IC Determination of 4 Trace Anions in Industrial Formic Acid

IC was applied to the determination of 4 trace anions, i.e., F-, Cl-, NO3- and SO42-. The sample (20.000 g) was evaporated to dryness with addition of 0.4 mL of 100 g·L-1 Na2CO3 solution on a water bath, to eliminate matrix interference of HCOOH and to prevent loss of F- and Cl- by volatilization as HF and HCl during evaporation. The residue was taken up with water and its volume was made up to 100 mL for use in IC analysis. The columns of IonPacTM AG23 and IonPac AS23 were used as guarding column and analytical column respectively, and buffer solution of 4.5 mmol·L-1 Na2CO3-0.8 mmol·L-1 NaHCO3 solution was used as eluant in IC separation. Under the optimized condition, linear relationships between values of peak area and mass concentration of the 4 anions in definite ranges were kept, with detection limits (3S/N) of 0.01, 0.02, 0.03, 0.03 mg·L-1 respectively. Using substantial samples as matrixes, recovery was tested by standard addition method, giving results in the range of 96.2% to 106%.