Headspace SPME

Organic solvent-less techniques (e.g. subcritical water extraction, headspace SPME). 

S. Hamm, J. Bleton, J. Connan, A. Tchapla, A chemical investigation by headspace SPME and GC MS of volatile and semi volatile terpenes in various olibanum samples, Phytochemistry, 66, 1499 1514(2005). 

The first results encouraged the authors to analyse, by headspace SPME, substances mentioned in ancient texts or hieroglyphics as components of embalming fluids [true resins such as mastic, labdanum and pine resin or pine pitch and gum resins such as olibanum, myrrh and galbanum] [27, 28] with the aim of finding characteristic chemical compounds for each type of resin or gum resin. 

Among the characteristic furanosesquiterpenes of myrrh trapped by headspace SPME, curzerene (65) (= isofuranogermacrene), furanoeudesma-1,3-diene (80) and lindestrene... 

S-dihydroagarofuran (64) and epi-ligulyl oxide (72) could represent potential biomarkers [39]. However, due to their very low concentration, it will be difficult to detect them by headspace SPME in complex archaeological mixtures. 

Figure 10.2 Total ion current chromatograms obtained for modern resins and gum resins after headspace SPME. Peak labels correspond to compound identification given in Table 10.1. Reproduced from S. Hamm, j. Bleton, A. Tchapla, j. Sep. Sci., 27, 235 243 (2004). Copyright Wiley VCH Verlag GmbH Co. KgaA. Reproduced with permission...

The method allowed the authors to characterise a pine pitch (viscous tar derived from the distillation of wood of pine trees). The main constituents detected by headspace SPME result from the pyrolysis of the lignin, guaiacol (11) and its p-w-alkyl derivatives [methyl... 

Table 10.1 Compounds trapped by headspace SPME from different resins, gum resins and archaeological samples, presented by Increasing retention indices, with the corresponding relative peak areas (%) for each substance... 

Diterpenes require more than 80 min to reach equilibrium. This is expected for compounds that exhibit low vapour pressure in combination with a high partition coefficient between the fibre coating and the gaseous phase. During headspace SPME the amount of such compounds present in the gaseous phase is absorbed by the fibre coating at a much faster rate than their release from the matrix, thus the amount of mass in the headspace at any time is small and a long time is required to reach equilibrium [58]. 

Comparison between Headspace SPME and Solvent Extraction... 

The main compounds detected by headspace SPME in six olibanum samples are given in Table 10.3. Qualitative results obtained by headspace SPME were identical to those obtained by classical extraction with dichloromethane, except for the tri terpenes. 

Table 10.3 Main components detected by headspace SPME/GC MS in the six reference olibanum samples with certified botanical origin and in three olibanum samples without botanical origin... 

Figure 10.9 Total ion current chromatogram obtained for sample 1998 after headspace SPME. Peak labels correspond to compound identification given in Table 10.4...

Table 10.6 Terpenes detected by headspace SPME/GC MS in four samples from the tomb of Khnoumit (Dachour, Egypt)...

These results demonstrate clearly that headspace SPME/GC-MS is well adapted to the detection of volatile or semi-volatile terpenes from resins or gum resins. The method is rapid and simple. A moderate heating (80°C) of the sample allows the extraction of less volatile compounds such as particular diterpenes or diterpenoids which are more specific. 

SPME/GC/MS is an efficient technique to reveal the presence of resinic substances in archaeological samples. Indeed, volatile terpenes are still present in very old archaeological samples (4000 years old), particularly in the case of compact matrixes, and can be trapped by the SPME fibre. In comparison with methylene chloride extraction, SPME is very specific and allows the direct analysis of the volatile terpenes content in complex mixtures including oils, fats or waxes. For this reason, headspace SPME is the first method to use when analysing an archaeological sample it will either allow the identification of the resin or indicate further sample treatment in order to detect characteristic triterpenes. The method is not really nondestructive because it uses a little of the sample but the same sample can be used for several SPME extractions and then for other chemical treatments. 

J. A. Field, G. Nickerson, D. D. James, C. Heider, Determination of essential oils in hops by headspace SPME, J. Agric. Food Chem., 44, 1768 1772 (1996). 

T. Watanabe, A. Namera, M. Yashiki, Y. Iwasaki, T. Kojima, Simple analysis of local anaesthetic in human blood using headspace SPME and GC MS electron impact ionization selected ion monitoring, J. Chromatogr. B, 709, 225 232 (1998). 

This method is based on the partitioning of compounds between a sample and a coated fibre immersed in it [16-18]. The volatiles and other compounds are first adsorbed onto the fibre immersed in a liquid sample, an extract, or in the headspace above a sample for a certain period of time. After adsorption is complete, the compounds are thermally desorbed into a GC injector block for further analysis. Particularly in food applications, headspace SPME is preferred to avoid possible contamination of the headspace system by non-volatile food components [16]. 

Headspace SPME is a solventless extraction method where a silica fiber coated with adsorbant or absorbant polymer material is exposed to a gas phase to extract analytes. The food of interest is placed in a closed or open container (such as a mouth simulator). After extraction, the fiber is desorbed in a GC injection port for separation and detection of the extracted analytes. 

SPME can concentrate a compound in a headspace up to 300-fold, possibly more. It extracts and concentrates compounds in a selective manner, so that compound A may be concentrated 150 times while compound B is concentrated only 10 times during the same extraction. Only volatilized compounds are extracted by headspace SPME. Not all compounds found by solvent extraction will be extracted by headspace SPME, primarily because not all compounds volatilize. Immersion SPME gives similar results to those obtained by solvent extraction. 

SPME (Figure 2.48) can be conducted as a direct extraction in which the coated fiber is immersed in the aqueous sample in a headspace configuration for sampling air or the volatiles from the headspace above an aqueous sample in a vial (headspace SPME analyses are discussed elsewhere) or by a membrane protection approach, which protects the fiber coating, for analyses of analytes in very polluted samples [136]. The SPME process consists of two steps (Figure 2.49) (a) the sorbent, either an externally coated fiber or an internally coated tube, is exposed to the sample for a specified period of time (b) the sorbent is transferred to a device that interfaces with an ana-... 

Figure 2.48. Modes of SPME operation (a) direct extraction (b) headspace SPME (c) membrane-protected SPME. (Reprinted with permission from Ref. 51. Copyright 2000 Elsevier Science.)...

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