Sample preparation sequential extraction

Validation is needed to demonstrate that the analytical method complies with established criteria for different performance characteristics [82]. When these different characteristics are being evaluated individually, this is generally done for the analytical method as such—where the input is the purified or isolated analyte and the output is the analytical result. However, MU covers the whole analytical procedure, starting from the original sample lot. The assessment of MU (see Section 8.2.2) is in line with the so-called modular validation approach. Modular validation refers to the modularity of an analytical procedure divided up into several sequential steps needed to analyze the material. These may be sample preparation, analyte extraction, and analyte determination (Figure 7). Each step in the procedure can be seen as an analytical system and can thus be validated separately and combined... 

Abbreviations ASTED, automated sequential trace enrichment of dialysate CFS, continuous flow system ASPEC, automated sample preparation with extraction columns SPE, solid phase extraction BSA, bis(trimethylsilyl)acetamide. 

Place the Cig SPE column on the vacuum manifold, and prepare for extraction by washing the column sequentially three times with approximately 3-mL volumes of methanol and Optima water, respectively. Following the final water wash, allow a volume of liquid to remain on top of the resin bed, and avoid allowing the column to become dry before sample addition. 

Prepare sequential dilutions of a liquid extract sample in the same solvent used to prepare the extract (e.g., pentane). 

Sample preparation. For the study of trace compounds we used two different sample preparation procedures SPI and SPII for wine no. 1 and wine no. 2, respectively. The first flavor extract SP I was obtained by liquid-liquid extraction with fluorochloromethane and dichloromethane (9+1) from 45 L Scheurebe wine. For further analysis a portion of 1/3 was used. After separation on silica gel (pentane/diethyl ether) 6 fractions were analyzed. For the second flavor extract SP II we started from 200 L wine stripping off volatile compounds with vapour in a spinning cone column (SCC) system (5). The condensate was sequentially collected in two main portions of 8 and 2 L, respectively. The first condensate was discarded. The second condensate (2 L) was subjected to liquid-liquid extration with fluorochloromethane and dichloromethane (9+1). After separation on silica gel (pentane/diethyl ether) using medium pressure chromatography (MPLC) 4 fractions were analyzed. 

There are many sample preparation techniques listed in texts, from a simple filtration or centrifugation to many other kinds of extraction procedures, including both liquid-liquid and solid-phase extraction. When any type of sample preparation is used, it often is done manually if only a few samples are involved. If a large number of samples are to be analyzed, the entire procedure should lend itself to automation. Regardless of the number of samples, most sample preparation is done off-line that is, the samples are prepared first with one of the methods listed, then placed into an automated sample injection system for sequential analysis of all samples. 

One of the requirements of any nuclear facility is to monitor the effluent uxiste water to show compliance with existing standards. This paper describes a sequential procedure for the separation of the transuranic elements from water samples up to 60 1. The elements of interest are coprecipitated with calcium fluoride and then individually separated using a combination of ion exchange and solvent extraction, with a final sample preparation by electrodeposition. Alpha spectrometry of these samples allows the measurement of neptunium, plutonium, and transplutonium nuclides at sub-fCi/l, levels. 

A fourth experiment would be an evaluation of precision and recovery at one to four concentration levels (n — 6 to 24 plus a recovery standard), plus recovery of an internal standard (n — 3 plus recovery standard). Therefore, as a minimal method development exercise, 60—70 spiked samples would be prepared and extracted within 1 day. The experiments need to be performed sequentially because the results from each will impact how subsequent experiments are designed. Selectivity is assessed through the course of the method development. The analytical chemist with access to API LC/MS/MS will spend less time on solid-phase extraction selectivity development. 

G. Theodoridis, C.K. Zacharis, RD. Tzanavaras, D.G. Themelis, A. Economou, Automated sample preparation based on the sequential injection principle. Solid-phase extraction on a molecularly imprinted polymer coupled on-line to high-performance liquid chromatography, J. Chromatogr. A 1030 (2004) 69. 

K.L. Peterson, B.K. Logan, G.D. Christian, J. Ruzicka, Sequential-injection extraction for sample preparation, Anal. Chim. Acta 337 (1997) 99. 

Metals associated with various binding sites on sediments have been assessed using extraction procedures applied as single digests or as a set of sequential steps. Selective dissolution of trace metals from the particle surfaces is followed by determination using atomic absorption spectrometry (AAS), ICP-MS, or total reflection X-ray fluorescence. The use of sequential extraction schemes for the operational definition of metal species in sediments has proved contentious. They have been criticized on the basis that the reactions are not sufficiently phase selective and labile phases could be transformed during sample preparation, causing a marked reduction... 

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