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Silica, 8282

How to use instrument-specific information

The Instrument-specific informationtable displays requirements that may vary between

instruments. To use this table, select an instrument then read across to find the corresponding

information required to perform this test.

Silica DOC316.53.01130Heteropoly Blue Method1

1 Adapted fromStandard Methods for the Examination of Water and Wastewater.

Method 8282

ULR(3 to 1000 g/L as SiO2) Pour-Thru Cell

Scope and Application: For testing trace levels of soluble silica in pure and ultrapure water

Test preparation

Table 383 Instrument-specific information

Instrument Pour-Thru Kit Cell Orientation Adapter

DR 6000 LQV175.99.20002 Arrow faces right

DR 5000 LZV479

DR 3900LQV157.99.10002 Align cell flow arrows with arrows on cell

compartment

DR 3800, DR 2800, DR 27005940400 1-inch (round) path aligned with arrow on

the adapter

LZV585 (B)

Before starting the test:

See the user manual for Pour-Thru Module installation instructions.

Clean the Pour-Thru cell and all labware as specified in Labware.

Protect the Pour-Thru Cell from contamination when not in use by inverting a small beaker over the top of the glass funnel.

See Reagent preparationfor instructions on preparing the Amino Acid F Reagent.

The four-minute reaction time in step 10is for samples at 20 C; for samples at 10 C, wait eight minutes; for samples at

30 C, wait two minutes.

The one-minute reaction time in step 12is for samples at 20 C; for samples at 10 C, wait two minutes; for samples at

30 C, wait 30 seconds.

Make sure the PourThru cell is completely seated in the sample cell compartment.

Collect the following items:

Description Quantity

Amino Acid F Reagent Solution 1 mL

Citric Acid F Reagent 1 mL

Molybdate 3 Reagent 1 mL

Cylinder, graduated, 50-mL, poly 1

Flask, Erlenmeyer, 250-mL, PMP, with cap 2

Pipet, TenSette, 0.1 to 1.0 mL with tips 1

http://doc316.53.01000.pdf/http://doc316.53.01000.pdf/http://doc316.53.01000.pdf/http://doc316.53.01000.pdf/http://doc316.53.01000.pdf/http://doc316.53.01000.pdf/http://doc316.53.01000.pdf/http://doc316.53.01000.pdf/http://doc316.53.01000.pdf/

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Silica

See Consumables and replacement itemsfor reorder information.

Heteropoly Blue method

1. Select the test.

Insert an adapter if

required (see Instrument-

specific information).

2. Activate the reagent

blank option to account forthe Molybdate 3 reagent

blank. The value is printed

on the reagent blank.

3. Use the numeric

keypad on the instrumentto manually adjust the

reagent blank value.

4. Fill two clean 250-mL

Erlenmeyer flasks tooverflowing with sample.

5. Fill a clean 50-mL

plastic graduated cylinder

with sample from one of

the flasks; then discard the

contents of the cylinder.

Repeat three times.

6. Fill the rinsed cylinder

to the 50-mL mark with

sample from the same

flask. Discard any

remaining sample in the

flask.

7. Pour the contents of

the 50-mL cylinder back

into the original flask.

8. Repeat steps 5

through 7for the second

flask containing sample.

Collect the following items:

Description Quantity

645 Silica ULR

Stored Programs

Start

Reagent Blank

ON

Repeat

Steps 57

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9. Use a TenSettePipet

to add 1.0 mL of

Molybdate 3 Reagent to

each flask. Swirl to mix.

10. Start the instrument

timer.

A four-minute reaction

period will begin.

11. When the timer

expires, add 1.0 mL of

Citric Acid F Reagent to

each flask. Swirl to mix.

12. Start the instrument

timer.

A one-minute reaction

period will begin. The

destruction of possible

phosphate interference

occurs during this period.

13. When the timer

expires, pour the contentsof one flask into the

Pour-Thru Cell.

14. After the flow stops,

ZEROthe instrument.

The display will show:

0 g/L SiO2

15. Add 1.0 mL of Amino

Acid F Reagent to theremaining flask. Swirl to

mix.

A faint blue color will

develop if silica is present.

16. Wait at least 15

seconds, then pour thecontents of the second

flask into the Pour-Thru

Cell.

17. READthe results in

mg/L SiO2.

18. Flush the Pour-Thru

Cell with at least 50 mL of

deionized water

immediately after use.

