Spectrophotometry flame emission

For additional information on this technique, the reader is referred to an earlier version of this chapter.  

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Table 25.1 Assay of Pharmaceutical Substances by Flame Emission Spectrophotometry (or FES) ...

Sodium may be determined by atomic absorption spectrophotometry (AAS), flame emission spectrophotometry (FES), electrochemically with an Na -ISE, or spectrophoto-metrically. Of these methods, ISE methods are by far the most common. Excellent accuracy and coefficients of variation of less than 1.5% are readily achieved with modern equipment, reliable calibrators, and a good quality assurance program. Because sodium and potassium are routinely assayed together, methods for their analysis are described together later in this chapter. 

If the measured Na concentration in plasma is decreased, but measured plasma osmolahty, glucose, and urea are normal, the only explanation is pseudohyponatremia caused by the electrolyte exclusion effect see Chapter 27). This occurs when Na" is measured by either flame emission spectrophotometry or by an indirect ion-selective electrode in patients with severe hyperlipidemia or in states of hyperproteinemia (e.g., paraproteinemia of multiple myeloma). 

Over many years, the simple flame test , whereby atoms of, say, sodium are excited in a flame, giving a characteristic yellow colour, has been developed as a sophisticated and sensitive instrumental technique (flame emission spectrophotometry). Sensitivity depends on dissociation of the injected materials into free atoms in order that the characteristic atomic emissions can be given. This in turn demands high flame temperatures. The combination of acetylene fuel with nitrous oxide as oxidant has proved highly successful for this purpose. What temperature is possible in theory The best mixture would correspond to the equation ... 

In flame-emission spectrophotometry, also frequently referred to for short as "flame photometry", the sample under investigation is converted to atomic vapour by applying thermal energy (a flame). As energy continues to... 

In river water silica is present in the form of barely ionized silicic acid, H2Si03, in concentrations of 5 to 30 mg-l depending on the soil. The amount can be determined by flame emission spectrophotometry or by ammonium molybdate colorimetry. 

The combustion of acetylene fuel with nitrous oxide as oxidant at 25°C (298 K) is widely performed in flame emission spectrophotometry. Calculate the maximum temperature attained if the best mixture corresponds to the reaction... 

When the concentration of K " in nitrobenzene was to be determined, one mil of nitrobenzene solution was taken by a pipet and transferred to a platinum crucible. The solution in the crucible was combusted in an electrical furnace. The combustion products were then dissolved in measured amount of deionized distilled water. The solution was subjected to flame emission spectrophotometry using cesium as an ionization retarder. 

Sulphate, chloride (Cl ), nitrate (NO ), and ammonium (NH ) in water were measured with a Technicon Autoanalyzer II system by the methylthymol blue, mercuric thiocyanate, cadmium reduction and sodium nitroprusside methods, respectively. Sulphate and Cl in highly colored samples were measured by means of ion chromatography. Cations were analyzed with an atomic-absorption spectrophotometer by means of flame-emission spectrophotometry for potassium (K ) and... 

Potassium is analyzed in chemicals that are used in the fertilizer industry and in finished fertilizers by flame photometric methods (44) or volumetric sodium tertraphenylboron methods (45) as approved by the AO AC. Gravimetric deterrnination of potassium as K2PtClg, known as the Lindo-Gladding method (46), and the wet-digestion deterrnination of potassium (47) have been declared surplus methods by the AO AC. Other methods used for control purposes and special analyses include atomic absorption spectrophotometry, inductively coupled plasma (icp) emission spectrophotometry, and a radiometric method based on measuring the radioactivity of the minute amount of the isotope present in all potassium compounds (48). 

Whereas flame emission photometry relies on the excitation of atoms and the subsequent emission of radiation, atomic absorption spectrophotometry relies on the absorption of radiation by non-excited atoms. Because the proportion of the latter is considerably greater than that of the excited atoms, the potential sensitivity of the technique is also much greater. 

