Hach DR 6000 Manual de usuario

Arsenic DOC316.53.01005

Silver Diethyldithiocarbamate Method1Method 8013

0 to 0.200 mg/L As

Scope and application: For water, wastewater and seawater. Distillation is required. USEPA accepted2 for

reporting for drinking and wastewater analysis.

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

2Procedure is equivalent to Standard Method 3500-As for drinking water analysis.

Test preparation

Instrument-specific information

Table 1 shows all of the instruments that can make a user calibration program for this

test. The table also shows sample cell and orientation requirements for reagent addition

tests, such as powder pillow or bulk reagent tests.

To use the table, select an instrument, then read across to find the applicable information

for this test.

Table 1 Instrument-specific information

Instrument Sample cell orientation Sample cell

DR 6000

DR 3800

DR 2800

DR 2700

DR 1900

The fill line is to the right. 2612602

DR 5000

DR 3900

The fill line is toward the user.

Before starting

A manual calibration is necessary for this procedure, refer to Calibration on page 5. Make a new calibration and update

the user program for each new lot of arsenic absorber solution.

Prepare the arsenic absorber solution before starting the test procedure. Refer to Reagent preparation on page 5.

Set up the distillation apparatus in a fume hood to prevent exposure to hazardous gas.

In bright light conditions (e.g., direct sunlight), close the cell compartment, if applicable, with the protective cover during

measurements.

Do not use the Pour-Thru Cell or sipper module (for applicable instruments) with this test.

Review the Safety Data Sheets (MSDS/SDS) for the chemicals that are used. Use the recommended personal protective

equipment.

Dispose of reacted solutions according to local, state and federal regulations. Refer to the Safety Data Sheets for disposal

information for unused reagents. Refer to the environmental, health and safety staff for your facility and/or local regulatory

agencies for further disposal information.

Items to collect

Description Quantity

Apparatus (refer to Required apparatus on page 7) –

Arsenic Standard Solution, 1000–mg/L As varies

Hydrochloric Acid, ACS 25 mL

Items to collect (continued)

Description Quantity

Lead Acetate Solution, 10% 1 mL

Potassium Iodide Solution, 20% 3 mL

Pyridine, ACS 50 mL

Sample cells (For information about sample cells, adapters or light shields, refer to Instrument-

specific information on page 1.) 2

Silver Diethyldithiocarbamate 1 g

Stannous Chloride Solution 1 mL

Water, deionized varies

Zinc, 20-mesh, ACS 6 g

Refer to Consumables and replacement items on page 6 for order information.

Sample collection and storage

• Collect samples in clean glass or plastic bottles that have been cleaned with 6 N (1:1)

hydrochloric acid and rinsed with deionized water.

• To preserve samples for later analysis, adjust the sample pH to less than 2 with

concentrated sulfuric acid (approximately 2 mL per liter). No acid addition is

necessary if the sample is tested immediately.

• Keep the preserved samples at room temperature for a maximum of 6 months.

• Before analysis, adjust the pH to approximately 7 with 5 N sodium hydroxide solution.

• Correct the test result for the dilution caused by the volume additions.

Test procedure

WARNING

Gas inhalation hazard. Operate the instrument in a fume hood to prevent exposure to

hazardous gas.

User Programs

1. Prepare a calibration and

user program for this

method. Refer to Enter the

calibration as a user

program on page 5.

Record the program

number.

Select User Programs.

Start

2. Start the user-entered

program from step 1. For

information about sample

cells, adapters or light

shields, refer to Instrument-

specific information

on page 1.

3. Prepare the distillation

apparatus, refer to the

Distillation Manual for

assembly instructions. Do

not connect to the

aspirator.

4. Soak a cotton ball with

10% Lead Acetate Solution.

Put the cotton ball in the gas

scrubber. Make sure that

the cotton seals against the

glass.

2Arsenic Silver Diethyldithiocarbamate Method (0.200 mg/L)

5. Use a graduated cylinder

to pour 25-mL of prepared

arsenic absorber solution

(refer to Reagent

preparation on page 5)

into the cylinder/gas bubbler

assembly.

6. Attach the cylinder/gas

bubbler assembly to the

distillation apparatus.

7. Use a graduated cylinder

to pour 250 mL of sample

into the distillation flask.

8. Set the heater power to

on. Set the stir control to 5.

Set the heat control to 0.

9. Use a graduated cylinder

to add 25 mL of

Hydrochloric Acid ACS to

the distillation flask.

