Calcium flame photometric determination

K4. Kingsley, G. R., and Schaffert, R. R., Micro-flame photometric determination of sodium, potassium, and calcium in serum with organic solvents. J. Biol. Chem. 206, 807-815 (1954). 

L6. Leyton, L., Phosphate interference in the flame-photometric determination of calcium. Analyst 79, 497-500 (1954). 

Strasheim, A., and Nell, J. P., The flame photometric determination of calcium in plant and biological materials. J. S. African Chem. Inst. 7, 79-89 (1954). 

W6. Williams, C. H., The use of lanthanum chloride to prevent interferences in the flame photometric determination of exchangeable calcium in soils. Arud. Chim. Acta 22, 163-171 (1960). 

Yl. Yofe, J., and Firrkelstein, R., Elimination of anionic interference in flame photometric determination of calcium in the presence of phosphate and sulfate. Anal. Chim. Acta 19, 166-173 (1958). 

Z. Fang, J. M. Harris, J. RdiiCka, and E. H. Hansen, Simultaneous Flame Photometric Determination of Lithium, Sodium, Potassium and Calcium by Flow Injection Analysis with Gradient Scanning Standard Addition. Anal. Chem., 57 (1985) 1457. 

Several instrument manufacturers supply flame photometers designed specifically for the determination of sodium, potassium, lithium, and sometimes calcium in blood serum, urine, and other biological fluids. Single-channel and multichannel (two to four channels) instruments are available for these determinations. In the multichannel instruments, each channel can be used to determine a separate element without an internal standard, or one of the channels can be reserved for an internal standard such as lithium. The ratios of the signals from the other channels to the signal of the lithium channel are then taken to compensate for flame noise and noise from fluctuations in reagent flow rate. Flame photometers such as these have been coupled with flow injection systems to automate the sample-introduction process (see Section 33B-3). Typical precisions for flow-injection-analysis-based flame photometric determinations of lithium, sodium, and potassium in serum are on the order of a few percent or less. Automated flow injection procedures require l/KIO the amount of sample and 1/10 the time of batch procedures. -... 

The results obtained with ISEs have been compared several times with those of other methods. When the determination of calcium using the Orion SS-20 analyser was tested, it was found that the results in heparinized whole blood and serum were sufficiently precise and subject to negligible interference from K and Mg ([82]), but that it is necessary to correct for the sodium error, as the ionic strength is adjusted with a sodium salt [82], and that a systematic error appears in the presence of colloids and cells due to complexa-tion and variations in the liquid-junction potential [76]. Determination of sodium and potassium with ISEs is comparable with flame photometric estimation [39, 113, 116] or is even more precise [165], but the values obtained with ISEs in serum are somewhat higher than those from flame photometry and most others methods [3, 25, 27, 113, 116]. This phenomenon is called pseudohyponatremia. It is caused by the fact that the samples are not diluted in ISE measurement, whereas in other methods dilution occurs before and during the measurement. On dilution, part of the water in serum is replaced by lipids and partially soluble serum proteins in samples with abnormally increased level of lipids and/or proteins. 

More recent flame photometric methods rely on direct measurement of the phosphorus emission. If organophosphorus compounds are injected into a hydrogen flame, a continuous emission is obtained in the 490-650 nm region. A broad band system, with an intensity maximum at 526 nm, is superimposed on this background139 it is attributed to the HPO species formed in the flame. An early determination of phosphorus at 0.01-0.04 m concentrations was based on examination of the continuous emission standard and sample solutions were injected into the burner and the intensities were measured at 540 nm the calibration graph was linear down to the detection limit of 10 4 M phosphorus sodium or calcium, if present in the sample, interfered with the results140. 

Calcium may be determined by flame photometry but in common with the other alkaline earth metals it is considered one of the more difficult elements to determine by flame photometric methods because so many extraneous anions and cations cause variations in the intensity of its flame emission. However, with modern instrumentation the difficulties can usually be overcome and most samples can be examined satisfactorily. 

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