Solid-phase microextraction from liquid samples

Experiments to identify disinfection by-products (DBFs) have been carried out using two different procedures. In the first, natural waters (e.g., river, lake) are reacted with the disinfectant, either in a pilot plant, an actual treatment plant, or in a controlled laboratory smdy. fii the second type of procedure, aquatic humic material is isolated and reacted with the disinfectant in purified water in a controlled laboratory study. This latter type of study is relevant because humic material is an important precursor of THMs and other DBFs. Aquatic humic material is present in nearly all natural waters, and isolated humic material reacts with disinfectants to produce most of the same DBFs found from natural waters. Because DBFs are typically formed at low levels (ng/L-pg/L), samples are usually concentrated to allow for DBF detection. Concentration methods that are commonly used include solid phase extraction (SFE), solid phase microextraction (SFME), liquid-liquid extraction, and XAD resin extraction (for larger quantities of water) [9]. 

Among the numerous techniques for separating and enriching organic compounds from water samples, the following are worthy of mention solid-phase extraction (SPE), solid-phase microextraction (SPME), liquid-liquid extraction (LLE), and lyophilization. 

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. 

Yang et al. [47,48,53,54] developed a HWG sensing system for liquid and soil analyses based on an extractive polymer membrane coated onto the inside of the HWG. The polymer coating performs a solid-phase microextraction of the analyte from the headspace of the sample and preconcentrates the analyte prior to IR analysis. 

Solid-phase microextraction (SPME) is a fast and solventless modification of SPE techniques [20]. SPME involves the use of fiber (fused silica fiber or polymer-coated fused fiber) coated by an adsorbent. The method is applied for extraction of different kinds of both volatile and nonvolatile analytes from different kinds of media, which can be in liquid or gas phase. In the direct extraction mode, coated fiber is immersed in the sample for a defined time, until equilibrium between the sample matrix and the solid phase is reached. The analyte is transported by diffusion directly to the extracting phase. In the next stage, the compound of interest... 

Solid-phase microextraction, first reported by Belardi and Pawliszyn in 1989, is an alternative sampling technique. The method has the advantages of convenience and simplicity, and it does not release environmentally polluting organic solvents into the atmosphere. The method is based on the extraction of analytes directly from liquid samples or from headspace of the samples onto a polymer- or adsorbent-coated fused silica fiber. After equilibration, the fiber is then removed and injected onto the gas chromatograph. ... 

Sample preparation represents a formidable challenge in the chemical analysis of the real-world samples. Not only is the majority of total analysis time spent in sample preparation, but also it is the most error-prone, least glamorous, and the most labor-intensive task in the laboratory. The components to be separated from the matrix are usually taken up with an auxiliary substance such as a carrier gas, an organic solvent, or an adsorbent. These separation processes can be regarded as extraction procedures (i.e., liquid-liquid extraction, liquid-solid extraction, Soxhlet extraction, solid-phase extraction, supercritical fluid extraction, solid-phase microextraction, etc.). 

A related technique, called solid-phase microextraction, uses a fused silica fiber coated with a nonvolatile polymer to extract organic analytes directly from aqueous samples or from the headspace above the samples. The analyte partitions between the fiber and the liquid phase. The analytes are then desorbed thermally in the heated injector of a gas chromatograph (see Chapter 31). The extracting fiber is mounted in a holder that is much like an ordinary syringe. This technique combines sampling and sample preconcentration in a single step. 

Generally, preconcentration of pollutants from water samples and sample preparation steps are accomplished by extraction techniques based on enrichment of liquid phase (liquid/liquid extraction) or solid phase (solid/liquid extraction) ". Historically, liq-uid/liquid extraction (LEE) was used exclusively to enrich phenols from water samples. LEE is still used as a preconcentration step . However, there is an increasing tendency to replace LEE by solid phase extraction (SPE) and solid phase microextraction (SPME). Among the reasons for replacing LEE are foam formation, the large volume of organic solvents needed, the length of the analysis time and difficulties in the automation of LEE procedures. On the other hand, SPE requires incomparable smaller amounts of solvents (SPME requires no solvent at all) and can be easily automated . Finally, SPE and SPME are cheaper in comparison with LEE. 

