Experimental conditions at the donor stream were also evaluated to increase the HCN diffusion.
Hydrochloric, nitric and sulfuric acids at the same H3O+ concentration yielded results in agreement (variations lower than 2%).
Hydrochloric acid was then selected in agreement with most procedures which employ gas-diffusion [7,9,10,15,18].
The response was 60% higher when the donor flowed countercurrent to the acceptor solution.
The analytical sig-nal increased with the sample to HCl volumetric fraction (Fig. 2d) due to the decrease of sample dilution (HCl is in large excess at 1.0 mol L−1).
A similar result was observed by increasing the num-ber of sampling cycles because of the higher cyanide mass in the donor stream.
Ten sampling cycles was selected as a compromise between sensitivity and sample throughput.
The analytical signal increased 33% when the pulse frequency of sample was changed from 5 Hz to 1 Hz in view of the higher residence time for HCN diffusion.