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<br /> <br />ANALYTICAL -GENERAL <br />Sample Preservation for Cyanide <br />An accurate cyanide determination is always easier to achieve when the sample is taken, <br />prepared and analyzed immediately. When immediate on site analysis are impossible, steps must <br />be taken to ensure sample stability. To ensure stability, the solids are removed, the pH raised <br />and the sample stored in a refridgerator. The following procedure is a suitable sample <br />preparation method for long term stability. <br />1) Sample is taken and allowed to settle for 5 to 10 minutes. <br />2) The sample is fil[ered through a fine filter paper to ensure separation of solids that are <br />larger than 0.45 micron size. (Recommended equipment: Gelman filtering apparatus with <br />47 mm size, 0.45 micron filter membrane). To our knowledge there i~ no guaranteed <br />method of sample preservation when solids aze present. <br />Note: If the sample is suspected to contain sulphides, these should be removed <br />by precipitation with lead carbonate before raising the pH to 12 for <br />preservation. Solid lead carbonate (2- 5 grams) is added to the sample, <br />which is then stirred, and allowed to settle as in step 1. Elimination of <br />the sulphides will prevent possible interference during colour development <br />after sample distillation. A quick check for sulphides Can be done by <br />adding a small amount of lead cazbonate to 10 - 50 mL of the supernatant <br />unfiltered sample. If a dark coloration is observed theh sulphides are <br />present and the entire sample should be treated with lead cazbonate as <br />suggested above. <br />3) A 1 litre portion of the filtered sample is placed in a plastic bottle. Dark plastic is <br />preferred since it prevents breakdown of iron cyanide and thiocyanate caused by UV <br />radiation. <br />w~K~~~ <br />15 <br />