DR/4000 PROCEDURE OXYGEN DEMAND, Chemical

DR/4000
PROCEDURE
OXYGEN DEMAND, Chemical
✔ Method 8000
Reactor Digestion Method*
(0 to 1500 and 0 to 15,000 mg/L COD)
Scope and Application: For water, wastewater and seawater; digestion required; 0–1500 mg/L range is USEPA
Approved** for wastewater analyses. The detection limit is 3 mg/L or 30 mg/L COD for the 0–1500 mg/L and the
0–15,000 mg/L range, respectively.
* Jirka, A.M.; Carter, M.J., Analytical Chemistry, 1975, 47(8), 1397
** Federal Register, April 21, 1980, 45(78), 26811-26812. The 0–15,000 mg/L range is NOT USEPA approved.
Colorimetric Measurement, 0 to 1,500 and 0 to 15,000 mg/L COD
HACH
PROGRAM
2
7
2
0
HACH PROGRAM: 2720
COD, HR, HR PLUS
ENTER
1. Perform the digestion
for this method as
described in “Oxygen
Demand, Chemical,
Digestion Procedure”
which precedes the COD
colorimetric procedures.
2. Press the soft key
under HACH PROGRAM.
Select the stored program
number for high range and
high range plus COD by
pressing 2720 with the
numeric keys.
Press: ENTER
Note: If samples cannot
be analyzed immediately,
see Sample Collection,
Preservation and Storage
following these steps.
OxygenCOD_None_High_RCD_Eng_4000.fm
3. The display will show: 4. Insert the Test ‘N
HACH PROGRAM:
2720
COD, HR, HR PLUS
The wavelength (λ),
620 nm, is automatically
selected.
Tube Adapter into the
sample cell module by
sliding it under the thumb
screw and into the
alignment grooves. Fasten
with the thumb screw.
Note: The Test Tube Adapter
is NOT designed to allow
readings on hot vials
(150 °C).
OXYGEN DEMAND, Chemical
Page 1 of 8
OXYGEN DEMAND, Chemical, continued
ZERO
5. Clean the outside of
the blank with a towel.
Note: Wiping with a damp
towel, followed by a dry one,
will remove fingerprints or
other marks.
6. Place the blank into
the adapter with the
Hach logo facing the
front of the instrument.
Close the light shield.
7. Press the soft key
under ZERO.
Note: Preparation of the
blank is described in the
digestion procedure.
Note: For alternate
concentration units
press the soft key under
OPTIONS. Then press the
soft key under UNITS to scroll
through the available
options. Press ENTER to
return to the read screen.
Note: The blank is
stable when stored in
the dark; see Blanks for
Colorimetric Measurement
following these procedures.
9. Place the sample vial
into the adapter with the
Hach logo facing the front
of the instrument. Close
the light shield. Results in
mg/L COD (or chosen
units) will be displayed.
Note: When High Range
Plus COD Digestion
Reagent Vials are used,
multiply the displayed value
by ten.
OXYGEN DEMAND, Chemical
Page 2 of 8
The display will show:
8. Clean the outside
of the sample vial with
a towel.
0 mg/L COD
Note: For most accurate
results with samples near
1,500 or 15,000 mg/L COD,
repeat the analysis with a
diluted sample.
Note: Results may be
expressed as mg/L COD or
mg/L O2. Press the soft keys
under OPTIONS and then
press FORM: to scroll
through the available
choices.
OxygenCOD_None_High_RCD_Eng_4000.fm
OXYGEN DEMAND, Chemical, continued
Interferences
Chloride
Chloride is the primary interference when determining COD concentration.
Each COD vial contains mercuric sulfate that will eliminate chloride interference
up to the level specified in column 2. Samples with higher chloride concentrations
should be diluted. Dilute the sample enough to reduce the chloride concentration
to the level given in column 3.
Table 1 Interfering Substances and Suggested Treatments
Maximum Cl – concentration
in sample (mg/L)
Suggested Cl –concentration
of diluted sample (mg/L)
Maximum Cl – concentration
in sample with 0.5 g HgSO4
Added (mg/L)
Ultra Low Range
2000
1000
NA
Low Range
2000
1000
8000
High Range
2000
1000
4000
20,000
10,000
40,000
Vial Type Used
Ultra High Range
If sample dilution will cause the COD concentration to be too low for accurate
measurement, add 0.50 g of mercuric sulfate (HgSO4) to each COD vial before the
sample is added. The additional mercuric sulfate will raise the maximum chloride
concentration allowable to the level given in column 4.
