Extraction matrix

The effect of co-extracted matrix components on the analyte response in the final determination step should be assessed. Normally, this is done by comparing the response of standards in solvent with matrix-matched standards, i.e., standards prepared in the extract of a control sample without residues. Because matrix effects tend to be inconsistent, the guidelines propose the general use of matrix-matched calibration unless it is demonstrated to be unnecessary. 

The separation of analytes from undesirable matrix components, or cleanup , of sample extracts can be accomplished through a variety of techniques that take advantage of differences in the physicochemical properties of the analytes from co-extracted matrix components. 

A cleanup procedure is usually carried out to remove co-extracted matrix components that may interfere in the chromatographic analysis or be detrimental to the analytical instrument. The cleanup procedure is dependent on the nature of the analyte, the type of sample to be analyzed, and the selectivity and sensitivity of the analytical instrument used in the analysis. Preliminary purification of the sample extracts prior to chromatographic separation involves liquid-liquid partitioning and/or solid-phase extraction (SPE) using charcoal/Celite, Elorisil, carbon black, silica, or aminopropyl-silica based adsorbents or gel permeation chromatography (GPC). 

Vestal, M. L. Juhasz, R Martin, S. A. Delayed extraction matrix-assisted laser desorption time-of-flight mass spectrometry. Rapid Comm. Mass Spectrom. 1995, 9, 1044-1050. 

M.L. Vestal, P. Juhasz, and S.A. Martin, Delayed Extraction Matrix assisted Laser Desorption Time of flight Mass Spectrometry, Rapid Commun. Mass Spectrom., 9, 1044 1050 (1995). 

As a general rule, APCI is less likely to demonstrate matrix effects and ESI is more likely to be affected by matrix effects. Sample clean-up is another important factor—protein precipitation is more likely to result in matrix effects than is solid phase extraction. Matrix effects may be caused by sample constituents that are not parts of the biological matrix. Mei et al.126 129 showed that certain brands of sample tube containers can produce matrix effects. They also demonstrated that Li-heparin, a common anticoagulant for plasma samples, can produce significant matrix effects... 

Extraction Method EPA SW-846 Method Number Extraction Matrix Compounds Extracted Purpose... 

Supercritical fluids were soon found to be highly efficient extraction media, chiefly because of their high solvating power, their low viscosities (intermediate between a gas and a liquid), and their low surface tensions that enable their penetration deep into the extraction matrix. Supercritical fluid extraction (SEE) used in isolation is generally not selective enough to separate specific solutes from the matrix without further cleanup or resolution from coextracted species prior to qualitative and quantitative analysis. Consequently, for analytical applications, SFE is usually used in combination with chromatographic techniques to improve the overall selectivity in the isolation of specific solutes. The combined use of SFE with chromatographic techniques is quite recent. 

In a STD0 (extracted matrix sample that does not contain analyte but does contain internal standard at the level specified in the assay), or... 

In some applications like newborn screening and filter paper blood spots, the internal standard that is labeled cannot be mixed with blood. It can only be present in the extraction solvents. Therefore, only the extracted metabolites can be quantitatively measured. I have denoted a term called pseudo-isotope dilution to account for the differences between traditional isotope dilution and the technique commonly used in newborn screening by MS/MS. A special analysis is capable using this technique, however, in terms of an extraction efficiency experiment. With isotope-labeled standards you can perform an experiment whereby a traditional isotope-dilution technique (internal standard added to liquid blood and spotted) is compared to pseudo-isotope dilution techniques (internal standard is added to the extraction matrix). The ratio of the results of these two analysis (pseudo/traditional) is the extraction efficiency. 

In most published methods, the primary sample extracts are subjected to various types of cleanup procedures including conventional liquid-liquid partitioning, solid-phase extraction, matrix solid-phase dispersion, and online trace enrichment. In many cases, some of these procedures are used in combination in order to help obtaining highly purified extracts. 

The aqueous or organic extract obtained at this step of analysis may be a very dilute solution of the analyte(s) of interest. It may also contain coextractives, which, if allowed in the final extract, will increase the background noise of the detector, making it impossible to determine trace level concentrations of the analyte(s). To reduce interferences and concentrate the analyte(s), the primary sample extracts are subjected to some kind of cleanup including liquid-liquid partitioning, solid-phase extraction, matrix solid-phase dispersion, online trace enrichment, affinity chromatography, immunoaffinity chromatography, and ultrafiltration. In many instances, more than one of these procedures may be used in combination to increase extract purification. 

