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The steel containers are steam cleaned and baked repeatedly under vacuum between uses. Unused containers are rebaked frequently. When Tedlor bags are used, they are flushed with zero air just prior to use. Bags are brought to the point of sampling in an inflated condition by surface transport. Unused bogs are reflushed weekly. Bags are not reused. Canisters are numbered and usage logged so that those canisters known to have been used for source sampling may be segregated from those used for ambient sampling. USE OF APPROPRIATE SAMPLING TECHNIQUES In order to further minimize contact of sampling gases with reactive surfaces, grab samples are collected by immersing the sampling container in liquid nitrogen and allowing an appropriate volume of sample air to liquefy within the container. The containers are then withdrawn from the liquid nitrogen and vented twice prior to retention of the sample. This flushing technique serves to remove any materials which may have leached out of the sample container enroute to the point of sampling. Pressurized samples are obtained even though no pumps or manifolds are employed. CCAS has employed this method extensively for the collection of grab samples in the vicinity of impoundments. It is especially convenient for the simultaneous collection of matched upwind/downwind samples. Since approximately 5 minutes are required to collect samples, some integration is achieved. If the ARB permits this type of sampling in the vicinity of the on-site sources, it will conserve the limited supply of integrated samplers and thereby speed the completion of the project. USE OF MASS SPECTROMETRIC METHODS Even with the higher resolution of fused silica capillary gas chromatography, coelution of sample components is not a rare event. The mass -spectrometer, however, permits independent measurements to be made even in a case of triple coelution such as is observed for cyclohexane, benzene and carbon tetrachloride under some conditions of analysis. Compound identities are certified by comparison with authentic spectra contained in the EPA/NBS mass spectral data base. This data base of more than 40,000 mass spectra is a part of the software available with the CCAS. instrumentation. The quality of this searching has been recently upgraded by the use of our new Hewlett/Packard RTE -1000 central data processing station equipped with the powerful Aquarius software. All data system matches are reviewed before being included in our reports. Our analysts closely compare retention times with daily standard runs. Assignments which are "out of step" with the rest of the chromatogram are rejected on the basis of these compairsons. Because CCAS has six GC/MS systems, we are able to dedicate one of the instruments exclusively to air analysis. In this way contamination