Fraction of Metals Ionized

Flame photometer readings for potassium effect of sodium. Curve A, solutions containing 2 mg K/lOO ml (as KCl) -)- Na (as NaCl), as shown by abscissas Curve B, solutions containing no K, but Na, as shown by abscissas. Asterisks denote ordinate and abscissa for curve A only. (By permission of Domingo and Klyne (D2).) 

If there is a difference in physical properties between the test solution and the standards it is likely that erroneous results will be obtained. This is quite well recognized and can be readily overcome. Together with variation in flame characteristics between test and standard reading, this is the only type of interference in which a lithium internal standard is really effective. 

The determination of sodium and potassium in biological fluids and tissues is so widely practiced that no detailed discussion is necessary. A simple filter instrument with absorption or interference filters is perfectly adequate for most purposes. However, the determination of calcium and magnesium in biological fluids and tissues has proved more difficult and merits further discussion. 

Calcium has a higher excitation potential than sodium and potassium (Table 5), and consequently a higher flame temperature is necessary for its determination. In addition, anionic interference is particularly trouble- 

The determination of magnesium has presented more diflBculty than calcium and this for several reasons the excitation potential of the magnesium line 285.2 mp is 4.3 ev compared with values of 2.1, 1.6, and 

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