Sampling methods micromethods

Merriman et al. improved the method of Grab and Reinstein. They developed a gas chroma tographic-mass spectrometric micromethod. As little as 20 ng of caffeine can be measured, and, therefore accurate estimates of caffeine concentrations in 100 pi or less of biological samples can be made. The method is rapid, specific and sensitive. A packed column of 3 % Dexsil 300 on Chromosorb Q was used at 210°C, and glutethimide was used as an internal standard. 

X-ray fluorescence XRF is one of the longest established techniques for trace elemental analysis. While XRF is not a very sensitive technique, its main advantages are the capability for direct solid sample analysis combined with multielement determinations. While sample pretreatment of solids can be substantially reduced or even omitted in some cases, perfect matching between standards and samples is required for accurate results, because of severe matrix effects. The main application field of XRF is, therefore, the analysis of solid materials, such as metallurgical and geological samples, where solid standards are readily available. Liquid samples can be analyzed either directly in special cells or by using preconcentration techniques with solid sorbents, which can be directly analyzed after sample loading. More modern methods, like total-reflection X-ray fluorescence, which is a multielement technique mainly for solutions, or particle-induced X-ray emission, which is a micromethod with some spatial resolution, have found limited application in some special areas. For speciation purposes, species separation has to be carried out in front in an offline mode. 

Although the AOCS method can be carried out with 50 to 100 mg. of sample, micromethods have been devised for use when limited amounts of fat are available. Thus, Herb and Riemenschneider (1953) devised a procedure which requires only 1 to 10 mg. of fat, and two microprocedures have been devised for the determination of polyunsaturated acids in blood (O Connell et al, 1952 Wiese and Hansen, 1952). 

So far the method is a micromethod the authors recommended the use of one or two millimoles of the sample to be analyzed. This is of course advantageous in many cases, but in other-cases not. The authors discussed different possibilities of increasing the capacity of the apparatus. Further work is also needed to make the method quantitative it was not possible to recover the amino acids and peptides completely from the silica. Consden et al. reported sdelds of 80-100%. The losses were probably due to irreversible adsorption. 

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