Spectroscopy flame emission

The high stability of the flame source, when compared to arc or spark excitation, was recognized as the key to the construction of simple instruments for the determination of easily excited elements, such as the alkali metals. Thus the first flame photometer produced in the U.S. in 1945 by Barnes used filters rather than a prism or grating, and used a modified Meeker burner as the flame excitation source. The instrument was especially useful for sodium and potassium determinations and was also soon utilized for calcium and magnesium analyses despite the handicap of poor detection limits. 

After 1945 the development of flame photometers or flame attachments for existing equipment was rapid. The Beckman Company introduced a flame attachment for their DU spectrophotometer in 1948 and subsequently introduced their very popular total-consumption burner. The signal was detected by either a phototube or photomultiplier with a dc amplifier 

Flame excitation methods, coupled with simple read-out devices, provided high sensitivity and high reliability for the determination of the alkali metals in simple liquid systems. Further development of burners and aspirators, higher flame temperatures, better spectral isolation using gratings or prisms, and more sensitive detection and read-out devices has increased the list of elements that can be detected by flame excitation to between 50 and 60. 

A table of elements, detection limits, and wavelengths used in flame emission and atomic absorption spectroscopy is presented in Appendix VIII. The table was compiled by Pickett and Koirtyohann.  

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Analysis. Lithium can be detected by the strong orange-red emission of light in a flame. Emission spectroscopy allows very accurate determination of lithium and is the most commonly used analytical procedure. The red emission line at 670.8 nm is usually used for analytical determinations although the orange emission line at 610.3 nm is also strong. Numerous other methods for lithium determinations have been reviewed (49,50). 

Barium can also be deterruined by x-ray fluorescence (XRF) spectroscopy, atomic absorption spectroscopy, and flame emission spectroscopy. Prior separation is not necessary. XRF can be appHed directly to samples of ore or products to yield analysis for barium and contaminants. AH crystalline barium compounds can be analy2ed by x-ray diffraction. 

This chapter describes the basic principles and practice of emission spectroscopy using non-flame atomisation sources. [Details on flame emission spectroscopy (FES) are to be found in Chapter 21.] The first part of this chapter (Sections 20.2-20.6) is devoted to emission spectroscopy based on electric arc and electric spark sources and is often described as emission spectrography. The final part of the chapter (Sections 20.7-20.11) deals with emission spectroscopy based on plasma sources. 

With flame emission spectroscopy, the detector response E is given by the expression... 

A schematic diagram showing the disposition of these essential components for the different techniques is given in Fig. 21.3. The components included within the frame drawn in broken lines represent the apparatus required for flame emission spectroscopy. For atomic absorption spectroscopy and for atomic fluorescence spectroscopy there is the additional requirement of a resonance line source, In atomic absorption spectroscopy this source is placed in line with the detector, but in atomic fluorescence spectroscopy it is placed in a position at right angles to the detector as shown in the diagram. The essential components of the apparatus required for flame spectrophotometric techniques will be considered in detail in the following sections. 

With flame emission spectroscopy, there is greater likelihood of spectral interferences when the line emission of the element to be determined and those due to interfering substances are of similar wavelength, than with atomic absorption spectroscopy. Obviously some of such interferences may be eliminated by improved resolution of the instrument, e.g. by use of a prism rather than a filter, but in certain cases it may be necessary to select other, non-interfering, lines for the determination. In some cases it may even be necessary to separate the element to be determined from interfering elements by a separation process such as ion exchange or solvent extraction (see Chapters 6, 7). 

Occasionally, separation, e.g. by solvent extraction or by an ion exchange process, may be necessary to remove an interfering element such separations are most frequently necessary when dealing with flame emission spectroscopy. 

There are now two main methods used for flame emission spectroscopy. The original method, known as flame photometry, is now used mainly for the analysis of alkali metals. 

Fick s law 592 Filter funnel 102 Filter papers 115 folding of, 116 incineration of, 120, 121 macerated, 450 quantitative, (T) 116 Filter pulp 450 Filtering crucibles 102 Filters, optical 661 Filtration 102, 106, 115 accelerated, 450 technique of, 116, 117 with filter papers, 116 with filtering crucibles, 117 Flame emission spectroscopy 779, 797 background correction, 795 elementary theory of, 780 D. of alkali metals by, 812... 

Flame emission spectroscopy - continued evaluation methods, 800 flames, temperature of, 784 general discussion, 779 interferences, 791 chemical, 792 spectral, 792... 

CHAPTER 21 ATOMIC ABSORPTION AND FLAME EMISSION SPECTROSCOPY... 

Tests. The compd can be quant detd by flame emission spectroscopy (Ref 14a) and by FeS04 — KMn04 titrimeteiy for active 02 (Ref 9b). Toxicity. Poisonous if ingested. Highly irritating to skin and mucous membranes (Ref 17)... 

Na+ and K+ with a detection limit of 10 9 M. The sensor compositions exhibited wide response ranges between 10 9 and 10 5 M Na+ or K+, and, therefore, may be an alternative method to flame emission spectroscopy. The sensor is fully reversible within the dynamic range and the response time is 3 min under batch conditions. Cross sensitivity to pH is negligible in the pH range of 6.2-7.3. 

A certain fraction of the atoms produced will become thermally excited and hence will not absorb radiation from an external source. These thermally excited atoms serve as the basis of flame photometry, or flame emission spectroscopy they can de-excite radiationally to emit radiant energy of a definite wavelength. 

McCracken et al. 164) compared atomic absorption with the tetraphenyl-boron method for determining potassium in 1190 fertilizers, and very close agreement was found between the two methods. Hoover and Reagor 16S) also found good agreement between the two methods, and atomic absorption was far more rapid. They reported that the 7665 A potassium line was more subject to interference than the less sensitive 4044 A line. Temperli and Misteli 166> reported far better results for low concentrations of potassium in soil extracts by atomic absorption spectroscopy than by flame emission spectroscopy. 

Applications of Flame Emission Spectroscopy in Pharmaceutical analysis... 

Metallic salts (or metallic compounds) after dissolution in appropriate solvents when introduced into a flame (for instance acetylene burning in oxygen at 3200°C), turns into its vapours that essentially contain mostly the atoms of the metal. Quite a few such gaseous metal atoms are usually raised to a particular high energy level that enables them to allow the emission of radiation characteristics features of the metal for example-the characteristic flame colourations of metals frequently encountered in simple organic compounds such as Na-yellow, Ca-brick-red Ba-apple-green. This forms the fundamental basis of initially called Flame Photometry, but more recently known as Flame Emission Spectroscopy (FES). 

Step-V The thermal excitation of some atoms into their respective higher energy levels will lead ultimately to a condition whereby they radiate energy (flame emission) measured by Flame Emission Spectroscopy (FES), and... 

The underlying principle of Flame Emission Spectroscopy (FES) may be explained when a liquid sample containing a metallic salt solution under investigation is introduced into a flame, the following steps normally take place in quick succession, namely ... 

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