IP 30: Detection of mercaptans, hydrogen sulfide, elemental sulfur and peroxides - Doctor test method

Overview:

Scope
The Standard describes the 'Doctor' test for detecting the presence of mercaptans (thiols), hydrogen sulfide, elemental sulfur and traces of peroxides, see note 1, in automotive fuels, kerosines, and other middle distillate petroleum products.

NOTE 1 - The presence of a number of substances in the test sample can affect the result of the test.

Peroxides

This method cannot be used if there are more than trace amounts of peroxides in the test sample.

Carbon disulfide

If the test sample contains more than 0,4% (m/m) of sulfur as carbon disulfide it causes a darkening of the aqueous layer on standing and caution is necessary to avoid confusing this darkening with the immediate blackening due to hydrogen sulfide or that produced by mercaptans.

Phenolic substances

Certain phenolic substances (which may have been introduced as inhibitors) cause colouration of the  aqueous layer and if their presence is suspected, a blank test with sodium hydroxide solution in place of the sodium plumbite solution should be carried out first for the purpose of comparison, see 6.1.