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<br />ANALYTICAL -GENERAL <br />Direct Coloritnetric Determination of Cyanide With Picric Acid <br />I Outline <br />Free cyanide and weak-acid dissociable cyanide reacts with the picric acid rertgent <br />to produce an orange colour which can be measured colorimetrically at 520 nm or can <br />be estimated by eye. As with all colorimetric methods, standards must be prepaze3 for <br />comparison purposes. <br />Chemically speaking, the dissolved alkali metal picrate is converted by cytutide <br />into the coloured salt of isopurpuric acid and its concentration is measured. For <br />determination of cyanide below 0.1 ppm extractive preconcentration techniques cam be <br />used which are described in the original method. The presence of a small amount of <br />nickel in the analyzed solutions has a positive effect on the overall performance of the <br />method, but is not absolutely necessary. <br />II Apnlicadon <br />The method is suitable for the determination of weak acid dissociable cy;tnide <br />(CNW,,o) in effluents from flotation mills, gold cyanidadon mills and electroplating shops. <br />Since the detection limit for this procedure is 0.26 ppm CNW,~ it is especially usefitl for <br />monitoring cyanide discharges to the environment Below is a comparison of the results <br />from the weak-acid dissociable cyanide distillation method (CNW„~ and that obCairted <br />with the picric acid method (CN,) described herein. It is apparent that CNW„p is <br />essentially the same as CNP though it is useful to retain the distinction between the <br />methods. <br />w.w+w~.u.rnum 4 <br />