Estimation of barium sulphate in faeces by emission flame photometry.

Received for publication 12 July 1968. ashed in a muffle furnace at 600'C for at least three hours. Of the acid ammonium sulphate, 10 ml, and 30 ml of water are added to the ashed sample, and after warming to dissolve soluble material the contents are decanted with washing into a 50 ml centrifuge tube, the BaSO4 being washed into the tube as far as possible. The tube is centrifuged for 5 min, the supematant decanted off and the tube allowed to drain. If necessary the supernatant (plus washings) may be used for the analysis of soluble minerals such as calcium. Meanwhile 10 ml ofammonium EDTA and 3 ml TMAH are added to the silica beaker which is then warmed on a steam bath for 10 min to dissolve any remaining BaSO4. The contents of the beaker are transferred to the tube with washing, and the tube placed in a boiling water bath for about 10 min with occasional stirring. The solution is cooled, made up to 50 ml, and filtered (if necessary) before flame photometry which is carried out in the usual manner.