Quantitative analysis flame photometry

Quantitative analysis Flame photometry is used for the quantitative determination of alkaline metals and alkaline-earth metals in blood, serum, and urine in clinical laboratories. It provides much simpler spectra than those found in other types of atomic emission spectrometry, but its sensitivity is much reduced. 

Instrumental Quantitative Analysis. Methods such as x-ray spectroscopy, oaes, and naa do not necessarily require pretreatment of samples to soluble forms. Only reUable and verified standards are needed. Other instmmental methods that can be used to determine a wide range of chromium concentrations are atomic absorption spectroscopy (aas), flame photometry, icap-aes, and direct current plasma—atomic emission spectroscopy (dcp-aes). These methods caimot distinguish the oxidation states of chromium, and speciation at trace levels usually requires a previous wet-chemical separation. However, the instmmental methods are preferred over (3)-diphenylcarbazide for trace chromium concentrations, because of the difficulty of oxidizing very small quantities of Cr(III). 

Flame photometry provides a robust, cheap and selective method based on relatively simple instrumentation for quantitative analysis of some metals. 

Atomic absorption and flame emission spectroscopy, also called flame photometry, are two methods of quantitative analysis that can be used to measure approximately 70 elements (metals and non-metals). Many models of these instruments allow measurements to be conducted by these two techniques, which rely on different principles. Their applications are numerous, as concentrations in the mg/l (ppm) region or lower can be accessed. 

This is a non-SI weight per volume (w/v) concentration term commonly used in quantitative analysis such as flame photometry, atomic absorption spectroscopy and gas chromatography, where low concentrations of solutes are to be analysed. The term ppm is equivalent to the expression of concentration as /igrnL" (10 gmL ) and a l.Oppm solution of a substance will have a concentration of 1.0/igmL (1.0 x 10 gmL ). A typical procedure for calculations in terms of ppm is shown in Box 6.2. 

Analytical applications have been found for all parts of the electromagnetic spectrum ranging from microwaves through visible radiation to gamma (y) rays (Table 1). The emission and absorption of electromagnetic radiation are specific to atomic and molecular processes and provide the basis for sensitive and rapid methods of analysis. There are two general analytical approaches. In one, the sample is the source of the radiation in the other, there is an external source and the absorption or scattering of radiation by the sample is measured. Emission from the sample may be spontaneous, as in radioactive decay, or stimulated by thermal or other means, as in flame photometry and fluorimetry. Both approaches can be used to provide qualitative and quantitative information about the atoms present in, or the molecular structure of, the sample. 

The use of flame photometry as a quantitative tool can be traced to work by Kirchhoff and Bunsen in the early 1860sJ Its modern history begins, however, in the 1940s, when instruments became available that successfully addressed the problems of reproducible sample introduction and detection. Flame photometry soon developed into a reliable analytical technique for the determination of several cations of pharmaceutical interest, notably sodium, potassium, and lithium. The technique is useful in the analysis of bulk drugs, dosage forms, and clinical samples such as blood and urine. 

Excitation of the outer ns electron of the M atom occurs easily and emission spectra are readily observed. We have aheady described the use of the sodium D-line in the emission spectrum of atomic Na for specific rotation measurements (see Section 3.8). When the salt of an alkali metal is treated with concentrated HCl (giving a volatile metal chloride) and is heated strongly in the non-luminous Bunsen flame, a characteristic flame colour is observed (Li, crimson Na, yellow K, lilac Rb, red-violet Cs, blue) and this flame test is used in qualitative analysis to identify the M ion. In quantitative analysis, use is made of the characteristic atomic spectrum in flame photometry or atomic absorption spectroscopy. 

See also Amperometry. Atomic Emission Spectrometry Flame Photometry. Chemiiuminescence Overview Liquid-Phase. Flow Injection Analysis Principles. Fluorescence Quantitative Analysis. Ion Exchange Ion Chromatography Instrumentation. Liquid Chromatography Overview. Ozone. Sampling Theory. Sulfur. Textiles Natural Synthetic. 

Provided it can be excited, the HPO emission is very specific for the identification of P (Figure 14.2). Detection limits down to 0.01 mg/mL of P from the HPO line at 5262 A, and 1 mg/mL of P from the PO line at 2464 A can be reached. These limits are very variable, however, and depend not only on the matrix, but on the nature of the phosphorus compound and the excitation technique which is used. Flame photometry, using HPO emission is in widescale use for the quantitative analysis of organophosphorus pesticides and their decomposition products. 

Emission of UV/VIS radiation Flame photometry, Auger electron spectroscopy (AES) Qualitative and quantitative multielement analysis... 

Atomic absorption spectroscopy involves beaming light of an appropriate wavelength into a flame into which the sample has been sprayed, and thus contains an atomic vapour of the metal. The diminution in the intensity of the radiation is correlated with the concentration of the element. The majority of atoms in the flame remain in the ground state, so the technique is potentially more sensitive than flame photometry. The first application of atomic absorption in quantitative analysis was the determination of mercury by Hewlett in 1930, but it was not until after A. Walsh introduced the hollow cathode lamp as the light source in 1955 that the method came into general use. Today, it is the most widely used method of estimating metals in solution, but is likely to be overtaken in the future by inductively coupled plasma spectroscopy. 

Except for minor differences, the performance of both the techniques is more or less comparable. Flame photometry, however, has a very important advantage over AAS in that it allows simultaneous quantitative multielement analysis to be performed. 

Table 2.3 clearly shows that flame photometry after dope ashing at 500 "C gives a quantitative recovery of sodium relative to results obtained by a non-destmctive method of analysis, i.e., neutron activation analysis (NAA). Direct ashing without the magnesium ashing aid at 500 °C causes losses of >10% of the sodium, whereas direct ashing at 800 °C causes even greater losses. 

Quantitative methods using flame emission photometry cannot be absolute because an unknown, although relatively constant, proportion of the sample will reach the flame of which only a further small proportion of atoms will actually be excited and subsequently emit radiation. Hence it is essential to construct calibration curves for any analysis. The radiation emitted by the flame when pure solvent is sprayed is used to zero the instrument and the maximum reading set when the standard with the highest concentration is sprayed. 

Carbamate pesticides can be determined using different detectors in GC or HPLC analysis. A characteristic feature of a carbamate molecule is the nitrogen atom, which can form the bases for quantitation and some carbamates also contain chlorine, sulfur, or other heteroatoms in the molecule. This allows the use of various detection techniques for their determination (139,140), such as electrical conductivity (165), alkali flame (141) photometry, and mass spectrometry (44,166). 

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