Method 306A

Chromium and/or Hexavalent Chromium from Stationary Sources (Mason Jar Method)

This method applies to the determination of chromium (Cr) in emissions from decorative and hard chromium electroplating facilities, chromium anodizing operations, continuous chromium plating at iron and steel facilities and electroplating and anodizing sources controlled by wet scrubbers.  This method is also known as the Mason jar method and is less expensive and less complex to conduct than Method 306. Correctly applied, the precision and bias of the sample results should be comparable to those obtained with the isokinetic Method 306.  The method is used under nominal ambient moisture, temperature, and pressure conditions.  Samples can be analyzed for total chromium via ICP or GFAA and for hexavalent chromium via IC/PCR.

Samples are collected at a constant rate from a source using a modified Method 306 train consisting of a glass or rigid plastic nozzle, series of 1quart glass Mason jars with vacuum sealed lids, a pump, and dry gas meter.  No filter is required and there should be no metal parts in the sampling train.  Per the method, sample for a minimum of 2 hours.  The sampling procedures are a little different for the collection of total Cr versus hexavalent Cr.

For Total Cr sampling, the first jar is filled with 250mL of 0.1N NaOH or 0.1N NaHCO₃ (sodium bicarbonate), the second jar is left empty, and thethird jar is filled with 300-400g of silica gel.  Once the sample has been collected, the volume of the contents of jars 1-2 and the silica gel jar is measured to determine the moisture content of the stack gas.  The contents of jars 1-2 are combined along with the jar and connecting tubing rinse in a polyethylene, polypropylene, or glass container.  Use the absorbing solution selected for sampling for the rinse.  The samples do not have to be refrigerated.  Samples can be analyzed by ICP (inductively couple plasma spectrometry) or GFAA (graphite furnace atomic absorption spectroscopy) for Total Cr.  Samples for ICP analyses require no further preparation.  Samples for analysis via GFAA are digested with nitric acid (HNO₃).

For Hexavalent Cr sampling, the first jar is filled with 250mL of 0.1N NaOH or 0.1N NaHCO₃ (sodium bicarbonate), the second jar is left empty, and thethird jar is filled with 300-400g of silica gel.  Once the sample has been collected, the pH of jar1 is measured using a pH strip.  The pH must be >8.5 for a NaOH absorbing solution or > 8.0 for a NaHCO₃  absorbing solution.  If the pH doesn't meet this criteria, then the sample must be discarded and resampled increasing the normality of the absorbing solution to 0.5N.  If the pH is within requirements then measure the volume of the contents of jars 1-2 and the silica gel jar to determine the moisture content of the stack gas.  The contents of jars 1-2 are combined along with the jar and connecting tubing rinse in a polyethylene, polypropylene, or glass container.  Use the absorbing solution selected for sampling for the rinse. The samples are to be refrigerated during shipping and storage.  The pH of the sample is measured and then the sample is filtered.  The filter is retained for Total Cr analysis if required.  The filtrate is analyzed using IC/PCR (ion chromatography with a post column reactor). 

This method is similar to SW-846 0061/7199 for Hexavalent Cr.