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<br />ANALYTICAL -GENERAL <br />4) The pH is raised to 12 by the addition of solid sodium hydroxide (the amount of NttOH <br />used depends on the volume of sample to be preserved and the initial pH, approximately <br />2 g/L). Sample preservation by pH adjustment should never be attempted without <br />prior sample filtration. Iron cyanide which has been precipitated while in the <br />cyanide destruction reactor may redissolve at high pH (such as at pH 12). <br />5) The sample should be chilled or kept in a refrigerator before transportation to an outside <br />laboratory. A small amount of foam insulation would help to protect the sample and <br />keep it cold while in transit. The above step is simply an added insurance to mauitain <br />sample freshness. <br />K~w„~ 16 <br />