Lithium flame photometry

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. 

Nixon277 compared atomic absorption spectroscopy, flame photometry, mass spectroscopy, and neutron activation analysis as methods for the determination of some 21 trace elements (<100 ppm) in hard dental tissue and dental plaque silver, aluminum, arsenic, gold, barium, chromium, copper, fluoride, iron, lithium, manganese, molybdenum, nickel, lead, rubidium, antimony, selenium, tin, strontium, vanadium, and zinc. Brunelle 278) also described procedures for the determination of about 20 elements in soil using a combination of atomic absorption spectroscopy and neutron activation analysis. 

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... 

All the cations of Group 1 produce a characteristic colour in a flame (lithium, red sodium, yellow potassium, violet rubidium, dark red caesium, blue). The test may be applied quantitatively by atomising an aqueous solution containing Group I cations into a flame and determining the intensities of emission over the visible spectrum with a spectrophotometer (flame photometry). 

Flame Photometry, Atomic Absorption, and Neutron Activation. Comparatively few substances amenable to measurement by these techniques are used therapeutically chief among those that are being sodium, potassium, lithium, calcium, magnesium, zinc, copper, and iron, for all of which one or other of the techniques is the method of choice. 

L8. Levy, A. L., and Katz, E. M., A comparison of serum lithium determinations using flame photometry and atomic absorption spectrophotometry. Clin. Chem. 16, 840-842 (1970). 

Conditioning of the manganese oxide suspension with each cation was conducted in a thermostatted cell (25° 0.05°C.) described previously (13). Analyses of residual lithium, potassium, sodium, calcium, and barium were obtained by standard flame photometry techniques on a Beckman DU-2 spectrophotometer with flame attachment. Analyses of copper, nickel, and cobalt were conducted on a Sargent Model XR recording polarograph. Samples for analysis were removed upon equilibration of the system, the solid centrifuged off and analytical concentrations determined from calibration curves. In contrast to Morgan and Stumm (10) who report fairly rapid equilibration, final attainment of equilibrium at constant pH, for example, upon addition of metal ions was often very slow, in some cases of the order of several hours. 

In environmental analysis, flame photometry is most widely used for the determination of potassium, which emits at 766.5 nm. It is also often used for the determination of sodium at 589.0 nm, although spectral interference problems (see Chapter 3) then may be encountered in the presence of excess calcium because of emission from calcium-containing polyatomic species. Molecular species are more likely to be found in cooler flames than in hotter flames. Some instruments use single, interchangeable filters, while others have three or more filters, for example for the determinations of potassium, sodium and lithium,... 

Cesium and lithium analyses were by flame photometry. Uranium (2), neptunium (21), and plutonium (19) analyses were by controlled potential coulometric titration. 

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. 

The general viability of low-temperature flame photometry depends on two factors. First, the alkali and alkaline earth metals of analytical interest (sodium, potassium, lithium, cesium, rubidium, magnesium, calcium, strontium, and barium) reach their excited states at relatively lower temperatures than do most other elements. Second, the emission wavelengths offer enough resolution such that optical filtering can be accomplished at a relatively low cost. 

The analysis of clinical samples represents a typical application of flame photometry. Concentrations of sodium, potassium, and lithium in blood and urine are well within instrument working ranges. The specificity of the technique is a distinct advantage. Automated models of flame photometers, available during the past 25 years, are typically designed to serve the needs of the clinical chemist. Instrument calibration protocols are built into instruments to facilitate the timely analysis of sodium, potassium, and lithium in clinical samples. 

There are at least 25 USP or BP formulation monographs that use flame photometry to assay ions of interest (Table This technique is applicable to a variety of situations because of the relatively low cost per sample (in analyst time, instrument capital expense, and testing supplies) reasonable precision (typical relative standard deviation values are 0.6% for sodium, 1% for potassium, and 2% for lithium) low sample volume requirements (as low as 10 pi in some cases) and ease of operation. 

Potassium can be determined by flame emission spectrometry (flame photometry) using a lithium internal standard. The following data were obtained for standard solutions of KCl and an unknown containing a constant known amount of LiCl as the internal standard. All the intensities were cor-... 

