Determination of aflatoxins in rice from Penang, Malaysia by dispersive liquid-liquid micro-extraction and LC-MS/MS

Rice is one of the crops cultivated in Malaysia, and it is the main diet for most of the population. In this study, dispersive liquid-liquid micro-extraction (DLLME) and liquid chromatography-tandem mass spectrometry (LC-MS/MS) were used to develop, optimise and validate a reliable, easy-to-use and quick approach to detect aflatoxin B1 (AFB1), aflatoxin B2 (AFB2), aflatoxin G1 (AFG1) and aflatoxin G2 (AFG2). The extraction recoveries in DLLME were enhanced by the addition of 5% salt, utilising chloroform as the extraction solvent and acetonitrile as the dispersive solvent. The DLLME parameters - the extraction solvent volume, salt concentration and dispersive solvent volume were optimised with Box-Behnken design (BBD) and response surface methodology (RSM). Under optimised experimental conditions, excellent linearity was obtained with a limit of detection (LOD) ranging from 0.125 to 0.25 ng g^-1, a limit of quantitation (LOQ) ranging from 0.25 to 0.3 ng g^-1 and a correlation value (R²) of 0.990. The matrix effects were between -11.1% and 19.9%, and recoveries ranged from 87.4% to 117.3%. The optimised and validated method was used effectively to assess aflatoxins contamination in 20 commercial rice samples collected from local supermarkets in Penang, Malaysia. AFB1 was detected at 0.41-0.43 ng g^-1 in two rice samples, below the regulatory limit.