One often unsuspected source of error can arise from interference by the substances originating in the sample which are present in addition to the analyte, and which are collectively termed the matrix. The matrix components could enhance, diminish or have no effect on the measured reading, when present within the normal range of concentrations. Atomic absorption spectrophotometry is particularly susceptible to this type of interference, especially with electrothermal atomization. Flame AAS may also be affected by the flame emission or absorption spectrum, even using ac modulated hollow cathode lamp emission and detection (Faithfull, 1971b, 1975). 

Tbe metal may most conveniently be analyzed in tbe aqueous phase by atomic absorption spectrophotometry using flame or a graphite furnace or by ICP emission spectrophotometry at wavelength 206.83 or 217.58 nm. Such measurements are accurate at trace concentration levels. The metal or its ore is digested with hot nitric acid and the acid extract is appropriately diluted and measured. 

Elemental composition Ba 58.89%, Ti 20.53%, O 20.58%. The sobd is digested with a mixture of concentrated H2SO4 and HNO3, diluted and the aqueous solution is analyzed for the metals Ba and Ti by flame or furnace atomic absorption or ICP emission spectrophotometry. The compound in the crystalline powdered form may be identified by various x-ray techniques. 

Cadmium in acidified aqueous solution may be analyzed at trace levels by various instrumental techniques such as flame and furnace atomic absorption, and ICP emission spectrophotometry. Cadmium in solid matrices is extracted into aqueous phase by digestion with nitric acid prior to analysis. A much lower detection level may be obtained by ICP-mass spectrometry. Other instrumental techniques to analyze this metal include neutron activation analysis and anodic stripping voltammetry. Cadmium also may be measured in aqueous matrices by colorimetry. Cadmium ions react with dithizone to form a pink-red color that can be extracted with chloroform. The absorbance of the solution is measured by a spectrophotometer and the concentration is determined from a standard calibration curve (APHA, AWWA and WEF. 1999. Standard Methods for the Examination of Water and Wastewater, 20th ed. Washington, DC American Public Health Association). The metal in the solid phase may be determined nondestructively by x-ray fluorescence or diffraction techniques. 

Cesium can be analyzed by various instrumental techniques including atomic absorption and atomic emission spectrophotometry and various x-ray methods. The most sensitive wavelength for AA measurement is 852.1 nm. It imparts a reddish violet color to flame. It is identified by specific line spectra having two bright lines in the blue region and several other lines in the red, yellow, and green. 

Elemental composition H 2.49%, Se 97.51%. The gas may be analyzed by GC using a TCD, FID or a flame photometric detector. The compound may be identified by GC/MS the molecular ions have masses 82 and 80. The compound may be absorbed in water and the solution analyzed for elemental selenium by flame or furnace atomic absorption—or by ICP atomic emission spectrophotometry. 

The following method employs atomic emission spectrophotometry (flame photometry), and is... 

The most commonly used technique of sample introduction is aspiration of the solution into the argon plasma flame. Because of the high temperatures in the flame, many of the problems associated with atomic absorption are eliminated. However, matrix effects such as significant differences in viscosity between sample and standard solutions can still have an effect. When needed, most of the techniques of sample introduction used in atomic absorption spectrophotometry can also be used for sample introduction in emission spectrophotometry [see the review articles " listed in the references]. 

Inductively coupled argon plasma emission spectrophotometry (ASTM D-5708) has an advantage over atomic absorption spectrophotometry (ASTM D-4628, ASTM D-5863) because it can provide more complete elemental composition data than the atomic absorption method. Flame emission spectroscopy is often used successfully in conjunction with atomic absorption spectrophotometry (ASTM D-3605). X-ray fluorescence spectrophotometry (ASTM D-4927, ASTM D-6443) is also sometimes used, but matrix effects can be a problem. 

A.M.R. Ferreira, A.O.S.S. Rangel, J.L.F.C. Lima, Flow injection systems with stream splitting and a dialysis unit for the soil analysis of sodium and potassium by flame emission spectrometry, and calcium and magnesium by atomic absorption spectrophotometry, Commun. Soil Sci. Plant Anal. 26 (1995) 1532. 

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