Development and validation of a method for direct, underivatized analysis of free amino acids in rice using liquid chromatography-tandem mass spectrometry

Inspired by the apparent relationship of free amino acids (FAAs) which are present in minute quantities with the organoleptic characteristics of food, there is an increased demand for analytical methods sensitive in trace level detection. This study presents the validation results of a simple and rapid method developed for direct, underivatized analysis of FAAs in rice using liquid chromatography-tandem mass spectrometry (LC-MS/MS) with electrospray ionization (ESI). The method demonstrated satisfactory selectivity for twenty FAAs with minimum matrix effect. The recoveries obtained for samples fortified at three concentration levels: low mid and high, covering the working range of the method were in the range 80%-110%. The precision measured in terms of repeatability and reproducibility of the method expressed as percentage relative standard deviation (% RSD) were below 10% for the amino acids analyzed. The detection limits (LODs) and quantification limits (LOQs) of the method were in the range 0.4-1.0 mg/kg and 0.6-1.2 mg/kg respectively. Method had a wide linear range between 1.25-100 mg/kg with regression coefficients greater than 0.999 obtained over seven calibration levels. The method was also found robust over other cereals including corn, wheat and finger millet with satisfactory recoveries and precision values. The percentage expanded uncertainties calculated with the coverage factor of 2 (k = 2), were below 14% for the analyzed amino acids. The developed, simple and rapid LC-MS/MS method is accurate and reproducible, allowing determination of underivatized FAAs in rice and comply with the international method validation guideline requirements. (C) 2018 Elsevier B.V. All rights reserved.