Microextraction procedures

As already reported, extraction yield does not attain 100 per cent. For immuno-extraction there can be an insufficient number of active sites. It is therefore indispensable to introduce a known amount of a tracer. 

The purification of small quantities of aqueous solutions traditionally performed using a separating funnel (liquid-liquid extraction) can be carried out advantageously by a small column containing a porous chemically inert material which is strongly water adsorbent. The aqueous sample is first absorbed into the column (the size must be such that all of the solution should be absorbed). At this stage 

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G. A. Mills, V. Walker, Headspace solid phase microextraction procedures for gas chromato graphic analysis of biological fluids and materials, J. Chromatogr. A, 902, 267 287 (2000). 

Wennrich [167] optimised important accelerated solvent extraction parameters, such as extraction temperature and time, using a spiked wetland soil. The effect of small amounts of organic modifiers on the extraction yields was studied. An extraction temperature of 125 °C and ten-minute extractions performed three times proved optimal. Two accelerated solvent extraction-solid-phase microextraction procedures without and with an organic modifier (5% acetonitrile) were evaluated with respect to precision and detection limits. 

Frias, S., M.A. Rodriquez, J.E. Conde, and J.P. Perez-Trujillo (2003). Optimization of a solid-phase microextraction procedure for the determination of triazines in water with gas chromatography-mass spectrometry detection. J. Chromatogr. A, 1007 127-135. 

Few review articles have been published on microextraction procedures based on the use of a liquid-phase extractant.1314 One drawback of drop-based microextraction procedures is drop vulnerability this relates to its instability and potential dislodgement, which could be caused by sample complexity, a long extraction time, and a fast stirring speed. As a result, precision will often suffer significantly. 

Blasco, C., G. Font, and Y. Pico. 2002. Comparison of microextraction procedures to determine pesticides in oranges by liquid chromatography-mass spectrometry. J. Chromatogr. A 970 201-212. 

Bosch Ojeda, C., Rojas, F.S. Separation and preconcentration by dispersive liquid-liquid microextraction procedure. Chromatographia 69, 1149-1159 (2009)... 

Abalos, M., Bayona, J. M., and Pawliszyn, J., Development of a headspace solid-phase microextraction procedure for the determination of free volatile fatty acids in waste waters, J. Chromatogr. A, 873, 107-115, 2000. 

Pezo, D. Salafranca, J. Nerin, C. Development of an automatic multiple dynamic hollow fibre liquid-phase microextraction procedure for specific migration analysis of new active food packaging containing essential oils. J. Chromatogr. A, 2007,1174, 85-94. 

Chai, M. K. and Tan, G. H. 2009. Validation of a headspace solid-phase microextraction procedure with gas chromatography-electron capture detection of pesticide residues in fruits and vegetables. Food Chem. 117 561-567. 

The following discussion of methods used for sample extraction and clean-up attempts to cover the more commonly used techniques as well as those that appear to offer some potential for the future but are not yet routine. A review of microextraction procedures used in analytical toxicology (Flanagan 2006) is mainly concerned with extraction of analytes from plasma with particular emphasis on LLE and protein precipitation however, miniaturized LLE and SPE are also described as promising ancillary methods. 

SW Lloyd, JM Lea, PV Zimba, CC Grimm. Rapid analysis of geosmin and 2-methylisoborneol in water using solid phase microextraction procedures. Water Res 32 2140-2146, 1998. 

The most widely employed techniques for the extraction of water samples for triazine compounds include liquid-liquid extraction (LLE), solid-phase extraction (SPE), and liquid-solid extraction (LSE). Although most reports involving SPE are off-line procedures, there is increasing interest and subsequently increasing numbers of reports regarding on-line SPE, the goal of which is to improve overall productivity and safety. To a lesser extent, solid-phase microextraction (SPME), supercritical fluid extraction (SEE), semi-permeable membrane device (SPMD), and molecularly imprinted polymer (MIP) techniques have been reported. 

