The principle involved in this method is the determination of the sulfide content from the absorbance at 835 mμ of phosphomolybdenum blue which is resulted from a reaction between hydrogen sulfide and added phosphomolybdic acid (Scheme 1).
Values for sulfide contents of bottom mud samples in Hakata Bay area which were determined by the present colorimetric method, were fairly identical with those of the distillation-iodometric method²⁾ (Table 3), when the colorimetric values were corrected for the phosphomolybdenum blue value caused by ferrous ion (Scheme 2). Among various interfering redox substances so far studied, the presence of Fe⁸⁺, Sn²⁺ Cu and cysteine gave rise to an appreciable erroneous value. However, with most naturally occurring bottom mud the error due to possible redox substances excepting Fe²⁺ can be overlooked if any.