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A 5 C 1 <br />I_~ :,,,:,._~._: ~, .: <br />' based on previous experience, it is not unusual for free cyanide <br />' determinations to be significant overestimates of the cyanide present when <br />thiocyanate is present in the solutions being analysed. Thiocyanate is a <br />positive interference in the free cyanide analytical method; and <br />' if the WAD cyanide values determined by Laboratory "A" are not considered <br />(as discussed above), and the total cyanide values are accepted as correct <br />' (they are, in fact, overestimated), the free cyanide values determined by <br />Laboratory "A" are not correct. This is because if the free cyanide value is <br />added to the metallo-cyanide complexes which would report to the WAD <br />cyanide analyses, (based on the metal values determined in the samples), <br />these exceed even the total cyanide overestimate (e.g., sample 4: FCN = <br />' 93 mg/L, metal cyanide complexes require at least 80 mglL cyanide giving a <br />total of 173 mg/L cyanide. Total cyanide estimate is 160 mg/L by Laboratory <br />"A" and 126 mg/L by Laboratory "C"). <br />' The computations given for sample 4 to illustrate the observations made above can <br />be repeated for each of the samples, with similar conclusions. Accordingly, it is <br />' concluded that the free cyanide values determined on these four samples are <br />incorrect. <br />1 <br />1 <br />1 <br />J <br />1 <br /> <br />1 <br />t <br />7 <br />