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<br />ANALYTICAL -GENERAL <br />The assay laboratory may also use [he picric acid method since it is much less time <br />consuming than conventional distillation methods. Generally an assays obtained with the picric <br />are either equal or slightly higher than aweak-acid dissociable distillation. Ir1 the picric acid <br />procedure for cyanide analyses, weakly complexed cyanides are liberated using <br />diethylenetriaminepentaacetic acid (DTPA) or ethylenediaminetetraacedc acid (EDTA) and along <br />with free cyanide, react with a buffered picric acid solution causing colour development. The <br />intensity of this colour development is proportional to the amount of cyanide present in the <br />solution. <br />No other cyanide assaying method is as easy when trying to rrleasure cyanide <br />concentrations of less than 1.0 ppm CNW,,D. The operators use the picric method to obtain a <br />rough estimate of the cyanide concentration for control purposes; though the laboratory can <br />obtain over two significant digits by exercising more care and by using a colorvilreter. One must <br />be aware of the distinction between the using picric for operating purposes and Using the method <br />as an accurate analytical tool by chemists. <br />The applicability of the picric acid method for cyanide determinations is discussed on the <br />following pages under the sub-section "laboratory procedure". Actually the laboratory procedure <br />is incomplete since the preparation of reagents and standazds have been removdd and placed on <br />separate pages. In this way the routine preparation of buffered picric acid reagent, mill picric, <br />and coloured standards can be photocopied for ready laboratory reference. <br />The "mill picric" is simply the fully strength "buffered picric acid reagent" with the <br />required dilution water all ready added which simplifies the procedure when the operators are <br />instructed to control the cyanide concentrations above 5 ppm CNw„o. <br />The procedures used by the operators are also included here for reference by the <br />laboratory. These procedures also appear in the "operating procedure" section of this manual. <br />K~Km~,m 3 <br />