Oceanography

4. Sampling and analysis

The sample must be collected in plastic containers or in metallic containers with inner surface plastic coated.

The sample is first collected in an ordinary Winkler bottle as in the case of oxygen determination. Then, reagents diamine and ferric chloride (1 ml each) are immediately added to this sample. The stopper is now replaced without trapping air bubbles. The blue colour starts developing in a few minutes and the bottle is left for 30-60 minutes for full colour development. The colour intensity of the sample is then measured against distilled water at 670mm using 1 or 5 cm cells in a spectrophotometer or colorimeter.

If the sample contains higher concentrations of hydrogen sulphide (>20 µg at/l or 3.2mg/l) it should be diluted with oxygen free distilled water prior to analysis.

If the level of hydrogen sulphide is appreciably high in the water, the titration method can be conveniently adopted. For this type of analysis procedure given under ‘standardisation of sulphide working solution’ may be followed by substituting 50ml of the water sample for 50ml of the standard solution.