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Chlorine, Free

DOC316.53.01023

 

 

USEPA DPD Method1

Method 8021

(0.02 to 2.00 mg/L)

Powder Pillows or AccuVac® Ampuls

Scope and Application: For testing free chlorine (hypochlorous acid and hypochlorite ion) in water, treated waters, estuary and seawater. USEPA accepted for reporting for drinking water analyses.2

1 Adapted from Standard Methods for the Examination of Water and Wastewater.

2 Procedure is equivalent to USEPA and Standard Method 4500-Cl G for drinking water.

Test preparation

How to use instrument-specific information

The Instrument-specific information table 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.

Table 1 Instrument-specific information

 

 

Powder pillows

 

AccuVac Ampuls

Instrument

 

 

 

 

 

Sample cell

Cell orientation

Adapter

Sample cell

Adapter

 

 

 

 

 

 

 

DR 5000

2495402

Fill line faces user

A23618

2427606

A23618

 

 

 

 

 

 

DR 2800

2495402

Fill line faces right

—

2122800

LZV584 (C)

 

 

 

 

 

 

DR 2700

2495402

Fill line faces right

—

2122800

LZV584 (C)

 

 

 

 

 

 

DR/2500

2427606

—

—

2427606

—

 

 

 

 

 

 

DR/2400

2427606

—

—

2427606

—

 

 

 

 

 

 

Before starting the test:

If the test over-ranges, dilute the sample with a known volume of high quality, chlorine demand-free water and repeat the test. Some loss of chlorine may occur due to the dilution. Multiply the result by the dilution factor. Alternatively, samples with high chlorine concentrations may be analyzed directly without dilution by using Method 10069, Chlorine, Free HR.

The SwifTest Dispenser for Free Chlorine can be used in place of the powder pillow in step 4.

Analyze samples immediately. Do not preserve for later analysis.

The sample cell shown is a generic representation. Refer to Instrument-specific information for the correct sample cell and adapter configuration.

An empty AccuVac ampule can be used as a blank in place of the sample cell in Step 2.

Do not use the same sample cells for free and total chlorine. If trace iodide from the total chlorine reagent is carried over into the free chlorine determination, monochloramine will interfere. It is best to use separate, dedicated sample cells for free and total chlorine determinations.

Chlorine, Free

Page 1 of 8

Chlorine, Free

Collect the following items:

Description

Quantity

 

 

Powder Pillow Test:

 

 

 

DPD Free Chlorine Reagent Powder Pillows, 10-mL

1

 

 

Sample Cells (see Instrument-specific information)

2

 

 

AccuVac Test:

 

 

 

DPD Free Chlorine Reagent AccuVac® Ampuls

1

Beaker, 50-mL

1

 

 

Sample Cell (see Instrument-specific information)

1

 

 

See Consumables and replacement items for reorder information.

 

Powder pillow procedure

Stored Programs

80 Chlorine, F&T PP

Start

1. Select the test.

Insert an adapter if required (see Instrument- specific information).

Refer to the user manual for orientation.

5. Swirl the sample cell for 20 seconds to mix.

A pink color will develop if chlorine is present. Proceed to step 6 immediately.

2. Blank Preparation:

Fill a sample cell with 10 mL of sample.

6. Within one minute of adding the reagent, insert the prepared sample into the cell holder.

Results are in mg/L Cl2.

3. Wipe the blank and insert it into the cell holder.

ZERO the instrument.

The display will show:

0.00 mg/L Cl2

4. Prepared Sample:

Fill a second cell with 10 mL of sample.

Add the contents of one DPD Free Chlorine Powder Pillow to the sample cell.

Chlorine, Free

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Chlorine,Free

AccuVac Ampuls procedure

Stored Programs

85 Chlorine, F&T AV

Start

1. Select the test.

Insert an adapter if required (see Instrument- specific information).

5. Quickly invert the Ampul several times to mix. Wipe off any liquid or fingerprints.

2. Blank Preparation:

Fill a sample cell with 10-mL of sample.

