Determination of trace levels of total carbonate-carbon by indirect photometric ion chromatography with nitrogen purging

Abstract

Purging with nitrogen substantially prevented atmospheric carbon dioxide from dissolving in the eluent used in indirect photometric ion chromatography. Total carbonate-carbon at trace levels could be determined as hydrogencarbonate by this method. By using an analytical column (250 × 4.6 mm I.D.) packed with MCI SCA-02 and 5.0 · 10 −4 M sodium hydrogenphthalate—1.5 · 10 −4 M N-2-hydroxyethyl-piperazine-N′-2-ethanesulphonic acid (HEPES) (pH 6.5) as the eluent, hydrogen-carbonate was detected as a negative peak at 250 nm. The detection limit (signal-to-noise ratio = 2) was 1.4 · 10 −11 mol (7 · 10 −7 M with an injection volume of 20 μl) and the calibration graph was linear from 3.0 · 10 −11 to 3.8 · 10 −9 mol ( r = 0.994). The coefficient of variation was less than 2% on injection of 4 · 10 −10 mol. Total carbonate-carbon at levels as low as 10 −4-10 −6 M level could be determined accurately. The errors in the analysis of practical samples by the method without nitrogen purging are demonstrated.