Comparison of amino acid derivatization reagents for liquid chromatography atmospheric pressure chemical ionization mass spectrometric analysis of seven amino acids in tea extract

Abstract

The applicability of five amino acid derivatization reagents was tested for liquid chromatography atmospheric pressure chemical ionization mass spectrometry (LC-APCI-MS). The aim of the study was to investigate the matrix effects (ME) during LC-APCI-MS analysis. The derivatization reagents were diethyl ethoxymethylenemalonate (DEEMM), dibenzyl ethoxymethylene malonate (DBEMM), dansyl chloride (DNS), 9-fluorenylmethyl chloroformate (FMOC-Cl) and 2,5-dioxopyrrolidin-1-yl N-tri(pyrrolidino)phosphoranylideneamino carbamate (FOSF).APCI-MS parameters were optimized and the suitability of methanol and acetonitrile as eluent component was assessed. For the evaluation of ME, post-column infusion for some DEEMM and FMOC-derivatives and sample dilution approach for seven amino acids in green tea extract with DEEMM, DBEMM, DNS and FMOC-Cl were used. The measurements with electrospray ionization (ESI) were carried out using the same chromatographic conditions for comparing ME in ESI and APCI.The method development showed that acetonitrile was suitable for APCI ionization. From the derivatization reagents, FOSF was not suitable for APCI analysis. In general, APCI showed less ME compared to ESI in case of all the derivatization reagents. Although the derivatives of DEEMM and DNS exhibited the least ME in APCI, some amino acids could not be analyzed. ME was evaluated for DBEMM derivatives with both ESI and APCI for the first time, and despite some ME, the sensitivity of DBEMM allowed elimination of ME with sample dilution. Analysis of seven amino acids in green tea extract was carried out and concentrations obtained with ESI and APCI agreed (differences were not statistically significant).