Abstract:

Objective: To establish a method for determining Congo red in chili powder by ultra-high performance liquid
chromatography (UPLC). Methods: Samples were extracted with a mixture of ammonia and ethanol (30:70, V/V). The
extraction process was aided by ultrasonic treatment and repeated three times. The combined extract was concentrated
and then clean-up on an HLB solid-phase extraction cartridge by washing with 5 mL of 1% formic acid in methanol
and elution with 5 mL of 10% ammonia in methanol. The collected eluate was concentrated under a stream of nitrogen
prior to analysis. The chromatographic separation was achieved within 4 min on a BEH C18 column (50 mm×2.1 mm,
1.7 μm) by gradient elution using acetonitrile as mobile phase A and 10 mmol/L ammonium acetate as mobile phase B at a
flow rate of 0.4 mL/min. The detection wavelength was set at 498 nm and the column temperature was maintained at 40 ℃.
Results: Average recoveries of Congo red from chili samples spiked three concentration levels ranged from 72% to 96% with
relative standard deviation of 2.16%–5.97% (n = 6). The detection limit of the proposed method was 0.029 0 mg/kg, and the
correlation coefficient for the calibration curve was 0.999 9. Conclusion: This method is simple, rapid, accurate, sensitive
and suitable for detecting Congo red dye in chili powder.

Key words: ultra-high performance liquid chromatography (UPLC), chili powder, Congo red, quantitative determination