Sorptive Extraction

Sorptive extraction (SPME and Stir Bar extraction methods, see 3.2.4.S Sorptive Extraction for a description of the methods) is an equilibrium method, which like solvent extraction, is dependent upon the extraction phase water partition coefficient. The theoretical recovery of a given analyte (mg, uj ,tej/mto )lTom an aqueous solution by a PDMS (polydiemthylsiloxane) SPME fiber is given by David et al. [15] as  

FIGURE 3.1 Recovery of solutes as influenced by by SPME and Stir Bar methodologies (From David, F.T., B. Tienpont, P. Sandra, LC/GC, 21(2), p. 109, 2003. With permission.) 

A consideration of volatility as a means of aroma isolation requires an appreciation for the factors that influence the amount (or proportion) of an aroma compound in the gaseous phase vs. in the food at equilibrium (static headspace isolation methods) and nonequiUbrium conditions (dynamic headspace isolation methods). In both cases, our methodology requires that the aroma compound partitions into the gas phase for isolation. Considering equilibrium conditions first, the amount of an aroma compound in the gaseous phase is defined by the gas food partition coefficient (kg,). This can be most simply expressed as  

If our food was a dietetic beverage (almost a pure aqueous solution), we could readily predict kg, for an aroma compound (and therefore recovery during isolation). Unfortunately, the presence of various solutes in the food (simple sugars, complex carbohydrates, lipids, proteins, water, minerals, etc.) enormously complicates this equation and our task.. Some factors can be predicted and thus understood, for example, lipid effects. Others, for example binding by proteins or salting out by simple sugars, are not predictable and thus cannot currently be accounted for in a theoretical treatment. 

While we have difficulty with complex food systems, we can also estimate the concentration of an aroma component in the gas phase at equilibrium over simple water and oil systems, i.e., food emulsions. In these food systems, the aroma compounds will partition into the oil and water phases based on their ko and ultimately into the gas phase based primarily on the final concentration in the continuous phase. The concentration in the gas phase (Cg) over an emulsion can be expressed as  

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To overcome the problems of relatively low sample capacity associated with SPME, a technique known as stir-bar sorptive extraction has been reported by Baltussen etal. A glass-coated magnetic stir bar was coated with 50-100 iL of PDMS. Sample extraction was performed by placing the stir bar in the sample with subsequent stirring for 30-120 min. After extraction, the stir bar was removed and analytes were thermally desorbed at 150-300 °C for 5 min for GC, or liquid desorbed for LC. Qualitative analysis of organochlorine residues in wine has been reported using a commercially available product known as Twister. ... 

Another recently developed technique is headspace sorptive extraction (HSSE) with PDMS stir bars [552]. HSSE-GC was compared with SHS and HS-SPME. SBSE and HSSE extract organic analytes from aqueous or vapour samples. In SBSE, the stir bar is inserted into the aqueous sample and extraction takes place during stirring whereas in HSSE the glass rod is suspended within the headspace volume and sampling takes place during headspace equilibration. New trends are the development of selective sorbents. 

Miniaturisation of scientific instruments, following on from size reduction of electronic devices, has recently been hyped up in analytical chemistry (Tables 10.19 and 10.20). Typical examples of miniaturisation in sample preparation techniques are micro liquid-liquid extraction (in-vial extraction), ambient static headspace and disc cartridge SPE, solid-phase microextraction (SPME) and stir bar sorptive extraction (SBSE). A main driving force for miniaturisation is the possibility to use MS detection. Also, standard laboratory instrumentation such as GC, HPLC [88] and MS is being miniaturised. Miniaturisation of the LC system is compulsory, because the pressure to decrease solvent usage continues. Quite obviously, compact detectors, such as ECD, LIF, UV (and preferably also MS), are welcome. 

PLE pressurized liquid extraction, SPE solid phase extraction, UE ultrasonic extraction, DSPE dispersive solid phase extraction, SBSE stir bar sorptive extraction, TD-GC-MS thermal desorption-gas chromatography-mass spectrometry, LAS linear alkylbenzene sulfonates, CDEAs coconut diethanol amides, NPEOs nonylphenol ethoxylates, DP degradation products, SPC sulphenyl carboxylates, PCDD dibenzo-p-dioxins (PCDD), PCDF dibenzofurans, PCBs biphenyls... 

Rodil R, Moeder M (2008) Development of a method for the determination of UV filters in water samples using stir bar sorptive extraction and thermal desorption-gas chromatography-mass spectrometry. J Chromatogr A 1179(2) 81—88... 

