Development of LC-MS and LC-MS/MS Methods for Free Asparagine in Grains

New analytical methods for the determination of free asparagine (Asn), which is a precursor of acrylamide, in grains were developed using LC-MS and LC-MS/MS. Asn was extracted from a sample with 5% (w/v) aqueous trichloroacetic acid solution, appropriately diluted with 0.1% (v/v) formic acid solution, and then analyzed by LC-MS or LC-MS/MS. HPLC separation was performed by isocratic elution on a Penta Fluoro Phenyl (PFP) column using 0.1% (v/v) formic acid and acetonitrile mixture as the mobile phase. The calibration curve was linear in the range of 0.005-0.1 mu g/mL. The mean recoveries from potato starch, non-glutinous rice flour and whole wheat flour ranged from 95.4 to 100.9%, repeatability (RSD) ranged from 0.9 to 6.0%, and within-laboratory reproducibility (RSDwr) ranged from 2.8 to 7.1%. Limits of quantitation (LOQs) were 7 mg/kg for potato starch, and 5 mg/kg for non-glutinous rice flour. In addition, an inter-laboratory study was performed in 10 laboratories using 5 kinds of grains (non-glutinous brown rice flour, corn flour, strong flour, whole wheat flour, and whole rye flour), which naturally contained free asparagine. The HORRAT(R) values ranged from 0.4 to 1.0. These results are within the range of the procedural manual of the Codex Alimentarius Commission, confirming the effectiveness of the developed procedures.