Determination of hippuric acid and o-, m- and p-methylhippuric acids in urine by capillary gas chromatography

Application of biological monitoring for exposure assessment following chemical incidents: a procedure for decision making

Determination of the level of exposure during and after a chemical incident is crucial for the assessment of public health risks and for appropriate medical treatment, as well as for subsequent health studies that may be part of disaster management. Immediately after such an incident, there is usually no opportunity to collect reliable quantitative information on personal exposures and environmental concentrations may fall below detectable levels shortly after the incident has passed. However, many substances persist longer in biological tissues and thus biological monitoring strategies may have the potential to support exposure assessment, as part of health studies, even after the acute phase of a chemical incident is over. Reported successful applications involve very persistent chemical substances such as protein adducts and include those rare cases in which biological tissues were collected within a few hours after an incident. The persistence of a biomarker in biological tissues, the mechanism of toxicity, and the sensitivity of the analysis of a biomarker were identified as the key parameters to support a decision on the feasibility and usefulness of biological monitoring to be applied after an incident involving the release of hazardous chemicals. These input parameters could be retrieved from published methods on applications of biomarkers. Methods for rapid decision making on the usefulness and feasibility of using biological monitoring are needed. In this contribution, a stepwise procedure for taking such a decision is proposed. The persistence of a biomarker in biological tissues, the mechanism of toxicity, and the sensitivity of the analysis of a biomarker were identified as the key parameters to support such a decision. The procedure proposed for decision making is illustrated by case studies based on two documented chemical incidents in the Netherlands.

Hippuric acid and methyl hippuric acid in rat hair: possible monitoring of xylene and toluene exposure

Thinner is mainly composed of toluene and xylenes, and we studied the incorporation of the main metabolites of toluene and xylenes, hippuric acid (HA) and o-, m-, and p-methyl hippuric acids (o-, m-, p-MHA), in dark agouti rats' hair. Rat black hair was shaved before any exposure with an electric shaver designed for animals. Studies were performed in vivo with exposures of 30 min per day at three different concentrations (100, 300, and 1000 ppm) of toluene and o-, m-, and p-xylene for a total of 10 times over 2 weeks. Newly grown hair was tweezed out from the root with tweezers at seventh of the last exposure. Hair samples were then washed, extracted, derivatized, and analyzed by gas chromatography-mass spectrometry (GC-MS). HA and o-, m-, and p-MHA were not detected (ND) in the unexposed rat hair. After exposure, the metabolite concentration in the hair changed depending on the exposure concentration. Mean concentrations ranged from ND to 7.6 ng/mg, from ND to 13.8 ng/mg, from ND to 10.1 ng/mg, and from ND to 9.2 ng/ml hair for HA, o-, m-, and p-MHA, respectively. These results indicate that the metabolites concentrations in hair are effective indices of thinner exposure.

Simultaneous detection of hippuric acid and methylhippuric acid in urine by Empore disk and gas chromatography-mass spectrometry

A method is described for the determination of hippuric acid (HA) and o-, m-, and p-methylhippuric acids (o-, m-, p-MHAs) in urine using solid-phase extraction and gas chromatography-mass spectrometry (GC-MS). The extraction procedure uses an Empore disk, derivatized into the respective trimethyl silyl derivatives. All metabolites including the internal standard (I.S.) were clearly able to be analyzed by the DB-17 column. The calibration curves for the four acids show linearity in the range of 5-70 microg/ml. The detection limit of each acid was 1.0-2.5 microg/ml.

Simultaneous determination of the urinary metabolites of toluene, xylene and styrene using high-performance capillary electrophoresis. Comparison with high-performance liquid chromatography

A simple and rapid method using high-performance capillary electrophoresis (HPCE) for the simultaneous determination of the urinary metabolites of toluene, xylene and styrene, plus creatinine and uric acid in human urine specimens and standard solutions is described. The compounds were well separated from each other on a fused-silica capillary utilizing a 20 mM sodium tetraborate buffer (pH 9.65) with 15 mM beta-cyclodextrin and UV detection at 200 and 225 nm. The total analysis time was less than 6 min per sample. The capillary zone electrophoresis (CZE) method shows a good correlation with the high-performance liquid chromatography (HPLC) method with respect to urinary hippuric acid concentrations in the urine specimens of subjects exposed to the vapors of a solvent mixture of toluene and xylene. In comparing these two techniques, HPCE was found to be superior to HPLC because the analysis time is shorter, and the separation of m-MHA and p-MHA takes a long time with HPLC.

