Determination of caprolactam and 6-aminocaproic acid in human urine using hydrophilic interaction liquid chromatography-tandem mass spectrometry

A simple and rapid assay based on hydrophilic interaction liquid chromatography with tandem mass spectrometry has been first developed and validated for simultaneous determination of caprolactam (CA) and 6-aminocaproic acid (6-ANCA) in human urine using 8-aminocaprylic acid as internal standard. A 20 μL aliquot of urine was injected directly into the liquid chromatography tandem mass spectrometry (LC–MS–MS) system. The analytes were separated on a Phenomenex Luna HILIC column with gradient elution. Detection was performed on Triple Quadrupole LC–MS in positive ions multiple reaction monitoring mode using electrospray ionization. The calibration curves were linear (r2 ≥ 0.995) over the concentration range from 62.5 to 1250 ng/mL for CA and 31.25 to 1000 ng/mL for 6-ANCA. The detection limits of CA and 6-ANCA were 62.5 and 15.6 ng/mL, respectively. The intra-day and inter-day precisions were within 8.7% and 9.9%, respectively. The intra-day and inter-day accuracy were between 5.3% and 3.5%, and between 6.1% and 6.6%, respectively. The method proved to be simple and time efficient, and was successfully applied to evaluate the kinetics of caprolactam in one unusual case of caprolactam poisoning.