Sampling and sample preparation methods for the analysis of trace elements in biological material

In general, trace element analysis of biological material includes the following steps: Formulation of the question to be answered by the analytical data, sampling, sample preparation, ashing, dissolution, preconcentration, separation, preparation of the measurement sample, physical measurement (integral, spectral, calibration), data processing, data evaluation and answering the question. Both sampling and the sample preparation are crucial stages for any trace analysis. Knowledge of numerous factors and strict adherance to all the requirements is unavoidable, if results are to be reliable. Sampling of biological material involves some fundamental aspects such as representative mean composition, representative variance, accuracy and efficiency of sampling. The general sampling methods used may be random, systematic or of differentiated types. Various parameters such as size of the totality of material, number and size of the particles, distribution of trace elements between different types of particles influence the optimal size of the sample. There are some basic hazards in trace element analysis, which arise from contamination of the sample by the elements, lass of trace elements and change in mean composition with respect to the elements to be analysed. Contamination of the sample may occur fromthe environment, the sampling operation itself and the operating personnel. Trace elements may be lost by volatilization during drying and ashing, adsorption on container walls and handling tools, overlooked differences in the chemical state of the element and also bysputtering and spraying in case of liquids. The changes in the mean trace element composition of the sample may result from the physical or chemical changes and by redistribution of the elements. The main sampling operations for solid tissues include the selection of an optimal sampling method, the sampling site and the preparation of the sampling equipment. Liquid samples require additional treatment such as the use of a stabilizer and phase separation. lt is also necessary to obtain timed collection for samples such as urine and feces. Special restrictions have to be observed for both liquid and solid samples due to medical reasons, especially for in-vivo samples. Same sort of a preliminary preservation of both the solid and liquid samples is necessary du ring transport to the laboratory.Sample preparation of biological material is necessary in order to prepare the samples for obtaining the analytical signal. A few requirements such as a weil defined analytical programme, prior knowledge of the approximate elemental composition of the sample matrix and a reasonably clean bench to suit the low concentration level analytical work and adequate precautions against the basic hazards mentioned above are some of the basic necessities. [...