Abstract
The photometric method using Phenazo was applied to the determination of a small amount of magnesium in common salt. The colored magnesium-Phenazo lake had the maximum absorption of 580 mμ in sodium hydroxide solution. The proposed method was as follows:
Weigh 10g. of common salt, dissolve with water and dilute to 500 ml. exactly with water. Pipet a 5-25 ml.(Mg2+ 0.02-0.13 mg.) aliquot into a 100ml. volumetric flask, add 5 ml. of polyvinyl alcohol (1%), 5 ml. of potassium cyanide (1%), 5 ml. of hydroxylamine-hydrochloride (1%), 5 ml. of Phenazo (0.005%) and 5 ml. of sodium hydroxide solution (20%), and dilute to the mark with water.
The color was stable for 60 min., and sodium and calcium did not interfere. The calibration curve followed Beer's law in the range of 0.01-0.15mg. magnesium per 100 ml. of water.
The time required for the determination of magnesium was about 40 min, and good results were obtained.
