11. Add 1 ml of Reagent I to 35 ml standards and blanks, wait for
10 min, and then add 1 ml each of Reagents II and III and wait
for 30 min (mix gently after each addition).
12. Measure the absorbance of standards and blanks in a 1 cm
cuvette at 810 nm for a calibration curve (see Note 5).
13. Collect the samples in polyethylene bottles and analyze the
samples immediately after collection. The sample can be stored
in a plastic bottle in a refrigerator for about one day.
14. Place samples in the autosampler of an analyzer or perform
manual analyses with a spectrophotometer. Verify proper operation of the instrument with certified reference material and
include ultrapure water blanks in the run (see Note 6).
15. For manual analyses, measure 35 ml of the sample with a
graduated cylinder.
16. Add 1 ml of Reagent I, wait for 10 min, and then add 1 ml each
of Reagents II and III and wait for 30 min (mix gently after
each addition).
17. Measure the absorbance of samples in a 1 cm cuvette at 810 nm
(if the absorbance is greater than that of the highest standard,
prepare diluted sample) and calculate the silicon concentration
by the calibration curve (see Note 7).
3.2 Biogenic Silica
1. Place the polycarbonate filter in the filtration device and apply
suction with the vacuum pump.
2. Pipette a known volume of culture through the filter
(see Note 8).
3. Remove filter and place in a plastic screw-capped plastic bottle.
4. Let the filter dry and store at room temperature in a desiccator
until determination of BSi.
5. Place a clean filter into a vial for laboratory blank (Note 9).
6. Prepare 3.6 mol/l sulfuric acid solution (see Sect. 3.1, step 1).
7. Prepare molybdate solution (see Sect. 3.1, step 2).
8. Prepare Reagent I (see Sect. 3.1, step 3).
9. Prepare Reagent II (see Sect. 3.1, step 4).
10. Prepare Reagent III (see Sect. 3.1, step 5).
11. Prepare standard solution 1000 mg Si/l (see Sect. 3.1, step 6).
12. Prepare 0.2 mol/l sodium hydroxide solution by dissolving 8 g
NaOH in 1000 ml ultrapure water. Store in polyethylene bottle at room temperature.
13. Prepare 0.2 mol/l hydrochloric acid solution. Carefully add
16 ml of concentrated HCl to 500 ml of ultrapure water
(see Note 2), cool and make up to 1000 ml with ultrapure
water. Store in a polyethylene bottle at room temperature.
Determining Dissolved and Biogenic Silica
99
10 min, and then add 1 ml each of Reagents II and III and wait
for 30 min (mix gently after each addition).
12. Measure the absorbance of standards and blanks in a 1 cm
cuvette at 810 nm for a calibration curve (see Note 5).
13. Collect the samples in polyethylene bottles and analyze the
samples immediately after collection. The sample can be stored
in a plastic bottle in a refrigerator for about one day.
14. Place samples in the autosampler of an analyzer or perform
manual analyses with a spectrophotometer. Verify proper operation of the instrument with certified reference material and
include ultrapure water blanks in the run (see Note 6).
15. For manual analyses, measure 35 ml of the sample with a
graduated cylinder.
16. Add 1 ml of Reagent I, wait for 10 min, and then add 1 ml each
of Reagents II and III and wait for 30 min (mix gently after
each addition).
17. Measure the absorbance of samples in a 1 cm cuvette at 810 nm
(if the absorbance is greater than that of the highest standard,
prepare diluted sample) and calculate the silicon concentration
by the calibration curve (see Note 7).
3.2 Biogenic Silica
1. Place the polycarbonate filter in the filtration device and apply
suction with the vacuum pump.
2. Pipette a known volume of culture through the filter
(see Note 8).
3. Remove filter and place in a plastic screw-capped plastic bottle.
4. Let the filter dry and store at room temperature in a desiccator
until determination of BSi.
5. Place a clean filter into a vial for laboratory blank (Note 9).
6. Prepare 3.6 mol/l sulfuric acid solution (see Sect. 3.1, step 1).
7. Prepare molybdate solution (see Sect. 3.1, step 2).
8. Prepare Reagent I (see Sect. 3.1, step 3).
9. Prepare Reagent II (see Sect. 3.1, step 4).
10. Prepare Reagent III (see Sect. 3.1, step 5).
11. Prepare standard solution 1000 mg Si/l (see Sect. 3.1, step 6).
12. Prepare 0.2 mol/l sodium hydroxide solution by dissolving 8 g
NaOH in 1000 ml ultrapure water. Store in polyethylene bottle at room temperature.
13. Prepare 0.2 mol/l hydrochloric acid solution. Carefully add
16 ml of concentrated HCl to 500 ml of ultrapure water
(see Note 2), cool and make up to 1000 ml with ultrapure
water. Store in a polyethylene bottle at room temperature.
Determining Dissolved and Biogenic Silica
99