Abstract:

A new method for the determination of the hexafluorosilicic acid in the wasted hydrofluoric acid by ion chromatography (IC) with UV-Vis (ultraviolet-visible) detector after post column reaction was investigated. The wasted hydrofluoric acid was produced in the silicon etching bath. The separation was achieved on a Metrosep A Supp 7 column with 3.2 mmol/L sodium carbonate and 1.0 mmol/L sodium bicarbonate at a flow rate of 0.7 mL/min. In this thesis, the derivatization reaction temperature, reagent adding rate and the UV detector wavelength were studied. The other mineral acids in the etching bath, such as hydrofluoric acid, chloric acid, nitric acid, phosphoric acid, acetic acid and sulfuric acid also could be determined in the same time by the suppressed conductivity detection. The method showed that hexafluorosilicic acid had good linearities in the range of 2.4-120 mg/L. The average recovery of the hexafluorosilicic acid in the real sample was 97.2%. The limit of quantification of hexafluorosilicic acid was 0.24 mg/L. The method is accurate, fast and suitable for the determination of hexafluorosilicic acid in the etching bath solution.

Key words: conductivity detector, hexafluorosilicic acid, ion chromatography (IC), ultraviolet (UV) detector