Heteropoly Blue method (continued)

Zero

Read

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Silica

Interferences

Table 384 Interfering substances

Interfering substance Interference level

Color Eliminated by zeroing the instrument with the blank (follow procedure).

Iron Interferes at high levels.

pH (extreme) Adjust pH to less than 7.

Phosphate (PO43) Interferes at levels greater than 50 mg/L PO4

3.

Sulfides Interfere at all levels.

Turbidity Eliminated by zeroing the instrument with the blank (follow procedure).

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Sample collection, preservation and storage

Use only plastic containers with tight-fitting closures. Do not use glass containers; they will

contaminate the sample with silica.

Soak sampling containers with a solution made of one part Molybdate 3 Reagent to 50 parts of

high quality deionized water of low silica concentration. Fill the containers completely and let

stand for several hours. Rinse thoroughly with low-level silica water, drain and close. Repeat

this cleaning periodically.

Allow the sample stream to flow for 12 minutes before collection. Do not adjust the flow

during the sampling period as this may introduce particulates.

Rinse the container well with sample before collecting the portion for analysis.

Analyze samples as soon as possible.

Reagent preparation

Amino Acid F Reagent Solution is available in either 100-mL bottles or a package of 20 unit-dose

ampules. The bottled reagent is stable for up to one year if the bottle is kept closed when not in

use. The ampuled reagent is sealed under argon and is more stable with a shelf life greater than 1

year. Reduced sensitivity at high concentrations (1000 g/L) indicates reagent instability. Checkthe bottled reagent on a routine basis by performing an analysis on a 1-mg/L (1000 g/L) Silica

Standard Solution. If the concentration is less than 950 g/L, use a fresh bottle of Amino Acid F

Reagent Solution.

Prepare larger or smaller volumes of Amino Acid F Reagent by dissolving Amino Acid F Reagent

Powder in Amino Acid F Reagent Solvent at a ratio of 11 grams per 100 mL of reagent solvent.

These reagents are available as the Amino Acid F Reagent Package. This prepared solution has

limited stability; test routinely with the 1-mg/L Silica Standard Solution.

Labware

All containers used in this test must be cleansed thoroughly to remove any traces of silica. Use

plastic containers for all analysis and storage because glass can contaminate the sample withsilica. Small bottles or flasks with screw-type closures work well.

1. Clean containers by normal means (do not use phosphate detergents), then rinse with high

quality deionized water of low-level silica concentration.

2. Soak for 10 minutes with a 1:50 dilution of Molybdate 3 Reagent in low-level silica water.

3. Rinse repeatedly with either low-level silica water or the sample before use. Keep containers

tightly closed when not in use.

4. Fill the Pour-Thru Cell with this same mixture of Molybdate 3 and water and let stand for

several minutes before use.

5. Rinse with low-level silica water.

Cleaning the Pour-Thru Cell

The Pour-Thru Cell may accumulate a buildup of colored products, especially if the reacted

solutions are allowed to stand in the cell for long periods after measurement.

1. Remove the color by rinsing with a 1:5 dilution of ammonium hydroxide and deionized water.

2. Rinse several times with deionized water.

3. Cover the Pour-Thru Cell when it is not in use.

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Silica

Accuracy check

Standard additions method (sample spike)

Required for accuracy check:

1-mg/L (1000-g/L) Silica standard

TenSette Pipet and Pipet tips.

250-mL plastic Erlenmeyer flasks (3)

1. After reading test results, leave the sample cell (unspiked sample) in the instrument. Verify the

chemical form.

2. Select standard additions from the instrument menu: OPTIONS>MORE>STANDARD

ADDITION.

3. Accept the default values for standard concentration, sample volume and spike volumes. After

the values are accepted, the unspiked sample reading will appear in the top row. See the user

manual for more information.

4. Prepare three samples. Fill three plastic Erlenmeyer flasks with 50 mL of prepared sample.

5. Use the TenSette Pipet to prepare spiked samples: add 0.2 mL, 0.4 mL and 0.6 mL of the1-mg/L standard to each flask and mix thoroughly.

6. Follow the Heteropoly Blue methodtest procedure for each of the spiked samples, starting

with the 0.2 mL sample spike. Measure each of the spiked samples in the instrument.

7. Select GRAPHto view the results. Select IDEAL LINE (or best-fit) to compare the standard

addition results to the theoretical 100% recovery.

Standard solution methodNote: Refer to the instrument user manual for specific software navigation instructions.

