A rapid determination of sodium dodecyl sulfate with methylene blue

A rapid procedure of sodium dodecyl sulfate determination was established. The method is sensitive (0–6 μg of SDS), accurate, easy to operate and uninfluenced by the presence of protein. The method is a modification of Mukerjee's that takes advantage of water-insoluble salt formation between the detergent and methylene blue, which was extracted by chloroform. Absorbance was measured in a test-tube-push-in type spectrophotometer (Bausch and Lomb Spectronic 20) with an aqueous layer on top of the chloroform; thus evaporation of chloroform was avoided and steps for removal of the aqueous phase and transfer of chloroform to cuvettes were omitted to greatly abbreviate the whole procedure.