Bromide
Bromide interference will not be controlled by mercuric sulfate.
Sample Collection, Preservation and Storage
Collect samples in glass bottles. Use plastic bottles only if they are known to
be free of organic contamination. Test biologically active samples as soon as
possible. Homogenize samples containing solids to assure representative samples.
Samples treated with sulfuric acid to a pH of less than 2 (about 2 mL per liter) and
refrigerated at 4 °C can be stored up to 28 days. Correct results for volume
additions; see Section 1.2.2 Correcting for Volume Additions.
Accuracy Check
Standard Solution Method
0–1500 mg/L range: Check the accuracy of the 0 to 1,500 mg/L range by using
either a 300-mg/L or 1000-mg/L COD Standard Solution. Use 2 mL of one of
these solutions as the sample volume; the expected result will be 300 or 1000 mg/L
COD respectively.
Or, prepare a 500-mg/L standard by dissolving 425 mg of dried
(120 °C, overnight) KHP in 1000 mL of deionized water.
0–15,000 mg/L range: Check the accuracy of the 0 to 15,000 mg/L range by using
a 10,000-mg/L COD standard solution. Prepare the 10,000-mg/L solution by
dissolving 8.500 g of dried (120 °C, overnight) KHP in 1 liter of deionized water.
Use 0.2 mL of this solution as the sample volume; the expected result will be
10,000 mg/L COD (display x 10).
OxygenCOD_None_High_RCD_Eng_4000.fm
OXYGEN DEMAND, Chemical
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OXYGEN DEMAND, Chemical, continued
To adjust the calibration curve using the reading obtained with 1000-mg/L COD
Standard Solution, press the soft keys under METHOD OPTIONS, (MORE) then
STD:OFF. Press ENTER to accept the value and return to the read screen. The
instrument will only allow adjustment if the entered concentration is within 10%
of the measured concentration. See Section 1.5.5 Adjusting the Standard Curve for
more information.
Method Performance
Precision
0–1500 mg/L range
Standard: 1000 mg/L COD
Program
95% Confidence Limits
2720
998-1002 mg/L COD
0–15,000 mg/L range
Standard: 10,000 mg/L COD
Program
95% Confidence Limits
2720
9980-10,020 mg/L COD
For more information on determining precision data and method detection limits,
refer to Section 1.5.
Estimated Detection Limit
Program
EDL
2720 (0-1500 mg/L)
3 mg/L COD
2720 (0-15,000 mg/L)
30 mg/L COD
For more information on derivation and use of Hach’s estimated detection limit,
see Section 1.5.2. To determine a method detection limit (MDL) as defined by the
40 CFR part 136, appendix B, see Section 1.5.1.
Sensitivity
Program Number: 2720
Portion of Curve
∆Abs
∆Concentration
Entire Range
0.010
23.5 mg/L
See Section 1.5.3 Sensitivity Explained for more information.
OXYGEN DEMAND, Chemical
Page 4 of 8
OxygenCOD_None_High_RCD_Eng_4000.fm
OXYGEN DEMAND, Chemical, continued
Blanks for Colorimetric Measurement
The blank may be used repeatedly for measurements using the same lot of vials.
Store it in the dark. Monitor decomposition by measuring the absorbance at
620 nm. Zero the instrument in the absorbance mode using a culture tube
(see OPTIONAL EQUIPMENT AND SUPPLIES) containing 5 mL of deionized
water. Measure the absorbance of the blank and record the value. Prepare a blank
when the absorbance has changed by about 0.01 absorbance units.
Calibration Standard Preparation
High Range:
To perform a high range (0 –1500 mg/L) calibration using the reactor digestion
method, prepare a 10,000-mg/L COD stock solution by diluting 0.85 g of dried
(120 °C, overnight) KHP to 100-mL with deionized water using Class A
glassware. Mix thoroughly.
