Determination of the Content and Related Substances of Alendronate Sodium Tablet Using the Mixed-mode Chromatographic Column in All Aqueous System

OBJECTIVE To establish a mixed-mode chromatographic column coupled with charged aerosol detector method for the determination of related substances and content of the alendronate sodium tablets. METHODS The chromatographic separation was achieved on Acclaim Trinity P2 column(2.1 mm×100 mm, 3 μm) with column temperature of 35℃ by a gradient elution using the mobile phase of water(A)-100 mmol·L^-1 ammonium formate(B, adjusted with formic acid to pH 3.3)(0-4 min, 20%→50%B; 4-6 min, 50%→40%B; 6-8 min, 40%→20%B). The flow rate was 0.3 mL·min^-1, and the injection volume was 20 μL. Charged aerosol detector was used. Nebulization temperature was 50℃, collection frequency was 5 Hz, and the filter constant was 3.6 s. RESULTS The method for content determination of alendronate sodium had a good linearity in the range of 0.70-1.40 mg·mL^-1(r²=0.999 2), the repeatability was good(RSD=0.53%). The average recovery(n=9) of alendronate sodium was 99.8%(RSD=1.25%). Under the terms of dertermination of related substances, the main component of alendronate sodium, impurity of phosphate, phosphite and 4-aminobutyric acid had good linear range in 19.04-76.16, 3.95-49.38, 3.97-49.69, 3.94-49.23 μg·mL^-1, respectively(r²>0.998), and the corrected factors for each impurity were 0.67, 0.56, 0.55. The limit of quantitation concentration of each impurity was about 0.05% of the concentration of the main component. In addition, the average recoveries(n=9) of impurity test method were 86.2%, 85.4%, 91.0%, and RSD<2%, respectively; the labeled content of alendronate in alendronate sodium tablets produced by three companies were 92.0%, 91.5% and 95.2%, respectively, and the content of each impurity was less than the limit of 0.5% under alendronate sodium in the Chinese Pharmacopoeia. CONCLUSION The method is simple, accurate, sensitive, and applicable for the content determination and related substances inspection of alendronate sodium tablets.