30
Installation
4.11.4 Reagent 3 - Reducing reagent
• Rinse a 2 liter volumetric flask three times with ultra pure water
• Fill two-thirds of the flask with ultra pure water which has less than 5 ppb of SiO
2
• Stirring continuously, gently pour 25mL of sulfuric acid into the water
• Stirring continuously, gently add 40g of ammonium-iron(II) sulfate hexahydrate to the
solution
• Top up the solution to 2 liters with additional ultra pure water, and transfer the solution to
the canister labelled R3
4.11.5 Calibration solution
CONCENTRATED SOLUTION
Use of Titrisol® (Merck) cartridge
Dilute one cartridge of Titrisol® Merck 109947 solution with one liter of demineralized water to
give a concentration of 1000 mg/liter of Si, i.e. 2139 mg/liter of SiO
2
. Dilute this solution 100
times, i.e. 10 mL per liter to give a concentration of 10 mg/liter of Si, i.e. 21.39 mg/liter SiO
2
.
CALIBRATION SOLUTION
By diluting the concentrated solution (at 21.39 mg/liters) with demineralized water, various
calibration solutions with a known concentration of SiO
2
may be prepared. The following table
gives the nominal values when using demineralized water having a zero concentration of silica:
Given that the demineralized water may often have a non-zero silica content, use of one two
methods for determining the nominal silica values of the final calibration solution. On
completion, transfer 2 liters of the solution to the calibration canister labelled CAL.
Note: It is recommended to use demineralized water with a silica content of no more than 5 ppb when
diluting the concentrated solution.
Method 1:
Determine the silica content of the demineralized water by using a laboratory measurement
technique (e.g. Hach Lange laboratory photometer), or by using the grab sample mode of an
accurately calibrated POLYMETRON 9210 if available on site. The concentration value can then
be added to the values in the above table, giving the following revised table when (for example)
using demineralized water with a silica content of 5 ppb (which equates to 2.33 ppb Si):
Label Composition Concentration
R3 Ammonium-iron(II) sulfate hexahydrate (NH
4
)
2
Fe(SO
4
)
2
, 6H
2
O
(Puriss analytical grade; Fluka# 09720, Merck# 103792 or equivalent)
20 g/L
Sulfuric acid (H
2
SO
4
) (95-97%; Fluka# 84721 or equivalent) 12.5 mL/L
mL of concentrated
solution 21.39 mg/l
Calibration solution
ppb Si
Calibration solution
ppb SiO
2
Analyzer measuring
range
10 50 107 0-200 ppb
20 100 213.9 0-200 ppb
25 125 267.4 0-500 ppb
50 250 534.8 0-1000 ppb
mL of concentrated
solution 21.39 mg/l
Calibration solution
ppb Si
Calibration solution
ppb SiO
2
Analyzer measuring
range
10 52.3 112 0-200 ppb
20 102.3 218.9 0-200 ppb
25 127.3 272.4 0-500 ppb
50 252.3 539.8 0-1000 ppb
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