Draft Method for Sampling and Analysis of Hydrogen Cyanide Emissions from Stationary Sources
This method is for the collection and analysis of hydrogen cyanide (HCN) from stationary sources. This method is a conditional test method meaning it must be approved as an alternative before a source may use it to meet Federal requirements under 40 CFR Parts, 60, 61, and 63.
Samples are collected isokinetically from emission sources using a Method 5 type sampling train. The basic train setup includes a heated probe and filter, two 0.1N NaOH (sodium hydroxide) impingers (100mL), an empty impinger, and a silica gel impinger (200-300g). Hydrogen cyanide (HCN) in the stack gas stream reacts with the NaOH to form a cyanide ion, which is retained in the alkaline solution until analyzed by IC using an ion selective electrode (ISE). The typical MDL for HCN by this method is 12 ug/m3. Particulates, if needed, can also be determined from the sampling train.
There are two situations that call for the use of an alternate train configuration using a 100mL of a 10% lead acetate impinger (lead acetate impinger, empty impinger, followed by two NaOH impingers). This is when the source has high concentrations of sulfides (> 50ppm) and high concentrations of acidic gases (including CO2). Note that the method specifies the lead acetate impinger must be used within 10 days of preparation. The lead acetate impinger primarily removes sulfides but also will reduce the amount of some of the acid gases that reach the NaOH impinger. Sulfides cause intereferences with the analysis of HCN because the sulfide peak elutes just prior to the cyanide peak from the IC. A large sulfide peak will completely obscure the cyanide peak. Also, cyanide is known to degrade over time in the presence of sulfide at any concentration. High concentrations of acidic gases may lower the pH of the NaOH impinger solutions. The lower the pH, the lower the HCN collection efficiency of the NaOH impinger solution.
The pH of the NaOH impinger solution should be monitored every 15 minutes during analysis using either a pH sensor or pH paper. It is critical that the pH of the solution remain above 12 during sampling. When sampling a highly acidic source, it is permissible to add another NaOH impinger to the sampling train or increase the concentration of the NaOH solution.
After collection, the NaOH impingers and connecting glassware of the back half of the train are rinsed with 0.1N NaOH. The rinses and impinger contents are combined and submitted for analysis. Do not rinse the back half of the filter holder as this may transfer more water soluble cyanide salts from the front half and cause a positive bias in the HCN results.
If a particulate determination is needed, rinse the nozzle, probe, and connecting glassware in front of the filter and submit this rinse for particulate determination. Remove the filter, fold it keeping the particulate catch to the inside, place in a glass jar and submit it for analysis. If particulates are not needed then these portions of the sampling train are not needed for the HCN determination since they only contain particulate cyanide material which shouldn't be added to the HCN result.
If the 10% lead acetate impinger is used, rinse the impinger, the empty impinger, and connecting glassware. The rinses and contents of the 10% lead acetate and empty impinger are combined and submitted for analysis. The lead acetate impinger contents should be analyzed separately from the NaOH impingers.
The method calls for a field spike sample to be prepared in the field and submitted for analysis along with the collected samples.
(EPA-Conditional Test Method)