Determination of Zinc Content

NOTE - All reagents used in this test should have as low a content of heavy metals as practicable. All glassware should be rinsed with warm dilute nitric acid followed by water previously distilled in hard or borosilicate glass apparatus. Separators should not be greased with materials that dissolve in chloroform.

Method

Pipette 1 to 5 ml of the preparation under examination into a centrifuge tube graduated at 40 ml. If necessary, add 0.25 M hydrochloric acid dropwise, to obtain a clear solution. Add 5 ml of trichloroacetic acid solution and sufficient water to produce 40.0 ml. Mix well and centrifuge. Pipette into a hard-glass separator a volume of the supernatant liquid equivalent to about 5 to 20 mg of zinc and add water to produce 20 ml. 

Add 1.5 ml of alkaline ammonium citrate solution and 35 ml of dithizone standard solution. Shake vigorously several times and allow the chloroform to separate. Collect the chloroform extract through a cotton plug placed in the stem of the separator and discard the first few ml. Measure the absorbance of the extract at about 530 nm, using as the blank an extract obtained by repeating the determination omitting the preparation under examination.

Calculate the amount of zinc by reference to standard graph obtained by using 0.5 ml, 1.0 ml, 1.5 ml and 2.0 ml of zinc standard solution (10 ppm Zn) and repeating the determination as outlined above.