[Determination of free and total S-phenylmercapturic acid in the biologic monitoring of exposure to benzene]. / Determinazione dell'acido S-fenilmercapturico libero e totale nel monitoraggio biologico dell'esposizione a benzene.

One of the biomarkers suggested by the ACGIH to assess the professional exposure to benzene is the S-phenylmercapturic acid in the end-shift urine. The existence in the urine of N-acetyl-S(1,2-dihydro-2hydroxypHenyl)-L-Cysteine, a precursor of SPMA that can be turned into it by acid hydrolysis, is a possible cause of miscorrelation between environmental and biological monitoring. The amount of measured SPMA depends on the degree of hydrolysis and therefore it is a function both of the urine PH and of the storage conditions of the sample. 40 urine samples have been collected from workers exposed to benzene, both smokers and not smokers, and for each sample the percentage of SPMA measurable at pH 2 and without pH correction (free SPMA) has been calculated with respect to the SPMA measured after quantitative hydrolysis, with the objectives to determine if a correct assessment of the exposure requires the determination of total SPMA and which concentration value could correspond to the BEI of 25 microg/g of creatinine established by the ACGIH. An aliquot of the urine samples has been treated with 9M H2SO4, a second one is brought to pH 2 and a third one is analyzed as it is. All samples are analyzed by HPLC/MS/MS in negative ions/MRM mode, and quantitative analysis is performed using the internal standard method. The percentage found in samples treated at pH 2 is on average 45% of the total SPMA for smokers and 60% for non smokers, while the free SPMA varies from 1% to 66% due to the urine pH variability and to the lower concentrations detected. The determination of total SPMA allows the standardization of the preanalyticalfactors and the dosage with analytical methods less sensitive than HPLC/MS/MS.

Determination of free and total S-phenylmercapturic acid by HPLC/MS/MS in the biological monitoring of benzene exposure.

Urinary S-phenylmercapturic acid (SPMA) is a biomarker suggested by the American Conference of Governmental Industrial Hygienists (ACGIH) for assessing occupational exposure to benzene. A possible cause of the miscorrelation between environmental monitoring and biological monitoring for benzene exposure, which many authors complain about, is the existence of a urinary metabolite that turns into SPMA by acid hydrolysis. Forty urine samples were tested to determine which concentration value would correspond to the ACGIH Biological Exposure Index (BEI) of 25 microg g(-1) creatinine if exposure assessment was based on the determination of SPMA after quantitative hydrolysis of its precursor. An aliquot of each sample was hydrolysed with 9 M H2SO4, a second one was brought to pH 2 and a third one was used as it was (free SPMA). SPMA was determined by high-performance liquid chromatography/tandem mass spectrometric technique (HPLC/MS/MS) using an internal standard. The analytical method was validated in the range 0.5-50 microg 1(-1). The average SPMA in pH 2 samples is 45-60% of the total, while free SPMA varies from 1% to 66%. The hydrolysis of pre-SPMA reduces the likelihood of variability in the results by reducing pH differences in urine samples and increasing the amount of measured SPMA. The BEI limit value would be about 50 microg g(-1) creatinine.

Comparison between external and internal standard calibration in the validation of an analytical method for 1-hydroxypyrene in human urine by high-performance liquid chromatography/tandem mass spectrometry.

1-Hydroxypyrene is a metabolite of pyrene, a member of the class of polycyclic aromatic hydrocarbons (PAHs) whose toxic properties in some cases include carcinogenicity. The determination of 1-hydroxypyrene in human urine is used as a biological indicator for exposure to PAHs, which is related to the combustion of organic materials, like smoking, living in urban environments, and eating grilled or smoked food. The determination of 1-hydroxypyrene by high-performance liquid chromatography (HPLC) with fluorescence detection has very good sensitivity but it is not highly specific: this can reduce accuracy in the quantitative determination of low levels of analyte in a complex matrix like urine. An HPLC method that uses triple quadrupole mass detection has been validated with the objective both to improve the signal-to-noise (S/N) ratio and to achieve the maximum specificity for the analyte in those urine samples that are richer in possible inteferents. The calibration range for 1-hydroxypyrene is from 0.005-0.1 microg/L in the urine of non-smoking healthy volunteers. After solid-phase extraction, samples were analyzed by HPLC/tandem mass spectrometry (MS/MS) in the multiple reaction monitoring (MRM) mode. In order to obtain reliable results quantitative analysis must be performed by means of the internal standard method (we used deuterium-labelled 1-hydroxypyrene): the method accuracy is not less than 85%. The S/N ratio at a concentration of 0.1 microg/L is about 10, and therefore this can be considered the lowest limit of quantitation. The method performance does not change if urine samples are measured using a calibration curve prepared in methanol, thus reducing the time of analysis and costs.