Most spectrophotometric methods for determining magnesium are based on the formation of lakes or soluble colored complexes. These lakes have some disadvantages for quantitative analysis because reproducibility and stability of the colors are not satisfactory in heterogeneous systems (1). Moreover, the sensitivity of such reactions is not sufficiently high for determining microquantities of magnesium in biological samples. Based on lake formation are the Titan yellow method (2) and azovan blue (Evans' blue) method (3).
On the other hand, colored complexes are formed by the use of eriochrome black T (4)) bis-salicylidenediaminoethane ( 5)) Magon ( 6)) Magon sulfate (7, 8), methylthymol blue complexone (9), and o-cresolphthalein complexone (10) as indicators. Though more sensitive than the methods based on lake formation, these colored complexes are, however, subjected to interference due to, calcium, which always accompanies magnesium in biological materials.
The application of o-cresolphthaiein complexone in the determination of calcium in biological materials, after masking the magnesium with 8-hydroxyquinoline and thus eliminating the step of separating magnesium from calcium, was reported recently from this laboratory (10). Now it remains to be seen whether a similar procedure involving the use of a suitable masking agent and a highly sensitive indicator can be adopted for the determination of traces of magnesium in biological materials. The results of a critical study made in this context are reported below.
METHODS
Reagents
All chemicals were A.R. grade unless otherwise specified. (i) Standard solution of magnesium sulfate, 10 pg Mg2+/ml, obtained