Gas and high-performance liquid chromatography of phenols

Perspectives on the relevance of the circadian time structure to workplace threshold limit values and employee biological monitoring

The circadian time structure (CTS) and its disruption by rotating and nightshift schedules relative to work performance, accident risk, and health/wellbeing have long been areas of occupational medicine research. Yet, there has been little exploration of the relevance of the CTS to setting short-term, time-weighted, and ceiling threshold limit values (TLVs); conducting employee biological monitoring (BM); and establishing normative reference biological exposure indices (BEIs). Numerous publications during the past six decades document the CTS substantially affects the disposition - absorption, distribution, metabolism, and elimination - and effects of medications. Additionally, laboratory animal and human studies verify the tolerance to chemical, biological (contagious), and physical agents can differ extensively according to the circadian time of exposure. Because of slow and usually incomplete CTS adjustment by rotating and permanent nightshift workers, occupational chemical and other contaminant encounters occur during a different circadian stage than for dayshift workers. Thus, the intended protection of some TLVs when working the nightshift compared to dayshift might be insufficient, especially in high-risk settings. The CTS is germane to employee BM in that large-amplitude predictable-in-time 24h variation can occur in the concentration of urine, blood, and saliva of monitored chemical contaminants and their metabolites plus biomarkers indicative of adverse xenobiotic exposure. The concept of biological time-qualified (for rhythms) reference values, currently of interest to clinical laboratory pathology practice, is seemingly applicable to industrial medicine as circadian time and workshift-specific BEIs to improve surveillance of night workers, in particular. Furthermore, BM as serial assessments performed frequently both during and off work, exemplified by employee self-measurement of lung function using a small portable peak expiratory flow meter, can easily identify intolerance before induction of pathology.

Use of disposable GRC electrodes for the detection of phenol and chlorophenols in liquid chromatography

In this study, a wall-jet flow cell with a GRC (graphite reinforced by carbon) electrode was designed for the amperometric detection of phenol and chlorophenols in liquid chromatography. The voltammetric responses of these analytes at the GRC electrodes are very similar to those at conventional glassy carbon electrodes. As the GRC electrodes were made of the same materials as commercially available mechanical pencil leads, they exhibit the advantages of low cost, simple surface renewability, lower residual current, and good electrode-to-electrode reproducibility, and thus can be used as disposable-type electrodes. Chromatographic separations of phenol, o-chlorophenol (o-CP), 2,4-dichlorophenol (2,4-DCP), 2,4,6-trichlorophenol (2,4,6-TCP), and pentachlorophenol (PCP) were achieved with an ODS column using a mobile phase containing a mixture of CH3CN and H20 (40:60) containing 25 mM L-(+)tartaric acid (pH = 4.5). Amperometric detections were based on the electrochemical oxidation of these compounds around +0.9 V vs. Ag/AgCl. Under the optimized conditions, linear calibrations were obtained in a range up to 100 microM for phenol, o-CP, 2,4-DCP, 2,4,6-TCP, and 200 microM for PCP, with the correlation coefficients r2 of 0.9992, 0.9997, 0.9986, 0.9992, and 0.9968, respectively. The chromatographic detection limits for the tested analytes were obtained at pmol levels.

Quantitation of o-, m- and p-cresol and deuterated analogs in human urine by gas chromatography with electron capture detection

A gas chromatographic method for the analysis of cresol metabolites of toluene and [2H8]toluene in urine was developed. Cresol glucuronides and sulfates in urine were hydrolyzed with beta-glucuronidase and arylsulfatase. Following extraction with tert.-butyl methyl ether and solvent exchange into benzene, the cresols were derivatized with heptafluorobutyric anhydride to form the heptafluorobutyrate esters. The derivatives were analyzed by gas chromatography with electron capture detection. Chromatographic resolution was achieved between all cresol isomers and their 2H7 analogs. Calibration ranged from 0.001 to 500 microg/ml. Recoveries were 55-97% and showed no trend with respect to analyte concentration. Within-day precision of analyses of benchmark urine samples had a coefficient of variation of less than 4%. The assay sensitivity was limited by chromatographic background but was sufficient for quantification of the unlabeled cresols in urine from men with only environmental exposure to toluene. Average levels in urine samples from 45 men were 0.023, 0.054 and 37 microg/ml for o-, m- and p-cresol, respectively.

