Sample preparation trace matrix separation

Sample preparation, which is generally minimized for solid samples, can be a time consuming and labour intensive process, especially if trace matrix separation is required. Due to the huge variety of different matrices, of more or less complex matrix composition, many different decomposition principles have been developed. 

As the most important inorganic mass spectrometric technique, ICP-MS is also employed for the precise and accurate isotope ratio measurements of a multitude of elements (such as Li, B, S, Fe, Sr, Pb, U, Pu) in environmental samples (see Chapter 8).9,88-90 Isotope ratio measurements of environmental samples require special careful sample preparation techniques including trace/matrix separation and enrichment procedures if the analytes are at the trace and ultratrace level. As an example, the schematic diagrams of the separation and enrichment procedures for the precise isotope analysis of Pu, U and Sr in water samples from the Sea of Galilee using double-focusing... 

The analytical accuracy of methods can only be discussed with regard to the complete analytical procedure applied. Therefore, it is necessary to optimize sample preparation procedures and trace-matrix separations specifically to the requirements of the analytical results in terms of accuracy, power of detection, precision, cost and the number of elements and increasingly of the species to be determined. However, the intrinsic sensitivity to matrix interferences of the different methods of determination remains important. 

Spectrometric methods require a prior sampling preparation containing a separation step. The separation step is necessary especially to eliminate interference. Nonspectral interferences in flame atomic absorption spectrometry can be overcome by using a calibration model.221 The model uses two independent variables for analyte quantification (the amount of the sample and the amount of analyte added) the measured absorbance is the dependent variable. To control the matrix interferences without prior knowledge of the matrix composition, it is necessary to carry out nine calibration points to obtain accurate analytical information. This confers high reliability of the analytical information for determination of trace elements in complex matrices. 

Many different trace/matrix separation procedures are also applied prior to the ICP-MS determination, or even on-line (e.g. Muller and Heumann 2000). ID finds increasing application in combination with ICP-MS, thereby reducing the problems of analyte losses in sample preparation, but not the problem of interferences in the ICP-MS measurements (e.g., Yi and Madusa 1996) and that of contamination during sample preparation. Schuster and Schwarzer (1998) have described a new very versatile online capable column t/m-separation and preconcentration procedure for the selective separation and preconcentration of Pd even from solutions containing high concentrations of the other PGM. Moldovan et al. (2003) recently published another method for on-line preconcentration and determination of Pd using ICP-MS. 

The two examples of sample preparation for the analysis of trace material in liquid matrixes are typical of those met in the analytical laboratory. They are dealt with in two quite different ways one uses the now well established cartridge extraction technique which is the most common the other uses a unique type of stationary phase which separates simultaneously on two different principles. Firstly, due to its design it can exclude large molecules from the interacting surface secondly, small molecules that can penetrate to the retentive surface can be separated by dispersive interactions. The two examples given will be the determination of trimethoprim in blood serum and the determination of herbicides in pond water. 

Recently, in many demanding sample preparation situations, more selective sorbents have been used. Affinity type sorbents, particularly immunosorbents, have gained popularity in trace analysis, not only for biological macromolecules but also for small molecules, like aflatoxins. MIPs have properties resembling those of affinity phases and therefore they may find unique applications where other sample pretreatment methods are tedious. This relates both to the separation of a single analyte and to the separation of a group of related analytes from the sample matrix. 

Figure 8 Automated high-throughput RNA analysis by capillary electrophoresis. Typical batch processing profiles of a 96-well sample plate. Total RNA sample preparations from rice (traces 1-76 from top), arabidopsis (traces 77-95), and yeast (trace 96) 6 pL each in 96-well plate. Conditions 50-pm-i.d. capillary, =10 cm (L = 30 cm) sieving medium, 1% PVP (polyvinylpirrolidone, MW= 1.3 MDa), 4 M urea, 1 xTBE, 0.5 pM ethidium bromide =500 V/cm 25°C. RNA samples were diluted in deionized water and denatured at 65°C for 5 min prior to analysis. Sample tray was stored at 4°C in the CE instrument during processing. Injection vacuum (5 s at 3.44 kPa). Separation matrix was replaced after each run, 2 min at 551 kPa. (Reproduced with permission from Ref. 102.)...

The analytical process can be divided into four major steps sample preparation, separation, detection, and data treatment. Eor the analysis of drugs and metabolites in biological matrices, sample preparation remains the most challenging task since the compounds of interest are often present at trace level in a complex matrix containing a large number of biomolecules (e.g. proteins) and other substances, such as salts. 

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