POD diffusive samplers loaded with Carbopack X and Carbograph 5TD were exposed to certified calibration mixtures containing a total of 110 different ozone precursor and air toxic compounds. Constant sampling rates were identified for 39 ozone precursors and 33 air toxics. As 9 of these compounds were included in both mixtures, this meant a total of 63 different volatile and very volatile compounds were sampled using the POD with overall expanded uncertainties below 30 % for the sampling rate associated with the whole range of sampling times from 2 to 24 h.Carbograph 5TD exhibited superior performance for diffusive sampling of oxygenated and halogenated compounds in the air toxics mixture, while Carbopack X showed higher sampling efficiencies for aliphatic and aromatic hydrocarbons, as well as halogenated compounds derived from benzene and C2 carbon number hydrocarbons.A model has been developed and applied to estimate sampling rates, primarily for the more volatile and weakly adsorbed compounds, as a function of the collected amount of analyte and the exposure time. For an additional 9 ozone precursors on Carbopack X, and 11 air toxics on Carbograph 5TD, the expanded uncertainties of modelled sampling rates were reduced to below 30 % and have a significantly reduced uncertainty compared to those associated with an averaged sampling rate.The paper provides Freundlich's isotherm parameters for the estimated (modelled) sampling rates and defines a pragmatic approach to their application. It does so by identifying the best sampling time to use for the expected exposure concentrations and associated analyte masses. This allows for expansion of the sampling concentration range from hundreds ng m- 3 to mg m- 3, while avoiding saturation of the adsorbent.Finally, field measurement comparisons of POD samplers, pumped tube samplers and online gas chromatography (GC), for sampling periods of 3 and 7 days in a semi-rural background area, showed no significant differences between reported concentrations.

Thermal desorption (TD) is arguably the most powerful and versatile of all sample introduction technologies for gas chromatography (GC). It combines sampling/sample preparation, selective concentration, and efficient GC injection into one fully automated procedure and allows target analytes to be concentrated by factors up to 10 6 . It also forms the basis for several other important GC introduction procedures such as purge and trap, sorptive extraction, and headspace trap.

Sorbent tubes/traps are widely used in combination with gas chromatographic (GC) analytical methods to monitor the vapour-phase fraction of organic compounds in air. Applications range from atmospheric research and ambient air monitoring (indoor and outdoor) to occupational hygiene (personal exposure assessment) and measuring chemical emission levels. Part 1 of this paper reviewed the main sorbent-based air sampling strategies including active (pumped) tube monitoring, diffusive (passive) sampling onto sorbent tubes/cartridges plus sorbent trapping/focusing of whole air samples that are either collected in containers (such as canisters or bags) or monitored online. Options for subsequent extraction and transfer to GC(MS) analysis were also summarised and the trend to thermal desorption (TD)-based methods and away from solvent extraction was explained. As a result of this trend, demand for TD-compatible sorbents (alternatives to traditional charcoal) is growing. Part 2 of this paper therefore continues with a summary of TD-compatible sorbents, their respective advantages and limitations and considerations for sorbent selection. Other analytical considerations for optimizing sorbent-based air monitoring methods are also discussed together with recent technical developments and sampling accessories which have extended the application range of sorbent trapping technology generally.

Sorbent tubes/traps are widely used in combination with gas chromatographic (GC) analytical methods to monitor the vapour-phase fraction of organic compounds in air. Target compounds range in volatility from acetylene and freons to phthalates and PCBs and include apolar, polar and reactive species. Airborne vapour concentrations will vary depending on the nature of the location, nearby pollution sources, weather conditions, etc. Levels can range from low percent concentrations in stack and vent emissions to low part per trillion (ppt) levels in ultra-clean outdoor locations. Hundreds, even thousands of different compounds may be present in any given atmosphere. GC is commonly used in combination with mass spectrometry (MS) detection especially for environmental monitoring or for screening uncharacterised workplace atmospheres. Given the complexity and variability of organic vapours in air, no one sampling approach suits every monitoring scenario. A variety of different sampling strategies and sorbent media have been developed to address specific applications. Key sorbent-based examples include: active (pumped) sampling onto tubes packed with one or more sorbents held at ambient temperature; diffusive (passive) sampling onto sorbent tubes/cartridges; on-line sampling of air/gas streams into cooled sorbent traps; and transfer of air samples from containers (canisters, Tedlar® bags, etc.) into cooled sorbent focusing traps. Whichever sampling approach is selected, subsequent analysis almost always involves either solvent extraction or thermal desorption (TD) prior to GC(/MS) analysis. The overall performance of the air monitoring method will depend heavily on appropriate selection of key sampling and analytical parameters. This comprehensive review of air monitoring using sorbent tubes/traps is divided into 2 parts. (1) Sorbent-based air sampling option. (2) Sorbent selection and other aspects of optimizing sorbent-based air monitoring methods. The paper presents current state-of-the-art and recent developments in relevant areas such as sorbent research, sampler design, enhanced approaches to analytical quality assurance and on-tube derivatisation.