Solid-phase microextraction (SPME) of wine was developed by both headspace (HS) (Vas et al., 1998) and liquid-phase sampling (De la Calle et al., 1996). Exhaustive overviews on materials used for the extraction-concentration of aroma compounds in wines were published from Ferreira et al. (1996), Cabredo-Pinillos et al. (2004), and Nongonierma et al. (2006). 

Sample preparation for GC/MS analysis of volatile compounds in wines and extracts was usually performed by liquid-liquid extraction with dichloromethane (Cutzach et al., 1997 Perez-Coello et al., 1999 Cadahia et al., 2003). Direct extraction of volatiles from the wood by headspace (HS) solid-phase microextraction (SPME) using a polydimethylsiloxane (PDMS) fiber allowed to analyze compounds,... 

Solid-phase microextraction Isolation from liquid samples, direct immersion or headspace Partition or adsorption from solution or gas Inexpensive segments of coated fused silica... 

Solid-phase microextraction (SPME) is a technique that was first reported by Louch et al. in 1991 (35). This is a sample preparation technique that has been applied to trace analysis methods such as the analysis of flavor components, residual solvents, pesticides, leaching packaging components, or any other volatile organic compounds. It is limited to gas chromatography methods because the sample must be desorbed by thermal means. A fused silica fiber that was previously coated with a liquid polymer film is exposed to an aqueous sample. After adsorption of the analyte onto the coated fiber is allowed to come to equilibrium, the fiber is withdrawn from the sample and placed directly into the heated injection port of a gas chromatograph. The heat causes desorption of the analyte and other components from the fiber and the mixture is quantitatively or qualitatively analyzed by GC. This preparation technique allows for selective and solventless GC injections. Selectivity and time to equilibration can be altered by changing the characteristics of the film coat. 

Another useful technique is solid phase microextraction. A fused silica fibre is attached to the base of a syringe with a fixed metal needle. The fibre is coated with a thin layer of stationary phase that is selective for the analytes of interest. The fibre is dipped into the liquid sample or into the headspace above the liquid for a period of time, allowing a fraction of the analyte to be extracted into the fibre. The fibre is then retracted into the syringe and the syringe injected into the injection port where the analyte is thermally desorbed from the fibre into the GC. 

The newly developed solid-phase microextraction (SPME) technique, first reported by Pawliszyn in 1989, is increasingly used for the gas chromatographic determination of a wide variety of volatile and semivolatile organic compounds in water or aqueous extracts of different substrates. Basically, it involves the extraction of specific organic analytes directly from aqueous samples or from the headspace of these samples in closed vials. The extraction is achieved onto a fused-silica fiber coated with a polymeric liquid phase. After equilibration, the fiber containing the absorbed or adsorbed analyte is removed and thermally desorbed in the hot injector port of a gas chromatograph or in an appropriate interface of a liquid chromatograph. ... 

The procedure to be used to extract carbamate pesticides from environmental samples depends on their polarity and on the type of sample matrix involved. Various choices exist for the extraction of pesticides ranging from conventional procedures (e.g., Soxhlet extraction, liquid-liquid extraction (LLE), evaporation, steam distillation) to new methodologies including solid-phase extraction (SPE), solid-phase microextraction (SPME), supercritical fluid extraction (SEE), matrix solid-phase dispersion (MSPD), accelerated solvent extraction (ASE) and microwave-assisted extraction. " ... 

Automated in-tube solid-phase microextraction (SPME) has recently been coupled with liquid chromatography/electrospray ionisation mass spectrometry (LC/ESI-MS), e. g. for the determination of drugs in urine [60, 62]. In-tube SPME is an extraction technique in which analytes are extracted from the sample directly into an open tubular capillary by repeated draw/eject cycles of sample solution. The analyte is then desorbed with methanol and transferred to an analytical HPLC-column. 

SPE is an extraction method that uses a solid phase and a liquid phase to isolate and preconcentrate analytes of interest from a solution. The technique is based on partitioning of the analyte between the liquid phase and the extraction material (solid phase), with the mechanism of interaction depending on the extraction material. SPE is very popular, not only because it concentrates the sample, but can also be used to remove the analyte from interfering molecules if the interfering molecules do not show interactions with the SPE material. Chapter 27 of this book is devoted to SPE and its cousin, solid-phase microextraction. 

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