10. Use a serological pipet

to add 1 mL of Stannous

Chloride Solution to the

distillation flask.

11. Use a serological pipet

to add 3 mL of Potassium

Iodide Solution to the

distillation flask. Put the cap

on the flask.

12. Start the instrument

timer. A 15-minute reaction

time starts.

13. When the timer expires,

weigh and add 6.0 g of

20-mesh zinc to the

distillation flask. Put the cap

on the flask immediately.

14. Set the heat control to

15. Start the instrument

timer. A 15-minute reaction

time starts.

16. When the timer expires,

set the heat control to 1.

Arsenic Silver Diethyldithiocarbamate Method (0.200 mg/L) 3

17. Start the instrument

timer. A 15-minute reaction

time starts.

18. When the timer expires,

set the heater power to off.

Remove the cylinder/gas

bubbler assembly as a unit.

19. Move the gas bubbler

up and down in the arsenic

absorber solution to rinse

the bubbler.

20. Prepare the blank: Fill

a dry 10-mL sample cell with

unreacted arsenic absorber

solution. Put the stopper on

the sample cell.

21. Clean the blank sample

cell.

22. Insert the blank into the

cell holder.

Zero

23. Push ZERO. The

display shows the (non-

zero) intercept that is

calculated from the user-

entered calibration curve.

24. Prepare the sample:

Pour the reacted arsenic

absorber sample into a

sample cell. Put the stopper

on the sample cell.

25. Clean the prepared

sample cell.

26. Insert the prepared

sample into the cell holder.

Read

27. Push READ. Results

show in mg/L As.

Interferences

Interfering substance Interference level

Antimony Salts Can interfere with color development.

4Arsenic Silver Diethyldithiocarbamate Method (0.200 mg/L)

Reagent preparation

CAUTION

Chemical exposure hazard. Obey laboratory safety procedures and wear all of the

personal protective equipment appropriate to the chemicals that are handled. Refer to the

current safety data sheets (MSDS/SDS) for safety protocols.

Prepare the arsenic absorber solution as follows:

1. Weigh 1.00 g of silver diethyldithiocarbamate on an analytical balance.

2. Add the powder to a 200-mL volumetric flask. Dilute to the mark with pyridine.

3. Mix well to dissolve. Keep the reagent, tightly sealed, for a maximum of 1 month in an

amber bottle.

Calibration

This method requires a user-prepared calibration curve. Enter the calibration curve into

the instrument as a user program. Make a new calibration curve when a new lot of

reagents is used.

Prepare the standard solutions

Prepare the standard solutions for calibration as follows.

Items to collect:

• 1000-mg/L Arsenic Standard Solution

• 1000-mL volumetric flask

• 500-mL volumetric flasks (3), Class A

• 1–10 mL TenSette pipet and tips

• Deionized water

1. Prepare a 10.0-mg/L Arsenic Standard Solution as follows:

a. Use a pipet to add 10.0 mL of the 1000-mg/L Arsenic Standard Solution into a

1000-mL volumetric flask.

b. Dilute to the mark with deionized water.

2. Prepare three calibration standard solutions (0.02, 0.04 and 0.20 mg/L arsenic) as

follows:

a. Use a pipet to add 1.0 , 2.0 and 10.0 mL of the 10.0-mg/L Arsenic Standard

Solution into three different 500-mL volumetric flasks. Use Class A glassware.

b. Dilute each flask to the mark with deionized water. Mix well.

Enter the calibration as a user program

After the calibration standards are prepared, make a user program to store the calibration

information in the instrument. Select the user program to measure the concentration of

samples. The steps that follow are general instructions for all instruments. Refer to the

user manual for the instrument that is used for the correct menu options.

1. Use the test procedure to prepare the standard solutions for measurement. Make

sure to distill the standard solutions as shown in the test procedure.

2. Go to User Programs.

3. For the initial calibration, make a new user program. Set up the basic information for

the new program:

Option Description

Program number Enter an available number for the user program.

Arsenic Silver Diethyldithiocarbamate Method (0.200 mg/L) 5

Option Description

Program name Enter a name for the user program, (e.g., the name of the parameter).

Program type Select single wavelength (for applicable spectrophotometers).

