Rapid ion chromatography of l-ascorbic acid, nitrite, sulfite, oxalate, iodide and thiosulfate by isocratic elution utilizing a postcolumn reaction with cerium(IV) and fluorescence detection

Abstract

Rapid separation and determination of mixtures of l-ascorbic acid, nitrite, sulfite, oxalate, iodide and thiosulfate by conventional ion chromatography is often difficult due to incomplete separation of l-ascorbic acid and nitrite from the water peak when using eluents giving short elution times for iodide and thiosulfate. Separation of the six species within about 15 min has been achieved by isocratic elution using a resin-based ion-exchange column with a carbonate eluent containing a trace amount of 1,3,5-benzenetricarboxylic acid (BTA) and fluorescence measurement of cerium(III) formed via postcolumn reactions of the separated sample species with cerium(IV). Calibration plots of peak height versus concentration were linear up to 10.0 μ M (1.76 ppm) for l-ascorbic acid, 8.0 μ M (0.37 ppm) for nitrite, 8.0 μ M (0.70 ppm) for oxalate, 80.0 μ M (10.2 ppm) for iodide and 25.0 μ M (2.80 ppm) for thiosulfate, whilst the sulfite calibration was linear up to 25.0 μ M (2.00 ppm) when peak area was plotted against concentration. Detection limits (defined as S/ N=3) were 18 ppb for l-ascorbic acid, 4 ppb for nitrite, 16 ppb for sulfite, 7 ppb for oxalate, 72 ppb for iodide and 37 ppb for thiosulfate. The proposed method was applied successfully to the determination of l-ascorbic acid, nitrite, sulfite, oxalate, iodide or thiosulfate in water samples.