Sample preparation techniques importance

The need to understand the fate of pesticides in the environment has necessitated the development of analytical methods for the determination of residues in environmental media. Adoption of methods utilizing instrumentation such as gas chro-matography/mass spectrometry (GC/MS), liquid chromatography/mass spectrometry (LC/MS), liquid chromatography/tandem mass spectrometry (LC/MS/MS), or enzyme-linked immunosorbent assay (ELISA) has allowed the detection of minute amounts of pesticides and their degradation products in environmental samples. Sample preparation techniques such as solid-phase extraction (SPE), accelerated solvent extraction (ASE), or solid-phase microextraction (SPME) have also been important in the development of more reliable and sensitive analytical methods. 

In general, new sample preparation technologies are faster, more efficient and cost effective than traditional sample preparation techniques. They are also safer, more easily automated, use smaller amounts of sample and less organic solvent, provide better target analyte recovery with enhanced precision and accuracy. Attention to the sample preparation steps has also become an important consideration in reducing contamination. A useful general guide to sample preparation has been published [3]. A recent review on sample preparation methods for polymer/additive analysis is also available [4]. 

A comparative study of extraction methods from formalin-fixed mouse liver by Jiang et al.11 highlights the importance of sample preparation technique. Formalin-fixed mouse tissue was extracted using five different protocols (1) 6M guanidine-HCl without heating (2) 6M guanidine-HCl... 

A review of sample preparation techniques written recently by Smith (2003) purports that derivatization is not very useful and that with advances in separation techniques or by using a different analytical technique, such as HPLG, derivatization can be avoided. While a laboratory will examine almost any alternative to avoid derivatization according to Smith (2003), switching equipment can be prohibitively expensive, and so derivatization certainly still has an important role in most laboratories. 

As the most important inorganic mass spectrometric technique, ICP-MS is also employed for the precise and accurate isotope ratio measurements of a multitude of elements (such as Li, B, S, Fe, Sr, Pb, U, Pu) in environmental samples (see Chapter 8).9,88-90 Isotope ratio measurements of environmental samples require special careful sample preparation techniques including trace/matrix separation and enrichment procedures if the analytes are at the trace and ultratrace level. As an example, the schematic diagrams of the separation and enrichment procedures for the precise isotope analysis of Pu, U and Sr in water samples from the Sea of Galilee using double-focusing... 

Some analytical methods for the determination of radium in biological materials are given in Table 6-1. It is important to note that the major contributions of these studies are descriptions of sample preparation techniques rather than advances in alpha or gamma spectrometry. 

Considering all these, the recovery in sample preparation method is an important parameter that affects quantitative issues such as detection limit, sensitivity, LOQ, and even the LOL. Sample preparation techniques that enhance performance (see Chapters 6, 9, and 10) result in a recovery (r) larger that 1, thus increasing the sensitivity and lowering detection limits. 

Solid-phase extraction (SPE) has evolved to be an important sample preparation technique, due to its ease of automation, high analyte recovery, and excellent selectivity. The commercial availability of compact SPE devices with a wide selection of sorbent materials adds to their attraction. A major advantage of SPE is that multiple samples can be prepared in parallel using low volumes of solvents. 

The objective of this book is to provide an overview of a variety of sample preparation techniques and to bring the diverse methods under a common banner. Knowing fully well that it is impossible to cover all aspects in a single text, this book attempts to cover some of the more important and widely used techniques. The first chapter outlines the fundamental issues relating to sample preparation and the associated quality control. The... 

The selection of appropriate sample preparation technique is very important for accurate analysis. Techniques of sample preparation for raw rubber identifications are as follows ... 

Knapp, G. Sample preparation techniques an important part in trace element analysis for environmental research and monitoring. Int. J. Environ. Anal. Chem. 22, 71-83 (1985)... 

The topic of apple flavor should also be considered in relation to the modern developments in isolation and preparation technology. The important Influence of the sample preparation techniques on the composition of biologically derived aromas was recently reviewed by Parliment (16). 

Sample preparation is important here because matrices of biological fluids are so comphcated that interfering signals are likely to appear in typical separation-based determinations. Among various sample preparation techniques, there are two major approaches combined with CE liquid-hquid extraction (LEE) and solid-phase extraction (SPE) [or solid-phase microextraction (SPME)]. 

Liquid-liquid extraction is an important sample preparation technique from both historical and practical perspectives.18,19 LLE has been in use for many decades as an analytical sample pretreatment to remove unwanted matrix components20 or to selectively extract components of interest from a mixture, thereby purifying and concentrating them for further workup. It is based on the principles of differential solubility and partitioning equilibrium of analyte molecules between two immiscible phases, usually aqueous and organic. Depicted in Figure 2, LLE initially involves pH adjustment of the original (aqueous) sample with an appropriate buffer. This pH adjustment is... 

Serious consideration and time must be given to whether the component of interest is in exceptionally high concentration which, in such cases, may have to be diluted to fit calibration standards or, if low, may require pre-concentration. In some cases it may be necessary to carry out a trial-and-error to ascertain the approximate concentration of metals in samples. The low value must at least be at quantitative limits (i.e. ten times the standard deviation of baseline noise, to be confident of results see Section 3.8.1.7). If it is lower than ten times standard deviation of the baseline the sample may have to be preconcentrated prior to analysis to a level that can be comfortably detected and is suitable for reproducible measurements. The following is a list of common methods of sample preparation techniques. Choosing the correct method is of primary importance and poses a challenge to most analysts, particularly for unknown samples ... 

The conclusion so far must be that synthesis and sample preparation techniques play an important role. Diffusion data to be used in permeation experiments should be measured on membranes with techniques which reflect as closely as possible the transport phenomena during permeation. This also minimises heat effects due to adsorption/desorption which play an important role in diffusion experiments based on large crystals, but is of minor importance in membrane experiments [101]. 

It is important in thermal analysis, as for any other analytical techniques, to obtain reproducible results. However, there are many experimental variables associated with thermal analysis and it is necessary to define at least five of these for each thermal analysis investigation. These five variables are the nature of the sample and its container (crucible), the heating (or cooling) rate, the sample-chamber atmosphere, and the sample mass. Some thermal analysis techniques require the recording of other variables, such as the load on the sample in thermomechanical analysis. In thermal analysis, the samples are usually in the solid state, but liquids can also be studied using special sample preparation techniques. Gases are not normally studied by thermal analysis techniques. 

Many different sample-preparation techniques are available to a drug-discovery scientist performing bioanalytical sample preparation. These techniques vary in several regards, such as simplicity (number of steps), time requirement, materials cost per sample, expertise of the analyst, ease of method development, ability to be automated, concentration factor attained, and cleanliness of the final extract. It is important to note that the sample-preparation needs within drug discovery are different from those in other phases of drug development. In drug discovery, new compounds are introduced as often... 

Each of the laboratories contributed to the research and development of analytical methods, to cross-checking methods developed in participating laboratories, and to publication of the information which was derived. Among the areas of research and development to which the Project addressed itself were sample preparation techniques, measurement techniques, and possibly most important of all, sources of error. 

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