Development of a method for the determination of total bisphenol a at trace levels in human blood and urine and elucidation of factors influencing method accuracy and sensitivity.

This publication describes a method for the determination of total bisphenol A (BPA and conjugated BPA) following enzyme hydrolysis and is intended as a companion to our previously developed analytical method for the determination of free BPA (the aglycone) in human blood and urine using high-performance liquid chromatography-tandem mass spectrometry ( 1). That free BPA method provided a means to account for and/or eliminate background contamination and demonstrated accuracy and reproducibility in both matrices fortified with BPA or a surrogate analyte ((13)C BPA) at a low method quantitation limit (MQL) of 0.1-0.2 ng/mL. In contrast to the free BPA method results and based on stringent accuracy, precision and confirmation criteria set for the MQLs of the method developed for total BPA, the MQL achieved in blood was 1.020-2.550 and 0.510-1.020 ng/mL in urine. These data showed higher MQLs than the desired MQLs of 0.5 ng/mL (blood) and 0.2 ng/mL (urine) with increased variability between analyses which demonstrates the importance of generating method validation data with each analysis. In contrast, the MQL achieved for (13)C BPA-G (monoglucuronide as a surrogate analyte in blood was 0.2-0.5 and 0.2 ng/mL in urine illustrating that the method is capable of meeting lower MQL requirements if the contribution from exogenous BPA can be well controlled. This method for the determination total BPA in human blood and urine is intended to be used in conjunction with the free BPA method ( 1) to obtain accurate and complete BPA biomonitoring data to support human exposure assessments.

Determination and confirmation of parent and total ractopamine in bovine, swine, and turkey tissues by liquid chromatography with tandem mass spectrometry: First Action 2011.23.

A candidate method selected by the AOAC Expert Review Panel (ERP) for Ractopamine for determination and confirmation of parent and total ractopamine by LC/MS/MS was validated in a single laboratory for bovine, swine, and turkey tissues. The candidate method utilizes methanol extraction of the tissues, followed by an optional enzymatic hydrolysis for determination of total (parent plus conjugate) ractopamine. A mixed-mode cation exchange SPE cartridge is used to purify the initial extract before LC/MS/MS. Matrix-matched standards and a ractopamine-d6 internal standard are used for quantification of parent and total ractopamine in unknown samples. Validation data demonstrated that mean intertrial recoveries for ractopamine across all concentrations tested ranged from 79.7 to 102.2% for parent ractopamine and from 79.0 to 100.0% when a hydrolysis step was included. Intertrial repeatability precision ranged from 2.44 to 11.1% for parent ractopamine and 4.97 to 15.0% with hydrolysis. Estimated LOD values were below 0.1 ng/g and LOQ values were validated at 0.25x the maximum residue limits. The data satisfy the requirements of the AOAC Stakeholder Panel for Veterinary Drug Residue Methods for single laboratory validation studies. The method was awarded Official Methods of Analysis First Action 2011.23 by the AOAC ERP on Veterinary Drug Residues.