For the first time, a very simple and fast method combining the use of a guard column coupled to tandem mass spectrometry (guard column-MS/MS) has been proposed for the determination of plasticizer metabolites in urine. Briefly, samples (1.0 mL) were submitted to enzymatic hydrolysis for 10 min, filtered, diluted 1/10 v/v with ultrapure water and directly injected into the system. A fast run of only 2 min (3 min including the injection cycle) allowed the determination of 19 analytes. Enzymatic hydrolysis, filtering material, and guard column-MS/MS conditions were optimized. Intra-day precision at the low-level concentration (expressed as relative standard deviation, %RSD) obtained from the analysis of synthetic urine samples varied between 11 and 20%. Limits of quantification ranged from 2.8 to 60 ng/mL. Trueness values, calculated as apparent recoveries, ranged from 70 to 135%. To correct for matrix effects, analyte concentrations in real urine were quantified by the standard addition method. To confirm the results obtained by guard column-MS/MS, an ultra(high)-performance liquid chromatography tandem mass spectrometry (UHPLC-MS/MS) method was also applied (total chromatographic run time 17 min, including column re-equilibration). Concentrations measured with both methods were in good agreement. Hence, we propose the use of guard column-MS/MS to analyse a large number samples in a very short time (semi-quantification), and apply the chromatographic analysis only to those samples with levels close to/higher than the concentrations equivalent to the safe maximum daily intakes of the parent compounds (confirmation). This double strategy (semi-quantification by guard column-MS/MS and confirmation-when needed-by UHPLC-MS/MS) implies important savings in time and money.
Keywords: Guard column; Phthalate metabolites; Tandem mass spectrometry; Ultra(high)-performance liquid chromatography; Urine.
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