Spectrophotometric analysis of sulphide sulphur as methylene blue

2 Spectrophotometric analysis of sulphide sulphur as methylene blue General remarks 

Hydrogen sulphide and dimethyl-p-phenylenediamine form a sulphurous intermediate compound (intermediate stage), which changes into leucomethylene blue. The leucomethylene blue is oxidized by iron (III) ions to methylene blue. The methylene blue is measured photometrically at 670 nm. 

The reactions described above may be formulated as follows (after K. E. Quentin and F. Pachmayr)  

This method can be used for direct determination of sulphide sulphur in 

In the case of modification B, the sulphide sulphur fixed as zinc sulphide is distilled in distillation apparatus as hydrogen sulphide after adding phosphoric acid, and collected in a receiver containing zinc acetate solution. Further treatment is as for modification A. 

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