4. Enter the settings for the user program:

Option Description

Units mg/L

Wavelength 520 nm

Concentration resolution 0.001

Chemical form As

Upper limit 0.220

Lower limit –0.020

Timer 1 15:00

Timer 2 15:00

Timer 3 15:00

Calibration Read standards

5. Select CALIBRATION: C = A + BA. Push EDIT.

6. In the Read Standards menu, enter the concentration of the prepared standard

solutions.

7. Prepare the blank solution: Use a 25-mL sample cell that only contains unreacted

arsenic absorber solution.

8. Insert the blank solution into the cell holder and push ZERO.

9. Insert the first prepared standard solution into the cell holder. Make sure that the

standard solution concentration is selected on the display and push READ.

10. Continue to measure the remaining standard solutions.

11. Push GRAPH. Make sure that FORCE ZERO is off.

12. If the graph is acceptable select DONE>EXIT.

13. Save (store) the user program. When the user program is selected in the test

procedure, the calibration curve is used to measure the sample concentration.

Summary of Method

A mixture of zinc, stannous chloride, potassium iodide and hydrochloric acid reduces the

arsenic into arsine gas in a specially equipped distillation apparatus. The arsine goes

through a scrubber that uses a cotton ball soaked with lead acetate for sulfide removal.

Then the arsine goes into an absorber tube that contains a solution of silver

diethyldithiocarbamate in pyridine. The arsenic reacts to form a red complex that is read

colorimetrically. A manual calibration is necessary for this procedure. The measurement

wavelength is 520 nm.

Consumables and replacement items

Required reagents

Description Quantity/test Unit Item no.

Arsenic Standard Solution, 1000-mg/L As varies 100 mL 1457142

Hydrochloric Acid, ACS 25 mL 500 mL 13449

Lead Acetate Solution, 10% 1 mL 100 mL 1458042

Potassium Iodide Solution, 20% 3 mL 100 mL 1456842

Pyridine, ACS 50 mL 500 mL 1446949

6Arsenic Silver Diethyldithiocarbamate Method (0.200 mg/L)

Consumables and replacement items (continued)

Description Quantity/test Unit Item no.

Silver Diethyldithiocarbamate 1 g 25 g 1447624

Stannous Chloride Solution 1 mL 100 mL 1456942

Water, deionized varies 4 L 27256

Zinc, 20-mesh, ACS 6 g 454 g 79501

Required apparatus

Description Quantity/test Unit Item no.

Balance, analytical, Zeta series, 80-g capacity 1 each 2936701

Balls, cotton 1 100/pkg 257201

Boat, weighing, 8.9-cm square 2 500/pkg 2179000

Bottle, amber, 237-mL, glass 1 6/pkg 714441

Cap, polypropylene, for amber bottle 1 6/pkg 2166706

Cylinder, graduated, 25-mL 1 each 50840

Cylinder, graduated, 250-mL 1 each 50846

Distillation Apparatus, arsenic accessories 1 set 2265400

Distillation Apparatus, general purpose accessories 1 set 2265300

Flask, volumetric, Class A, 1000-mL, with glass stopper 1 each 1457453

Flask, volumetric, Class A, 200-mL 1 each 1457445

Flask, volumetric, Class A, 500-mL 6 each 1457449

Pipet filler, safety bulb 1 each 1465100

Pipet, serological, 5-mL 1 each 53237

Pipet, volumetric, Class A, 1.00-mL 1 each 1451535

Pipet, volumetric, Class A, 2.00-mL 1 each 1451536

Pipet, volumetric, Class A, 4.00-mL 1 each 1451504

Pipet, volumetric, Class A, 6.00-mL 1 each 1451506

Pipet, volumetric, Class A, 8.00-mL 1 each 1451508

Pipet, volumetric, Class A, 10.00-mL 1 each 1451538

Select one based on available voltage:

Distillation heater and support for apparatus set, 115 VAC option 1 each 2274400

Distillation heater and support for apparatus set, 230 VAC option 1 each 2274402

Optional reagents and apparatus

Description Unit Item no.

Mixing cylinder, graduated, 25-mL each 189640

Sulfuric Acid Standard Solution, 1 N 100 mL MDB 127032

Gloves, chemical resistant, size 9–9.5 pair 24101041

1Other sizes available

Arsenic Silver Diethyldithiocarbamate Method (0.200 mg/L) 7

HACH COMPANY

WORLD HEADQUARTERS

Telephone: (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 [email protected]

In the U.S.A. –

Outside the U.S.A. –

On the Worldwide Web – ; E-mail –

toll-free

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