Sample preparation simplifying

Preparation of soil—sediment of water samples for herbicide analysis generally has consisted of solvent extraction of the sample, followed by cleanup of the extract through Uquid—Uquid or column chromatography, and finally, concentration through evaporation (285). This complex but necessary series of procedures is time-consuming and is responsible for the high cost of herbicide analyses. The advent of soUd-phase extraction techniques in which the sample is simultaneously cleaned up and concentrated has condensed these steps and thus gready simplified sample preparation (286). 

Elimination of sample preparation and handling of toxic solvents such as carbon disulphide Absence of solvent simplifies chromatograph Increased sensitivity Sample tubes can be reused ... 

Analysis of methyl parathion in sediments, soils, foods, and plant and animal tissues poses problems with extraction from the sample matrix, cleanup of samples, and selective detection. Sediments and soils have been analyzed primarily by GC/ECD or GC/FPD. Food, plant, and animal tissues have been analyzed primarily by GC/thermionic detector or GC/FPD, the recommended methods of the Association of Official Analytical Chemists (AOAC). Various extraction and cleanup methods (AOAC 1984 Belisle and Swineford 1988 Capriel et al. 1986 Kadoum 1968) and separation and detection techniques (Alak and Vo-Dinh 1987 Betowski and Jones 1988 Clark et al. 1985 Gillespie and Walters 1986 Koen and Huber 1970 Stan 1989 Stan and Mrowetz 1983 Udaya and Nanda 1981) have been used in an attempt to simplify sample preparation and improve sensitivity, reliability, and selectivity. A detection limit in the low-ppb range and recoveries of 100% were achieved in soil and plant and animal tissue by Kadoum (1968). GC/ECD analysis following extraction, cleanup, and partitioning with a hexane-acetonitrile system was used. 

Specifically for triazines in water, multi-residue methods incorporating SPE and LC/MS/MS will soon be available that are capable of measuring numerous parent compounds and all their relevant degradates (including the hydroxytriazines) in one analysis. Continued increases in liquid chromatography/atmospheric pressure ionization tandem mass spectrometry (LC/API-MS/MS) sensitivity will lead to methods requiring no aqueous sample preparation at all, and portions of water samples will be injected directly into the LC column. The use of SPE and GC or LC coupled with MS and MS/MS systems will also be applied routinely to the analysis of more complex sample matrices such as soil and crop and animal tissues. However, the analyte(s) must first be removed from the sample matrix, and additional research is needed to develop more efficient extraction procedures. Increased selectivity during extraction also simplifies the sample purification requirements prior to injection. Certainly, miniaturization of all aspects of the analysis (sample extraction, purification, and instrumentation) will continue, and some of this may involve SEE, subcritical and microwave extraction, sonication, others or even combinations of these techniques for the initial isolation of the analyte(s) from the bulk of the sample matrix. 

Principles and Characteristics A sample can contain a great number of compounds, but analysts are usually interested only in the qualitative presence (and the quantitative amount) of a small number of the total compounds. Selectivity is an important parameter in analytical separations. The total analytical process clearly benefits from selectivity enhancement arising from appropriate sample preparation strategies. Selective separation of groups or compound classes can simplify a mixture of analytes before analysis, which in turn enhances analytical precision and sensitivity. Selective fractionation, in some cases, allows easier resolution of the compounds of interest, so analysts can avoid the extreme conditions of high-resolution columns. 

Techniques such as SPE simplify the labour of sample preparation, increasing its reliability, and eliminating the cleanup step by using more selective extraction procedures. 

Both the CMP and information process in Fig. 3.1 have been simplified in comparison with the representations in Figs. 2.1 and 2.2 because sample preparation has not been considered here and the measurement begins with the measuring sample as information source from which the signals are obtained. 

