Analysis of abietic acid and dehydroabietic acid in food samples by in-tube solid-phase microextraction coupled with liquid chromatography-mass spectrometry

A simple and sensitive method for the determination of abietic acid and dehydroabietic acid in food samples was developed using a fully automated method consisting of in-tube solid-phase rnicroextraction (SPME) coupled with liquid chromatography-mass spectrometry (LC/MS). These compounds were separated within 5 min by HPLC using an ODS-3 column and 5 mM ammonium formate/acetonitrile (10/90, v/v). Electrospray ionization conditions in the negative ion mode were optimized for MS detection of abietic acid and dehydroabietic acid. The optimum in-tube SPME conditions were 20 draw/eject cycles of 40 mu L of sample using a Supel Q PLOT capillary column as an extraction device. The extracted compounds were easily desorbed from the capillary by passage of the mobile phase, and no carryover was observed. Using the in-tube SPME LC/MS method, good linearity of the calibration curve (r > 0.9998) was obtained in the concentration range from 0 to 50 ng/mL, and the detection limits (S/N = 3) of abietic acid and dehydroabietic acid were 2.9 and 2.1 pg/mL, respectively. The in-tube SPME method showed above 75-fold greater sensitivity than the direct injection method (5 mu L injection). This method was applied successfully to analysis of food samples without interference peaks. The recoveries of abietic acid and dehydroabietic acid spiked into liquid samples were above 79%, and the relative standard deviations were below 6.6%. These compounds were detected at ng/mL or ng/g levels in various liquid or solid food samples contacted with paper. (c) 2007 Elsevier B.V. All rights reserved.