Determination of Boric Acid and Borate in Toothpaste by Ion Exclusion Chromatography

The toothpaste sample (0.50 g) was dispersed with 90% (volume fraction) methnol solution by vortex for 1 min. The mixture was dilluted to 25.0 mL with water, extracted by ultrasound for 20 min and centrifuged for 5 min. The supernatant obtained was purified by Cleanert IC-RP column, and the effuent (the first 4 mL of effluent was discarded) was analyzed by ion exclusion chromatography. Target was seperated by IonPac ICE Borate column with mixed solution of 3 mmol·L^-1 methanesulfonic acid and 60 mmol·L^-1 mannitol as eluant and mixed solution of 25 mmol·L^-1 tetramethylammonium hydroxide and 15 mmol·L^-1 mannitol as regenerant, and detected by suppressed conductance detector. It was shown that linear relationship between values of mass concentration of boric acid and peak area was kept in the range of 1.0-100.0 mg·L^-1, with detection limit (3S/N) of 0.002%. The proposed method was applied to the analysis of actual samples, and RSD (n=6) of the determined values was 1.9%. Results of test for the spiked recovery were found in the range of 98.3%-105%, and the detection amounts were lower than the limit specified by GB 22115-2008.