Determination of Tranexamic Acid in Toothpaste by Pre-Column Derivatization Coupled with UPLC-ECD

Tranexamic acid in the ca. 1 g of toothpaste sample was extracted with 50 mL of water by ultrasound for 30 min. After centrifuging for 10 min, the supernatant was reacted with the same volume of derivative reagent solution (containing 150 mg·L^-1 OPA and 1.3 g·L^-1 sulfite) at room temperature for 5 min. Sample solution after derivatization was analyzed by UPLC-ECD. Waters ACQUITY UPLC BEH C₁₈ column was selected as the stationary phase, and the mixture of acetonitrile and 30 mmol·L^-1 ammonium acetate buffer solution (pH 3.6) at a volume ratio of 2:8 was used as the mobile phase in the isocratic elution. The results showed that a good linear relationship between mass concentration of tranexamic acid and its respective peak area was found in the range of 0.495-19.800 mg·L^-1, with detection limit of 0.18 μg·g^-1. Recovery test was made by standard addition method in the toothpaste sample, and value of recovery obtained was 98.6%, with RSD (n=6) of determined values of 2.4%. The derivatization product was stable within 12 hours when its peak area reduced by less than 5%. The proposed method was used to analyze the 6 toothpaste samples, tranexamic acid with mass fraction of 0.23 mg·g^-1 was found in one sample known to be added.