Organic compound analysis limitations

Another tool that enables us to evaluate analytical accuracy of organic analyses is surrogate standards. These are compounds that do not naturally occur in the environment and that are similar in chemical nature and behavior to target analytes. In organic compound analysis, known amounts of surrogate standards are added to each sample prior to extraction. The comparison of surrogate standard recoveries to laboratory control limits permits the laboratory to monitor the efficacy of extraction and to measure the accuracy of analysis for each individual sample. 

Similar to LCS recoveries, surrogate standard recoveries should be monitored by the laboratory and plotted as control charts. The EPA recommends the use of in-house laboratory control limits for surrogate standards recoveries for all organic compound analyses (EPA, 1996a). The exception is the CLP SOW, which specifies these limits for soil and water analysis. Unless affected by matrix interferences, surrogate standard recoveries normally have relatively narrow control limits, 65-135 percent for most organic compound analysis. (Many laboratories, however, default to arbitrary limits of 50-150 percent for GC analyses, instead of using statistical control limits.)... 

The Clean Water Act (1972) requires discharge limits to be set on industrial and municipal wastewater, and these analyses are outlined in the National Pollution Discharge Elimination System for the 600 Series Methods. Method 624 covers the analysis of purgeable organic compounds Method 625 covers the analysis of 81 bases, neutrals, and acids Method 613 describes the analysis of dioxins and furans. 

In Section F, we saw that one technique used in modern chemical laboratories to determine the empirical formulas of organic compounds is combustion analysis. We are now in a position to understand the basis of the technique, because it makes use of the concept of limiting reactant. 

Headspace analysis has also been used to determine trichloroethylene in water samples. High accuracy and excellent precision were reported when GC/ECD was used to analyze headspace gases over water (Dietz and Singley 1979). Direct injection of water into a portable GC suitable for field use employed an ultraviolet detector (Motwani et al. 1986). While detection was comparable to the more common methods (low ppb), recovery was very low. Solid waste leachates from sanitary landfills have been analyzed for trichloroethylene and other volatile organic compounds (Schultz and Kjeldsen 1986). Detection limits for the procedure, which involves extraction with pentane followed by GC/MS analysis, are in the low-ppb and low-ppm ranges for concentrated and unconcentrated samples, respectively. Accuracy and precision data were not reported. 

Limited data is available on the concentration of volatile organic compounds, semi-volatile organic compounds (SVOCs), and polycyclic aromatic hydrocarbons (PAHs) from gasification processes. The data that is available indicate that VOCs, SVOCs, and PAHs are either non-detectable in flue gas streams from IGCC process or, in some cases where they were detected, they are at extremely low levels (on the order of parts per billion and lower). The analysis of syngas also indicates greater than 99.99 percent chlorobenzene and hexachlo-robenzene destruction and removal efficiencies and part per billion or less concentration of selected PAHs and VOCs.9-14... 

Detectors range from the universal, but less sensitive, to the very sensitive but limited to a particular class of compounds. The thermal conductivity detector (TCD) is the least sensitive but responds to all classes of compounds. Another common detector is the flame ionization detector (FID), which is very sensitive but can only detect organic compounds. Another common and very sensitive detector is called electron capture. This detector is particularly sensitive to halogenated compounds, which can be particularly important when analyzing pollutants such as dichlorodiphenyltrichloroethane (DDT) and polychlorobiphenyl (PCB) compounds. Chapter 13 provides more specific information about chromatographic methods applied to soil analysis. 

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