Study of the matrix effects and sample dilution influence on the LC-ESI-MS/MS analysis using four derivatization reagents

For liquid chromatographic analysis of amino acids involving derivatization and mass-spectrometric detection, it becomes more important to evaluate the presence of matrix effects in complex samples. This is somewhat complicated for amino acid analysis where analyte free sample matrix is often unavailable. In this work, matrix effects were investigated using post-column infusion method for 9-fluorenylmethyl chloroformate (FMOC-Cl) derivatives of β-Ala, Gly and Phe and diethyl ethoxymethylenemalonate (DEEMM) derivative of β-Ala. While for DEEMM derivatives, the main signal suppression was due to the borate buffer, in case of FMOC-Cl, other FMOC-derivatives caused signal suppression. Analysis of amino acids in tea and honey with DEEMM, FMOC-Cl, p-N,N,N-trimethylammonioanilyl N'-hydroxysuccinimidyl carbamate iodide (TAHS) and dansyl chloride (DNS) showed that amino acid concentrations found with different reagents do not agree well. Sample dilution experiments indicated that the sample matrix affected the analysis results obtained with DEEMM the least, but with FMOC-Cl, TAHS and DNS, sample dilution had an influence on the results. When sample dilution and extrapolative dilution approach were applied on the latter results, an agreement of amino acid concentrations measured with different reagents was achieved within relative standard deviation (RSD) of 22% for most cases.