Sample Preparation Using Fusion Methods

A number of materials requiring analysis that are difficult to dissolve by conventional methods are best fused with a fusion reagent to form a fused mixture that dissolves 

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. 

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The Benefits of the X Series 2 ICP-MS for the Analysis of Geological Samples Prepared Using the Lithium Metaborate Fusion Method, Thermo Scientific Application Note—40790, 2007, http //www.thermo.com/eThermo/CMA/PDFs/Articles/articles-File 2375.pdf. 

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... 

Basically, the literature provides two dissolution methods sample preparation with sample weights of 0.2—1 g and large dilutions, or smaller sample weights with less dilution (III.B). The relatively large dilution, in general after a fusion [51], for the determination of main and lesser components, as for example in silicate analysis [2], the determination of Al, Ca, Mg, Mn and Si in slags [4], Si [55], Pb and Mn [143], and also Cd, Ca, Cu, Pb, Mg and Si in ores or iron sinter [97, 147] and Cr, Mg in refractories [93] is presently used in routine analysis. 

The book begins with a discussion of the basic physico-chemical aspects of reactions utilised in qualitative inorganic analysis. A description of laboratory equipment follows, and operations which include semimicro and micro techniques, and simple electrochemical, spectroscopic and chromatographic methods. The reactions of the most important cations and anions are described, followed by a treatment of systematic qualitative analysis. Sample preparation, dissolution and fusion of insoluble materials are treated in detail. A separate chapter deals with the reactions of less common ions, with guidelines to their separation and identification in the course of systematic analysis. Finally, a simplified course of qualitative analysis is given this chapter will be particularly useful where the time allocated to qualitative analysis is limited. 

The EPA developed two methods for the radiochemical analysis of uranium in soils, vegetation, ores, and biota, using the equipment described above. The first is a fusion method in which the sample is ashed, the silica volatilized, the sample fused with potassium fluoride and pyrosulphate, a tracer is added, and the uranium extracted with triisooctylamine, purified on an anion exchange column, coprecipitated with lanthanum, filtered, and prepared in a planchet. Individual uranium isotopes are separately quantified by high resolution alpha spectroscopy and the sample concentration calculated using the yield. The second is a nonfusion method in which the sample is ashed, the siUca volatilized, a tracer added, and the uranium extracted with triisooctylamine, stripped with nitric acid, co-precipitated with lanthanum, transferred to a planchet, and analyzed in the same way by high resolution a-spectroscopy (EPA 1984). 

The calibration is established from solutions prepared by diluting a solution of I 000 mg/1 of the element to be determined. When sample solutions are prepared using the fusion method, the reference solutions used for this analysis contain the same quantity of lithium metaborate as the sample solution. The origin of the calibration curve is determined by a blank test solution prepared in the same way as the standards, but without the element to be determined. 

The preparation of the sample consists of dissolving the solid sample, adding the internal standard and diluting so as to create a suitable salt level in the solution to be introduced into the plasma. The time required for this preparation will depend on the complexity of the composition and the physical and chemical characteristics of the catalyst. Conversion into solution form using the alkaline fusion method can be carried out in 30 minutes, whereas solubilisation via acid attack with heating on a hot plate may require a period of several days. The choice of method to achieve a solution depends not only on the chemical nature of the sample but also on the elements to be ascertained and above all the detection limit sought. 

The optical microscope is a valuable tool in the laboratory and has numerous applications in most industries. Depending on the type of data that is required to solve a particular problem, optical microscopy can provide information on particle size, particle morphology, color, appearance, birefringence, etc. There are many accessories and techniques for optical microscopy that may be employed for the characterization of the physical properties of materials and the identification of unknowns, etc. Utilization of a hot-stage accessory on the microscope for the characterization of materials, including pharmaceutical solids (drug substances, excipients, formulations, etc.), can be extremely valuable. As with any instrument, there are many experimental conditions and techniques for the hot-stage microscope that may be used to collect different types of data. Often, various microscope objectives, optical filters, ramp rates, immersion media, sample preparation techniques, microchemical tests, fusion methods, etc., can be utilized. 

Standard Practice for Sample Preparation for X-Ray Emission Spectrometric Analysis of Uranium in Ores Using the Glass Fusion or Pressed Powder Method... 

Quantitative analysis usually requires the use of standards and/or certified reference materials (CRMs), the selection of an appropriate elemental optical emission line, and, in most cases, the selection of a normalization line, used as an IS. Calibration curves are then constructed using the normalized peak area versus concentration, as previously described for calibration using an IS. When there is a dominant matrix component for which the concentration will remain approximately constant across the calibration set, it is best to use an emission line from that matrix element for normalization. This approach helps minimize effects due to changes in plasma conditions caused by shot-to-shot fluctuations in laser intensity. Alternatively, chemometric correlation analysis of the entire observed spectrum with the concentration of the analyte can be used to construct calibration curves automatically. In general, RSDs of 5%-10% are readily achievable. To improve quantitation, sample preparation methods such as pressing pellets may improve results for soils and sediments and fusion with salts to convert the sample into a glass bead can eliminate matrix effects. Fusion was discussed in Chapter 1 and is used extensively in XRF analysis (Chapter 8). 

Both oxygen and carbon were determined by the inert gas fusion method which is quite useful in measuring small amounts of these elements. Tie data show no difference in the average oxygen content of the riffled vs. the unriffled samples. Tlie carbon content is typical of the silicon nitride powders prepared by the vendor s method. 

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