Analytical methods for trace elements

A clean laboratory and equipment are undoubtedly crucial to all analytical methods. For trace element and POP measurements, however, additional precautions need to be taken. Glassware and other materials used for storing samples may act as both a source and a sink for some transition and heavy metal ions. Consequently, it is important to clean glassware and polyethylene equipment several times with dilute solutions of nitric acid followed by deionized water. Gloves must be worn whenever working with samples and sampling equipment. 

The sensitivity of analytical methods for trace elements needs to be high, and ideally the reaction or property utilized should be entirely specific. The sensitivity of activation analysis is dependent on the element estimated and in many cases it is extremely high. Specificity is covered by three parameters, half-life of the nuclide produced, its maximum beta energy, and its gamma spectrum. 

ICP-MS is a powerful analytical method for trace elements due to its unique combination of high selectivity and sensitivity, wide linear dynamic range, nearly interference free operation and multi element capabilities. Its coupling of SEC with other detection methods allows simultaneous... 

Batley, G.E. (1989b) Physicochemical separation methods for trace element speciation in aquatic samples. In Trace Element Speciation Analytical Methods and Problems (ed. Batley, G.E.). CRC Press, Boca Raton, FL, pp. 43-76. 

The analytical results for trace elements appear better than those for the major elements. Table IV is a summary of results for the raw shale (OS-1), and the spent shale from the TOSCO II pilot plant (SS-2), and the spent shale (FS), unacidified water and unfiltered oil from the Fischer assay studies. The spent shale SS-2 is the residue from the retorting of the same raw feedstock from which OS-1 was taken. In the case of the solid samples, the concentrations are from multiple analyses of different splits. In all cases, the relative deviations of multiple analyses lie within 10%. Comparison of these results with those from other laboratories on different splits of the same solid samples show agreement within 2cr SI), The two exceptions are manganese and zinc for which the results reported here are low in comparison with other methods. Analyses of NBS standard coal (SRM 1632) and coal fly ash (SRM 1633) are included also in Table IV. The concentrations in raw and spent shale are similar to those reported by TOSCO except for selenium where their values range from 10-16 ppm (3). 

A special case is spectral interference from the matrix. CPAA being primarily a method for trace element determinations, the concentration of the analyte element is much lower (typically 10 times) than the concentration of the major matrix element(s). If a major matrix element (C) is activated, it often happens that the activity of D is much higher (also 10 times) than that of B. Even for quite different y-energies or half-lives, selective measurement becomes quite difficult. The interference can only be avoided by a proper choice of the incident energy or by chemical separation of B from D. In the former case an instrumental analysis (i.e., without chemical separation) is possible. 

Van der Jagt H and Stuyfzand PJ (1996) Methods for trace element analysis in surface water atomic spectrometry in particular. Fresenius Journal of Analytical Chemistry 354 32-40. 

Cation-exchange chromatography in combination with a postcolumn derivatization is also suitable for analyzing uranium and thoriiun [46]. Because both elements are actinides and in close relation with lanthanides, they are always associated with them. Due to the lack of simple and sensitive colorimetric methods, the trace analysis of these elements represents a challenge. Although alternative analytical methods for these elements such as neutron activation analysis (NAA) [47] and ICP-MS [48] are described in literature, they are not suitable for routine analysis and are prone to interferences. Major interferences include... 

Plasma source mass spectrometry is a powerful analytical technique for trace element analysis with species selectivity when coupled with a suitable chromatographic sample introduction method. It combines the ability of the analytical plasma to atomize and ionize samples efficiently, with the sensitivity and selectivity of mass spectrometry. Following the commercial introduction of inductively coupled plasma mass spectrometry (ICP-MS) instrumentation in 1983, interest in plasma source MS increased rapidly. The enormous popularity of ICP-MS is not surprising considering the low levels of detection possible for a wide range of elements. In addition, multielement capability and the availability of isotope ratio information help make plasma source MS particularly... 

The analytical chemistry of titanium has been reviewed (179—181). Titanium ores can be dissolved by fusion with potassium pyrosulfate, followed by dissolution of the cooled melt in dilute sulfuric acid. For some ores, even if all of the titanium is dissolved, a small amount of residue may still remain. If a hiU analysis is required, the residue may be treated by moistening with sulfuric and hydrofluoric acids and evaporating, to remove siUca, and then fused in a sodium carbonate—borate mixture. Alternatively, fusion in sodium carbonate—borate mixture can be used for ores and a boiling mixture of concentrated sulfuric acid and ammonium sulfate for titanium dioxide pigments. For trace-element deterrninations, the preferred method is dissolution in a mixture of hydrofluoric and hydrochloric acids. 

A logical approach which serves to minimise such uncertainties is the use of a number of distinctly different analytical methods for the determination of each analyte wherein none of the methods would be expected to suffer identical interferences. In this manner, any correspondence observed between the results of different methods implies that a reliable estimate of the true value for the analyte concentration in the sample has been obtained. To this end Sturgeon et al. [21] carried out the analysis of coastal seawater for the above elements using isotope dilution spark source mass spectrometry. GFA-AS, and ICP-ES following trace metal separation-preconcentration (using ion exchange and chelation-solvent extraction), and direct analysis by GFA-AS. These workers discuss analytical advantages inherent in such an approach. 

The nonlinearity of the system of partial differential equations (51) and (52) poses a serious obstacle to finding an analytical solution. A reported analytical solution for the nonlinear problem of diffusion coupled with complexation kinetics was erroneous [12]. Thus, techniques such as the finite element method [53-55] or appropriate change of variables (applicable in some cases of planar diffusion) [56] should be used to find the numerical solution. One particular case of the nonlinear problem where an analytical solution can be given is the steady-state for fully labile complexes (see Section 3.3). However, there is a reasonable assumption for many relevant cases (e.g. for trace elements such as... 

Both microwave closed-vessel dissolution and laboratory robotics are relatively new to the analytical laboratory. However, it is this marriage of new methods which provides useful combinations of flexible laboratory automation to meet a variety of individualized needs. Because of the large number of biological samples which are prepared for analysis each day, it is reasonable to assume that this type of innovative automation wiU be of great benefit. It should be evaluated for its ability to improve the preparation technology for trace element analysis of biological materials. 

LA-ICP-MS is a very suitable analytical method for direct trace element analysis on a small area of thin pure foil, because no sample preparation is required. The results of the determination of noble metals in a thin difficult to dissolve rhodium foil measured by LA-ICP-MS are... 

An accurate determination of copper and zinc traces in human serum samples from the International Measurement Evaluation Programme-17 launched by IRMM (Geel) has been made by isotope dilution TIMS.38 An analytical method for the multi-element determination of metals (Ti, V, Cr, Co, Ni and Mo) potentially released from dental implants and prostheses into human body fluids (in blood and urine) by ICP-MS (double-focusing sector field instrument and quadrupole instrument with octopole collision cell) for medical studies was developed in Sanz-Medel s group.39 The Cr and Co concentrations found in blood samples of patients with chromium-cobalt based alloy varied in the sub-p,gl 1 range and were not significantly higher than the basal levels found by other authors.40... 

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