Initial sample preparation

Modem analytical methods can provide a rapid and highly sensitive examination of contaminated soils, sediments, landfill, etc., provided that the samples presented for analysis are homogeneous and in an appropriate physical form. 

Initial sample preparation can be differentiated broadly into four main processes. 

The high productivity achieved by modern analytical instrumentation means that sample preparation is typically slower and considerably more labour intensive than chemical analysis. As a result there is often a considerable incentive to prepare samples as rapidly as possible, because the costs of analytical down time are usually very high. Unfortunately, there is a potential for error (e.g. an unwanted change in the composition of the sample) at each stage of the initial sample preparation process and great care must be taken to ensure that the need for high productivity does not overshadow the need for quality in the preparation methods used. 

Because initial sample preparation is essentially practical in nature and because the processes utilised are often considered to be well understood, the potential for serious error during sample preparation is frequently underestimated. The provision of a sufficient supply of representative sub-samples for analysis irrespective of sample type involves applying a fit for purpose method for each individual sample prepared. The following chapter describes some of the most widely used initial sample preparation methods and proposes practical solutions to problems encountered in the preparation laboratory. 

Before initial sample preparation commences, it is essential that the customer and analyst confirm the purpose and nature of the sample preparation processes needed to ensure that analytical and risk assessment objectives are achieved. 

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What may prove to be the ultimate choice for an internal standard when using an MS (37) is the addition of a PGS standard as a deuterated compound to the initial sample preparation. The deuterated compound is quantified directly on the MS rather than having to subsequently subject the sample to conventional radioisotope detection methods. This procedure has been applied to ABA (29) and IAA (38, 39) analyses. A high deuterium content (labeled at five or more positions) should be sought to avoid confusion with naturally "heavy" isotopic compounds (39). 

The ease of initial sample preparation is one of the clear advantages of static headspace extraction. Often, for qualitative analysis, the sample can be placed directly into the headspace vial and analyzed with no additional... 

Initial Sample Preparation. When received, the sample must be handled according to the proper protocol to maintain its chemical and legal integrity. Some pretreatment to preserve the sample usually is performed at collection time and should be properly described in chain of custody documentation that accompanies the sample, as described in the Radioanalytical Chemistry text. 

Protein precipitation is often used as the initial sample-preparation scheme in the analysis of small drug molecules, since one universal procedure is followed for all compounds and method development is unnecessary. The speed of this technique presents a real time savings. The high resolving power of LC-MS/MS analytical methods accommodates this nonselective cleanup procedure. This mode of sample preparation is also inexpensive and does not chemically alter the analyte. Typical sample matrices that are used with protein-precipitation techniques are plasma, serum, tissue homogenates, and in vitro incubation mixtures. In general terms, a sensitivity of 1-10 ng/mL is often achieved from 50- 4L sample volumes with this technique with LC-MS/MS analysis. 

This book attempts to cover chemical and ecotoxicological analysis related to routine contaminated land investigations. It does not cover analysis related to research or specialist one-off project type investigations. The following chapter deals with soil analysis method requirements, how methods should be validated and the need for all methods to meet clearly defined performance requirements. It also covers quality assurance/quality control aspects. Chapter 3 covers the key, and problematic area of sample homogenisation and the initial sample preparation. Chapter 4 covers the analysis of metals and elemental... 

Figure 3.1 Initial sample preparation flow diagram of regularly used methods.

Table 3.3 Common problems associated with initial sample preparation processes...

Good laboratory practice in initial sample preparation... 

At present there is no universally accepted Standard Method for Preparation of Samples from Contaminated Sites and few laboratories operate strictly comparable sample preparation methods. So it is important that the methods used for initial sample preparation are verifiably/// for their analytical purpose and applied by trained staff under an appropriate level of quality control. The design of sample preparation methods is generally constrained by the need to produce powders or finished samples with uniform physical characteristics by the most rapid method, whilst preventing the loss or alteration of any part of the sample by contamination, cross-contamination or chemical reaction. 

The chemistry work in the radioanalytical laboratory is described in Chapters 6 and . Chapter 6 discnsses the radioanalytical chemistry process from initial sample preparation to complete pnrification and gives examples of separation methods for the commonly enconntered radionnchdes. Chapter 7 describes preparation of the connting sonrce that is snbmitted for the measnrements by radiation detection instmments presented in Chapter 8. 

Sample identification review at initial sample preparation and each subsequent sample transfer. 

Slejkovec et al. [125] used HPLC-atomic fluorescence to separate and quantify the anionic arsenic compounds found in urban aerosol samples. The initial sample preparation produced aqueous extracts. These were found to contain only arsenate, although the separation worked for mixtures of arsenite, arsenate, monomethylar-sonic acid, and dimethylarsonic acid. The detection limit for arsenate was 80 pg mL . ... 

Automated radioanalytical chemistry can provide near real time monitoring of reprocessing plant operations (O Hara et al. 2009). A sequential injection chromatography system for the separation and analysis of Am, Pu, and Np isotopes is integrated in a modular system that automates the complete sample analysis process, from initial sample preparation to final data reporting. 

Generally, it would be expected that the OPCW would handle the initial sample preparation and splitting. This might involve ... 

However, contrary to the initial premise stated above, most polymeric samples, and particularly those of technological or commercial importance, do not naturally tend to occur in the form of a 50 nm-thick film. For bulk samples to be made amenable to examination by TEM they must therefore be subjected to some initial sample-preparation procedure. Indeed, the problems of sample geometry, beam sensitivity and intrinsically low contrast described above are such that they are often best overcome by the indirect examination of the sample. TEM techniques may therefore be divided into those in which the sample is examined directly and those in which a less direct approach is adopted,... 

We thank QUT for a Strategic Collaborative Research Grant to support this research. Thanks are also due to other project collaborators Professor R Crawford, Dr R Meder, H. Moody, Professor K Oloyede and S.K. de Visser. In addition, particular thanks are due to S.K. de Visser for initial sample preparation. The Vibrational Spectroscopy Group and the Faculty of Science at QUT were also generous in their financial support of JB. EWB thanks the TRR program (IHBI, QUT) for conference travel support. 

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