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is again a good compromise between the bag and the cartridge. Air shipment of bogs is not advised. Reanalysis from the some bag or canister is convenient. This degree of flexibility can be important when samples containing unexpectedly high or low levels of trace organics are encountered or when several different types of analysis are required. Gas phase reactions taking place as the bag or steel container is collected will continue during shipment and storage. Since many of these reactions are accelerated by light, CCAS recommends that bags be wrapped in foil or immediately overbagged with a dark plastic bag upon collection. Overbagging also provides a buffer of air similar to the collected air so that diffusional exchange with dissimilar air is reduced. Cartridge samples, once collected, are inherently more stable than bag or canister samples. We have seen virtually identical gas chromatographic patterns when comparing archived cartridge samples with companion samples analyzed a year earlier. Furthermore, thermally desorbable cartridges destined for analysis with legal implications should be preanalyzed to avoid questions arising from the use of contaminated cartridges. Even fresh cartridges supplied by commercial sources require rigorous precleaning. It is planned that canisters will be used exclusively in connection with the proposed study. DETECTION LIMITS Quantitation from full -scan mass spectrometric data is based upon area counts for one or more extracted ions. Since noise levels for extracted ions are typically 100 area counts, a signal of 1000 would provide a signal-to-noise ratio of 10 to 1. Detection limits can then be calculated from calibration data on the basis of this signal to noise ratio. Some examples are provided in Table 1. Frequent experimental verification, of course, is required. Please note that all detection levelt are less than or match your program requirements. Since the data are collected by full scan GC/MS, absolute confirmation of identity is practiced. This extra measure of quality assurance is not even possible with the selective detector methods. Furthermore the inspection of the data for additional compounds is possible so that reanalysis would not be necessary even if the list Of target compounds is extended after measurements have already been completed at a given site. Since only one run is required for both aromatic and halogenated components, this better technology does not require the incurrence of higher costs. Therefore, it would seem unlikely that the use of equivalent, but slightly less satisfactory techniques would be required.