Industry: Environmental
Instrument: AUTOCan 12 Whole Air Autosampler/Concentrator
Preparation of Gas Phase Standards for Ambient Air Analysis
Understanding gas phase standard preparation for ambient air methods is paramount to successful analyses. Standard preparation using EPA water, wastewater, and soil methods is routine. The analyst purchases stock methanolic standards and dilutes them into the working range of the instrument. Unlike conventional methods, air standard preparation is significantly more time consuming and technique intensive. Stock standards in compressed gas cylinders are available for specific method analytes, such as Compendium Method TO141 compounds. These, however, can be cost prohibitive and do not always address the needs of every customer. Custom blends are available in compressed gas cylinders, but are also costly and usually require four to eight weeks for preparation and stabilization.
This paper addresses several approaches to preparing gas phase standards for air toxics analysis. Included are techniques and calculations for making multi-component neat mixtures which can be diluted into static dilution bottles and ultimately into canisters for system calibration and performance checks. These techniques can be used to help alleviate cost when specific, non-routine analyses are requested. They can also be utilized by laboratories not receiving sufficient requests for air toxics analyses to justify the purchase of a compressed gas standard.
Also discussed are techniques for using compressed gas standards alone and combined with static dilution bottle standards to produce working standards in canisters. Some canister cleaning techniques are specified along with the importance of humidifying canisters for cleaning and standard preparation. Throughout the paper, good laboratory practices are described as these are essential to accurate and reproducible standard preparation.
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