Required for accuracy check:

500-g/L SiO2Standard Solution

1. Use a 500-g/L SiO2Standard Solution in place of the sample. Follow the Heteropoly Blue

methodtest procedure.

2. To adjust the calibration curve using the reading obtained with the standard solution, navigate

to Standard Adjust in the software: OPTIONS>MORE>STANDARD ADJUST.

3. Turn on the Standard Adjust feature and accept the displayed concentration. If an alternate

concentration is used, enter the concentration and adjust the curve to that value.

Method performance

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 Pour-

Thru Cell and liquid reagents. The Pour-Thru Cell 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

Program Instrument StandardPrecision95% Confidence

Limits of Distribution

SensitivityConcentration

per 0.010 Abs

645 DR 5000 500 g/L silica 496504 g/L silica 13 g/L silica

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remain when using powdered reagents. Use of liquid reagents in continuous monitors for silica

provides a means of confirming the analyzer performance.

Silica and phosphate in the sample react with molybdate ions 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.

Consumables and replacement items

Required reagents

Description Quantity/Test Unit Catalog number

ULR Silica Reagent Set (using Amino Acid F solution, 100 tests) 2553500

Includes: (2) 199532, (2) 2254232, (1) 2386442

ULR Silica Reagent Set (using Amino Acid F ampules, 40 tests) 2581400

Includes: (1) 199532, (1) 2254232, (2) 2386420

Amino Acid F Reagent Solution 1.0 mL 100 mL 2386442OR

Amino Acid F Reagent Solution, 1.2-mL Ampules 1 20/pkg 2386420

Citric Acid Reagent Solution 2 mL 500 mL 2254249

Molybdate 3 Reagent Solution 2.0 mL 500 mL 199549

Required apparatus

Description Quantity Unit Catalog number

Cylinder, graduated, 50-mL, poly 1 each 108141

Flask, Erlenmeyer, 250-mL, PMP, w/cap 2 each 2089846

Pipet, TenSette, 0.1 to 1.0 mL 1 each 1970001

Pipet Tips, for TenSette Pipet 19700-01 5 50/pkg 2185696

Recommended standards

Description Unit Catalog number

Silica Standard Solution, 1-mg/L SiO2 500 mL 110649

Silica Standard Solution, 500-g/L SiO2 3.78 L 2100817

Water, deionized 4 L 27256

http://www.hach.com/hc/search.product.details.invoker/PackagingCode=2553500http://www.hach.com/hc/search.product.details.invoker/PackagingCode=2581400http://www.hach.com/hc/search.product.details.invoker/PackagingCode=2386442http://www.hach.com/hc/search.product.details.invoker/PackagingCode=2386420http://www.hach.com/hc/search.product.details.invoker/PackagingCode=2254249http://www.hach.com/hc/search.product.details.invoker/PackagingCode=199549http://www.hach.com/hc/search.product.details.invoker/PackagingCode=199549http://www.hach.com/hc/search.product.details.invoker/PackagingCode=2254249http://www.hach.com/hc/search.product.details.invoker/PackagingCode=2386420http://www.hach.com/hc/search.product.details.invoker/PackagingCode=2386442http://www.hach.com/hc/search.product.details.invoker/PackagingCode=2581400http://www.hach.com/hc/search.product.details.invoker/PackagingCode=2553500

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HACH COMPANYWORLD HEADQUARTERSTelephone: (970) 669-3050

FAX: (970) 669-2932

FOR TECHNICAL ASSISTANCE, PRICE INFORMATION AND ORDERING:Call 800-227-4224

Contact the HACH office or distributor serving you.

www.hach.com techhelp@hach.com

In the U.S.A.

Outside the U.S.A.

On the Worldwide Web ; E-mail

toll-free

Hach Company, 2007, 2010, 2012. All rights reserved. Printed in the U.S.A. Edition 7

Optional reagents and apparatus

Description Unit Catalog number

Ammonium Hydroxide, 58% 500 mL 10649

Molybdate 3 Reagent 2.9 L 199503

Molybdate 3 Reagent 3.78 L 199517

Molybdate 3 Reagent 100 mL 199532

Molybdate 3 Reagent 1 L 199553

PourRiteampule breaker each 2484600

Amino Acid F reagent package each 2254117

Sampling Bottle with cap, low density polyethylene, 500 mL 12/pkg 2087079

Thermometer, Non-Mercury, -10 to 225 C each 2635700