High-throughput measurement for micro-segmental hair analysis using parallel column regeneration in liquid chromatography/tandem mass spectrometry.

Abstract

PURPOSE: We previously developed micro-segmental analysis (MSA), which measured detailed distributions of drugs in hair by segmenting a single hair strand at a 0.4-mm interval. MSA is effective in estimating the day of ingestion of hypnotics in drug-facilitated crimes. However, the disadvantage is that it needs considerable time to provide analytical results because hundreds of segments are analyzed using liquid chromatography (LC)-tandem mass spectrometry. In this study, the LC conditions were modified to improve the throughput of measurements. METHODS: Instrumental parts and parameters for LC were optimized to shorten the cycle time while maintaining separation between etizolam and triazolam, which have relatively similar retention times and the same nominal mass. Additionally, parallel column regeneration (PCR) available in two-dimensional LC system, which can switch channels through two identical columns, was used. RESULTS: The cycle time was reduced from 429 s to 235 s by changing the sample needle volume (from 15 to 30 µL), column length (from 150 to 50 mm) and injection volume (from 50 to 30 µL), and steepening the mobile phase gradient. Moreover, the use of PCR reduced the cycle time to 194 s by paralleling sample measurements with washing and equilibration of the lines. The effectiveness of the LC method modified using PCR was confirmed by the MSA of a long hair (978 segments) collected from a participant who had ingested hypnotics. CONCLUSIONS: This high-throughput measurement greatly contributed to saving machine time and early providing evidence of drug-facilitated crimes, showing detailed distributions of drugs in hair.