Techniques for Sample Preparation

The 1970 s demonstrated a trend chemistry is going out of analytical chemistry . However, what was not used anymore up-ffont for analysis came bade in the form of sample preparation techniques. For example, lUPAC devoted as much attention as ever before, but now to the chemistry needed to prepare the sample for measurement and to avoid losses and contamination. 

LC/MS/MS is the preferred means of detection, quantitation, and confirmation of sulfonylurea herbicides in biological and environmental matrices. Therefore, recommendations for establishing and optimizing LC/MS/MS analyses common to all matrices are given first, followed by specific rationales for methods and sample preparation techniques for plant, soil, and water matrices. 

Current interest in supercritical fluid extraction as a sample preparation technique for chromatographic analysis is intense, in spite of it receiving very little tion until the mid-1980s. Although neglected by analytical cl Hsts, during the... 

Solubilizing all or part of a sample matrix by contacting with liquids is one of the most widely used sample preparation techniques for gases, vapors, liquids or solids. Additional selectivity is possible by distributing the sample between pairs of immiscible liquids in which the analyte and its matrix have different solubilities. Equipment requirements are generally very simple for solvent extraction techniques. Table 8.2 [4,10], and solutions are easy to manipulate, convenient to inject into chromatographic instruments, and even small volumes of liquids can be measured accurately. Solids can be recovered from volatile solvents by evaporation. Since relatively large solvent volumes are used in most extraction procedures, solvent impurities, contaminants, etc., are always a common cause for concern [65,66]. 

Analytical techniques for the quantitative determination of additives in polymers generally fall into two classes indirect (or destructive) and direct (or nondestructive). Destructive methods require an irreversible alteration to the sample so that the additive can be removed from the plastic material for subsequent detention. This chapter separates the additive wheat from the polymer chaff , and deals with sample preparation techniques for indirect analysis. 

Principles and Characteristics Solid-phase microextraction (SPME) is a patented microscale adsorp-tion/desorption technique developed by Pawliszyn et al. [525-531], which represents a recent development in sample preparation and sample concentration. In SPME analytes partition from a sample into a polymeric stationary phase that is thin-coated on a fused-silica rod (typically 1 cm x 100 p,m). Several configurations of SPME have been proposed including fibre, tubing, stirrer/fan, etc. SPME was introduced as a solvent-free sample preparation technique for GC. 

G.J. DeMenna and W.J. Edison, Novel Sample Preparation Techniques for Chemical Analysis - Microwave and Pressure, Dissolution, Chemical Analysis of Metals, ASTM STP 994 (F.T. Coyle, ed.), American Society for Testing and Materials, Philadelphia, PA (1987), p. 45. 

Zimmer D. et al., 1999. Comparison of turbulent-flow chromatography with automated solid-phase extraction in 96-well plates and liquid-liquid extraction used as plasma sample preparation techniques for liquid chromatography-tandem mass spectrometry. J Chromatogr A 854 1999. 

Tan [71] devised a rapid simple sample preparation technique for analysing polyaromatic hydrocarbons in sediments. Polyaromatic hydrocarbons are removed from the sediment by ultrasonic extraction and isolated by solvent partition and silica gel column chromatography. The sulphur removal step is combined into the ultrasonic extraction procedure. Identification of polyaromatic hydrocarbon is carried by gas chromatography alone and in conjunction with mass spectrometry. Quantitative determination is achieved by addition of known amounts of standard compounds using flame ionization and multiple ion detectors. 

Nowicki et al. [51] point out that in the development of a Soxhlet sample preparation technique for sediment samples, the empty paper Soxhlet thimbles contained organic contaminants which adversely affected results. Glass thimbles were tried and found to be satisfactory. The authors detail the identification of organics solvent-extracted from paper and glass Soxhlet thimbles, and discuss the stability for multiple use of the two materials for trace organic sample preparation. 

The ideal sample preparation technique for HPLC would be nontoxic and capable of direct coupling to the chromatograph, allowing complete automation of the analysis. A potential tech-... 

The good recoveries reported above by some earlier workers in SFE clearly demonstrate the feasibility and comparative accuracy of SFE as a sample preparation technique for a variety of analytes and matrices. However, the question of the "robustness" of SFE as an analytical tool easily used on a routine basis by chemists throughout the analytical community remains to be answered. What is the expected variability of results for any given application and how much user interaction is required to maintain functional equipment sample after sample Such information - precision and mean-time-between-failures (or mean-time-between-maintenance) - has not been routinely reported in published literature since the emphasis has heretofore been on initial feasibility experiments. 

Florian, D. and G. Knapp. 2001. High-temperature, microwave-assisted UV digestion A promising sample preparation technique for trace element analysis. Anal. Chem. 73 1515-1520. 

FIGURE 13.8 Graphical overview of sample preparation techniques for organic and organometallic analytes in aqueous samples. For explanation of the abbreviations, see Table 13.2. (After Demeestere et al. 2007. J. Chromatogr. A 1153 130-144.)... 

Because of these distinct advantages over classical extractive sample preparation techniques, it is easy to understand why SPME has become one of the most popular sample preparation techniques for water analysis. Numerous monographs and reviews document this great popularity and discuss in detail the theory and practice of SPME,102 103 as well as applications in the field of environmental analysis104-105 and speciation analytics.106-107... 

Wardencki, W., J. Curylo, and J. Namiesnik. 2007. Trends in solventless sample preparation techniques for environmental analysis. J. Biochem. Biophys. Methods 70 275-288. 

Dong H, Kemptner J, Marchetti-Deschmann M, Kubicek C, Allmaier G (2009) Development of a MALDI two-layer volume sample preparation technique for analysis of colored conidia spores of Fusarium by MALDI linear TOF mass spectrometry. Anal Bioanal Chem 395 1373-1383. doi 10.1007/s00216-009-3067-3... 

Gawalko and coworkers elucidated the characteristics of closed-vessel and focused open-vessel MW sample preparation techniques for the subsequent determination of Cd, Cu, and Pb, and Se in wheat, wheat products, corn bran, and rice flour by ET-AAS with transverse-heated graphite furnace [23]. Both techniques were evaluated using a total of 15 CRMs for the three food types. In the case of rice, these were the NIES 10a, 10b, and 10c Rice Flour and the NRC Rice Flour. The two techniques were equivalent in terms of agreement with the certified figures. Up to 12 samples could be processed with the closed system with minimal amounts of acid and reduced risk of contamination. Larger masses of samples could be treated by the open-vessel system. 

J. Szpunar, B. Bouyssiere, R. Lobinski, Sample preparation techniques for elemental speciation studies, in K. L. Ackley (ed.), Elemental Speciation. New Approaches for Trace Element Analysis, Elsevier, Amsterdam, 2000, pp. 7D40. 

Bouyssiere, B., Szpunar, J., Potin-Gautier, M., Lobihski, R. Sample preparation techniques for elemental speciation studies. In Cornells, R. (ed.) Handbook of Elemental Speciation. Techniques and Methodology. Wiley, West Sussex (2003)... 

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