18. Refrigerator.
19. Water bath (100
C).
20. Spectrophotometer.
21. 1 cm plastic cuvette.
3 Methods
Use acid-washed plasticware (soaked for 4 h in 6% HCl and rinsed
with deionized water).
3.1 Dissolved Silica
The procedure follows that of Koroleff in the first edition of [6]
and [8].
1. Prepare 3.6 mol/l sulfuric acid solution. Carefully add 10 ml
concentrated acid to 37 ml ultrapure water in a plastic beaker
(see Note 2), cool and make up to 50 ml with ultrapure water in
a volumetric flask.
2. Prepare molybdate solution by dissolving 10 g ammonium
molybdate tetrahydrate in 40 ml ultrapure water slightly heating, and then add ultrapure water to a final volume of 50 ml.
3. Prepare Reagent I by adding 50 ml of the ammonium molybdate tetrahydrate solution (see step 2) to 50 ml 3.6 mol/l
sulfuric acid solution (see Note 3). Store in a polyethylene
bottle at room temperature protected from light.
4. Prepare Reagent II by dissolving 8.8 g oxalic acid in 90 ml
ultrapure water and then add ultrapure water to a final volume
of 100 ml. Store in a polyethylene bottle at room temperature.
5. Prepare Reagent III by dissolving 1.8 g ascorbic acid in 100 ml
ultrapure water. Store in a polyethylene bottle in a refrigerator
(usable as long as colorless) protected from light.
6. Prepare standard solution 1000 mg Si/l by diluting Silicon
standard with ultrapure water to a final volume of 1000 ml.
Store in a polyethylene bottle at room temperature.
7. On the day of analysis, prepare suitable working solutions of
silicon (0–1000 μg Si/l) for calibration by diluting the standard
stock solution (see step 6) with ultrapure water.
8. Prepare analyzer for analyses according to the operation manual (see Note 4). Dilute the reagents 1:10 for analyzer.
9. Place standards in the autosampler of an analyzer or measure
the standards manually by a spectrophotometer for a calibration curve and linearity test (see Note 5).
10. For manual analyses, measure three 35 ml portions of working
standard and three 35 ml portions of ultrapure water for blanks
with graduated cylinder to reaction flasks.
98
Jaana Koistinen et al.
19. Water bath (100
C).
20. Spectrophotometer.
21. 1 cm plastic cuvette.
3 Methods
Use acid-washed plasticware (soaked for 4 h in 6% HCl and rinsed
with deionized water).
3.1 Dissolved Silica
The procedure follows that of Koroleff in the first edition of [6]
and [8].
1. Prepare 3.6 mol/l sulfuric acid solution. Carefully add 10 ml
concentrated acid to 37 ml ultrapure water in a plastic beaker
(see Note 2), cool and make up to 50 ml with ultrapure water in
a volumetric flask.
2. Prepare molybdate solution by dissolving 10 g ammonium
molybdate tetrahydrate in 40 ml ultrapure water slightly heating, and then add ultrapure water to a final volume of 50 ml.
3. Prepare Reagent I by adding 50 ml of the ammonium molybdate tetrahydrate solution (see step 2) to 50 ml 3.6 mol/l
sulfuric acid solution (see Note 3). Store in a polyethylene
bottle at room temperature protected from light.
4. Prepare Reagent II by dissolving 8.8 g oxalic acid in 90 ml
ultrapure water and then add ultrapure water to a final volume
of 100 ml. Store in a polyethylene bottle at room temperature.
5. Prepare Reagent III by dissolving 1.8 g ascorbic acid in 100 ml
ultrapure water. Store in a polyethylene bottle in a refrigerator
(usable as long as colorless) protected from light.
6. Prepare standard solution 1000 mg Si/l by diluting Silicon
standard with ultrapure water to a final volume of 1000 ml.
Store in a polyethylene bottle at room temperature.
7. On the day of analysis, prepare suitable working solutions of
silicon (0–1000 μg Si/l) for calibration by diluting the standard
stock solution (see step 6) with ultrapure water.
8. Prepare analyzer for analyses according to the operation manual (see Note 4). Dilute the reagents 1:10 for analyzer.
9. Place standards in the autosampler of an analyzer or measure
the standards manually by a spectrophotometer for a calibration curve and linearity test (see Note 5).
10. For manual analyses, measure three 35 ml portions of working
standard and three 35 ml portions of ultrapure water for blanks
with graduated cylinder to reaction flasks.
98
Jaana Koistinen et al.