In acidic solution and in the presence of ferric ions the conventional reaction of sulfide (S(2-)) with p-aminodimethylaniline to form methylene blue dye has been applied for the improvement of the sulfide determination in natural water and waste water by the updated method named rimary-secondary wavelengths spectrophotometry (PSWS). The analtical precision and accuracy were both increased and gave the higher determination sensitivity than the ordinary spectrophotometry.
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