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The determination of very small amounts of selenium in plant samples with 2,3-diaminonaphthalene has been investigated. Losses of selenium are prevented by a controlled wet-oxidation procedure in a silicone bath. A method is proposed for the determination of selenium in plant materials at levels as low as 0·005 p.p.m. in dried material.

The distribution of fluorine compounds found in biological materials, including soils, is outlined. Several improvements are proposed for the sampling and ashing of animal and plant tissues, and soil, including the use of finely ground suspensions in dilute agar solution. Some modifications are suggested in the separation of fluorine by diffusion as hydrofluoric acid and its subsequent determination with alizarin complexan. The effect of silica in the analysis of plants and soils for fluorine is discussed.

Examination by paper and thin-layer chromatography of several preparations of titan yellow from different manufacturers has shown them to be complex mixtures.By using a titan yellow selected chromatographically, it has been possible to improve the stability and sensitivity of the coloured complex produced with magnesium. Studies have been made of the effects of alkalis, interfering ions and protective colloids, and the use of gelatin with a lithium hydroxide-glycine buffer is proposed for the determination of magnesium in soil extracts. Results have been compared with those obtained by atomic-absorption spectroscopy and show close correlation.

The determination of small amounts of fluorine in biological samples without distillation wse described. The method involves the collection of fluorine by diffusion in a polythene bottle, absorption by alkali-treated filterpaper and subsequent titration with thorium nitrate solution in the presence of alizarin sulphonate. The method is simple and it is not complicated by the problems associated with conventional distillation techniques. (auth)

The determination of available lysine in proteins by their reactions with 2,4,6-trinitrobenzenesulphonic acid has been examined in relation to the preparation of the sample, the conditions of the reaction, the hydrolysis of the trinitrophenylated protein and the effects of other amino-acids and related compounds. From these observations a revised method is proposed for the rapid routine screening of animal protein concentrates used in animal feeds. With the use of DL-lysine as a standard instead of Iµ-trinitrophenyllysine and with a simplified hydrolysis procedure, the technique is suitable for examining comparatively large numbers of samples. Interference by other amino compounds is slight, except that by cadaverine, hydroxylysine and ornithine.Results are given for the levels of available lysine in a range of animal proteins, which compare closely with values obtained by the Carpenter procedure in which 1-fluoro-2,4-dinitrobenzene is used.