Determination of aflatoxins in food samples by automated on-line in-tube solid-phase microextraction coupled with liquid chromatography-mass spectrometry

A simple and sensitive automated method for determination of aflatoxins (B1, B2, G1, and G2) in nuts, cereals, dried fruits, and spices was developed consisting of in-tube solid-phase microextraction (SPME) coupled with liquid chromatography-mass spectrometry (LC-MS). Aflatoxins were separated within 8 min by high-performance liquid chromatography using a Zorbax Eclipse XDB-C8 column with methanol/acetonitrile (60/40, v/v): 5 mM ammonium formate (45:55) as the mobile phase. Electrospray ionization conditions in the positive ion mode were optimized for MS detection of aflatoxins. The pseudo-molecular ions [M+H]⁺ were used to detect aflatoxins in selected ion monitoring (SIM) mode. The optimum in-tube SPME conditions were 25 draw/eject cycles of 40 μL of sample using a Supel-Q PLOT capillary column as an extraction device. The extracted aflatoxins were readily desorbed from the capillary by passage of the mobile phase, and no carryover was observed. Using the in-tube SPME LC-MS with SIM method, good linearity of the calibration curve (r > 0.9994) was obtained in the concentration range of 0.05-2.0 ng/mL using aflatoxin M1 as an internal standard, and the detection limits (S/N = 3) of aflatoxins were 2.1-2.8 pg/mL. The in-tube SPME method showed >23-fold higher sensitivity than the direct injection method (10 μL injection volume). The within-day and between-day precision (relative standard deviations) at the concentration of 1 ng/mL aflatoxin mixture were below 3.3% and 7.7% (n = 5), respectively. This method was applied successfully to analysis of food samples without interference peaks. The recoveries of aflatoxins spiked into nuts and cereals were >80%, and the relative standard deviations were <11.2%. Aflatoxins were detected at <10 ng/g in several commercial food samples.