In the early years of flame photometry, only relatively cool flames were used. We shall see below that only a small fraction of atoms of most elements is excited by flames and that the fraction excited increases as the temperature is increased. Consequently, relatively few elements have been determined routinely by flame emission spectrometry, especMly j ew of those that emit line spectra (several can exist in flames as molecular species, particularly as oxides, which emit molecular band spectra). Only the easily excited alkali metals sodium, potassium, and lithium are routinely deterniined by flame emission spectrometry in the clinical laboratory. However, with flames such as oxyacetylene and nitrous oxide-acetylene, over 60 elements can now be determined by flame emission spectrometry. This is in spite of the fact that a small fraction of excited atoms is available for emission. Good sensitivity is achieved because, as with fluorescence (Chapter 16), we are, in principle, measuring the difference between zero and a small but finite signal, and so the sensitivity is limited by the response and stability of the detector and the stability (noise level) of the flame aspiration system. 

Lithium May indicate some pollution AAS, flame photometry... 

The determination of lithium in water is carried out by AAS (methods 3.3.1.2 and 3.3.1.3), or by flame photometry (method 3.3.1.1) - still in use today - according to the "universal method" proposed by Schuhknecht/ Schinkel as described in the section on "Sodium". Since a concentration process is necessary in the case of concentrations of lithium ions below 1 mg/1, a number of departures from the method given for sodium are necessary. Direct determination of traces of lithium is also possible using "stable isotope dilution and field desorption mass spectroscopy" (Schulten et al. 1979). 

In clinical chemistry the determination of sodium, potassium, and calcium is well standardized. In the past decades flame photometry has been reputed to be the mediod of choice in the analysis of biological samples. The advantages of this procedure are a short requirement of time and materials for sample preparation, short duration of the analytical procedure, and the possibility of automation. The procedure became improved due to the application of lithium as internal standard. Excellent precision and accuracy could be obtained in sodium and potassium determination. In calcium determination inaccuracy occurs due to the matrix. It is of disadvantage that only the determination of total calcium and not the differentiation between free and protein bound calcium is possible. Furthermore special equipment (flame photometer) is necessary. 

The second wave of electrochemical devices replaced flame photometry in many clinical laboratories by the ISE method in blood electrolyte (Na, K ) measurements. Improvement of electrochemical technologies played an important role in this development as well as safety considerations related to the use of flame photometry. The measurement of ionized calcium by potentiometry soon followed. The techniques for the potentiometric measurement of chloride, lithium, ionized magnesium, and total calcium are also available but need perfection mainly with respect to avoiding interferences. 

Lithium can be measured by either atomic emission or atomic absorption flame photometry. 

Small quantities of calcium may be determined by flame photometry or atomic absorption. In the absence of suitable apparatus, milligram quantities may be determined by making use of picrolonic acid which forms an insoluble calcium salt. A neutral solution is treated with lithium picrolon-ate, the insoluble calcium salt is filtered off and the excess picrolonate titrated with cetylpyridinium bromide using bromophenol blue as indicator. ... 

Of the different techniques for atomic emission spectroscopy (AES) only those which use a flame or an ICP are of any interest for analysis of biomedical specimens. Flame AES, also called flame photometry, has been an essential technique within clinical laboratories for measuring the major cations, sodium and potassium. This technique, usually with an air-propane flame, was also used to determine lithium in specimens from patients who were given this element to treat depression, and was employed by virtually all clinical laboratories throughout the world until the recent development of reliable, rapid-response ion selective electrodes. Biological fluids need only to be diluted with water and in modern equipment the diluter is an integral part of the instrument so that a specimen of plasma or urine can be introduced without any preliminary treatment. 

The concentration of lithium in serum, plasma, urine, or other body fluids has been determined by flame emission photometry, atomic absorption spectrometry, or electro-chemically using an ion-selective electrode. Serum analysis, the most useful specimen for lithium monitoring, is most commonly quantified by automated spectrophotometric assay. 

Pickett EE and Hawkins JL (1987) Determination of lithium in small animal at physiological levels by flame emission photometry. Anal Biochem 112 213 and 219. 

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