Automatic switching valve system to minimize variation of liquid chromatography-tandem mass spectrometry-based chiral amino acid profiling.

Although d-amino acids are less prevalent in nature, they have been detected in mammals (including humans) and it is widely accepted that they might play important physiological roles. While an analytical method for chiral amino acid profiling is strongly required, it has not been well-established because of the difficulties associated with analysis. A high-sensitivity and high-throughput liquid chromatography-tandem mass spectrometry (LC-MS/MS) analytical method was recently reported by our group for chiral amino acids; however, it lacked sufficient repeatability for several d-amino acids. Thus, the aim of this research was to reduce the experimental variation of chiral amino acid analysis. By installing an automatic switching valve system in LC-MS/MS, it was possible to reduce the relative standard deviations of d-amino acid ratios (d/(d+l)) in rat urine obtained from three technical replicates. The results indicated that the automatic switching valve system was effective in minimizing the variation of d-amino acid ratios, and could be applied for profiling d-amino acids because of its high repeatability.