Emissions of (semi-)volatile organic compounds ((S)VOCs) from materials can adversely impact indoor and in-vehicle air quality. The European Construction Products Directive requires control/testing of VOC emissions to make sure that materials are safe. Risk of toxic emissions can also be reduced by ensuring that the (S-)VOC content of a material is kept inherently low. Direct thermal desorption (TD) may be used to measure (S-)VOCs in a wide range of solid, resinous and liquid materials and eliminates complex liquid extraction steps. This process of thermally extracting the (S)VOCs is a technique that has been used over a number of years for analysis of a range of material types. It is already used by the German automotive industry for testing car trim components (Method VDA 278, 2001). This paper demonstrates the performance of the latest automated technology for direct desorption of materials and demonstrates a novel approach to validation of analyte recovery. Recent development of a combined micro-chamber/thermal extraction system offering both content testing and approximate emissions data is also presented.

Accidental or deliberate release of toxic chemicals into the indoor or outdoor environment is a real threat in today's world (EmergencyNet NEWS 1995). The analysis of trace-level, vapourphase compounds in air requires thermal desorption (TD) to pre-concentrate the compounds before analysis by gas chromatography (GC), mass spectrometry (MS) or GCMS (Markes Intemational.TDTS12). This paper describes the latest continuous on-line monitoring technology with sub-ppt detection limits and pumped tube sampling with off-line analysis for monitoring human exposure at even lower levels.Rapid and accurate continuous monitoring is required in the most sensitive civilian locations in order to minimise loss of life in the event of a terrorist attack. A novel, peltier-cooled, twintrap sampling system is described which operates continually, with no blind spots, and enables near real time (NRT) analysis (cycle times < 15 minutes) with sub-ppt detection limits. Performance examples are presented, including the analysis of free underivatised VX nerve agents at low pg levels (Markes International Ltd.TDTS44).

This paper presents a review of current practice and recent research into the use of sorbent tubes for monitoring VOCs in ambient air. Data are presented that demonstrate the viability of sorbent tubes with regard to artifact formation, analyte range, storage stability, concentration range, and recovery; the implications of this data are discussed in terms of detection limits, method validity, and method limitations. Guidance is also presented on the practical application of sorbent tube sampling derived from this information-for example, sorbent selection, pump flow rates, safe sample volumes, storage conditions, etc.Techniques and practical considerations for the thermal desorption-capillary GC analysis of sorbent tubes-such as calibration methods, moisture management, method validation procedures, and typical analytical conditions-are also reviewed and discussed. Expected analytical performance is presented in terms of precision and detection limits.

This month, two guest authors review gas extraction techniques as alternatives to solvent extraction for the preparation of various sample matrices for gas chromatography.

Diffusive (passive) samplers of all kinds fulfil many of the logistical requirements of an ideal ambient air monitor. They are low cost, easy to distribute/use, suitable for a wide range of common volatile organic air pollutants, reliable, applicable to long-term sampling and do not require power. Several different kinds of diffusive sampler have been developed for VOCs. These were predominantly designed for occupational hygiene work and most require solvent extraction prior to GC analysis. The analyte dilution necessary with solvent extraction has been found to limit sensitivity and to preclude general application to ambient air assessment. A tube-form, sorbent-based diffusive monitor, specifically designed to minimise the air speed limitations of conventional badge-type diffusive samplers and to be compatible with analysis by thermal desorption-GC, was first reported in 1979. In common with other diffusive samplers for VOCs, this device was initially developed for use as a personal monitor for occupational hygiene measurements. However, several recent reports have demonstrated that it can also be applied to the measurement of low concentration VOCs in indoor and outdoor ambient air. This paper reviews the reported experiences of indoor and outdoor air monitoring using a tube-form diffusive monitor. Specific attention is paid to general sampling/analytical procedures, concentration/detection limits, applicable analyte ranges, minimising artefacts, quality assurance and method limitations. Practical recommendations regarding sampling and analytical parameters are also presented.