Solid-phase microextraction (SPME) consists of dipping a fiber into an aqueous sample to adsorb the analytes followed by thermal desorption into the carrier stream for GC, or, if the analytes are thermally labile, they can be desorbed into the mobile phase for LC. Examples of commercially available fibers include 100-qm PDMS, 65-qm Carbowax-divinylbenzene (CW-DVB), 75-qm Carboxen-polydimethylsiloxane (CX-PDMS), and 85-qm polyacrylate, the last being more suitable for the determination of triazines. The LCDs can be as low as 0.1 qgL Since the quantity of analyte adsorbed on the fiber is based on equilibrium rather than extraction, procedural recovery cannot be assessed on the basis of percentage extraction. The robustness and sensitivity of the technique were demonstrated in an inter-laboratory validation study for several parent triazines and DEA and DIA. A 65-qm CW-DVB fiber was employed for analyte adsorption followed by desorption into the injection port (split/splitless) of a gas chromatograph. The sample was adjusted to neutral pH, and sodium chloride was added to obtain a concentration of 0.3 g During continuous... 

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]. 

P. Kotianova and E. Matisova, Liquid-phase microextraction and its utilization for trace analysis of organic compounds in water matrix. Chemicke Listy, 2000,94(4), 220-225. Liu Jf, Chi Yg, Jiang Gb, C. Tai, Peng Jf and JT. Hu, Ionic liquid-based liquid-phase microextraction, a new sample enrichment procedure for liquid chromatography. Journal of Chromatography A, 2004,1026(1-2), 143-147. 

In this work, we adapted a method for the analysis of beer aldehydes using solid-phase microextraction (SPMF) with on-fiber derivatization. This extraction technique does not require solvents, consists of a one-step sample preparation procedure, and provides high sensitivity and reproducibility. It enabled a detailed study of aldehyde level changes during packaged beer storage. 

A fourth example (P17) is from the Introduction section of the article that examines PCBs in full-fat milk. For background information, the authors outline the general four-step procedure used to determine PCBs in full-fat milk. Conventional methods used to accomplish two of these steps, extraction and cleanup, are also described. In a new paragraph, the authors introduce solid-phase microextraction (SPME), a technique that greatly simplifies this four-step process. But SPME is not recommended for complex matrixes hence, the authors motivate the topic of their current paper, headspace mode SPME (HSSPME). 

P26 In this article, a simple and rapid saponification-HSSPMF procedure has been developed for the extraction of PCBs from different milk samples. Saponification of the fats helps the transference of the PCBs from the sample to the microextraction fiber. Moreover, saponification acts as a cleanup step, thereby improving selectivity and reliability in peak identification. (Adapted from Llompart et al., 2001)... 

Objective. To date, there is no simple or rapid procedure for testing PCBs in milk. Headspace solid-phase microextraction (HSSPME) is a promising approach, but only a few works have applied this technique to milk (1, 2). Here, we present a simple and rapid saponification-HSSPME procedure for extracting PCBs from milk. (119 words)... 

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. 

Some of the newer procedures use the same basic principles as the older extraction methods but provide fast and easy-to-use options and generally consume less organic solvent. For the most part, they have higher initial purchase price than the traditional methods. Examples include supercritical fluid extraction, accelerated solvent extraction, and automated solid-phase extraction and microextraction. Modular systems are now readily available that automate these proce-... 

A. M. Carro, I. Neira, R. Rodil and R. A. Lorenzo, Speciation of mercury compounds by gas chromatography with atomic emission detection. Simultaneous optimisation of a headspace solid-phase microextraction and derivatisation procedure by use of chemometric techniques, Chro-matographia, 56(11/12), 2002, 733-738. 

Here is a student procedure to measure nicotine in urine. A 1.00-mL sample of biological fluid was placed in a 12-mL vial containing 0.7 g Na2CO , powder. After 5.00 pig of the internal standard 5-aminoquinoline were injected, the vial was capped with a Teflon-coated silicone rubber septum. The vial was heated to 80°C for 20 min and then a solid-phase microextraction needle was passed through the septum and left in the headspace for 5.00 min. The fiber was retracted and inserted into a gas chromatograph. Volatile substances were desorbed from the fiber at 250°C for 9.5 min in the injection port while the column was at 60°C. The column temperature was then raised to 260°C at 25°C/min and eluate was monitored by electron ionization mass spectrometry with selected ion monitoring at m/z 84 for nicotine and m/z 144 for internal standard. Calibration data from replicate... 

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