Multiple-headspace extraction

Welch, W. G. Greco, T. G. An Experiment in Manual Multiple Headspace Extraction for Gas Ghromatography, ... 

Brachet, A. and Chaintreau, A. Determination of air-to-water partition coefficients using automated multiple headspace extractions. Anal Chem., 77(10) 3045-3052, 2005. 

The four most common approaches to quantitative HSGC calibration are classical external standard, internal standard, standard addition, and multiple headspace extraction (MHE). The choice of technique depends on the type of sample being analyzed. 

Multiple headspace extraction (MHE) is used to find the total peak area of an analyte in an exhaustive headspace extraction, which allows the analyst to determine the total amount of analyte present in the sample. This technique, along with the mathematical models behind it, was originally presented by McAuliffe [17] and Suzuki et al. [18]. Kolb and Ettre have an in-depth presentation of the mathematics of MHE in their book [15], and the reader is encouraged to reference that work for further information on the mathematical model. 

Kolb [203] describes a stepwise gas-extraction procedure called multiple headspace extraction (MHE). Using this method, Kolb found that the determination can be performed with only two extractions. The volume of the sample was compensated for by adding a similar volume of an inert material such as glass beads. Ethylene oxide in surgical silk sutures was determined by this procedure. The extrapolated total area (four steps) was nearly identical to the total area value obtained using the two-step MHE process, 184 versus 183, respectively. 

Methylene chloride in a tablet was analyzed by Kolb [203] using the multiple headspace extraction method (three steps). The sample was analyzed as a dry powdered material using a glass capillary column, Marlophen 87, isothermally at 35°C. A concentration of 35 ppm was found, which was in reasonable agreement with that obtained (40 ppm) when the sample was dissolved in water and analyzed by normal headspace analysis using the method of standard addition for quantitation. The extrapolated total area... 

B. Kolb, Multiple headspace extraction — a procedure for eliminating the influence of the sample matrix in quantitative headspace gas chromatography, Chromatographia, 75 587-594(1982). 

Headspace-GC-MS analysis is useful for the determination of volatile compounds in samples that are difficult to analyze by conventional chromatographic means, e.g., when the matrix is too complex or contains substances that seriously interfere with the analysis or even damage the column. Peak area for equilibrium headspace gas chromatography depends on, e.g., sample volume and the partition coefficient of the compound of interest between the gas phase and matrix. The need to include the partition coefficient and thus the sample matrix into the calibration procedure causes serious problems with certain sample types, for which no calibration sample can be prepared. These problems can, however, be handled with multiple headspace extraction (MHE) [118]. Headspace-GC-MS has been used for studying the volatile organic compounds in polymers [119]. The degradation products of starch/polyethylene blends [120] and PHB [121] have also been identified. 

Hakkarainen, M. Developments in multiple headspace extraction. J. Biochem. Biophys. Methods 70(2), 229-233 (2007)... 

HS-SPME-GC-MS showed that residual methyl methacrylate is released during thermal annealing of PMMA [40]. SPME fiber was carboxen/PDMS. The extraction time and temperature was 2 hours at 70 °C. A multiple headspace extraction method using a carboxen/PDMS fiber was developed for the quantitative determination of vinyl chloride monomer in PVC [41]. To reduce the equilibrium time, the PVC sample was finely ground before the extraction. Quantitative SPME methods have also been developed to determine vinyl chloride in liquid and solid samples [42] and to determine terephthalic acid and vinyl acetate monomers from aqueous solutions [43]. 

Keywords Degradation Multiple headspace extraction Quality control Recycling Solid-phase microextraction... 

In 1977 Kolb and Pospisil proposed a method for the quantitative analysis of volatiles in solid samples [48] by using headspace extraction and gas chromatographic detection. The method, termed discontinuous gas extraction, is based on stepwise gas extraction, followed by a subsequent analysis of the extracted volatiles. The method theoretically calculates the total amount of analyte in a soUd sample after a few successive extractions and makes the quantitation of volatile analytes in soUd matrices possible. The proposed method was validated by measuring the styrene content in polystyrene by discontinuous gas extraction and by a procedure proposed by Rohrschneider in which the polystyrene is dissolved in dimethyl formamide (DMF) [49]. The two methods were in good agreement, which supported the validity of the discontinuous gas extraction. Kolb and Pospisil later elaborated the theoretical treatment of discontinuous gas extraction and in 1981 the method was re-named as multiple headspace extraction (MHE) [50]. 

Fig. 4 The multiple headspace extraction plots of six consecutive 45-min extractions from (A) 75 mg Zytel at 50 °C (B) 75 mg Zytel at 80 °C (C) 75 mg Zytel at 120 °C and (D) 10 mg Zytel at 80 °C. The 10-mg samples were incubated for 25 h at 80 °C prior to extraction. Reprinted from [67] with permission of Elsevier. Elsevier (2004)...

HS-SPME is a very useful tool in polymer analysis and can be applied for absolute and semi-quantitative determination of the volatile content in polymers, for degradation studies, in the assessment of polymer durabihty, for screening tests and for quality control of recycled materials. For quantitative determination of volatiles in polymers, SPME can be combined with multiple headspace extraction to remove the matrix effects. If the hnearity of the MHS-SPME plot has been verified, the number of extractions can be reduced to two, which considerably reduces the total analysis time. Advantages of MHS-SPME compared to MAE are its higher sensitivity, the small sample amount required, solvent free nature and if an autosampler is used a low demand of labor time. In addition, if the matrix effects are absent, the recovery will always be 100%. This is valuable compared to other techniques for extracting volatiles in polymers in which the recovery should be calculated from the extraction of spiked samples, which are very difficult to produce in the case of polymeric materials. 

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