Sweeping-micellar electrokinetic chromatography versus reversed phase liquid chromatography for the determination of coumarin in curry

Coumarin is a phytotoxin found in the popular spice cinnamon, which is used to flavor many Asian curry dishes. In this work, we developed and compared the analytical performance of reversed-phase liquid chromatography (RP-LC) and sweeping-micellar electrokinetic chromatography (MEKC) methods for the determination of coumarin in complex curry (gravy) samples. Using a matrix matched sample (curry after solvent extraction with methanol and diluted with 100 mM phosphoric acid), the intra-day and inter-day repeatability of retention/migration time and (corrected) peak area for both methods were acceptable (%RSD (n=6) ≤ 5%). The linear range and limit of quantitation (LOQ) were an order of magnitude better in RP-LC (RP-LC linear range = 0.11-108 mg/kg, LOQ = 0.11 mg/kg) (Sweeping-MEKC linear range = 2.16-216 mg/kg, LOQ = 2.16 mg/kg). However, the limit of detection (S/N=3) and LOQ in sweeping-MEKC was 0.65 mg/kg and 2.16 mg/kg, which were sufficient to report the levels of coumarin ≥ the European limit of 2 mg/kg in foods. During the analysis of 25 curry samples, relatively similar results for sweeping-MEKC and RP-LC were obtained for 6 samples that contained coumarin >LOQ of sweeping-MEKC. Interferences in RP-LC lead to significant overestimation of coumarin levels in 3 samples. Coumarin levels above the EU limit was found in 6 curry samples using the more selective sweeping-MEKC. This work should also raise public awareness on the presence of potentially high levels of coumarin in some foods.