6. Within one minute after sample addition, wipe the AccuVac Ampul and insert it into the cell holder.

READ the results in mg/L Cl2

3. Wipe the blank and insert it into the cell holder.

ZERO the instrument. The display will show:

0.00 mg/L Cl2

4. Prepared Sample:

Collect at least 40 mL of sample in a 50-mL beaker.

Fill a DPD Free Chlorine Reagent AccuVac Ampul with sample. Keep the tip immersed while the Ampul fills completely.

Chlorine, Free

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Chlorine, Free

Interferences

Table 2 Interfering substances and levels

 

 

Interfering substance

Interference levels and treatments

 

 

 

Greater than 150 mg/L CaCO3. May not develop full color or

 

color may fade instantly. Neutralize to pH 6–7 with

Acidity

1 N Sodium Hydroxide. Determine amount to be added on

 

separate sample aliquot, then add the same amount to the

 

sample being tested. Correct for volume addition.

 

 

 

Greater than 250 mg/L CaCO3. May not develop full color or

 

color may fade instantly. Neutralize to pH 6–7 with 1 N

Alkalinity

Sulfuric Acid. Determine amount to be added on separate

 

sample aliquot, then add the same amount to the sample being

 

tested. Correct for volume addition.

 

 

Bromine, Br2

Interferes at all levels

 

 

Chlorine Dioxide, ClO2

Interferes at all levels

 

 

Chloramines, organic

May interfere

 

 

Hardness

No effect at less than 1000 mg/L as CaCO3

 

 

Iodine, I2

Interferes at all levels

 

 

 

1. Adjust sample pH to 6–7.

 

2. Add 3 drops Potassium Iodide (30-g/L) to a 10-mL

 

 

sample.

Manganese, Oxidized

3.

Mix and wait one minute.

4.

Add 3 drops Sodium Arsenite 1 (5-g/L) and mix.

(Mn4+, Mn7+) or Chromium, Oxidized (Cr6+)

 

 

 

5. Analyze 10 mL of the treated sample as described in

 

 

the procedure.

 

6. Subtract the result from this test from the original

 

 

analysis to obtain the correct chlorine concentration.

 

 

 

Causes a gradual drift to higher readings. When read within

Monochloramine

1 minute after reagent addition, 3 mg/L monochloramine

 

causes less than a 0.1 mg/L increase in the reading.

 

 

Ozone

Interferes at all levels

 

 

Peroxides

May interfere

 

 

Extreme sample pH or Highly buffered samples

Adjust to pH 6–7 using acid (Sulfuric Acid, 1.000 N) or base

(Sodium Hydroxide, 1.00 N).

 

 

 

 

1Samples treated with sodium arsenite for interferences will be hazardous waste as regulated by Federal RCRA for arsenic (D004). See the current MSDS for proper disposal of hazardous material.

Sample collection, preservation and storage

•Analyze samples for chlorine immediately after collection. Free chlorine is a strong oxidizing agent and it is unstable in natural waters. It reacts rapidly with various inorganic compounds and more slowly oxidizes organic compounds. Many factors, including reactant concentrations, sunlight, pH, temperature and salinity influence decomposition of free chlorine in water.

•Avoid plastic containers since these may have a large chlorine demand.

•Pretreat glass sample containers to remove any chlorine demand by soaking in a dilute bleach solution (1 mL commercial bleach to l liter of deionized water) for at least 1 hour. Rinse thoroughly with deionized or distilled water. If sample containers are rinsed thoroughly with deionized or distilled water after use, only occasional pre-treatment is necessary.

Chlorine, Free

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Chlorine,Free

•A common error in testing for chlorine is not obtaining a representative sample. If sampling from a tap, let the water flow for at least 5 minutes to ensure a representative sample. Let the container overflow with the sample several times, then cap the sample containers so there is no headspace (air) above the sample. If sampling with a sample cell, rinse the cell several times with the sample, then carefully fill to the 10-mL mark. Perform the chlorine analysis immediately.

