Hach DR2400 - Page 710

Silica
© Hach Company, 2003. All rights reserved. Printed in the U.S.A. 3/04 1ed
Page 4 of 4 Silica_PP_High_SLM_Eng_Ody.fm
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Method Performance
Precision
Standard: 50.0 mg/L SiO
2
See Section 3.4.3 Precision on page 44 for more information, or if the standard
concentration did not fall within the specified range.
Sensitivity
See Section 3.4.5 Sensitivity on page 44 for more information.
Summary of Method
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. Silica
is then determined by measuring the remaining yellow color. Test results are
measured at 452 nm.
Required Reagents
Quantity Required
Description per test Unit Cat. No.
High Range Silica Reagent Set for 10-mL samples (100 tests) ..................................................................24296-00
Includes:
Acid Reagent Powder Pillows for High Range Silica...................1 ....................... 100/pkg.............21074-69
Citric Acid Powder Pillows ..............................................................1 ....................... 100/pkg.............21062-69
Molybdate Reagent Powder Pillows for High Range Silica ........1 ....................... 100/pkg.............21073-69
Water, deionized .......................................................................................10 mL .............. 4 liters....................272-56
Required Apparatus
Clippers, for opening powder pillows ..................................................1 ....................... each........................968-00
Sample Cells, 10-mL, w/cap...................................................................2 ....................... 6/pkg.................24276-06
Required Standards
Silica Standard Solution, 50-mg/L................................................................................... 200 mL.................1117-29
Silica Standard Solution, 1000-mg/L............................................................................... 500 mL...................194-49
Program 95% Confidence Limits of Distribution
656 43.2–56.8 mg/L SiO
2
Portion of Curve ∆Abs ∆Concentration
Entire range 0.010 1.1 mg/L SiO
2