|
ASSAY.
(By complexometric titration of Mn). Weigh
accurately 0.8 g, transfer to a 500-mL beaker, and dissolve in 200
mL of water. Add a few milligrams of ascorbic acid to prevent
oxidation. From a burette, add about 30 mL of standard 0.1 M EDTA. Now
add 10 mL of pH 10 ammoniacal buffer solution and about 50 mg of
Eriochrome Black T indicator mixture. Continue the titration with
EDTA to a clear blue color (and disappearance of the last trace of
red). One milliliter of 0.1 M EDTA corresponds to 0.01979 g of MnCl2
. 4H2O.
% MnCl2 · 4H2O = (mL
× M EDTA × 19.79) / Sample wt (g)
pH OF A 5% SOLUTION. The pH
should be 3.5-6.0 at 25 C.
INSOLUBLE MATTER. Use 20 g
dissolved in 150 mL of water.
SULFATE.
Dissolve 10 g in 100 mL of water, add
1 mL of hydrochloric acid, filter, and heat the filtrate to boiling.
Add 10 mL of barium chloride reagent solution, digest in a covered
beaker on a hot plate ( 100C)
for 2 h, and allow to stand overnight. If a precipitate is formed,
filter through a fine ash less paper, wash thoroughly, and ignite.
Correct for the weight obtained in a complete blank test.
HEAVY METALS.
Dissolve 6.0 g in about 20 mL
of water, and dilute with water to 30 mL. Use 25 mL to prepare the
sample solution, and use the remaining 5.0 mL to prepare the control
solution. Adjust the pH with ammonium acetate solution.
IRON.
Use 2.0 g.
CALCIUM,
MAGNESIUM, POTASSIUM, SODIUM, AND ZINC.
(By flame AAS 39).
Sample Stock
Solution. Dissolve 5.0 g in
water in a 100-mL volumetric flask, add 0.5 mL of hydrochloric acid,
and dilute with water to the mark (1 mL = 0.05 g).
|
Element
|
Wavelength (nm)
|
Sample Wt (g) |
Standard Added (mg)
|
Flame Type* |
Background Correction
|
|
Ca |
422.7 |
0.80 |
0.02; 0.04 |
N/A |
No |
|
Mg |
285.2 |
0.20 |
0.005; 0.01 |
A/A |
Yes |
|
K |
766.5 |
0.20 |
0.01; 0.02 |
A/A |
No |
|
Na |
589.0 |
0.04 |
0.01; 0.02 |
A/A |
No |
|
Zn |
213.9 |
0.20 |
0.01; 0.02 |
A/A |
Yes |
*A/A is air
acetylene; N/A is nitrous oxide/acetylene. |
