High-performance liquid chromatographic determination of hippuric acid in human urine

Health hazards of xylene: a literature review

Xylene, an aromatic hydrocarbon is widely used in industry and medical laboratory as a solvent. It is a flammable liquid that requires utmost care during its usage. On exposure the vapours are rapidly absorbed through the lungs and the slowly through the skin. Prolonged exposure to xylene leads to significant amount of solvent accumulation in the adipose and muscle tissue. This article reviews the various acute and chronic health effects of xylene through various routes of exposure.

Urinary hippuric acid after ingestion of edible fruits

Aim of this study was to evaluate the biotransformation of simple phenols after ingestion of edible fruits and mixed food. It was analyzed hippuric acid in urine as biomarker of conjugation in the liver cells of glycine with aromatic phenolic acids such benzoic and salicylic acid from ingested food. Measurement of hippuric acid in urine samples of 10 healthy individuals: 5 female and 5 male with a mean age 51,5 years were recruited to participate in this study. Urine samples were collected for 24 hours. The additional meals 300 g of fruits: blueberry, cherry, raspberry, melon, blackberry and mixed food were given immediately before the 24 hr urine sampling. Otherwise, the meals given during 24 hr was a usually food. Biotransformation of phenols in edible fruits, that are together with liver glycins precursors of hippuric acid biosynthesis, was evaluated by direct spectrophotometric measurement of excreted hippuric acid in urine at 410 nm. It was established that the highest quantity of hippuric acid was after ingestion of 300 g of bilberry fruits (p< 0,003), and same quantity of cherries (p< 0,003). Concentration of excreted hippuric acid was twice higher after ingestion of these fruits in comparison with hippuric acid concentrations in urine after ingestion of common - mixed food. Quantity of biosynthesised hippuric acid was in direct correlation with the concentrations of its precursors, primarily phenol acids and other simple aromatic acids ingested with food.

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.

Determination of aromatic hydrocarbons and their metabolites in human blood and urine

Methods for the biological monitoring of aromatic hydrocarbons and their metabolites in the human blood and urine are reviewed. For the determination of the unchanged aromatic hydrocarbon in blood, gas chromatographic head-space analysis is recommended. The metabolites can be monitored by photometric, thin-layer chromatographic, high-performance liquid chromatographic and gas chromatographic methods. For the assessment of health risks caused by aromatic hydrocarbons, reference values and occupational limit values, expressed as biological tolerance values and biological exposure indices, have to be considered.

Simultaneous high-performance liquid chromatographic determination of urinary metabolites of benzene, nitrobenzene, toluene, xylene and styrene

A high-performance liquid chromatographic method is described for the simultaneous determination of six urinary metabolites of several aromatic chemicals: phenol (from benzene), hippuric acid (from toluene), 3-methylhippuric acid (from xylene), mandelic and phenylglyoxylic acid (from styrene) and 4-nitrophenol (from nitrobenzene). Reversed-phase liquid chromatography was performed in an isocratic mode at 1 ml/min on a 5-microns C18 column using two mobile phases: (A) acetonitrile-1% phosphoric acid (10:90); (B) acetonitrile-1% phosphoric acid (30:70). Phase A separates the six metabolites well, but phase B allows to a more rapid and reproducible simultaneous determination of phenolic compounds than phase A. For these compounds a prior enzymic hydrolysis step using Helix pomatia juice is performed to hydrolyse their sulphate and glucuronate conjugates. The reproducibility and the specificity are both excellent. Furthermore, the method is rapid, economical and easily automated. The proposed method appears very suitable for the routine monitoring of workers exposed to these chemicals on the basis of the biological threshold limit values.

A new derivatization procedure for the analysis of hippuric acid and m-methyl-hippuric acid by gas chromatography

The industrial solvents, toluene and xylene, have physicochemical properties that can be hazardous to the workers exposed. Since hippuric acid and m-methyl-hippuric acid represent the products of toluene and xylene biotransformation in urine, they are used as biological markers in studies on occupational exposure to these solvents. Several methods have been used to determine hippuric acid and m-methyl-hippuric acid--either based on gas chromatography or on high-performance liquid chromatography. In this study we propose the derivatization of hippuric acid and methyl-hippuric acid using methanol in acid medium (HCl), a low-cost reagent with a low level of toxicity. The method has been routinely used in our laboratory for 1 year and has proven to be a reliable procedure for the biological control of occupational exposure to toluene and/or xylene.

