Headspace, solvents

Solvent Liquid/liquid extraction (LLE) Steam distillation/extraction (SDE) Solvent microextraction (SME) - SDME - LPME - DLLME Headspace-solvent-microextraction (HS-SME) - Headspace single-drop microextraction (HS-SDME) - Headspace liquid phase microextraction (HS-LPME) ... 

HSPE Headspace solvent microextraction HS extraction of volatile compounds into a single drop of solvent, which is then injected into the GC For volatile, GC-amenable compounds, particularly in water and flavor analysis... 

Yamini, Y., M. Hojjati, and M. Haji-Hosseini. 2004. Headspace solvent microextraction. Talanta 62 265-270. 

Bagheri, H. and A. Salemi. 2006. Headspace solvent microextraction as a simple and highly sensitive sample pretreatment technique for ultra trace determination of geosmin in aquatic media. J. Sep. Sci. 29 57-65. 

Headspace solvent microextract (HSME) of aniseed contained 90% f-anethole (Abbas et al., 2005). 

Abbas, B.S., Jabbari, A. and Yamini, Y. (2005) Headspace solvent microextraction a very rapid method for identification of volatile components of Iranian Pimpinella anisum seed. Analytics Chimica Acta 530(1), 155-161. 

Przyjazny, A. and Kokosa, J.M. Analytical characteristics of the determination of benzene, toluene, ethylbenzene and xylenes in water by headspace solvent microextraction. Journal of Chromatography A 2002, 977 (2), 143-153. 

Bahramifar, N. Yamini, Y. Shariati-Feizabadi, S. and Shamsipur, M. Trace analysis of methyl ferf-butyl ether in water samples using headspace solvent microextraction and gas chromatography-flame ionization detection. Journal of Chromatography A 2004,1042 (1-2), 211-217. 

Kaykhaii, M. Nazari, S. and Chamsaz, M. Determination of aliphatic amines in water by gas chromatography using headspace solvent microextraction. Talanta 2005,65 (1), 223-228. 

Deveaux M, Huvenne J-P. 1987. Identification of solvents of abuse using gas chromatography/fourier transform infrared spectrometry after headspace sampling. Chromatographia 23 626-630. 

Ramsey JD, Flanagan RJ. 1982. Detection and identification of volatile organic compounds in blood by headspace gas chromatography as an aide to the diagnosis of solvent abuse. J Chromatogr 240 423-444. 

The concept of SPME was first introduced by Belardi and Pawliszyn in 1989. A fiber (usually fused silica) which has been coated on the outside with a suitable polymer sorbent (e.g., polydimethylsiloxane) is dipped into the headspace above the sample or directly into the liquid sample. The pesticides are partitioned from the sample into the sorbent and an equilibrium between the gas or liquid and the sorbent is established. The analytes are thermally desorbed in a GC injector or liquid desorbed in a liquid chromatography (LC) injector. The autosampler has to be specially modified for SPME but otherwise the technique is simple to use, rapid, inexpensive and solvent free. Optimization of the procedure will involve the correct choice of phase, extraction time, ionic strength of the extraction step, temperature and the time and temperature of the desorption step. According to the chemical characteristics of the pesticides determined, the extraction efficiency is often influenced by the sample matrix and pH. 

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

Liquid (solvent) extraction is not the only way of sample preparation, but stands along with various forms of heat extraction (headspace, thermal desorption, pyrolysis, etc.) and with laser desorption techniques. 

Principles and Characteristics In boiling under reflux procedures a small amount of ground polymer (typically 3g) is placed in a headspace jar (typically 100 mL) and solvent (typically 30 mL) is added. After sealing, the jar is placed in an oven at a temperature where the solvent slowly refluxes. The solvent is, therefore, at the highest temperature possible without applying an external pressure. Consequently, reflux extractions tend to be much faster than Soxhlet extractions. Examples are Soxtec , Soxtherm , FEXTRA and intermittent extraction. Whilst, in theory, partitioning of the analyte between the polymer and solvent prevents complete extraction, this hardly ever constitutes a problem in practice. As the quantity of solvent is much larger than that of the polymer, and the partition coefficients usually favour the solvent, very low additive levels in the polymer result at equilibrium. Any solvent or solvent mixture can be used. 

Principles and Characteristics Pare et al. [475] have patented another approach to extraction, the Microwave-Assisted Process (MAP ). In MAP the microwaves (2.45 GHz, 500 W) directly heat the material to be extracted, which is immersed in a microwave transparent solvent (such as hexane, benzene or iso-octane). MAP offers a radical change from conventional sample preparation work in the analytical laboratory. The technology was first introduced for liquid-phase extraction but has been extended to gas-phase extraction (headspace analysis). MAP constitutes a relatively new series of technologies that relate to novel methods of enhancing chemistry using microwave energy [476]. 

Two basic methods are used for SPME direct immersion of the fibre into the sample and headspace sampling. Experimental parameters comprise the polarity of the sample matrix and coating material, solvent and salting-out. Other parameters for optimisation of SPME conditions include desorption time, injector port temperature and initial oven temperature. 

Solid-phase microextraction eliminates many of the drawbacks of other sample preparation techniques, such as headspace, purge and trap, LLE, SPE, or simultaneous distillation/extraction techniques, including excessive preparation time or extravagant use of high-purity organic solvents. SPME ranks amongst other solvent-free sample preparation methods, notably SBSE (Section 3.5.3) and PT (Section 4.2.2) which essentially operate at room temperature, and DHS (Section 4.2.2),... 

There are basically three methods of liquid sampling in GC direct sampling, solid-phase extraction and liquid extraction. The traditional method of treating liquid samples prior to GC injection is liquid-liquid extraction (LLE), but several alternative methods, which reduce or eliminate the use of solvents, are preferred nowadays, such as static and dynamic headspace (DHS) for volatile compounds and supercritical fluid extraction (SFE) and solid-phase extraction (SPE) for semivolatiles. The method chosen depends on concentration and nature of the substances of interest that are present in the liquid. Direct sampling is used when the substances to be assayed are major components of the liquid. The other two extraction procedures are used when the pertinent solutes are present in very low concentration. Modem automated on-line SPE-GC-MS is configured either for at-column conditions or rapid large-volume injection (RLVI). 

Diffusive sampler Membrane extraction (MESI) Liquid-liquid extraction (LLE) Solid-phase extraction (SPE) SPE-PTV-GC Solid-phase microextraction (SPME) Headspace GC (SHS, DHS) Large-volume injection (LVI) Coupled HPLC-GC Membrane extraction (MESI) Difficult matrix introduction (DMI) Conventional solvent extraction methods 1 Pressurised solvent extraction methods Headspace GC (SHS, DHS) Thermal desorption (TD, DTD) Pyrolysis (Py) Photolysis Photon extraction (LD) Difficult matrix introduction (DMI)... 

Table 4.25 lists the main characteristics of headspace sampling. In HS-GC sample preparation is very often limited to placing a sample in a vial. Sample extraction, clean-up and preconcentration are not necessary. Elimination of solvents in preparing samples for GC has several benefits ... 

With regard to the solution approach, it is imperative that the solvent used be of the highest possible purity. Solution headspace is applicable to a much wider range of samples than the solid approach. When working with... 

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