Flame photometry

Flame photometry is the name given to the technique that measures the intensity of the light emitted by analyte atoms in a flame. It is the oldest of all the atomic techniques. It is not highly applicable because of the low temperature of the flame. Only a handful of elements can be measured with this technique, including sodium, potassium, lithium, calcium, strontium, and barium. The technique was formerly used 

Alkali compounds possess the capability to colour a flame by the emission of light rays as they are vaporized in the flame. Each element emits a characteristic spectrum. Over a certain period of time a constant supply of the sample solution is sprayed into the flame, which must burn evenly and non-luminously. The 389 nm spectral line characteristic of sodium is separated out of the light emitted in this way with the aid of a filter, grating or prism, and its intensity is measured with a photometer. 

The use of a buffer solution containing caesium chloride as a spectroscopic buffer and aluminium nitrate as a physical buffer largely eliminates the potential interferences otherwise caused by alkali metals in flame photometry. Since it is easily ionizable, the caesium chloride has the effect of almost totally suppressing the ionization of the K, Na and Li atoms which are also present and exert a mutual influence on excitation. To this must be added the spectroscopic buffer action of caesium which has a smoothing effect on operational fluctuations of the burner. 

The interfering effect of cross sensitivity which occurs in the presence of alkaline earths, particularly calcium, can be suppressed by adding aluminium nitrate. Sparingly volatile alkaline-earth-aluminium compounds are formed which no longer influence the intensity of sodium emission. (See Chapter 2, Flame Emission). 

Depending on the quality of the instrument available, sodium can be determined at concentrations of 0.1 up to 100 mg/1. In addition to parallel determinations and three to five readings per individual determination so as to compensate for fluctuations in the readings of the instrument display, the possibility of further interference and the ubiquitousness of sodium make it necessary to carry out a blank test, the result of which should be taken into account in the evaluation. 

Flame photometer with appropriate filter or with monochromator Pre-chamber atomizer or burner for direct atomization Air-acetylene or air-propane with pre-chamber atomizer Hydrogen-air or hydrogen-oxygen with direct atomization Buffer solution  

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Calcium, strontium and barium produce characteristic flame colours like the Group 1 cations (calcium, orange strontium, red barium, green) and flame photometry can be used for their estimation. All give insoluble carbonates in neutral solution. 

The majoiity of the various analyte measurements made in automated clinical chemistry analyzers involve optical techniques such as absorbance, reflectance, luminescence, and turbidimetric and nephelometric detection means. Some of these ate illustrated in Figure 3. The measurement of electrolytes such as sodium and potassium have generally been accomphshed by flame photometry or ion-selective electrode sensors (qv). However, the development of chromogenic ionophores permits these measurements to be done by absorbance photometry also. 

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). 

The detection and determination of traces of cobalt is of concern in such diverse areas as soflds, plants, fertilizers (qv), stainless and other steels for nuclear energy equipment (see Steel), high purity fissile materials (U, Th), refractory metals (Ta, Nb, Mo, and W), and semiconductors (qv). Useful techniques are spectrophotometry, polarography, emission spectrography, flame photometry, x-ray fluorescence, activation analysis, tracers, and mass spectrography, chromatography, and ion exchange (19) (see Analytical TffiTHODS Spectroscopy, optical Trace and residue analysis). 

Determination of Na " and Na" ions in raw cosmetic materials was conducted with the developed method of flame photometry. A necessity of development of method of samples preparation arose up in the work process, as this spicily-aromatic raw material contained pectin in amount 0.1-0.5% and that prevented preparation of samples by standard method of extracts dilution and required incineration of analyzed sample, time of analysis was increased in 60 times. It was established that CaCl, solution with the concentration 0,4 % caused destmctions of the carbopol gel. It was established that the addition of 0,1% CaCl, and 0,1% NaCl salts solutions into the system intensified the effect of negative action of these salts onto the gel stmcture and the gel destmcted completely. 

Figure 14-9 also shows a flowchart for analysis of wet and dry precipitation. The process involves weight determinations, followed by pH and conductivity measurements, and finally chemical analysis for anions and cations. The pH measurements are made with a well-calibrated pH meter, with extreme care taken to avoid contaminating the sample. The metal ions Ca, Mg, Na, and are determined by flame photometry, which involves absorption of radiation by metal ions in a hot flame. Ammorda and the anions Cl, S04 , NO3 , and P04 are measured by automated colorimetric techniques. 

Sulphur compounds Flame photometry Coulometry UV fluorescence... 

All the alkali metals have characteristic flame colorations due to the ready excitation of the outermost electron, and this is the basis of their analytical determination by flame photometry or atomic absorption spectroscopy. The colours and principal emission (or absorption) wavelengths, X, are given below but it should be noted that these lines do not all refer to the same transition for example, the Na D-line doublet at 589.0, 589.6 nm arises from the 3s — 3p transition in Na atoms formed by reduction of Na+ in the flame, whereas the red line for lithium is associated with the short-lived species LiOH. 

The phenomenon of ion exchange has been confirmed by chemical analysis Films were exposed to potassium chloride solutions of increasing pH, ashed and their potassium content determined by flame photometry. It was found that the potassium content of the films increased as the pH of the solutions rose until saturation was reached at a value which corresponded to that of the change-over in the mechanism of conduction. It was concluded that the change-over in the mechanism of conduction corresponded to the point at which the exchange capacity of the film had reached its limit. 

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. 

Sodium, D. of as zinc uranyl acetate, (g) 467 by flame photometry, 812 Sodium arsenite solution prepn. of standard, 390... 

In flame photometry, signal drift and lamp flicker require that one or a few unknowns be bracketed by calibrations. Here, independent measurements on the same solutions means repeating the whole calibration and measurement cycle. 

Presence of aluminium and calcium. The quantity of aluminium in vaccines containing aluminium hydroxide or aluminium phosphate as an adjuvant is limited to 1.25 mg per dose and it is nsnally estimated compleximetrically. The qnantity of calcium is limited to 1.3 mg per dose and is usually estimated by flame photometry. 

Ion-selective electrodes allow the measurement of ionic activity in diluted or undiluted whole blood, plasma or rum. The direct (undiluted) measurement may be preferred, since no sample pretreatment is necessary and the assay values are independent of hematocrit and amount of solids present. However, direct potentiometry by its very nature does not provide total concentration values similar to those obtained by flame photometry and indirect (diluted) potentiometry... 

Gas chromatograph equipped with a flame photometrie deteetor High-performance liquid ehromatograph... 

If serum sodium is measured by flame photometry ° Uncommon today with the use of ion (sodium) specific... 

Flame Photometry and Gas Chromatography (CyTerra) -Aerodynamic Particle Size and Shape Analysis (BIRAL) -Flow Cytometry (Luminex, LLNL) -Semiconductor-Based Ultraviolet Light (DARPA) -Polymer Fluorochrome (Echo Technology) -Laser-Induced Breakdown Spectroscopy -Raman Scattering -Infrared Absorption -Terahertz Spectroscopy -UV LIDAR... 

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