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

A capillary gas chromatographic (GC) method for the simultaneous determination of urinary hippuric acid (HA) and o-, m- and p-methylhippuric acids (MHAs), metabolites of toluene and o-, m- and p-xylenes, respectively, is described. These metabolites are converted into their isopropyl derivatives by extractive alkylation with tetrahexylammonium ion as extracting agent and isopropyl bromide as alkylating reagent in benzene. The derivatives are analysed using a chromatograph equipped with hydrogen flame ionization detector, split injection system and DB-17 capillary column. Benzoylleucine is used as an internal standard. The derivatives are well separated within 5 min and no interfering peaks are observed. The calibration curves of HA and MHAs in the range 1-50 micrograms are linear and sufficiently reproducible for quantitative analysis. Urine can be analysed accurately and precisely by this method without prior clean-up of the sample.

The role of the laboratory in the investigation of solvent abuse

1 A wide range of compounds which may be abused by inhalation such as butane, the halons, 1,1,1-trichloroethane, trichloroethylene and toluene can be detected and identified in blood specimens by means of headspace gas chromatography. Quantitative analysis of a number of the less volatile compounds of interest may also be accomplished. 2 The measurement of the urinary concentrations of benzoic and hippuric acids (metabolites of toluene) and of the toluric acids (metabolites of the xylenes) by high performance liquid chromatography may provide useful information. In general, a hippurate/creatinine ratio of greater than 1 is indicative of recent toluene exposure. 3 Analysis of the product abused by vapor-phase infra-red spectrophotometry and/or gas chromatography may also be valuable, especially since manufacturers' data as to the constituents of a given product are not always accurate. 4 Toxicological analyses can provide clinically valuable diagnostic information where inhalational abuse of volatile substances is suspected, and provide the only unequivocal means of defining the agent(s) abused by a given population.

Detection and identification of volatile organic compounds in blood by headspace gas chromatography as an aid to the diagnosis of solvent abuse

A gas chromatographic method has been developed for the detection and identification of some volatile organic compounds in whole blood, plasma or serum. After incubation of the sample (200 microliters) together with the internal standard solution in a sealed vial, a portion of the headspace is analysed using a 2-m glass column packed with 0.3% (w/w) Carbowax 20M on Carbopack C, 80-100 mesh. The column oven, after a 2-min isothermal period, is programmed from 35 to 175 degrees C at 5 degrees/min and held for 8 min. The effluent is monitored by both flame-ionisation and electron-capture detection, and peak assignment is by means of retention time and relative detector response. The method has proved applicable to the detection of bromochlorodifluoromethane, n-butane, carbon tetrachloride, chlorobutanol, cryofluorane (Halon 114), dichlorodifluoromethane (Halon 12), ethyl acetate, halothane, isobutane, isopropanol, isopropyl nitrate, methyl ethyl ketone, propane, tetrachloroethylene, toluene, 1,1,1-trichloroethane, 2,2,2-trichloroethanol, trichloroethylene and trichlorofluoromethane (Halon 11) in blood specimens obtained from patients suspected of abusing these agents.

Determination of urinary hippuric acid and o-cresol, as indices of toluene exposure, by liquid chromatography on dynamically modified silica

Two simple and sensitive high-performance liquid chromatographic methods for the determination of hippuric acid and o-cresol in urine have been developed. The chromatographic system is the same for the two methods and is based on dynamically modified silica. The detection limits were found to be 0.05 mg/ml and 0.05 microgram/ml of urine for hippuric acid and o-cresol, respectively, when using UV detection at 254 nm. The recovery for hippuric acid was about 100% and for o-cresol 33-36%. The detection limit for o-cresol could be lowered by a factor of ten by using fluorescence detection. The methods were used for investigations of the urine from persons exposed to 100 ppm toluene for 6.5 h. The method for o-cresol may also be used for determination of other phenols in urine.