Secondary organic aerosol (SOA) accounts for a significant fraction of ambient tropospheric aerosol and a detailed knowledge of the formation, properties and transformation of SOA is therefore required to evaluate its impact on atmospheric processes, climate and human health. The chemical and physical processes associated with SOA formation are complex and varied, and, despite considerable progress in recent years, a quantitative and predictive understanding of SOA formation does not exist and therefore represents a major research challenge in atmospheric science. This review begins with an update on the current state of knowledge on the global SOA budget and is followed by an overview of the atmospheric degradation mechanisms for SOA precursors, gas-particle partitioning theory and the analytical techniques used to determine the chemical composition of SOA. A survey of recent laboratory, field and modeling studies is also presented. The following topical and emerging issues are highlighted and discussed in detail: molecular characterization of biogenic SOA constituents, condensed phase reactions and oligomerization, the interaction of atmospheric organic components with sulfuric acid, the chemical and photochemical processing of organics in the atmospheric aqueous phase, aerosol formation from real plant emissions, interaction of atmospheric organic components with water, thermodynamics and mixtures in atmospheric models. Finally, the major challenges ahead in laboratory, field and modeling studies of SOA are discussed and recommendations for future research directions are proposed.

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The formation, properties and impact of secondary organic aerosol: current and emerging issues

An analytical technique is described which combines solvent extraction with gas chromatographic (GC) analysis in a simple and inexpensive apparatus involving very little solvent consumption. A small drop (8 μL) of a water-immiscible organic solvent, containing an internal standard, is located at the end of a Teflon rod which is immersed in a stirred aqueous sample solution. After the solution has been stirred for a prescribed period of time, the probe is withdrawn from the aqueous solution, and the organic phase is sampled with a microsyringe and injected into the GC for quantification. The observed rate of solvent extraction is in good agreement with a convective−diffusive kinetic model. Analytically, the relative standard deviation of the method is 1.7% for a 5.00-min extraction of the analyte 4-methylacetophenone into n-octane.

Solvent microextraction into a single drop.

Solid-phase extraction: method development, sorbents, and coupling with liquid chromatography

Evolution of solid-phase microextraction technology

An overview of the methods used in the characterisation of natural organic matter (NOM) in relation to drinking water treatment

Passive sampling in environmental analysis.

Extraction of analytes by the new porous polymer solid phase microextraction (SPME) fibres is based on adsorption rather than absorption. The equilibrium theory developed for the liquid poly(dimethylsiloxane) (PDMS) coating does not apply to these coatings. The paper presents theoretical description of the extraction process for adsorption-type fibres, including PDMS–DVB (divinyl benzene), Carbowax–DVB and Carbowax–TR (template resin). The model is based on Langmuir adsorption isotherm. Expressions describing the amount of analyte extracted by the fibre in two- and three-phase systems are presented and discussed. The effect of selected experimental variables is discussed. In general, there is a non-linear dependence between the amount of an analyte extracted by the fibre and its concentration in a sample. The dependence can be approximated by a straight line for low concentrations only. Matrix composition can significantly affect the amount extracted. Interferences co-extracted with the analyte of interest may reduce the amount extracted and the quasi-linear range of the response. Great care should be exercised therefore when performing quantitative analysis with porous polymer SPME fibres. The phenomena discussed are illustrated on an example of benzene and 4-methyl-2-pentanone extraction from water by PDMS–DVB and Carbowax–DVB fibres.

Theory of analyte extraction by selected porous polymer SPME fibres

Solid-phase microextraction (SPME) is a sample preparation method developed to solve some of the analytical challenges of sample preparation as well as sample introduction and integration of different analytical steps into one system. Since its development, the utilization of SPME has addressed the need to facilitate rapid sample preparation and integrate sampling, extraction, concentration and sample introduction to an analytical instrument into one solvent-free step. This achievement resulted in fast adoption of the technique in many fields of analytical chemistry and successful hyphenation to continuously developing sophisticated separation and detection systems. However, the facilitation of high-quality analytical methods in combination with SPME requires optimization of the parameters that affect the extraction efficiency of this sample preparation method. Therefore, the objective of the current protocol is to provide a detailed sequence of SPME optimization steps that can be applied toward development of SPME methods for a wide range of analytical applications.

Protocol for solid-phase microextraction method development

Applications of polydimethylsiloxane in analytical chemistry: A review

This paper discusses the effect of sample volume on the amount of analyte extracted from a sample by solid-phase microextraction (SPME) in two-phase (sample-fiber coating) and three-phase (sample-headspace-fiber coating) systems. Up-to-date knowledge is summarized, and new concepts are introduced. The effect of sample volume on quantification and precision of results can be neglected only in rare cases. The minimum sample volume which ensures that the amount extracted, n, is lower than 1% of the initial amount of the analyte present in the sample, as well as the volume for which exactly half of the initial amount of the analyte is extracted, have been calculated for both two- and three-phase systems. It is critical that the volumes of samples and standards are the same during analysis by SPME. Extraction kinetics in headspace analysis is dependent on the headspace capacity. If it is sufficiently large, the analyte is extracted almost exclusively from the gaseous phase, and equilibration can be very fast. On the other hand, this causes a significant loss of sensitivity. The effect of sample volume on the determination of the value of the partition coefficient, K, is also discussed. If the change in concentration of the analyte in the sample at equilibrium is not taken into account, erroneous results are obtained. Even when a proper procedure is used, there are practical limitations to the accuracy of the K value determination. Large sample volumes should always be used for K value determination, as they enable broader ranges of K values to be covered with good accuracy.

Tadeusz Górecki

Papers

Passive sampling in environmental analysis.

Theory of analyte extraction by selected porous polymer SPME fibres

Protocol for solid-phase microextraction method development

Applications of polydimethylsiloxane in analytical chemistry: A review

Effect of Sample Volume on Quantitative Analysis by Solid-phase MicroextractionPart 1. Theoretical Considerations