with electron-capture detection suffered from background interference caused by the derivatizing reagent pentafluorobenzyl bromide. Background was reduced by keeping the derivatization anhydrous, using an inert solvent, minimizing the amount of pentafluorobenzyl bromide, using hypernucleophilic bases and displacing the derivatization solvent with isooctane. However, these strategies proved difficult to reproduce. Post-derivatization clean-up with HPLC was much more reliable and provided sufficient sensitivity for the analysis of extracts of plasma and brain homogenate. The assay was validated for plasma and brain samples from humans, rats and mice.

Determination of short-chain aliphatic, oxo- and hydroxy-acids in drinking water at low microgram per liter concentrations

A fast and reliable ion chromatography method has been developed and applied to study the formation and consumption of organic acid ozonation by-products in a drinking water treatment plant. Water samples are injected directly into the ion chromatograph using a large sample loop (740 mu l) without any sample preparation step other than possibly filtration. Organic and inorganic anions are determined by separation on a high-capacity anion-exchange column followed by conductivity detection. The average recovery for the organic acids investigated (beta-hydroxybutyric, acetic, glycolic, butyric, formic, alpha-ketobutyric and pyruvic acid) ranged from 96 to 105%, and their method detection limits ranged from 1 to 5 mu g/l. When applied to samples taken from a drinking water treatment plant, the method proved to be reliable.

Detection of malignancy-associated metabolites in the sera of cancer patients by electron capture gas chromatography

A reliable test that detects malignancy and indicates response to therapy is needed. Frequency-pulsed electron-capture gas-liquid chromatography (FPEC-GLC), a selective analytical technique that is sensitive to 15 fmol quantities of metabolites, was used to analyse derivatised acidic chloroform extracts of sera from patients with biopsy-proven cancer, non-malignant infectious and non-infectious disease, and healthy controls. Two peaks designated P1 and P10, not found in serum from healthy controls (n = 7) or patients with non-malignant disease (n = 85), were detected in biopsy-proven samples (n = 52) from cancer patients. P1 and P10 were later shown by chemical and mass spectral studies to be carboxylic acids. When one or both of these peaks were detected in the sera of non-treated patients they were always associated with malignancy. In patients responding to therapy, a reduction or disappearance of these peaks was observed. Further, it was noted that P10 persisted or increased in sera of patients with progressive cancer not responding to therapy. We conclude that this test has potential in diagnosis and for following the response of the disease to therapy.

Trace analysis of quinapril and its active metabolite, quinaprilat, in human plasma and urine by gas chromatography-negative-ion chemical ionization mass spectrometry

A highly specific and sensitive method for the simultaneous determination of quinapril and its active metabolite, quinaprilat, in human plasma and urine by gas chromatography-negative-ion chemical ionization mass spectrometry is described. Quinapril and quinaprilat were extracted from human plasma and urine by using a Bond-Elut C18 cartridge. The plasma or urine extract was treated with pentafluorobenzyl bromide followed by trifluoroacetic anhydride to convert quinapril and quinaprilat into their pentafluorobenzyl-trifluoroacetyl derivatives, which were analysed by a selected-ion monitoring method using deuterium-labelled internal standards. The limits of quantitation for both quinapril and quinaprilat were 0.05 ng/ml in plasma and 0.5 ng/ml in urine. The proposed method is applicable to pharmacokinetic and clinical pharmacological studies with satisfactory reliability.

Applications of cellular fatty acid analysis

More than ever, new technology is having an impact on the tools of clinical microbiologists. The analysis of cellular fatty acids by gas-liquid chromatography (GLC) has become markedly more practical with the advent of the fused-silica capillary column, computer-controlled chromatography and data analysis, simplified sample preparation, and a commercially available GLC system dedicated to microbiological applications. Experience with applications in diagnostic microbiology ranges from substantial success in work with mycobacteria, legionellae, and nonfermentative gram-negative bacilli to minimal involvement with fungi and other nonbacterial agents. GLC is a good alternative to other means for the identification of mycobacteria or legionellae because it is rapid, specific, and independent of other specialized testing, e.g., DNA hybridization. Nonfermenters show features in their cellular fatty acid content that are useful in identifying species and, in some cases, subspecies. Less frequently encountered nonfermenters, including those belonging to unclassified groups, can ideally be characterized by GLC. Information is just beginning to materialize on the usefulness of cellular fatty acids for the identification of gram-positive bacteria and anaerobes, despite the traditional role of GLC in detecting metabolic products as an aid to identification of anaerobes. When species identification of coagulase-negative staphylococci is called for, GLC may offer an alternative to biochemical testing. Methods for direct analysis of clinical material have been developed, but in practical and economic terms they are not yet ready for use in the clinical laboratory. Direct analysis holds promise for detecting markers of infection due to an uncultivable agent or in clinical specimens that presently require cultures and prolonged incubation to yield an etiologic agent.

Two-dimensional gas chromatography with electron capture detection for the sensitive determination of specific mycobacterial lipid constituents

A method was developed for determining two characteristic mycobacterial lipid constituents, tuberculostearic acid (as its pentafluorobenzyl ester) and 2-eicosanol (as its pentafluorobenzoyl ester), by using gas chromatography with electron capture detection. A microprocessor-controlled column-switching system (two-dimensional gas chromatography) facilitated sample preparation and increased specificity. The usefulness of the technique was illustrated by its ability to reveal picogram amounts of tuberculostearate in a suspension of Mycobacterium leprae isolated from a naturally infected armadillo. Two-dimensional gas chromatography with electron capture detection may in some instances provide a convenient alternative to gas chromatography-mass spectrometry for use in demonstrating the presence of mycobacteria in a complex environment.