Microsampling Methods

If a microscope facility is not available, there are other special sampling accessories available which allow examination of microgram or microlitre amounts. This is accomplished by using a beam condenser so that as much as possible of the beam passes through the sample. Microcells are available with volumes of 4 jjul and pathlengths up to 1 mm. 

There are a number of microsampling cells available. A diamond anvil cell (DAC) uses two diamonds to compress a sample to a thickness suitable for measurement, and to increase the surface area. This technique can be used at normal atmospheric pressures, but it may also be applied to the study of samples under high pressures and to improve the quality of the spectra of trace samples. 

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Microreactor technology, application in combinatorial chemistry, 7 401, 422 Micro RNAs (miRNA), 17 620-621 Micro-routing, in waste collection, 25 869 Microsampling methods, in infrared spectroscopy, 14 232-233 Microscale microbial cultures, shaken, 16 406... 

An advantage of IR spectroscopy in general, and as applied to humic substances in particular, is the small quantity of sample required. For example, the alkali halide pressed-pellet technique, as normally carried out, requires about 1-2 mg of sample, which is considerably less than that required for the other most useful spectroscopic method, NMR, in the study of humic substances (see Chapter 22). However, microsampling methods have been developed which can record IR spectra on less than 0.01 /xg of sample (Alpert et al., 1964 Parker, 1971 Price, 1972 Griffiths and Block, 1973). These special techniques may have advantage in the study of humic samples isolated only in minute quantities, or for investigating small samples obtained in the fractionation of humic substances. 

When working with any of the microsampling methods, cleanliness is of utmost importance. Traces of impurities picked up during sample preparation can have higher concentrations, and therefore greater impact on the final spectrum, than the sample itself This attention to cleanliness must extend to the purity of any solvent used during sample preparation and also to preparation materials, such as KBr, if micropellets are to be prepared. 

Delves, H.T. (1970). A microsampling method for the rapid determination of lead in blood by atomic absorption spectrophotometry. Analyst, 95, 431-438... 

The majority of FI A applications are modifications of conventional titrimetric, spectrophotometric, and electrochemical methods of analysis. For this reason it is appropriate to evaluate FIA in relation to these conventional methods. The scale of operations for FIA allows for the routine analysis of minor and trace analytes and for macro-, meso-, and microsamples. The ability to work with microliter injection volumes is useful when the sample is scarce. Conventional methods of analysis, however, may allow the determination of smaller concentrations of analyte. 

Portland cement is susceptible to corrosion by CO2 and H2S. The chemical attack by CO2 is called carbonation. A microsample technique has been developed to study the CO2 corrosion in cements, because the corrosion is difficult to monitor with common test procedures [264]. This technique is also advantageous as an accelerated testing method. A polymer-modified cement has been tested in field studies [694]. The addition of silica also improves chemical resistance [146], in particular brine corrosion. 

The book has been structured into roughly three parts. First (Chap. 1), an overview of analytical methods applied in the study of cultural goods is presented to situate electrochemical methods in their analytical context. The second part contains voltammetric methods devoted to the identification (Chap. 2), speciation (Chap. 3), and quantitation (Chap. 4) of microsample components from works of art and/or cultural and archaeological pieces. The third part of the book presents selected examples of the deterioration of metal artifacts, outlining aspects peculiar to the cultural heritage conservation field (Chap. 5), and describes hisforic and current issues regarding electrochemical techniques used in restoration treatments and preventive conservation (Chap. 6). 

Infrared analyses are conducted on dispersive (scanning) and Fourier transform spectrometers. Non-dispersive industrial infrared analysers are also available. These are used to conduct specialised analyses on predetermined compounds (e.g. gases) and also for process control allowing continuous analysis on production lines. The use of Fourier transform has significantly enhanced the possibilities of conventional infrared by allowing spectral treatment and analysis of microsamples (infrared microanalysis). Although the near infrared does not contain any specific absorption that yields structural information on the compound studied, it is an important method for quantitative applications. One of the key factors in its present use is the sensitivity of the detectors. Use of the far infrared is still confined to the research laboratory. 

As techniques for chemical analysis are used in continually smaller domains, experimental challenges for inherently insensitive methods such as NMR spectroscopy become increasingly severe. Among the various schemes to boost the intrinsic sensitivity of an NMR experiment, the development of small-volume RF probes has experienced a renaissance during the past decade. Commercial NMR probes now allow analyses of nanomole quantities in microliter volumes from natural product extracts and combinatorial chemical syntheses. Figure 7.3.1.9 illustrates the range of volumes that can be examined by NMR probes and accessories such as microsample tubes and inserts. With recently reported advances in sample preconcentration for microcoil NMR analysis [51], dilute microliter-volume samples can now be concentrated into nanoliter-volume... 

Microsamples for Fourier transform infrared (FUR) imaging are prepared for analysis by one of the following three methods ... 

It is the main advantage of this rapid two-dimensional technique that it applies the important principle of a two-dimensional method to microsamples there is no mixing of fractions running simultaneously on the same migration path as in zone electrophoresis, but on the contrary, uncontaminated fractions are separated within very short time. For clinical research the method has a bright future because of the theoretical purity of the spot, which is not obtainable with zone electrophoresis. Good results have already been gained in work on animal serum (Dl). 

Handling and processing of microsamples (e. g. pi and sub-pl sized samples) are difficult, and most of the current analytical methods used in the life sciences usually analyze samples at volumes of > 2 pi. Analysis of sub-pl volume samples has a series of attendant problems, including ... 

Glazkov, V.P., Naumov, I.V., Somenkov, V.A., Shilstein, S.Sh. (1988) Superposition manydetector systems and neutron diffraction of microsamples, Nucl. Instrum. Methods Phys. Res. A 264, 367-374. 

Ferraro JR, Basile LJ (1978) Fourier transform infrared application to national problems In Ferraro JR, Basile U (eds) Fourier transform infrared spectroscopy - applications to chemical systems, Vol 4 Academic Press, New York, 275-302 Ferraro JR, Rein AJ (1985) Application of diffuse reflectance spectroscopy in the far-infrared region In Ferraro JR, Basile LJ (eds) Fourier transform infrared spectroscopy -applications to chemical systems, Vol 4 Academic Press, New York, 244-282 Frank IE, Feikema J, Constantine N, Kowalski BR (1984) Prediction of product quality from spectral data using the partial least squares method J Chem Inf Comput Sci 24 20-24 Fuller MP, Griffiths PR (1980) Infrared microsampling by diffuse reflectance Fourier transform spectrometry Appl Spectrosc 34 533-539... 

This method is particularly useful for analysis of the qualitative composition of trace amounts of various substances secured as material evidence in court cases, analysis of the homogeneity of a sample, identification of inclusions and contaminations on a surface, and detection of defects in a structure. Its main drawback is the fact that the physical nature of the microsample can affect the photometric accuracy of measurement and cause distortion of the obtained spectra. 

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