Analysis techniques sample requirements

One key issue of a study is to minimize sampling and analytical errors, loss of target compound and other artifacts through the preparation steps. Therefore it is important to check all steps in the method. Preparation of samples collected on filters and sorbents, dust samples, and material samples will be discussed here. In Section 2.6 some analysis techniques that require no or minimal sample preparation will be mentioned briefly. 

TLC Analysis. Small sample requirements, minimal sample preparation, high sensitivity, and low cost make TLC an attractive method for organic archaeometry. Its suitability for the detection of resin acids in complex mixtures was tested by subjecting the Carthaginian samples to a two-dimensional technique. Ether solutions of the organic material were spotted onto the plate and first freed from nonpolar components by elution in one direction with heptane. The residual carboxylic acids were then developed, with reference standards in adjacent tracks, in the second direction with heptane-toluene-ether (1 1 1). Under these conditions, 7-ketodehydro-abietic acid remains at or very near the origin (maximum retardation factor [Rf] = 0.04), but abietic acid and dehydroabietic acid are readily identified. 

In most Materials Characterization experiments the sample is subjected to some kind of radiation electromagnetic, acoustic, thermal, or particles (electrons, ions, neutrons, etc.). The surface analysis techniques usually require a high vacuum. As aresult of interactions between the solid (or liquid) and the incoming radiation abeam of a similar (or a different) nature will emerge from the sample. Measurement of the physical and/or chemical attributes of this emerging radiation will yield qualitative, and often quantitative, information about the composition and the properties of the material being probed. 

Trace versus bulk samples A trace sample is considered to be one, which is barely visible to the naked eye. Samples such as this will be present on the insides of reaction vessels, scales, knives, and other drug paraphernalia. In many cases, trace samples are swabbed from these items and are analyzed using confirmatory techniques first. Such samples are very easily contaminated and significant care should be taken in their analysis. Bulk samples require a sampling methodology and are generally subjected to presumptive tests and TLC followed by confirmatory tests. 

The STEM instrument itself can produce highly focused high-intensity beams down to 2 A if a field-emission source is used. Such an instrument provides a higher spatial resolution compositional analysis than any other widely used technique, but to capitalize on this requires very thin samples, as stated above. EELS and EDS are the two composition techniques usually found on a STEM, but CL, and even AES are sometimes incorporated. In addition simultaneous crystallographic information can be provided by diffraction, as in the TEM, but with 100 times better spatial resolution. The combination of diffraction techniques and analysis techniques in a TEM or STEM is termed Analytical Electron Microscopy, AEM. A well-equipped analytical TEM or STEM costs well over 1,000,000. 

ICP-OES is one of the most successful multielement analysis techniques for materials characterization. While precision and interference effects are generally best when solutions are analyzed, a number of techniques allow the direct analysis of solids. The strengths of ICP-OES include speed, relatively small interference effects, low detection limits, and applicability to a wide variety of materials. Improvements are expected in sample-introduction techniques, spectrometers that detect simultaneously the entire ultraviolet—visible spectrum with high resolution, and in the development of intelligent instruments to further improve analysis reliability. ICPMS vigorously competes with ICP-OES, particularly when low detection limits are required. 

Operationally, the electron techniques all require high-vacuum or, more likely, ultrahigh-vacuum environments, and the magnetic material of interest must be within a few atomic layers of the surface. MOKE analysis is not restricted by these constraints, although interesting samples may be. 

Where extreme accuracy is required in the identification of pollutants or in the quantification of compounds that are highly toxic, laboratory analysis of samples is conducted. Highly sophisticated techniques have, for example, been... 

The peak profile analysis techniques allow separating the intrinsic and extrinsic causes producing peak broadening and shift. Accurate peak profile analysis requires the instrumental broadening well characterized and, in general, significantly smaller than the one due to sample defects (size and strain). New high quality X-ray sources and... 

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