Determination of polythionates in an active crater lake by nitrate ion-selective electrode.

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A nitrate ion-selective electrode, Orion model 93-07, has been examined to determine in situ tri- to hexathionate in an active crater lake. The electrode (ISE) showed a linear response to aqueous polythionates within a range of 10-5-10-2M. The slope in the plot of log concentration vs electrode potential was slightly larger than the Nernst slope for S3O62-, S4O62- and S5O2-6, while a considerably larger one was observed for S6O2-6. Selectivity coefficients determined by the fixed interference method were k34pot=23, k45pot=10 and k56pot=7.0 for a pair of S3O2-6--S4O2-6, S4O2-6-S5O2-6 and S5O2-6-S6O2-6, respectively. The observed variation in the electrode potential for polythionate solution was best explained in terms of the Nicholsky-Eisenman equation. Chloride and sulfite ions less than 2500 ppm and 500 ppm, respectively, did not interfere with the potential measurement. The sum of three polythionates (tetra-plus penta- plus hexathionate) of volcanic origin determined by the ISE method has agreed well with those by the microbore column HPLC.
日本地球化学会の論文