Accuracy check

Standard additions method (Sample spike)

Required for accuracy check:

•Chlorine Standard Solution, 2-mL Voluette® Ampule, 25–30 mg/L

•Breaker Kit, Voluette Ampules

•Pipet, TenSette®, 0.1–1.0 mL

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

2.Select standard additions from the instrument menu:

Instrument

Navigate to:

 

 

DR 5000

OPTIONS>MORE>STANDARD ADDITIONS

 

 

DR 2800

OPTIONS>MORE>STANDARD ADDITIONS

 

 

DR 2700

OPTIONS>MORE>STANDARD ADDITIONS

 

 

DR/2500

OPTIONS>STANDARD ADDITIONS

 

 

DR/2400

OPTIONS>STANDARD ADDITIONS

 

 

3.Enter the average chlorine concentration shown on the certificate that is enclosed with the Voluette ampules.

4.A summary of the standard additions procedure will be displayed. Press OK to 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.

5.Open one Voluette ampule standard.

6.Prepare spiked samples: add 0.1 mL, 0.2 mL and 0.3 mL of standard to three 10-mL portions of fresh sample.

Note: For AccuVac® Ampuls, add 0.4 mL, 0.8 mL and 1.2 mL of standard to three 50-mL portions of fresh sample.

7.Follow the test procedure for each of the spiked samples using the powder pillows or AccuVac ampules, starting with the 0.1 mL sample spike. Measure each of the spiked samples in the instrument.

8.Select GRAPH to view the results. Select IDEAL LINE (or best-fit) to compare the standard addition results to the theoretical 100% recovery.

Note: If results are not within acceptable limits (± 10%), be sure that the sample volumes and sample spikes are measured accurately. The sample volumes and sample spikes that are used should agree with the selections in the standard additions menu. If all procedures are followed correctly but the standard additions results are not within acceptable limits, the sample may contain an interference.

Chlorine, Free

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Chlorine, Free

Method performance

 

 

 

Precision

Sensitivity

Program

Instrument

Standard

95% Confidence Limits of

Concentration change

 

 

 

Distribution

per 0.010 Abs change

 

 

 

 

 

80

DR 5000

1.25 mg/L Cl2

1.23–1.27 mg/L Cl2

0.02 mg/L Cl2

 

DR 2800

1.25 mg/L Cl2

1.23–1.27 mg/L Cl2

0.02 mg/L Cl2

 

DR 2700

1.25 mg/L Cl2

1.23–1.27 mg/L Cl2

0.02 mg/L Cl2

 

DR/2500

1.07 mg/L Cl2

1.00–1.14 mg/L Cl2

0.02 mg/L Cl2

 

DR/2400

1.07 mg/L Cl2

1.00–1.14 mg/L Cl2

0.02 mg/L Cl2

 

 

 

Precision

Sensitivity

Program

Instrument

Standard

95% Confidence Limits of

Concentration change

 

 

 

Distribution

per 0.010 Abs change

 

 

 

 

 

85

DR 5000

1.25 mg/L Cl2

1.21–1.29 mg/L Cl2

0.02 mg/L Cl2

 

DR 2800

1.25 mg/L Cl2

1.21–1.29 mg/L Cl2

0.02 mg/L Cl2

 

DR 2700

1.25 mg/L Cl2

1.21–1.29 mg/L Cl2

0.02 mg/L Cl2

 

DR/2500

1.07 mg/L Cl2

1.03–1.11 mg/L Cl2

0.02 mg/L Cl2

 

DR/2400

1.07 mg/L Cl2

1.03–1.11 mg/L Cl2

0.02 mg/L Cl2

Summary of method

Chlorine in the sample as hypochlorous acid or hypochlorite ion (free chlorine or free available chlorine) immediately reacts with DPD (N,N-diethyl-p-phenylenediamine) indicator to form a pink color, the intensity of which is proportional to the chlorine concentration.

