Isolation solid-phase microextraction

An attractive approach to isolating analytes is a solid-phase microextraction (SPME). In one approach, which is illustrated in Figure 12.19, a fused silica fiber is placed inside a syringe needle. The fiber, which is coated with a thin organic film, such as polydimethyl siloxane, is lowered into the sample by depressing a plunger and is exposed to the sample for a predetermined time. The fiber is then withdrawn into the needle and transferred to the gas chromatograph for analysis. 

More recently, solid phase microextraction (SPME) [22] has been applied to the analysis of bug pheromones, using two techniques. In the first, headspace volatiles are trapped on the SPME fiber, analogous to trapping on SuperQ [e.g., 23]. Alternatively, if the source of the pheromone is known, the SPME fiber can be wiped on the cuticle to directly adsorb the compounds [24]. In either case, the fiber is then thermally desorbed directly into a GC or GC-MS. Whereas this method is excellent for analysis, with good recoveries, it does not provide a sample that can be used for bioassays or for isolation of an active compound. 

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]. 

The use of headspace solid-phase microextraction (HS-SPME) combined with GC was effective for isolation and determination of alkylpyrazines in cocoa liquor <2004JBS267, 2004MI291>, and similarly methoxypyrazine in wine was analyzed by HS-SPME/2-D GC <2005MI1075>. 

Recently, the procedures that are suitable to isolate the volatile fraction of a sample under mild conditions have been reviewed [1]. Three techniques—solvent extraction, distillation and solid-phase microextraction (SPME)—will be presented here. 

Another relatively new SPE approach originally developed for the analysis of volatile organic compounds in environmental samples is solid-phase microextraction (SPME). This technique has gained acceptance for a wide variety of additional applications for the isolation of organic compounds from aqueous solu-... 

You need to decide the goal of an analysis before developing a chromatographic method. The key to successful chromatography is to have a clean sample. Solid-phase microextraction, purge and trap, and thermal desorption can isolate volatile components from complex matrices. After the sample preparation method has been chosen, the remaining decisions for method development are to select a detector, a column, and the injection method, in that order. 

The time required for quantification of volatiles by both the Basic Protocol and the Alternate Protocol depends on the isolation/extrac-tion procedure chosen. A complete homogenization of the labeled standards with the sample usually requires not more than 30 min and GC-MS analysis is accomplished within 1 hr. In combination with a high-throughput method like solid-phase microextraction, the GC cycle times (-1 hr) become the limiting factor in the quantification of multiple samples by IDAs. 

A. Alcaraz, S.S. Hulsey, R.E. Whipple and B.D. Andresen, On-site sample work-up procedures to isolate chemical warfare related compounds using solid phase extraction and solid phase microextraction technology, NATO ASI Ser. Ser. 1, 13, 65-76 (1997). 

Solid Phase Microextraction Out of the many sample preparation methods, solid phase microextraction (SPME) is one of the most frequently used. SPME is used for the determination of VOCs in liquid, gas, and solid samples. The great advantage of the method is that it combines, in one stage, the isolation and enrichment of compounds, and completely eliminates the need for organic solvents. 

The method is different from conventional SPE in that SPE isolates the majority of the analyte from a sample (> 90%) but only injects about 1 to 2% of the sample onto the GC. Solid-phase microextraction isolates a much smaller quantity of analyte (2-20%), but all of that sample is injected into the GC. The extraction efficiency of the fiber is a combination of extraction time, the thickness of the stationary phase, and the magnitude of the partition coefficient for the stationary phase. 

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

Quantification of aroma-impact components by isotope dilution assays (IDA) was introduced in food flavor research by Schieberle and Grosch (1987), when trying to take into account losses of analytes due to isolation procedures. The labeled compounds have to be synthesized, the suitable fragments have to be chosen, and calibration has to be effected. A quantitative determination of ppb levels of 3-damascenone (Section 5,D.38) in foods, particularly in roasted coffee (powder and brew), was developed by Sen et al. (1991a). Semmelroch et al. (1995) quantified the potent odorants in roasted coffee by IDA. Hawthorne et al. (1992) directly determined caffeine concentration in coffee beverages with reproducibility of about 5 % using solid-phase microextraction combined with IDA. Blank et al. (1999) applied this combined method to potent coffee odorants and found it to be a rapid and accurate quantification method. They also concluded that the efficiency of IDA could be improved by optimizing the MS conditions. 

The procedures most often used for isolation and preconcentration of phthalate esters from water are LEE and SPE. Both techniques are included in official methods to perform the extraction of phthalates (see Table 28.3A). In the last years, solid phase microextraction (SPME) have acquired an increased importance in the analysis of semivolatile compounds, such as phthalates, in water. After extraction, the final analysis is usually carried out using a chromatographic technique. 

Various extraction techniques are applied to isolate EDCs in aqueous samples, such as liquid-liquid extraction (LEE), solid-phase extraction (SPE), and solid-phase microextraction (SPME). LEE is frequently used in the extraction of EDCs with water immiscible organic solvents, most... 

The sample introduction system must be capable of introducing a known and variable volume of sample solution reproducibly into the pressurized mobile phase as a sharp plug without adversely affecting the efficiency of the column. The superiority of valve injection has been adequately demonstrated for this purpose and is now universally used in virtually all modern instruments for both manual and automated sample introduction systems [1,2,7,31,32]. Earlier approaches using septum-equipped injectors have passed into disuse for a several reasons, such as limited pressure capability, poor resealability, contamination of the mobile phase, disruption of the column packing, etc., but mainly because they were awkward and inconvenient to use compared with valves. For dilute sample solutions volume overload restricts the maximum sample volume that can be introduced onto the column without a dramatic loss of performance. On-column or precolumn sample focusing mechanisms can be exploited as a trace enrichment technique to enhance sample detectability. Solid-phase extraction and in-column solid-phase microextraction provide a convenient mechanism for isolation, concentration and matrix simplification that are easily interfaced to a liquid chromatograph for fully or semi-automated analysis of complex samples (section 5.3.2). 

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. 

However, a previous distillation is sometimes needed to separate the target compounds from a complex matrix sample. After they are condensed, they can then be either injected directly or through the HS mode. In other cases, the use of extraction techniques like solvent-solvent extraction, solid-phase extraction, and solid-phase microextraction not only achieves the isolation of the target compounds from the matrix but also produces a preconcentration of... 

ON-SITE SAMPLE WORK-UP PROCEDURES TO ISOLATE CHEMICAL WARFARE RELATED COMPOUNDS USING SOLID PHASE EXTRACTION AND SOLID PHASE MICROEXTRACTION TECHNOLOGY... 

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