Direct injection of pretreated biological samples (also called online sample cleanup) greatly simplified sample preparation for LC/MS/MS analysis. The normal process involves sample aliquot steps, internal standard addition, and centrifugation. Compared to traditional off-line LLE and SPE sample preparation procedures, online methods are easier and faster. Two types of online SPE columns are commercially available. One is the restricted access media (RAM) column. The other is the turbulent flow chromatography (TFC) column. 

Direct injections using RAM or TFC have simplified sample preparation and increased throughput. Matrix ion suppression was greatly reduced or eliminated in several cases compared with traditional off-line sample cleanup procedures such as PPT, SPE, and LLE. Method development time was minimized with generic methods15 that suit most applications. Detailed applications can be found in a recent review.8... 

This chapter is intended to serve as a general overview of new and emerging HPLC technologies and is divided into four sections simplifying sample preparation, new column technologies, improvements in detectors, and improvements in HPLC throughput. 

Simplifying Sample Preparation New Column Technologies Improvements in Detectors Improvements in HPLC Throughput... 

Recently, turbulent flow chromatography (TFC) has shown a great potential for online sample pre-treatment in the analysis of PFCs. Up to now, the use of this technique in food and environmental analysis is scarce, but some successful applications have been developed. Among them, the analysis of PFCs has been carried out in cord blood and also in less invasive human samples, hair and urine. In these works, the main advantages presented were the simplified sample preparation, robustness and sensitivity. In addition in the case of cord blood, a low volume of sample was required. 

A large number of methods have been developed for analysis of water-soluble vitamins simultaneously in pharmaceutical products (like multivitamin tablet supplements). In fact, for these products no particular sample preparations are required and the high concentrations simplify the detection, enabling the use of UV [636]. The use of MS is also reported [637]. As well, Moreno and Salvado [638] reports also the use of a unique SPE cartridge (C18) for separating fat-soluble and water-soluble vitamins, which are, then analyzed using different chromatographic systems. 

Ohie T, FuX, IgaM, Kimura M, Yamaguchi S (2000) Gas chromatography-mass spectrometry with tert.-butyldimethylsilyl derivation use of the simplified sample preparations and the automated data system to screen for organic acidemias. J Chromatogr Biomed Sci Appl 746 63-73... 

Either Basic Protocol 1 or the Alternate Protocol should first be conducted in analyzing an unknown sample. Because of its ease and simplicity, sample preparation of anthocyanins and their HPLC separation on silica Cl8 columns (see Basic Protocol 1) is usually the preferred choice, unless the presence of acylated anthocyanins is anticipated, in which case the protocol described for acylated anthocyanins is used (see Alternate Protocol). If the anthocyanin profile is inconsistent with previously published chromatograms, or if there are extraneous unidentified peaks, then simplification is recommended (see Basic Protocol 3). Acid hydrolysis will simplify the chroma-... 

Another short note For samples that are relatively clean, one could always resort to employing (and frequently replacing) a guard column. This might be a bit more costly, but it greatly simplifies any sample preparation procedure and will probably lead to better method precision. One should always keep in mind that the largest contributor to poor method precision is usually manual sample preparations. 

The earliest approach to amino acid analysis involved postcolumn reaction. This scheme offers several advantages compared to precolumn reaction. First, it simplifies the sample preparation necessary. Often, precolumn derivatizations require sample cleanup steps to eliminate sample... 

Most molecular species methods involve enzymatic conversion by phospholipase C of the phospholipids to diacylglycerols, which are subsequently converted either to UV-absorbing or fluorescent derivatives. This procedure has two main advantages. First of all, the same HPLC method can be used for all phospholipid classes, because the polar head group is removed during the sample preparation. In addition, quantification is highly simplified and becomes much more sensitive. 

FIGURE 9.19 Simplified schematic diagram illustrating sample preparation, separation, and detection for an on-line analyzer for the continuous monitoring of the total "Tc content of nuclear-waste process streams. A number of zero-dead volume syringe pumps and valves are not shown. 

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