Evaluation of organic pollutants in the open air and atmospheres in industrial sites using graphitized carbon black traps and gas chromatographic-mass spectrometric analysis with specific detectors

TVOC - Revisited

BACKGROUND

TVOC (total volatile organic compounds) has been used as a sum parameter in indoor air sciences for over 40 years. In the beginning, individual VOC concentrations determined by gas chromatography were simply added together. However, several methods for calculating TVOC have become established over time.

METHODS

To understand the manifold definitions of TVOC, one must trace the history of indoor air sciences and analytical chemistry. Therefore, in this work, the original approaches of TVOC are searched and explained. A detailed description of the measurement methods is followed by a critical evaluation of the various TVOC values and their possible applications. The aim is to give the reader a deeper understanding of TVOC in order to use this parameter correctly and to be able to better assess published results. In addition, related sum values such as TSVOC and TVVOC are also addressed.

RESULTS

A milestone was the analytical definition of VOCs and TVOC in 1997. A list of VOCs that should at least be considered when calculating TVOC was also provided. This list represented the status at that time, is no longer up-to-date and is being updated by a European working group as part of a harmonization process. However, there is still confusion about the exact definition and reasonable application of TVOC. The signals of other sum parameters, measured with photoacoustics, flame ionization, photoionization or electrochemical sensors, are also often given under the term TVOC.

CONCLUSIONS

It was recognized early that TVOC is not a toxicologically based parameter and is therefore only suitable for a limited number of screening purposes. Consequently, TVOC cannot be used in connection with health-related and odor-related issues. Nevertheless, such references are repeatedly made, which has led to controversial scientific discussions and even court decisions in Germany about the correct and improper use of TVOC.

Studies of adsorption of polychlorocarbons on carbon blacks by gas chromatography

Adsorption properties of carbon black before and after modification to polyhalogenohydrocarbons, including polyorganochlorine pesticides, have been investigated. It has been shown that graphitised thermal carbon blacks and carbochroms possess high adsorption capacity relative to the above compounds and can be used as supporting adsorbents to analyse these airborne chemicals. Modification raises the selectivity of adsorbents to the compounds being investigated and lowers retention volumes and heats of adsorption, which makes it possible to carry out thermal desorption of the accumulated species at lower temperatures.

The genotoxicity of ambient outdoor air, a review: Salmonella mutagenicity

Mutagens in urban air pollution come from anthropogenic sources (especially combustion sources) and are products of airborne chemical reactions. Bacterial mutation tests have been used for large, multi-site, and/or time series studies, for bioassay-directed fractionation studies, for identifying the presence of specific classes of mutagens, and for doing site- or source-comparisons for relative levels of airborne mutagens. Early research recognized that although carcinogenic PAHs were present in air samples they could not account for the majority of the mutagenic activity detected. The mutagenicity of airborne particulate organics is due to at least 500 identified compounds from varying chemical classes. Bioassay-directed fractionation studies for identifying toxicants are difficult to compare because they do not identify all of the mutagens present, and both the analytical and bioassay protocols vary from study to study. However, these studies show that the majority of mutagenicity is usually associated with moderately polar/highly polar classes of compounds that tend to contain nitroaromatic compounds, aromatic amines, and aromatic ketones. Smog chamber studies have shown that mutagenic aliphatic and aromatic nitrogen-containing compounds are produced in the atmosphere when organic compounds (even non-mutagenic compounds) are exposed to nitrogen oxides and sunlight. Reactions that occur in the atmosphere, therefore, can have a profound effect on the genotoxic burden of ambient air. This review illustrates that the mutagenesis protocol and tester strains should be selected based on the design and purpose of the study and that the correlation with animal cancer bioassay results depends upon chemical class. Future emphasis needs to be placed on volatile and semi-volatile genotoxicants, and on multi-national studies that identify, quantify, and apportion mutagenicity. Initial efforts at replacing the Salmonella assay for ambient air studies with some emerging technology should be initiated.

Sorbent trapping of volatile organic compounds from air

The use of sorbents in trapping volatile organic compounds in air for subsequent analysis is reviewed. Sorbents are classified in accordance with the mechanism used to recover the trapped compounds, either solvent or thermal desorption. The use of sorbents is contrasted with other sampling procedures, such as collecting whole air samples using canisters. New developments such as solid-phase microextraction are described. In particular, emphasis is placed on a holistic approach to sampling and analysis, and communication is encouraged between those who take samples in the field, and those who perform the analysis.

Thermal desorption-gas chromatography for the determination of benzene, aniline, nitrobenzene and chlorobenzene in workplace air

Sampling on Tenax TA of different mesh sizes followed by thermal desorption and gas chromatography was evaluated as a simple method for the determination of benzene, aniline, nitrobenzene and chlorobenzene in the workplace air. An alternative sampling technique in place of pump sampling was developed. Quantitative recoveries were obtained in the mass range 0.04-10 micrograms. It was found that air humidity had no effect on recovery. The charged tubes can be stored at room temperature for 5 days with no change in recovery. The particle size of Tenax TA has no significant effect on adsorption and desorption.

Improvement of activated carbon for air sampling

In order to improve the charcoal tube method, activated carbon was treated with benzyl chloride (5 and 20%) in methylene chloride and heated (300 degrees C). The carbons were evaluated with regards to water uptake, adsorption of toluene and carbon tetrachloride, desorption characteristics for polar compounds and storage stability of ketones. Carbons treated with benzyl chloride picked up less moisture, showed higher desorption efficiencies for polar compounds and lower catalytic activity compared with untreated carbons and those heat-treated with helium at 800 degrees C. The best results were obtained with 20% benzyl chloride.

Evaluation of porous polymer traps for analysis of four volatile N-nitrosamines using thermal desorption injection coupled with a gas chromatograph-thermal energy analyzer

Three porous polymer adsorbents, Tenax-TA, Chromosorb 102, and Chromosorb 103 were investigated as potential gas phase, trapping agents for volatile N-nitrosamines using a thermal desorption injector coupled with a gas chromatograph-thermal energy analyzer. N-Nitrosodimethylamine was used as the model N-nitrosamine for determining break-through volume, the effect of temperature on retention volume, and collection efficiency at 25 degrees C for each adsorbent. Results from these three parameters indicated that Chromosorb 103 exhibited the best adsorbent characteristics for the pre-concentration of volatile N-nitrosamines. A mixture of three dialkyl N-nitrosamines (dimethyl, diethyl, and dipropyl), and N-nitrosopyrrolidine were analyzed using a high-temperature mineral oil purge and trap procedure. Recoveries ranged from 82.2 to 102.8% at levels of 10 and 100 ng of each N-nitrosamine added.

Volatiles of exogenous origin from the human oral cavity

The volatiles found in the headspace above male and female saliva were examined by combined gas chromatography--mass spectrometry. This had led to the identification of a number of constituents of exogenous origin. The most likely source of these products are atmospheric and water pollutants as well as food stuffs and cosmetic products. Volatiles from saliva represent a potential medium for the detection of reproductive states as well as local and systemic diseases. Consequently, knowledge of compounds not arising from the body's metabolic process if important to prevent their identification as anomalous metabolites.