Spectroscopy molecular absorption

Frequently an analyst must select, from several instruments of different design, the one instrument best suited for a particular analysis. In this section we examine some of the different types of instruments used for molecular absorption spectroscopy, emphasizing their advantages and limitations. Methods of sample introduction are also covered in this section. 

Horwitz claims that irrespective of the complexity found within various analytical methods the limits of analytical variability can be expressed or summarized by plotting the calculated mean coefficient of variation (CV), expressed as powers of two [ordinate], against the analyte level measured, expressed as powers of 10 [abscissa]. In an analysis of 150 independent Association of Official Analytical Chemists (AOAC) interlaboratory collaborative studies covering numerous methods, such as chromatography, atomic absorption, molecular absorption spectroscopy, spectrophotometry, and bioassay, it appears that the relationship describing the CV of an analytical method and the absolute analyte concentration is independent of the analyte type or the method used for detection. 

Molecular absorption spectroscopy deals with measurement of the ultraviolet-visible spectrum of electromagnetic radiation transmitted or reflected by a sample as a function of the wavelength. Ordinarily, the intensity of the energy transmitted is compared to that transmitted by some other system that serves as a standard. 

Analysis. The most sensitive techniques for the analysis of Ge include ICPAES (1 ppb) and IGPMS (0.1 ppb). Colorimetric agents (phenylfluo-ronone) and molecular absorption spectroscopy can detect 100 ppb. One of the better spot tests involves treatment of a slightly basic germanate solution with phenolphthalein to produce a red color, then the addition of mannitol which turns the solution colorless. Sensitivity is 100 ppm. A major interference is B. 

GC, gas chromatography HPLC, high-performance liquid chromatography MS, mass spectroscopy AA, atomic absorption GFAA, graphite furnace atomic absorption ICP, inductively coupled plasma UV-VIS, ultraviolet-visible molecular absorption spectroscopy IC, ion chromatography. 

IUPAC. Molecular Absorption Spectroscopy, Ultraviolet and Visible (UV/VIS). PureAppl. Chem. 1988, 60, 1449-1460. 

In this chapter, we discuss the basic principles that are necessary to understand measurements made with electromagnetic radiation, particularly those deeding with the absorption of UV, visible, and IR radiation. The nature of electromagnetic radiation and its interactions with matter are stressed. The next four chapters are devoted to. spectroscopic instruments (Chapter 25), molecular absorption spectroscopy (Chapter 26), molecular fluorescence spectroscopy (Chapter 27), and atomic spectroscopy (Chapter 28). 

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