Radiometric determination of trace amounts of anionic surfactants in ground water and potable water

Abstract

The water sample is treated with an excess of ferroin solution labelled with iron-59. The solution is extracted with chloroform and the activity of a portion of the extract is measured. The anionic surfactant content of the sample is determined by the standard addition of sodium lauryl sulphate.

The application of the method to river-water and tap-water samples gives results that agree with those obtained by using Abbott's methylene blue method. The present method requires 30 minutes for each reading, i.e., blank, sample or sample plus standard.

The over-all standard deviation for river-water samples has been calculated to be ±4·3 per cent. at the level of 0·1 p.p.m. of sodium lauryl sulphate.

The limit of detection is 0·1 µg of sodium lauryl sulphate (0·005 p.p.m. in a 20-ml sample). This limit is the equivalent of the average blank. Blanks are minimised by extracting at pH 4 with chloroform equilibrated with water, by performing only one extraction, by centrifuging for a fixed period and by removing the extract for counting with a capillary device.

No species have been found to interfere when present at the levels that are normally encountered in river waters. Potential interferences by fluoride or iron are compensated for by the internal standard.