Simultaneous determination of dl-lactic acid and dl-3-hydroxybutyric acid enantiomers in saliva of diabetes mellitus patients by high-throughput LC–ESI-MS/MS

A simultaneous determination method for the enantiomers of chiral carboxylic acids by the combination of ultraperformance liquid chromatography and mass spectrometry (UPLC–MS/MS) has been developed. (S)(+)-1-(2-Pyrrolidinylmethyl)-pyrrolidine (S-PMP) was used as the derivatization reagent for the high-throughput determination of biological chiral carboxylic acids, i.e., lactic acid (LA) and 3-hydroxybutyric acid (HA). The S-PMP efficiently reacted with the carboxylic acids under mild conditions at room temperature in the presence of 2,2′-dipyridyl disulfide and triphenylphosphine. The resulting S-PMP derivatives were highly responsive in the electrospray ionization (ESI)-MS operating in the positive-ion mode and gave characteristic product ions during the MS/MS, which enabled the sensitive detection using selected reaction monitoring. The derivatization was effective for the enantiomeric separation of the chiral carboxylic acids, and the resolution values of dl-LA and dl-HA were 4.91 and 9.37, respectively. Furthermore, a rapid separation of the derivatives of dl-LA and dl-HA within 7 min was performed using the UPLC system. The limits of detection on the column were in the low femtogram range (5–12 fg). The proposed procedure was successfully applied for the determination of the d- and l-isomers of LA and HA in the saliva of diabetes mellitus (DM) patients and healthy volunteers. The d-LA in DM patients was clearly higher than that in normal subjects. The derivatization followed by UPLC–ESI-MS/MS enabled the enantiomeric separation and detection of trace amounts of LA and HA in human saliva with a simple pretreatment and small sample volume.