The procedure specified may be applied to products having contents in the range 1 to 1O OOO mg/kg and is particularly suitable for distillates with less than 3OO mg/kg. Test samples which are viscous, highly aromatic, or of high content may be first diluted with a sulfur-free solvent. The procedure can be used for natural and refinery gases, also for substances supplied to the burner in the liquid state and for the determination of volatile sulfur in substances supplied to the burner in the gaseous state after vaporisation from the liquid phase. It is not suitable for heavy-duty engine oils.