Trace impurity analysis

The conventional method for quantitative analysis of galHum in aqueous media is atomic absorption spectroscopy (qv). High purity metallic galHum is characteri2ed by trace impurity analysis using spark source (15) or glow discharge mass spectrometry (qv) (16). 

An efficient analytical procedure for the trace impurity analysis of Mg, K, Cr, Mn, Fe, Ni, Co, Cu, Zn, Ag, Cd, Ba and Pb in high purity silicon powder after a very simple matrix separation via microwave assisted volatihzation of silicon as silicon fluorides, was proposed by Ueng el al.59 The authors observed a nearly 99 % volatihzation of the matrix element silicon from the... 

A. M. Wolters, D. A. Jayawickrama, C. K. Larive, and J. V. Sweedler, Capihary isotachophoresis/NMR Extension to trace impurity analysis and improve instrumental coupling, Anal. Chem. 74 (2002), 2306 2313. 

The use of directed chemical reactions opens up a number of new opportunities in trace impurity analysis, such as the determination of compounds whose peaks are overlapped completely or partly by the zone of the main component or elimination of the superposition of the peaks of impurity components in their incomplete separation. Table 5.8 shows the application of the subtraction method to impurity analysis. 

Table II. Trace Impurity Analysis of Grade-A Helium...

Siegel MW, Fite WL. Terminal ions in weak atmospheric plasmas. Applications of atmospheric pressure ionization to trace impurity analysis in gases. J Phys Chem. 1976 80 2871-81. Sunner J, Ikonomou MG, Kebarle P. Sensitivity enhancements obtained at high temperatures in atmospheric pressure ionization mass spectrometry. Anal Chem. 1988 60 1308-13. Thomson BA. Micro and nano-electrospray ionization techniques. In Gross M, Caprioli R, editors. Encyclopedia of mass spectrometry Vol6. Ionization methods. Oxford Elsevier, 2007. pp. 435 4. 

Although the book on reagent chemicals contains many tests for the determination of trace impurities in reagents, it is not intended to be a text on the techniques of trace analysis but rather to provide tests that are reproducible in various laboratories, and which are accurate, economic, and feasible (see... 

The distribution of impurities over a flat sihcon surface can be measured by autoradiography or by scanning the surface using any of the methods appropriate for trace impurity detection (see Trace and residue analysis). Depth measurements can be made by combining any of the above measurements with the repeated removal of thin layers of sihcon, either by wet etching, plasma etching, or sputtering. Care must be taken, however, to ensure that the material removal method does not contaminate the sihcon surface. 

Process trouble shooting. Analysis or separation system operation and malfunc tion, examination of composition profiles, and tracking of trace impurities with implications for corrosion and process specifications. 

In Total Reflection X-Ray Fluorescence Analysis (TXRF), the sutface of a solid specimen is exposed to an X-ray beam in grazing geometry. The angle of incidence is kept below the critical angle for total reflection, which is determined by the electron density in the specimen surface layer, and is on the order of mrad. With total reflection, only a few nm of the surface layer are penetrated by the X rays, and the surface is excited to emit characteristic X-ray fluorescence radiation. The energy spectrum recorded by the detector contains quantitative information about the elemental composition and, especially, the trace impurity content of the surface, e.g., semiconductor wafers. TXRF requires a specular surface of the specimen with regard to the primary X-ray light. 

NAA is a quantitative method. Quantification can be performed by comparison to standards or by computation from basic principles (parametric analysis). A certified reference material specifically for trace impurities in silicon is not currently available. Since neutron and y rays are penetrating radiations (free from absorption problems, such as those found in X-ray fluorescence), matrix matching between the sample and the comparator standard is not critical. Biological trace impurities standards (e.g., the National Institute of Standards and Technology Standard Rference Material, SRM 1572 Citrus Leaves) can be used as reference materials. For the parametric analysis many instrumental fiictors, such as the neutron flux density and the efficiency of the detector, must be well known. The activation equation can be used to determine concentrations ... 

NAA is well suited for Si semiconductor impurities analysis. The sensitivity and the bulk mode of analysis make this an important tool for controlling trace impurities during crystal growth or fer monitoring cleanliness of various processing operations for device manufacturing. It is expected that research reactors will ser e as the central analytical facilities for NAA in the industry. Since reactors are already set up to handle radioactive materials and waste, this makes an attractive choice over installing individual facilities in industries. 

Chemical and catalytic. This grade of platinum is for conversion to catalysts, gauzes and chemical compounds. Spectrographic analysis is employed to control the presence of trace impurities harmful in these applications. 

The acceptance criterion for recovery data is 98-102% or 95-105% for drug preparations. In biological samples, the recovery should be 10%, and the range of the investigated concentrations is 20% of the target concentrations. For trace level analysis, the acceptance criteria are 70-120% (for below 1 ppm), 80-120% (for above 100 ppb), and 60-100% (for below 100 ppb) [2]. For impurities, the acceptance criteria are 20% (for impurity levels <0.5%) and 10% (for impurity levels >0.5%) [30], The AOAC (cited in Ref. [11]) described the recovery acceptance criteria at different concentrations, as detailed in Table 2. A statistically valid test, such as a /-test, the Doerffel-test, or the Wilcoxon-test, can be used to prove whether there is no significant difference between the result of accuracy study with the true value [29],... 

Identification and structural analysis of organic compounds. Determination of trace impurities in a wide range of inorganic materials (spark source mass spectrometry). 

The applicability of cITP-NMR for the analysis of trace impurities was demonstrated by the selective detection of 1.9 nmol of atenolol injected in a sample containing a 1000-fold excess of sucrose [100]. cITP-NMR has also been used for the analysis of a cationic neurotoxin present in a homogenate of the hypo-branchial gland of the marine snail Calliostoma canaliculatum [109]. Korir et al. [110] used an anionic cITP separation with online NMR detection to separate and identify nanomole quantities of heparin oligosaccharides. Although only a few cITP-NMR applications have appeared, the ability to selectively separate, concentrate, and detect charged analytes makes cITP-NMR a potentially powerful method for trace analysis. 

N. J. Haskins, C. Eckers, A. J. Organ, M. F. Dunk and B. E. Winger, The use of electrospray ionization with Fourier transform ion cyclotron resonance mass spectrometry in the analysis of trace impurities in a drag substance. Rapid Communications in Mass Spectrometry, 1995,9(11), 1027-1030. 

A convenient method is the spectrometric determination of Li in aqueous solution by atomic absorption spectrometry (AAS), using an acetylene flame—the most common technique for this analyte. The instrument has an emission lamp containing Li, and one of the spectral lines of the emission spectrum is chosen, according to the concentration of the sample, as shown in Table 2. The solution is fed by a nebuhzer into the flame and the absorption caused by the Li atoms in the sample is recorded and converted to a concentration aided by a calibration standard. Possible interference can be expected from alkali metal atoms, for example, airborne trace impurities, that ionize in the flame. These effects are canceled by adding 2000 mg of K per hter of sample matrix. The method covers a wide range of concentrations, from trace analysis at about 20 xg L to brines at about 32 g L as summarized in Table 2. Organic samples have to be mineralized and the inorganic residue dissolved in water. The AAS method for determination of Li in biomedical applications has been reviewed . 

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