Hach DR2400 - Page 720

Silica
© Hach Company, 2003. All rights reserved. Printed in the U.S.A. 3/04 1ed
Page 6 of 6 Silica_PT_ULow_HTB_Eng_Ody.fm
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Summary of Method
A number of modifications are necessary to adapt the Low Range Silica method
for analyzing trace levels in the Ultra Low Range method. It is absolutely
necessary to use the one-inch Flow-Thru and liquid reagents. The Flow-Thru
increases the reproducibility of the optics and reduces the instability of the
readings that result from moveable sample cells. Liquid reagents produce more
reproducible readings and lower blank values by eliminating slight turbidity
that may remain when using powdered reagents. In addition, the liquid reagents
are directly used with Hach process analyzers for continuous silica
measurement.
Silica and phosphate in the sample react with molybdate ion under acidic
conditions to form yellow silicomolybdic acid complexes and phosphomolybdic
acid complexes. Addition of citric acid destroys the phosphate complexes.
Amino Acid F Reagent is then added to reduce the yellow silicomolybdic acid to
an intense blue color, which is proportional to the silica concentration. Test
results are measured at 815 nm.
Required Reagents
Quantity Required
Description per test Unit Cat. No.
ULR Silica Reagent Set (using Amino Acid F solution, 100 tests)............................................................25535-00
Includes: (2) 1995-32, (2) 22542-32, (1) 23864-42
ULR Silica Reagent Set (using Amino Acid F ampules, 40 tests) .............................................................25814-00
Includes: (1) 1995-32, (1) 22542-32, (2) 23864-20
Amino Acid F Reagent Solution.............................................................1.0 mL ............. 100 mL...............23864-42
or
Amino Acid F Reagent Solution, 1.2-mL Ampules .............................1 each .............. 20/pkg...............23864-20
Citric Acid Reagent Solution ..................................................................2 mL ................ 500 mL...............22542-49
Molybdate 3 Reagent Solution................................................................2.0 mL ............. 1 L ........................1995-53
Required Apparatus
Adapter, multi-pathlength cell ...............................................................1 ....................... each....................59466-00
Cylinder, graduated, 50-mL, poly ..........................................................1 ....................... each......................1081-41
Flask, Erlenmeyer, 250-mL, PMP, w/cap ..............................................2....................... each....................20898-46
Pipet, TenSette
®
, 0.1 to 1.0 mL ................................................................1 ....................... each ...................19700-01
Pipet Tips, for 19700-01 Pipet..................................................................5 ....................... 50/pkg...............21856-96
Pour-Thru Cell Kit....................................................................................1 ....................... each....................59404-00
Required Standards
Silica Standard Solution, 1 mg/L SiO
2
............................................................................ 500 mL.................1106-49
Silica Standard Solution, 10 mg/L SiO
2
.......................................................................... 500 mL.................1403-49
Silica Standard Solution, 500 µg/L SiO
2
......................................................................... 3.78 L .................21008-17