Well purging techniques method

Headspace analysis (EPA 3810, 5021) also works well for analyzing volatile petroleum constituents in soil. In the test method, the soil is placed in a headspace vial and heated to drive out the volatiles from the sample into the headspace of the sample container. Salts can be added for more efficient release of the volatile compounds into the headspace. Similar to water headspace analysis, the soil headspace technique is useful when heavy oils and high analyte concentrations are present, which can severely contaminate purge-and-trap instrumentation. Detection limits are generally higher for headspace analysis than for purge-and-trap analysis. 

Finally, an improvement in the sensitivity of the detection limit for such compounds can be reached by using a Purge and Trap well-optimized enrichment approach instead of the HS-SPME technique (Fedrizzi et al., 2007b). This method provides enough sensitivity, and analysis times are suitable to perform routine analysis. The measured amounts are, in fact, within the variability ranges reported in the literature for both compounds in wine, and close to the sensory thresholds. Using both such methods, it has been possible for the first time to measure the contents and relevant ratios of such compounds in Italian wines of different varieties as represented in Figure 5.10. 

In water, GC-MS is coupled to purge and trap or headspace sample preparation for the analysis of VOCs like BTEX and MTBE. Another important group of volatile analytes in water are DBFs. Attention has been directed to volatile chlorinated compounds such as trihalomethanes (THMs), as well as other semivolatile compounds such as haloacetic acids (HAAs), haloacetonitriles, haloketones, and ha-loaldehydes. The methods used to determine these compounds include GC-EI-LRMS, where a after derivatization step is necessary due to the low volatility and high polarity of these analytes. Using this technique, limits of detection were in the microgram per liter range. 

Validation of a SPME method for target analytes should be performed using standard reference materials with similar matrix, when available. Another possible and frequently used way is validation of a SPME method against well-accepted extraction techniques, such as purge-and trap [13,25,46] or static head-space [46]. Several interlaboratory studies demonstrated that SPME is a reliable technique for the quantitative analysis of volatile organic compounds [46] and pesticides in water samples [47 48]. We have validated our SPME-GC-MS method for the determination of nitrous oxide in urine by means of the comparison with static headspace [33]. 

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