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1. Quality Assurance/Quality Control(QA/QC) additional quality control measures. Freshly packed or new sorbent tubes must be conditioned before use.Conditioning entails heating the tubes at specific The QA/QC requirements for Method TO-15 are different than that of EPA temperatures with a set gas Flow(See Table 2 of method). Tubes can be reused for Method 8260B/C. The calibration curve and tuning need to be checked every 24 multiple thermal desorption cycles until the"safe sampling volume"validation hours for Method TO-15 compared to every 12 hours for Method 8260131C. procedures fails(USEPA,1999,Method TO-17,Section 13.1.2). There are no requirements to verify the calibration curve with a second-source standard,to analyze matrix spikeimatrix spike duplicate samples(MS/MSD), For calibration,either gas(vapor)-phase or liquid standards can be used. Liquid laboratory control samples(LCS)or use surrogates for Method TO-15. standards are directly injected into the sorbent tubes for calibration. No calibration Consultants,regulators and other parties involved with using Method TO-15 for validation with gas-phase standards is needed if liquid standards are used. soil gas analysis may include additional QA/QC requirements not required by Method TO-15 to their testing protocol. Discretion should be used in deciding Furthermore,"sample tubes awaiting analysis on an automated desorption system • whether additional QA/QC will provide any additional data validation information. must be completely sealed before thermal desorption to prevent ingress of VOC contaminants from the laboratory air and to prevent losses of weakly retained 2. Autosamolers analytes from the tube."(USEPA,1999,Method TO-17,Section 8.2.1.2) Samples in passivated stainless steel canisters(i.e.,SUMMAIDs)can be analyzed Because of the manner by which gaseous samples are collected,this method has with an autosampler if the canisters are directly connected to the autosampler several inherent advantages over Methods TO-15 and 8260. One advantage is the without any further sample transfer. Additional blank samples should be included ability to collect and concentrate a larger volume of sample. Consequently,lower in the sample sequence to evaluate possible carryover of highly contaminated reporting limits can be achieved if the entire VOCs volume of sample trapped on the samples. sorbent tube is described completely as a single aliquot of sample. In comparison, only a smaller sub-sample is usually analyzed for TO-15 at a time;therefore,the 3. Canisters certification reporting limits are more elevated. Canisters used with EPA Method TO-15 must be certified clean with the same However,there are disadvantages in using TO-17. Some of the perceived data acquisition mode as the sample analysis. See Discussion on Scan vs.SIM disadvantages in using sorbent tube as a collection method include the inability to mode. repeat an analysis on the same sample,potential mass spectrometer(MS)overload due to desorption of concentrated sample and column breakthrough. The 4. Shipping of soil gas samples,especially in pressurized containers,by air should unfamiliarity of practitioners in handling and collecting soil gas samples onto sorbent be avoided. There are Federal restrictions on shipping pressurized containers by tubes is another potential disadvantage,since samples are mostly collected in air. Check with the shipper first if there is a need to ship such samples by air. canisters and syringes in the United Stales. Sorbent tubes are used less frequently Also consult with the federal code of regulations(49CFR,Parts 100-185)on for sampling in the:United States whereas they are used widely in the European specific regulations on the shipment and transportation of various materials. countries. C. EPA Method TO-17 With Method TO-15,additional analysis on the same sample can be easily • performed by withdrawing another sample aliquot from the sample canister. With EPA Method TO-17(Determination of Volatile Organic Compounds in Ambient Air Method TO-17,once all the compounds are desorbed from the sorbent tube,the Using Active Sampling Onto Sorbent Tubes, USEPA,1999)is another method sample is completely used. Repeating a sample analysis is possible only if multiple designed for collecting and analyzing VOCs in ambient air samples which is also (duplicate)sorbent tubes are collected. Multiple sorbent tubes can be collected used for soil gas analysis. A volume of air(or soil gas)is pulled through a sorbent concurrently if several sorbent tubes are manifolded in parallel during sampling. tube to collect the VOCs followed by thermal desorption of the VOC onto the GC Nevertheless,recent advances in thermal desorption(TD)technology have made it column for separation and analysis by the mass spectrometer. Other detectors or possible to split sample into fractions for repeat runs from the same sorbent tube. combinations of detectors such as ECD/FID in series can be used with this method provided that the criteria specified in Section 14 of the method are met. For quantification,the volume of air passing through the cartridge must be measured and documented. Moisture can be a problem with sorbent cartridges but it can be Method TO-17 is primarily a sampling method. Analysis of samples follows the managed by using alternative sorbents,sample splitting or dry purge(USEPA,1999, analytical approach in USEPA Method TO-15. The use of sorbent tubes requires Method TO-17,Section 7.2). The use of in-line water traps is not recommended 12/10/2009 -77- 12/10/2009 -78-