ATSDR evaluation of health effects of chemicals. V. Xylenes: health effects, toxicokinetics, human exposure, and environmental fate

Xylenes, or dimethylbenzenes, are among the highest-volume chemicals in production. Common uses are for gasoline blending, as a solvent or component in a wide variety of products from paints to printing ink, and in the production of phthalates and polyester. They are often encountered as a mixture of the three dimethyl isomers, together with ethylbenzene. As part of its mandate, the Agency for Toxic Substances and Disease Registry (ATSDR) prepares toxicological profiles on hazardous chemicals found at Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) National Priorities List (NPL) sites that are of greatest concern for public health purposes. These profiles comprehensively summarize toxicological and environmental information. This article constitutes the release of the bulk of this profile (ATSDR, 1995) into the mainstream scientific literature. An extensive listing of known human and animal health effects, organized by route, duration, and end point, is presented. Toxicological information on toxicokinetics, biomarkers, interactions, sensitive subpopulations, reducing toxicity after exposure, and relevance to public health is also included. Environmental information encompasses physical properties, production and use, environmental fate, levels seen in the environment, analytical methods, and a listing of regulations. ATSDR, as mandated by CERCLA (or Superfund), prepares these profiles to inform and assist the public.

Chromatographic determination of volatile solvents and their metabolites in urine for monitoring occupational exposure

The determination of volatile solvents and their metabolites in biological materials such as expired air, blood or urine allows the estimation of the degree of exposure of these chemicals. Chromatographic methods are now universally employed for this purpose and numerous analytical procedures are available for the determination of the most commonly used volatile solvents and their metabolites in urine. GC methods appear well adapted to the determination of the parent volatile solvents in blood and urine and may be used for the determination of their urinary metabolites, but these methods often require several prechromatographic steps. However, HPLC is becoming a powerful tool for the accurate and easy determination of urinary metabolites of volatile solvents, considering its decisive advantages for routine monitoring. Further, recent developments in HPLC could widen the usefulness of this method for most complex analytical problems that could be encountered during this measurement. However, despite the relative neglect of planar chromatography in this area of concern and considering the great interest in methods that could permit the simultaneous assay of numerous samples often required by routine monitoring, new approach using improved methods such as overpressured TLC could be very fruitful in the future.

Quantitative structure-metabolism relationships for substituted benzoic acids in the rat. Computational chemistry, NMR spectroscopy and pattern recognition studies

An extensive set of computed molecular properties, both steric and electronic, have been calculated using molecular orbital and empirical methods for benzoic acid (1) and a congeneric series of substituted benzoic acids, i.e. 2-, 3- and 4-fluorobenzoic acids (2-4), 2-, 3- and 4-trifluoromethyl benzoic acids (5-7), 2-, 3- and 4-methylbenzoic acids (8-10), 4-amino benzoic acid (11), 2-fluoro-4-trifluoromethyl benzoic acid (12), 4-fluoro-2-trifluoromethyl benzoic acid (13), 3-trifluoromethyl-4-fluorobenzoic acid (14). We have monitored the urinary excretion profiles and determined the metabolic fate of compounds 2-7, 12-14 in the rat using high resolution 1H and 19F NMR spectroscopy. Corresponding data for compounds 1,8-11 are taken from the literature. In all cases phase II glucuronidation or glycine conjugation reactions dominated the metabolism of these compounds. Compounds 5, 7, 12, 13 have ester glucuronides as their major metabolites; the rest primarily form glycine conjugates. Compounds (1-12) have been classified according to their calculated physicochemical properties using pattern recognition methods and principal components maps have been used as a novel type of structure-metabolism diagram. The maps of compounds in the physicochemical property space served to separate the compounds into the two major classes which related to their principal metabolic fate in vivo, namely glucuronidation versus glycine conjugation. Compounds 13 and 14 were used as further probes of the property space, and dominant metabolic fates of glucuronidation and glycine conjugation, respectively, were predicted from the previous "training set map". The metabolic fate of compounds 1-14 can thus be classified according to a simple set of physicochemical rules. Investigation of the physicochemical properties which are important in distinguishing the metabolic fate of the compounds may give insight into key features of the drug-metabolizing enzyme active sites and hence provide information on basic mechanisms of benzoate metabolism.