Derivatization of chiral carboxylic acids with (S)-anabasine for increasing detectability and enantiomeric separation in LC/ESI-MS/MS

Abstract

A simple and practical derivatization procedure for increasing the detectability and enantiomeric separation of chiral carboxylic acids in LC/ESI-MS/MS has been developed. (S)-Anabasine (ANA) was used as the derivatization reagent and rapidly reacted with carboxylic acids [3-hydroxypalmitic acid (3-OH-PA), 2-(β-carboxyethyl)-6-hydroxy-2,7,8-trimethylchroman (γ-CEHC), and etodolac] in the presence of 4-(4,6-dimethoxy-1,3,5-triazin-2-yl)-4-methylmorpholium chloride. The resulting ANA-derivatives were highly responsive in ESI-MS operating in the positive-ion mode and gave characteristic product ions during MS/MS, which enabled sensitive detection using selected reaction monitoring; the detection responses of the ANA-derivatives were increased by 20-160-fold over those of the intact carboxylic acids and the limits of detection were in the low femtomole range (1.8-11 fmol on the column). The ANA-derivatization was also effective for the enatiomeric separation of the chiral carboxylic acids; the resolution was 1.92, 1.75, and 2.03 for 3-OH-PA, γ-CHEC, and etodolac, respectively. The derivatization procedure was successfully applied to a biological sample analysis; the derivatization followed by LC/ESI-MS/MS enabled the separation and detection of trace amounts of 3-OH-PA in neonatal dried blood spot and γ-CEHC in human saliva with a simple pretreatment and small sample volume.