Chlorine, Free

Page 6 of 8

 

 

 

Chlorine,Free

 

 

 

 

Consumables and replacement items

 

 

 

Required reagents

 

 

 

 

 

 

 

Description

Quantity/Test

Unit

Catalog number

 

 

 

 

DPD Free Chlorine Reagent Powder Pillows, 10-mL

1

100/pkg

2105569

 

 

 

 

OR

 

 

 

 

 

 

 

DPD Free Chlorine Reagent AccuVac® Ampuls

1

1

2502025

Required apparatus (AccuVac)

 

 

 

 

 

 

 

Description

Quantity/Test

Unit

Catalog number

 

 

 

 

Beaker, 50-mL

1

each

50041H

 

 

 

 

AccuVac Snapper

1

each

2405200

 

 

 

 

Recommended standards

 

 

 

 

 

 

 

Description

 

Unit

Catalog number

 

 

 

 

Chlorine Standard Solution, 2-mL PourRite® Ampule, 25–30 mg/L

 

20/pkg

2630020

PourRite Ampule breaker, 2-mL

 

each

 

 

 

 

 

Optional reagents and apparatus

 

 

 

 

 

 

 

Description

 

Unit

Catalog number

 

 

 

 

Chlorine-demand Free Water

 

500 mL

2641549

 

 

 

 

Cylinder, mixing

 

25 mL

2088640

 

 

 

 

Cylinder, mixing

 

50 mL

189641

 

 

 

 

Sodium Hydroxide, 1 N

 

100 mL

104532

 

 

 

 

Sulfuric Acid, 1 N

 

100 mL

127032

 

 

 

 

Potassium Iodide, 30-g/L

 

100 mL

34332

 

 

 

 

Sodium Arsenite, 5-g/L

 

100 mL

104732

 

 

 

 

SwifTest Dispenser for Free Chlorine1

 

—

2802300

Pipet, TenSette®, Pipet, 0.1 - 1.0 mL

 

each

1970001

Pipet Tips, for TenSette Pipet 19700012

 

50/pkg

2185696

Pipet Tips, for TenSette Pipet 19700011

 

1000/pkg

2185628

pH Paper, 0 - 14 pH range

 

100/pkg

2601300

 

 

 

 

Voluette Ampule breaker 10 mL

 

each

2196800

 

 

 

 

AccuVac, vials for sample blanks

 

25/pkg

2677925

 

 

 

 

Chlorine Standard Solution, 2-mL PourRite® Ampule, 50–75 mg/L

 

20/pkg

1426820

 

 

 

 

Chlorine Standard Solution, 10-mL Voluette® Ampule, 50–75 mg/L

 

16/pkg

1426810

 

 

 

 

DPD Free Chlorine Reagent Powder Pillows, 10-mL

 

1000/pkg

2105528

 

 

 

 

DPD Free Chlorine Reagent Powder Pillows, 10-mL

 

300/pkg

2105503

 

 

 

 

DPD Free Chlorine Reagent, 10 mL, SwifTest Dispenser refill vial

 

250 tests

2105560

 

 

 

 

SpecCheck Secondary Standard Kit, Chlorine DPD

 

0–2.0 mg/L

2635300

 

 

 

 

1 Includes one vial of 2105560 for 250 tests

2 Other sizes are available

Chlorine, Free

Page 7 of 8

FOR TECHNICAL ASSISTANCE, PRICE INFORMATION AND ORDERING:

HACH COMPANY

In the U.S.A. – Call toll-free 800-227-4224

WORLD HEADQUARTERS

Outside the U.S.A. – Contact the HACH office or distributor serving you.

Telephone: (970) 669-3050

On the Worldwide Web – www.hach.com; E-mail – techhelp@hach.com

FAX: (970) 669-2932

 

 

 

© Hach Company, 2007. All rights reserved. Printed in the U.S.A.

Updated February 2008, Edition 5