Determination of sulfate ion by potentiometric back-titration using sodiumtetrakis (4-fluorophenyl) borate as a titrant and a titrant-sensitive electrode

A potentiometric back-titration method for the determination of sulfate ion s using a plasticized poly(vinyl chloride) membrane electrode sensitive to a titrant is described. The method is based on ion association between the excess of 2-aminoperimidinium added to the sulfate ion in the sample and so dium tetrakis (4-fluorophenyl) berate (FPB) in the titrant. The titration e nd-point was detected as a sharp potential change due to an increase in the concentration of the free FPB at the equivalence point. The end-point was detected even in the presence of a 20-fold excess of common cations and ani ons relative to the concentration of the sulfate ion within similar to 2% o f titration error. A linear relationship between the concentration of the s ulfate ion and the end-point volume of the titrant exists in the sulfate io n concentration range from 2 x 10(-4) to 3 x 10(-3) mol l(-1) using 10(-2) mol l(-1) FPB solutions as the titrant. The present method could be applied to determine sulfate ions in sea water. (C) 1999 Elsevier Science B.V. All rights reserved.