DETERMINATION OF FLUORIDE IMPURITIES IN CALCIUM ASCORBATE COMPARISON OF GAS-CHROMATOGRAPHY AND ION-SELECTIVE ELECTRODE POTENTIOMETRY

Fluoride impurities in pharmaceutical grade calcium ascorbate were det ermined analytically by capillary gas chromatography (GC) and ion-sele ctive electrode potentiometry (ISE). In the GC method, the amount of f luoride impurities was quantitatively analyzed following the conversio n of fluoride to its corresponding trimethylsilane derivative using tr imethylchlorsilane. The derivatization procedure was performed under a cidic conditions and the generated trimethylfluorsilane was subsequent ly extracted with n-hexane prior to GC analysis using isopentane as an internal standard. In the potentiometric method, the fluoride content was determined by relating the potential of the sample solution at di fferent concentrations to a calibration curve. A comparative evaluatio n between the two methods was validated according to their linearity, precision, and accuracy. The fluoride concentrations found by means of GC and ISE were (0.94 +/- 0.04) ppm and (0.85 +/- 0.12) ppm, respecti vely. The student's t-test (error of the first kind alpha = 0.1) indic ated that there was no significant difference between the results obta ined by the two methods.