N-benzoyl, L-glutamic acid as a suitable internal standard for the analysis of trans,trans-muconic acid in human urine by liquid chromatography

Direct analysis of urinary trans,trans-muconic acid by coupled column liquid chromatography and spectrophotometric ultraviolet detection: method applicability to human urine

A coupled column liquid chromatographic (LC-LC) method for the direct analysis in human urine of the ring opened benzene metabolite, trans,trans-muconic acid (t,t-MA) is described. The method was tested using urine samples collected from five refinery workers exposed to concentrations of airborne benzene (0.2-0.5 ppm), and from non-exposed volunteers. The analytical columns used were of 50 x 4.6 mm I.D. packed with 3 microm p.s. Microspher C18 material as the first column (C-1), and a 100 x 4.6 mm I.D. column packed with 3 microm p.s. Hypersil ODS material as the second one (C-2). The mobile phases applied consisted, respectively, of methanol-0.074% trifluoroacetic acid (TFA) in water (4:96, v/v) on C-1, and of methanol-0.074% TFA in water (10:90, v/v) on C-2. Under these conditions t,t-MA eluted 15 min after injection. The present method, coupling the LC-LC technique with UV detection at 264 nm, permits the quantitation of t,t-MA directly in urine at levels as low as 0.05 mg/l. The determination is performed with a sample throughput of 2 h(-1) requiring only pH adjustment and centrifugation of the sample. Calibration plots of standard additions of t,t-MA to pooled urine taken from five non-exposed subjects were linear (r>0.999) over a wide concentration range (0.05, 0.1, 0.5, 1.0, 2.0 mg/l). The precision of the method (RSD) was in the range of 0.5 to 3.8%, and the within-session repeatability on workers urine samples (levels 0.06, 0.1, 0.2, 1.0 mg/l) was in the range of 3 to 8%. The present method improves the applicability of routine t,t-MA analysis, where it is most desirable that a large number of biological samples can be processed automatically or with minimal human labour, at low cost, and with a convenient turn-around time.

Improved coupled column liquid chromatographic method for high-speed direct analysis of urinary trans,trans-muconic acid, as a biomarker of exposure to benzene

A coupled column liquid chromatographic (LC-LC) method for high-speed analysis of the urinary ring-opened benzene metabolite, trans,trans-muconic acid (t,t-MA) is described. Efficient on-line clean-up and concentration of t,t-MA from urine samples was obtained using a 3 microm C18 column (50x4.6 mm I.D.) as the first column (C-1) and a 5 microm C18 semi-permeable surface (SPS) column (150x4.6 mm I.D.) as the second column (C-2). The mobile phases applied consisted, respectively, of methanol-0.05% trifluoroacetic acid (TFA) in water (7:93, v/v) on C-1, and of methanol-0.05% TFA in water (8:92, v/v) on C-2. A rinsing mobile phase of methanol-0.05% TFA in water (25:75, v/v) was used for cleaning C-1 in between analysis. Under these conditions t,t-MA eluted 11 min after injection. Using relatively non-specific UV detection at 264 nm, the selectivity of the assay was enhanced remarkably by the use of LC-LC allowing detection of t,t-MA at urinary levels as low as 50 ng/ml (S/N>9). The study indicated that t,t-MA analysis can be performed by this procedure in less than 20 min requiring only pH adjustment and filtration of the sample as pretreatment. Calibration plots of standard additions of t,t-MA to blank urine over a wide concentration range (50-4000 ng/ml) showed excellent linearity (r>0.999). The method was validated using urine samples collected from rats exposed to low concentrations of benzene vapors (0.1 ppm for 6 h) and by repeating most of the analyses of real samples in the course of measurement sequences. Both the repeatability (n=6, levels 64 and 266 ng/ml) and intra-laboratory reproducibility (n=6, levels 679 and 1486 ng/ml) were below 5%.