Fluorescence selenium analysis

X-ray fluorescence is applicable to selenium analysis for biological and other samples, and show good correlation with neutron activation [20, 52]. The volatile nature of seleno-compounds makes them good subjects for gas chromatography. An advantage of gas chromatography is the available field units which can detect levels as low as 0.1 ppm [18]. 

Zinc smelters use x-ray fluorescence spectrometry to analyze for zinc and many other metals in concentrates, calcines, residues, and trace elements precipitated from solution, such as arsenic, antimony, selenium, tellurium, and tin. X-ray analysis is also used for quaUtative and semiquantitative analysis. Electrolytic smelters rely heavily on AAS and polarography for solutions, residues, and environmental samples. 

Selenium is converted to its volatile hydride by reaction with sodium boro-hydride, and the cold hydride vapor is introduced to flame AA for analysis. Alternatively, selenium is digested with nitric acid and 30% H2O2, diluted and analyzed by furnace-AA spectrophotometer. The metal also may be analyzed by ICP-AES or ICP/MS. The wavelengths most suitable for its measurements are 196.0 nm for flame- or furnace-AA and 196.03 nm for ICP-AES. Selenium also may be measured by neutron activation analysis and x-ray fluorescence. 

J. Gomez-Ariza, M.-A. Caro-de-la-Torre, I. Giraldez and E. Morales, Speciation analysis of selenium compounds in yeasts using pressurized liquid extraction and liquid chromatography-microwave-assisted digestion-hydride generation-atomic fluorescence spectrometry. Anal. Chim. Acta, 524(1-2), 2004, 305-314. 

Figure 18-23 Fluorescence calibration curve for the selenium-containing product in Reaction 18-15. The curvature and maximum are due to self-absorption. [From m.-c. Sheffield and T M. Nahir, "Analysis of Selenium in Bran Nuts by Microwave Digestion and Fluorescence Defection J. Chem. Ed. 2002, 79. 1345.]...

Simon, S., Barats, A., Pannier, F., Potin-Gautier, M. Development of an on-line UV decomposition system for direct coupling of liquid chromatography to atomic-fluorescence spectrometry for selenium speciation analysis. Anal. Bioanal. Chem. 383, 562-569 (2005)... 

The analytic methods generally fall into two groups (1) those that do not require the destruction of organic materials in the sample and (2) those that require the elimination of interfering matter before the selenium content can be measured. X-ray fluorescence and some of the neutron activation analysis techniques do not require sample destruction, whereas spectrophotometry, GC, atomic absorption spectrometry, polarography, titration, spark source, MS, fluorometry, and other neutron activation analysis techniques require some degree of sample destruction. Fluorometry, atomic absorption spectrometry, and neutron activation analysis are the most frequently used methods. 

Y Cai. Speciation and analysis of mercury, arsenic, and selenium by atomic fluorescence spectrometry. Trends Anal Chem 19 62-66, 2000. 

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... 

X-ray fluorescence spectrometry This technique is extensively used in the industrial analysis of plastics for routine determination of traces of metals and nonmetal elements, i.e., iron, cobalt, nickel, chromium, copper, zinc, chlorine, bromine, titanium, aluminum, sodium, potassium, calcium, magnesium, vanadium, cadmium, and selenium. The main advantages are simple sample preparation and independence on the element state in chemical combination. 

X-ray fluorescence spectrometry has several advantages over other methods. The analysis is non-destructive, specimen preparation is simple, measurement time is usually less than for other methods and x-rays interact with elements as such, ie. the intensity measurement of a constituent element is independent of its state of chemical combination. However, the technique does have some drawbacks, eg. absorption effects of other elements present, for instance, the carbon and hydrogen of the polyethylene matrix and excitation of one element by x-rays from another, eg. cadmium and selenium mutually affect one another. 

The most important methods involve reaction of selenium with aromatic orthodiamines to form colored piazoselenols. These reactions are the basis for most of the current standard methods of selenium determination [46]. In addition to spec-trophotometric analysis, the major instrumental methods include neutron activation, atomic absorption spectroscopy, x-ray fluorescence and gas chromatography. 

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