Biodegradation studies of hydrocarbons in soils by analyzing metabolites formed

Microbial degradation of diesel fuel and lubricating oil was studied in artificial soils. Soon after 1 week and until the end of the study (25 weeks) organic acids and ketones which were not original components of the oils contaminating the soil samples were identified. Predominantly alicyclic and branched-chain aliphatic organic acids as well as diacids and aromatic ketones were formed by degradation. Further degradation of these alicyclic acids was observed. Similar oxidized products were also identified in actual contaminated soils.

Gas chromatographic determination of phenol compounds with automatic extraction and derivatization

Two gas chromatographic procedures for the determination of a variety of substituted phenols in water samples are described. The phenols were extracted or extracted-derivatized by using a continuous liquid-liquid extraction-derivatization system and quantified with flame ionization detection. Ethyl acetate was found to be the most efficient solvent for phenols whereas n-hexane yielded essentially the same recoveries for derivatized phenols. Between 0.1 and 300 mg/l of the different phenols can be detected with a relative standard deviation 1.1 and 3.7%. The acetate esters of six phenols were formed by the direct addition of acetic anhydride to the organic extractant. The stable acetate esters thus formed were isolated by using a standard dimethyl polysiloxane gas chromatographic column.

Gas chromatographic and mass spectrometric determination of nitroaromatics in water

Several methods for the extraction of nitroaromatic compounds from water were compared. High recoveries were achieved with discontinuous or continuous extraction of water with dichloromethane and by adsorption on Amberlite XAD-2, -4 and -8 resins (1:1:1) and elution with dichloromethane. The recoveries obtained with solid-phase extraction using cyano-, phenyl- or octadecyl-bonded phases varied, depending on the compounds studied, and were often low. Nitroaromatic compounds were determined by gas chromatography using an electron-capture or a chemiluminescence detector (thermal energy analyser) and by mass spectrometry using electron impact and positive- and negative-ion chemical ionization.

Determination of tebufelone (a new anti-inflammatory drug) strength and stability in bulk drug, dosage formulations and feed admixtures by reversed-phase high-performance liquid chromatography

A rugged reversed-phase high-performance liquid chromatographic method suitable for the quantitative determination of tebufelone, a new anti-inflammatory drug, in bulk drug, various pharmaceutical formulations and animal feed admixtures is described. Tebufelone was easily separated from synthetic by-products and detected by ultraviolet absorption (280 nm). Standard curves were linear (r2 greater than 0.999) over 2 orders of magnitude with a detection limit of 0.1 microgram/ml at a signal-to-noise ratio of 2 (0.05 ml injected). Recovery of tebufelone from bulk drug and dosage formulations was greater than 99% with a coefficient of variation of 1.8% throughout the range of the standard curve. Recovery of tebufelone from feed admixtures was 96-102% with a less than 5% relative standard deviation at the levels assayed.

[Determination of residual monomers of epoxy resins in wine simulants]

Wine is widely stocked in epoxy resin vats. These bisphenol A epoxy resins are cured with methylenedianiline hardener. The residual monomers are able to migrate through the polymer matrix into the wine. So, migration studies were undertaken in order to prevent human health hazard. In this paper specific chromatographic methods for the determination of the residual monomers in simulants of wine are described. Liquid chromatographic methods were developed for the determination of methylenedianiline and bisphenol A, and a gas chromatographic method for the determination of epichlorhydrin. The procedures described proved to be sensitive, reproducible and efficient.

Determination of trace levels of phenol and cresols in rain by continuous liquid-liquid extraction and high-performance liquid chromatography

Trace levels of phenol and methylphenols (cresols) in aqueous samples were determined by continuous liquid-liquid extraction and normal-phase high-performance liquid chromatography with UV-fluorescence detection. The recovery of phenol from water at a concentration of 1.6 micrograms l-1 was 70 +/- 6%. The method successfully measured traces of phenol and cresols extracted from rainwater without further clean-up. The average reproducibility of the method for rain samples was +/- 16%. The results compared well with those obtained by high-resolution gas chromatography-mass spectrometry.