By means of a passive miniature distillation device, MICRO DIST, the cyanide in the samples is released by digesting and acidifying cyanide complexes, converting them to hydrocyanic acid (HCN). The cyanide ion is trapped in a 0.1 M sodium hydroxide absorbing solution which is diluted to 0.025 M solution during the distillation. By means of flow injection, the hydrocyanic acid (HCN) passes through a gas diffusion membrane into an alkaline receiving solution where it is converted back to cyanide ion. The cyanide ion is monitored amperometrically with a silver working electrode, silver/silver chloride reference electrode, and platinum/stainless steel counter electrode, at an applied potential of zero volts. The current generated is proportional to the cyanide concentration present in the original sample.
The MicroDist distillation apparatus is beneficial for the consumer because of it ease of use, multiple samples can be distilled/digested at one time.
The benefit of amperometric detection is there are no toxic reagents consumed; just the use of dilute acids and bases for the CN- measurement.
The applicable range is 5 to 400 μg CN-/L. Higher concentrations can be determined by dilution of the original sample or by reducing the volume of the sample loop. For distilled standards, the method detection limit (MDL) is 0.975 μg CN-/L, for non-distilled standards the MDL is 0.20 μg CN-/L. Sample throughput is 16 injections/hour, or 230 seconds/sample.
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