VOCs analytical methods

Some of the methods used for determination of organic pollutants in the environment follow (118). The most notable are polyaromatic hydrocarbons (PAHs) and volatile organic compounds (VOCs). Analytes Methods ... 

Automated analyzers may be used for continuous monitoring of ambient poUutants and EPA has developed continuous procedures (23) as alternatives to the referenced methods. Eor source sampling, EPA has specified extractive sampling trains and analytical methods for poUutants such as SO2 and SO [7446-11-9] sulfuric acid [7664-93-9] mists, NO, mercury [7439-97-6], beryUium [7440-41-7], vinyl chloride, and VOCs (volatile organic compounds). Some EPA New Source Performance Standards requite continuous monitors on specified sources. 

Over the last decade, interest in release and delivery of VOCs has been steadily growing, with a particular focus on food, environmental and medical applications [186-190]. Consequently, considerable effort was invested to develop analytical methods capable of capturing such dynamic VOC release processes (Fig. 15.14) [179, 191]. This led to improvements in electronic sensor methods (often termed electronic noses ) [192]. 

Diffusive samplers originally developed for workplace monitoring have been applied to a wide range of studies of VOCs in non-industrial indoor air through a modification of sampling times and analytical methods. The main types of... 

Soil gas surveys are widely used for delineating sites with VOC contamination. Even though soil gas data may be generated with the most definitive and accurate analytical method available, such as gas chromatography/mass spectrometry (GC/MS), they will always remain screening data due to uncertainty associated with the sample matrix. 

Sixteen groundwater samples were collected and analyzed for VOCs (EPA Method 8260), lead (EPA Method 6010), and nitrite (EPA Method 354.1). The intended use of all data is quarterly monitoring. The SAP states the sampling and holding time completeness goal of 100 percent analytical completeness goal is 90 percent. 

As can be seen from those simple examples, chemical monitoring of VOCs based on determination of their trace amounts (from parts per million [ppm] to parts per trillion [ppt]) with the use of modem analytical methods is necessary. It is a consequence of the ease with which VOCs permeate biological barriers (air-circulatory system, the internal and external activities of both plant and animal cells), and the relative ease with which they undergo conjugation reactions (enzymatic oxidation reactions, auto-oxidation, initiation, propagation, and termination). Therefore, new metabolites are created. These metabolites not only determine phenomena connected with the chemistry of the atmosphere but also are responsible for the vital functions of organisms (e.g., the uncontrolled de novo reaction that occurs in the presence of free radicals) (Fig. 14.2) [4]. 

The analysis of VOCs in water and solid samples is complex due to the large number of compounds to be analyzed and because precaution has to be taken to provide accurate and reliable results. The use of P T-GC-MS is the most adequate for trace analysis of VOCs because limits of detection at the ng/L levels can be achieved and confirmatory analysis can be performed. Although P T is a well-established technique, several analytical parameters can be optimized to obtain high sensitivity and selectivity. Eor the specific target analytes, method optimization and quality assurance are necessary. The main drawbacks of this technique result from the fact that high purity gases are required and that the system can... 

To date most indoor air investigations and the quality demands for indoor products have been limited to these compounds, as the potential emission sources have been documented in detail and sensitive analytic methods are available as a matter of routine. In contrast only a few VOCs of relevance indoors have been characterised until now as reactive or as reaction products . Some groups are as follows ... 

Brown and Crump (1998) report modification of the analytical method to provide a lower limit of detection for the measurement of VOCs in indoor and outdoor air. Using a Perkin-Elmer ATD 400 thermal desorber with the outlet split set at 16 1 and connected to an Autosystem GC, the detection limit was 2 ng of toluene on the tube which is equivalent to 0.2 pg/ m in air for a 4-week exposure period. 

In seawater systems, the oxidation method chosen for analysis of the organic carbon depends on the fraction (DOC, POC or VOC) of interest, the origin of the sample, and the type of information required. However, analytical results from different methods cannot be compared readily. By examining these various analytical methods for the measurement of the dissolved, particulate, and volatile fractions of the organic matter, the sources of the differences in the reported results may be better understood. 

Column selection is based on the compoimd list, detector used, and analytical method. For specific usage of different columns used for VOCs separations the reader is directed to the application table in each extraction section. Standardized analytical methods suggest the chromatographic column to use. 

The P T technique is recommended as an extraction technique for VOCs in several standard methods (Table 23.3). The US EPA has proposed different standard protocols for the analysis of volatiles in water using P T. These methods can be used for most of VOCs that have boiling points below 200°C and are insoluble or slightly soluble in water. The type of sample matrix being analyzed determines the implemented configuration of the extraction technique. The 500 series EPA methods are addressed to potable waters, whereas the 600 series refer to analysis of wastewaters. The analytical methods for determining hazardous waste are known as the 8000 series methods (US EPA SW-846). 

Using all of the analytical methods, the researchers were able to identify 50% of the mass associated with non-methane VOCs. The emission factors determined from the laboratory fires were fed into those obtained from their airborne and ground-based field campaigns. This revealed the dependence of emission factors on the ratio of flaming to smouldering combustion and fuel characteristics. This study has also provided recommended emission factors for all measured species for both primary deforestation fires and pasture maintenance fires. 

Given all of the problems associated with analytical methods for breath sampling and analysis, it is not surprising that to date the majority of research associated with breath analysis and PTR-MS has been limited to proof-of-principle trials which may not have been using ideal breath sampling procedures. Often these studies have also involved an insufficient number of patients and provided little detailed analysis. In-depth clinical trials to substantiate the effectiveness of VOCs as selective biological indicators of disease are required, but these are expensive and time-consuming. 

In summary, official analytical methods do exist in the US, notably those of the FDA, but apart from information in the USP, those pubhshed by the AOAC and the method for VOCs pubhshed by CARB in California, most of them have not been pubhshed officiaUy. In addition, concerning OTC products, it is the responsibihty of the suppliers to develop and formulate the analytical methods to control their final products individually. 

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