Fusion, trace analysis

Kashima, J., Yamazaki, T. Trace analysis for oxygen in metals by the inert gas fusion method with silicon carbide-graphite crucible. Bunseki Kagaku 15, 9 (1966). — Gas chromatog. Abstr. 1969, 701. 

The use of ICP-MS for trace analysis in sediments has recently been reviewed [326]. The advantages and disadvantages of acid digestion versus fusion-based sample dissolution were discussed. The problems involved in ICP-MS analysis of... 

Clearly, trouble-free universal methods are the ideal for trace analysis of oxide materials. Numerous materials can only be dissolved via melting fusion they then cannot be diluted overmuch and therefore contain a relatively high salt content. However, many laboratories are not yet equipped with furnace atomisers so the flame method must be used. 

The direct use of the Hoesch injection technique is useful for trace analysis of oxide substances after fusion [31, 99, 142]. It is possible to take up the fused substance in small quantities (max. 10 ml, usually 1 ml). It is best to use an acid mixture which contains 400ml HC1 (6 = 1.15gml-1) and 40g citric acid in 1000 ml. Generally, 10 pi, and in special cases 50 pi, of the analytical solution are injected. It is thus possible to determine all important ascertainable elements in 1 ml of analytical solution several times over. Salt concentrations of 100 mg ml-1 are no problem for the injection technique. 

Disadvantages of the fusion method are that some elements may be volatile at 900°C, the fusion reagent may cause contamination, and the presence of high amounts of dissolved solid content may not be suitable for trace analysis. Blanks of fusion reagents must also be prepared alongside samples. The fusion fluxes are expensive and give rise to spectral interferences and must be considered a last resort. 

The classic book on sample preparation is by Gorsuch (1970). He discussed wet and dry oxidation and fusion. Each element was considered separately. The book should be consulted in a new or difficult situation. The control of contamination in trace analysis has been addressed in a book by Zief and Mitchell (1976). They discussed the life of various standard solutions at the mg/l level at various pH after 24 hours. The losses were great for many ions at high pH, but there were no losses at pH lower than about 2. The same effect... 

F. J. M. J. Maessen and R W. J. M. Boumans, Critical examination of the borate fusion technique for spectrochemical trace analysis of geological materials using the dc arc, Spectrochem. Acta, 22fl 739 (1968). 

Alternative methods are used where XRF fails, i.e., for elements below sodium in the periodic table, for volatile elements and precious metals not amenable to fusion, for liquids, and for some trace analyses. In the case of trace analysis (in ceramics <100pg per g), XRF meets the requirements for many elements even with a 5 1 flux/sample ratio, particularly for U, Th, Y, La, V, Rb, Cs, Ga, Ge, Ce, Nd, Pr, Sc, and Ni. 

For trace analysis, the main ceramic elements of interest are Zn, Pb, Cu, Bi, Sb, Sn, Ag, As, Mn, Cr, Se, and Hg. Many of these are environmentally important. In certain cases the detection limits of flame AAS are inadequate, so that hydride generation for antimony, selenium, arsenic and bismuth, cold vapor for mercury, and graphite furnace AAS for lead and cadmium are required. A variation of AAS is atomic fluorescence, and this is used to achieve the detection limits needed for Hg and Se in environmental samples. Microwave digestion techniques for sample preparation are becoming more common, where, unlike fusion, there is no risk of loss of volatile elements from unfired samples and fewer reagents are... 

Fusion is the traditional approach to sample preparation for industrial and geological analyses [67], especially for the analysis of mineral samples (e.g., lithium metaborate melts [68]). The major problems associated with fusion include restricted means for purifying the required (solid) reagents and the presence of high salt concentrations in the resulting analyte solution. Especially for trace analysis, overloading of the matrix in this way is inadvisable. 

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. 

Applications Basic methods for the determination of halogens in polymers are fusion with sodium carbonate (followed by determination of the sodium halide), oxygen flask combustion and XRF. Crompton [21] has reported fusion with sodium bicarbonate for the determination of traces of chlorine in PE (down to 5 ppm), fusion with sodium bisulfate for the analysis of titanium, iron and aluminium in low-pressure polyolefins (at 1 ppm level), and fusion with sodium peroxide for the complexometric determination using EDTA of traces of bromine in PS (down to 100ppm). Determination of halogens in plastics by ICP-MS can be achieved using a carbonate fusion procedure, but this will result in poor recoveries for a number of elements [88]. A sodium peroxide fusion-titration procedure is capable of determining total sulfur in polymers in amounts down to 500 ppm with an accuracy of 5% [89]. 

Laser ablation ICP-MS (LA-ICP-MS) was established in the early 1990s as a potential routine tool for the measurement of trace and ultra-trace elements in silicate systems for geology. Early studies (Perkins et al. 1993) used sample preparation techniques identical to that used to prepare rock samples for WDXRF, i.e., either a pressed powder disk or a glass bead fusion method (see Appendix VIII). Such studies concluded that LA-ICP-MS had the potential to surpass XRF in terms of the limits of detection achieved and INAA in terms of the speed of analysis (Perkins et al. 1993 481). It has long been recognized that the main limit on the quantitative performance of LA-ICP-MS is the homogeneity at the trace and ultra-trace level of the solid calibration standards available. Subsequent work (e.g., Hollecher and Ruiz 1995, Norman et al. 1996) has demonstrated that some of the international... 

The primary dispersion halo and wallrock alteration around the Elura deposit was established from integrated petrographic, mineralogical and geochemical (major-, minor- and trace-element) analysis of diamond drill core samples. Seventy eight samples of variably altered and unaltered host rocks, as well as 67 near-surface weathered equivalents, were analysed for major elements using fusion disc. X-ray fluorescence analysis (XRF). Trace elements were determined by pressed powder XRF analysis. Carbonate carbon... 

Recently, in the fusion experiment DIII-D a steady decrease of the spectroscopic CD signal, representative for chemically eroded species, was observed over the course of several years [60], After the use of the same tiles for 10 years in divertor application the CD band virtually disappeared. As possible reasons the frequent boronizations and the development of surface topography were discussed. As surface analysis of the tiles used in DIII-D did not show any significant traces of impurities, also the assumption of a reduction due to impurities was ruled out [61]. 

Inductively coupled plasma atomic emission spectrometry (ICP-AES) was used for the determination of most major and trace elements. The samples are fused in a Claisse semi-automatic fusion device in Pt-Au crucibles with lithium metaborate (4). The fusion product is dissolved in diluted HNO and brought to volume. For trace elements determination the sample is decomposed by HF, HNOg and HCIO. Scandium serves as an internal standard and is added to all samples and solutions. The instrument (product of Jobin Yvon, France)is calibrated using multi-element synthetic standards. The aqueous solutions are nebulized and injected into the heart of a plasma fire ball. A computerized multi-channel vacuum spectrometer has been programmed for multi-element analysis. 

Combining the fusion technique with ICPES measurements gives a rapid and accurate method for the ash elemental analysis. The total analysis time needed is 20-25 minutes per sample. However, although the fusion procedure is excellent for the determination of all major elements, it is not suitable for the determination of trace elements, because the final solution (1 L) is too dilute for detection of trace elements. If the solution volume is kept small, extremely high concentrations of lithium and boron in the solution give an undesirable high background spectrum for trace element measurements. Hence, it is necessary to resort to a separate procedure where both trace and major elements can be simultaneously determined. 

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