What methods apply for collecting samples for HCN analysis?
The preferred method is EPA CTM 033 (http://www.epa.gov/ttn/emc/ctm/ctm-033.pdf). You may use a modified Method 26A or Method 26 sampling train. The analysis is then with ion chromatography. If a source chooses to use Method 26A to measure HCl, HF, and HCN simultaneously and they suspect that they have high levels of acid gases (>3% CO2), they must modify the sampling train to prevent the pH of the impinger solutions from dropping below 12. The concentration of the sodium hydroxide solution used in the impingers must be increased from 0.1 N to 1 N, an additional impinger containing sodium hydroxide must be added to the train (three impingers instead of two), additional sodium hydroxide solution may be added to each impinger, and the pH of the impinger solutions must be monitored periodically throughout the sample run (the simplest procedure is to add a pH indicating solution such as Alizarin-yellow R to the impinger solution). Sample runs should be limited to one hour instead of the th
