A rapid UHPLC-QDa method for quantification of human salivary amino acid profiles

Abnormal salivary amino acid (AA) levels may indicate dysfunction of the body. Being noninvasive, sampling easily and cost-effective of saliva, a rapid, precise and simple analysis method has become very important for quantitative salivary AA profiles. After one-step to precipitate protein, the resultant extraction was derived with 6-aminoquinolyl-N-hydroxysuccinimidyl carbamate (AQC) within 10 min. Quantitation of AA profile was achieved within 6 min in a single run by ultra-high performance liquid chromatography coupled with a single quadrupole mass spectrometry (UHPLC-QDA detector). The method was validated with acceptable accuracy ranging from 80.33 % to 122.31 %, appropriate linearity with the coefficient (R²) more than 0.991, good intra- and inter-day precision, repeatability and stability (RSD < 15 %). The recoveries at three different spiked concentrations ranged over 79.18 %-125.36 % while the matrix effect was from -19.86 % to 11.95 %. This simple, rapid and robust method was successfully applied to quantify human salivary 30 amino acids, in which the levels of taurine, γ-aminobutyric acid, methionine and tryptophan in healthy people were close to the LOQs. Besides, the levels of histidine and cystine were not able to be measured due to their relatively high LOQs, which were considered as the limitations of this developed method.