Tan BL, Hawker DW, Muller JF, Tremblay LA, Chapman HF (2008) Stir bar sorptive extraction and trace analysis of selected endocrine disrupters in water, biosolids and sludge samples by thermal desorption with gas chromatography-mass spectrometry. Water Res 42 404 112... 

Bicchi, C., loti, C., Rubiolo, P. and Sandra, P. (2002) Headspace sorptive extraction (HSSE), stir bar sorptive extraction (SBSE) and solid phase microextraction (SPME) applied to the analysis of roasted Arabica coffee and coffee brew. J.Agric. Food Chem. 50, 449-459. 

Soini, H.A., Bruce, K.E., Wiesler, D., David, F., Sandra, P. and Novotny, M.V. (2005) Stir bar sorptive extraction a new quantitative and comprehensive sampling technique for determination of chemical signal profiles from biological media J. Chem. Ecol., 31, 377-392. 

Abstract A relatively small number of mammalian pheromones has been identified, in contrast to a plethora of known insect pheromones, but two remarkable Asian elephant/insect pheromonal linkages have been elucidated, namely, (Z)-7-dodecen-1-yl acetate and frontalin. In addition, behavioral bioassays have demonstrated the presence of a chemical signal in the urine of female African elephants around the time of ovulation. Our search for possible ovulatory pheromones in the headspace over female African elephant urine has revealed for the first time the presence of a number of known insect pheromones. This search has been facilitated by the use of a powerful new analytical technique, automated solid phase dynamic extraction (SPDE)/GC-MS, as well as by novel macros for enhanced and rapid comparison of multiple mass spectral data files from Agilent ChemStation . This chapter will focus on our methodologies and results, as well as on a comparison of SPDE and the more established techniques of solid phase microextraction (SPME) and stir bar sorptive extraction (SBSE). 

Stir bar sorptive extraction (SBSE) is a more recent development, and offers some advantages over SPME (Baltussen, Sandra, David and Cramers 1999 ... 

Baltussen, E., Sandra, P., David, F. and Cramers, C. (1999) Stir bar sorptive extraction (SBSE), a novel extraction technique for aqueous samples theory and principles. J. Microcolumn Sep. 11,737-747. 

Tienpont, B., David, F., Desmet, K. and Sandra, P. (2002) Stir bar sorptive extraction-Thermal desorption-capillary GC-MS applied to biological fluids. Anal. Bioanal. Chem. 373, 46-55. 

Besides classical headspace analysis, simultaneous distillation-extraction and solvent extraction, new sampling and enrichment developments include solvent-assisted flavour evaporation (SAFE) [3] and sorptive techniques like SPME solid-phase microextraction (SPME) [4,5] and stir-bar sorptive extraction (SBSE) [6], which are treated in a dedicated chapter in this book. This contribution will deal with advanced developments of GC techniques for improvement of separation and identification (classical multidimensional GC, or... 

Kreck, M., Scharrer, A., Bilke, S., Mosandl, A. (2002) Enantioselective analysis of monoter-pene compounds in essential oils by stir bar sorptive extraction (SBSE)-enantio-MDGC-MS. Flavour Fragrance ]. 17 32-40. 

Stir-Bar Sorptive Extraction-Enantioselective Multidimensional Gas Chromatography-Mass Spectrometry... 

A novel solventless simple technique for extraction of organic analytes from aqueous samples, stir-bar sorptive extraction (SBSE), was introduced by Baltus-sen et al. [41]. 

Fig. 17.10 Stir-bar sorptive extraction-enantio-MDGC-MS analysis of tea tree oil, main column separation [45]...

Bicchi C, Cordero C, lori C, Rubiolo P, Sandra P (2000) Headspace sorptive extraction (HSSE) in the headspace analysis of aromatic and medicinal plants. J High Resol Chromatogr 23 539 KreckM, Scharrer A, Bilke S, Mosandl A (2001) Stir bar sorptive extraction (SBSE)—enantio-MDGC-MS, a rapid method for the enantioselective analysis of chiral flavour compoimds in strawberries. Eur Food Res Technol 213 389... 

Absorption methods (sorptive extraction) have become the method of choice for many researchers. They offer advantages of being rapid, solventless, automated, and reasonably sensitive and broad in isolation properties. However, they provide an aroma isolate that reflects the biases resulting from compound volatility and affinity for the absorbent matrix. 

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