Microwave‐assisted process (MAP™): Application to the headspace analysis of VOCs in water

Abstract

Abstract. A method combining the techniques of microwave-assisted process (MAP) and gas chromatography (GC) has been developed for the determination of volatile organic compounds in water. For comparison purposes, MAP and conventional gas-phase extractions using static headspace methods were performed on laboratory-spiked water samples. The analytes used as models in this preliminary investigation were benzene, toluene, ethylbenzene, chlorobenzene, 0-, m-, and p-xylenes, and 1,2-, 1,3-, and 1,4-dichlorobenzenes. MAP uses microwaves to very rapidly heat the bulk of the matrix and achieve a selective vaporization of the analytes that are then transferred onto the gas chromatographic apparatus via identical sampling conditions. The method was tested over a 10-5000 ppb range and proved capable of yielding excellent linearity (R2 > 0.99999) and precision (RSD 1.4%). Compared to the conventional static headspace extraction method, the MAP extraction method offered enhanced sensitivity as evidenced by a response in signal greater by 35% for aliquots from the same aqueous solutions. This level of performance is achieved within one minute of overall sample preparation time for the MAP method, whereas the conventional static headspace method used for comparison purposes required 30 minutes of equilibration time. Similar performance was observed with actual samples. Key words: microwave-assisted process, MAP, gas-phase extraction, headspace analysis, VOCs, water SAFETY CONSIDERATIONSThe microwave-assisted process is a simple technology that can be readily understood in terms of the operating steps to be performed. However, the application of microwave energy to various matrices in closed vessels, such as headspace vials, can pose serious hazards in inexperienced hands. The chemical and physical principles underlying the technology are deceptively simple and a wide range of temperature and pressure conditions can be produced according to the nature of the matrix being used. Hence, an extraordinary level of safety and attention to details when planning and performing experiments must be used by all personnel dealing with microwaves. The authors urge all readers to ensure that they seek proper information from knowledgeable sources and that they do not attempt to implement these techniques unless proper guidance is provided and only approved equipment and scientifically sound procedures are used at all times. The feeling of simplicity associated with microwaves can enhance the level of hazard and exposure to accidents if procedures are

Extraction for Analytical Scale Sample Preparation (IUPAC Technical Report)

“…Examples of these applications include the development of high temperature supercritical fluid extraction [88], followed by the evolution of both the hot solvent extraction approach [89], and microwave extraction (Fig. 21), with more selective energy focusing at the sample matrix/extraction phase interface [90]. There is also an indication that milder conditions can be applied by taking advantage of the catalytic properties of the extraction phase or additives [91]; however, more research is still needed to gain insight into the nature of interactions between analytes and matrices.…”

Sample Preparation: Quo Vadis?

“…For example, dissociation of the chemisorbed analytes can be accomplished either by use of high temperature or by application of additives, facilitating desorption. This led to the development of high-temperature supercritical fluid extraction and then to evolution of both the pressurized fluid extraction approach and microwave extraction, with more selective energy focusing at the sample matrix/extraction phase interface . There is also an indication that milder conditions can be applied by taking advantage of the catalytic properties of the extraction phase or additives .…”

Evaluation of Microwave-Assisted Process technology for HAPSITE's headspace analysis of volatile organic compounds (VOCs)

“…We evaluated the use of this microwave prototype by comparing analysis results of headspace samples generated between the HS and the microwave apparatus. It was concluded that the use of microwaves as an energy source for the generation of volatiles provided significant benefits in terms of incubation time and sensitivity [1][2][3][4][5]. While the former is not truly an issue in routine laboratory analysis where commercial apparatus make use of several incubation chambers simultaneously, it is a vital element for field-based analysis.…”