Hach DR 6000 User manual

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
1

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
3.
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

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© Hach Company/Hach Lange GmbH, 2007, 2010, 2012, 2014. All rights reserved. 03/2014, Edition 8