Starting with a description of the analytical challenge in Chapter 19, the third part, which is devoted to analytical attitudes, proceeds with a detailed description in Chapter 20 of modern sample preparation procedures including solid-phase extraction, matrix solid-phase dispersion, use of restricted-access media, supercritical fluid extraction, and immunoaffinity cleanup. Flexible derivatization techniques including fluorescence, ultraviolet-visible, enzymatic, and photochemical derivatization procedures are presented in Chapter 21. 

Extraction of fat by supercritical carbon dioxide was investigated as an important option for minimizing the expanded use of frequently flammable and carcinogenic solvents in food analysis. Unfortunately, the presence of moisture in foods has an adverse effect on the quantitative extraction of fat by supercritical fluid extraction (SEE). Hence, samples have to be lyophilized first. The total fat content of freeze-dried meat and oilseed samples was found to be comparable to values derived from Soxhlet-extracted samples (26). Besides, only small amounts of residual lipids could be recovered by an additional extraction of the SFE-extracted matrix by the Bligh and Dyer solvent extraction procedure. As far as the minor constituents are concerned, it was found that the extraction recovery ranged from 99% for PC to 88% for PA. Hence, Snyder et al. concluded that SFE can be used as a rapid, automated method to obtain total fat, including total phospholipids, from foods (26). 

Extractions generally rely on a favourable partition of PCBs from the sample matrix into the extraction matrix. The more favourable the partition coefficient, the higher is the extraction efficiency. Since PCBs are lipophilic, the extraction methods are based on the isolation of lipids from the sample matrix [30]. It should be noted that the concentration of planar or non-ortho-substituted PCBs, which are considered the most toxic PCB congeners, is generally 1000-fold lower (ng/kg) than... 

T. Fujiwaki, M. Tasaka, N. Takahashi, H. Kobayashi, Y. Murakami, T. Shimada, and S. Yamaguchi, Quantitative evaluation of sphingolipids using delayed extraction matrix-assisted laser desorption ionization time-of-flight mass spectrometry with sphingosylphosphorylcholine as an internal standard. Practical application to cardiac valves from a patient with Fabry disease, J. Chromatogr. B. 832 (2006) 97-102. 

Selectivity is the ability of an assay to measure the analyte of interest in the presence of other constituents in the sample. Because IAs are often performed without sample extraction, they are more prone to matrix interference than are chromatographic methods with extraction. Matrix interference could come from crossreactivity with structurally similar components in the sample, or from nonspecific binding to structurally dissimilar components in the matrix. The results are high background noise, loss of sensitivity, and inaccurate and nonreproducible data. Sometimes, the problem may only occur in a few exceptional patient samples that have structurally similar components such as unknown metabolites, or dissimilar components from samples with hyperlipidemia, hemolysis, complement components, rheumatoid factors, binding proteins, autoantibodies, and heterophilic anti-immunoglobulin Ab. 

Zrostlikova J, Hajslova J, Poustka J, Begany P (2002) Alternative calibration approaches to compensate the effect of co-extracted matrix components in liquid chromatography-electrospray ionization tandem mass spectrometry analysis of pesticide residues in plant materials. J Chromatogr A 973 13-26... 

Smirnov, I.P., Roskey, M.T., Juhasz, P. et al. (1996) Sequencing oligonucleotides by exonuclease digestion and delayed extraction matrix-assisted laser desorption ionization time-of-flight mass spectrometry. Anal. Biochem., 238 (1), 19-25. 

Keywords Pressurized liquid extraction supercritical fluid extraction ultra-sound-assisted extraction microwave-assisted extraction matrix solid-phase extraction high-performance liquid chromatography gas chromatography liquid-liquid extraction solid phase extraction column chromatography... 

Various cleanup procedures, including conventional liquid-liquid partitioning, sohd-phase extraction, matrix sohd-phase dispersion, and on-hne dialysis/trace enrichment, have all been employed to eliminate or reduce interfering compounds and to concentrate the analyte(s). In many instances, more than one of these cleanup procedures have been used in combination to enhance cleanup efficiency. ... 

Solid-phase extraction Matrix solid-phase... 

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