Prepare calibration standards containing 200, 600, 1000, 1400 and 1600 mg/L
COD as follows:
a. Into five different 100-mL volumetric flasks, pipet 2.0, 6.0, 10.0, 14.0, and
16.0 mL of the 10,000-mg/L COD stock solution using Class A glassware.
b. Dilute to the mark with deionized water. Stopper and invert 10 times
to mix.
c. Using the COD Reactor Digestion Method and the calibration procedure
described in the User-Entered Programs section of the DR/4000
Spectrophotometer Instrument Manual, generate a calibration curve
from the standards prepared above.
High Range Plus:
To perform a super high range (0 –15,000 mg/L) calibration using the reactor
digestion method, prepare a 50,000-mg/L COD stock solution by diluting 8.5 g
of dried (120 °C, overnight) KHP to 200-mL with deionized water using class A
glassware. Mix thoroughly.
Prepare calibration standards containing 2000, 6000, 10000, and 14000 mg/L
COD as follows:
a. Into four different 100-mL volumetric flasks, pipet 4.0, 12.0,
20.0 and 28.0 mL of the 50,000-mg/L COD stock solution using
Class A glassware.
b. Dilute to the mark with deionized water. Mix thoroughly.
c. Using the COD Reactor Digestion Method (with High Range Plus
COD vials) and the calibration procedure described in the User-Entered
Programs section of the DR/4000 Spectrophotometer Instrument Manual,
generate a calibration curve from the standards prepared above.
Alternatively, use the High Range procedure and multiply the results by 10.
Alternate Reagents—COD2 Reagent Vials
For non-reporting purposes, COD2 Reagent can provide a mercury-free testing
option, eliminating mercury waste and saving on disposal costs.
OxygenCOD_None_High_RCD_Eng_4000.fm
OXYGEN DEMAND, Chemical
Page 5 of 8
OXYGEN DEMAND, Chemical, continued
COD2 Reagent Vials use the same COD procedures and the same COD calibration
curves programmed into the DR/4000.
COD2 Reagent is not acceptable for USEPA reporting purposes. Request
Literature Code 1356 for applications where COD 2 Reagent Vials may be
suitable.
Summary of Method
The mg/L COD results are defined as the mg of O2 consumed per liter of sample
under the conditions of this procedure. In this procedure, the sample is heated for
two hours with a strong oxidizing agent, potassium dichromate. Oxidizable
organic compounds react, reducing the dichromate ion (Cr2O72–) to green chromic
ion (Cr3+). When the 0-150 mg/L colorimetric or titrimetric method is used, the
amount of Cr6+ remaining is determined. When the 0 –1,500 mg/L or 0 –
15,000 mg/L colorimetric method is used, the amount of Cr3+ produced is
determined. The COD reagent also contains silver and mercury ions. Silver is a
catalyst, and mercury is used to complex chloride interferences.
Safety
Good safety habits and laboratory techniques should be used throughout the
procedure. Consult the Material Safety Data Sheet for information specific to the
reagents used. For additional information, refer to SECTION 1 WASTE
MANAGEMENT AND SAFETY.
Pollution Prevention and Waste Management
Final samples will contain mercury (D009), silver (D011), and chromium (D007)
at concentration levels regulated as hazardous waste by the Federal RCRA. Please
see SECTION 1 WASTE MANAGEMENT AND SAFETY for further information on
proper disposal of these materials.
OXYGEN DEMAND, Chemical
Page 6 of 8
OxygenCOD_None_High_RCD_Eng_4000.fm
OXYGEN DEMAND, Chemical, continued
REQUIRED REAGENTS AND STANDARDS
Description
Quantity Required
per test
Unit
Cat. No.
Select the appropriate COD Digestion Reagent Vial:
High Range, 0 to 1,500 mg/L COD .............................................1 to 2 vials............ 25/pkg.................21259-25
High Range Plus, 0 to 15,000 mg/L COD....................................1 to 2 vials............ 25/pkg.................24159-25
Water, deionized ...............................................................................varies................ 4 liters.....................272-56
REQUIRED EQUIPMENT AND SUPPILES
COD Reactor, 115/230 VAC, North American plug ............................1 ....................... each.................45600-00
COD Reactor, 230 VAC, 50 Hz, European plug ..................................1 ....................... each.................45600-02
DR/4000 Test Tube Adapter.................................................................1 ....................... each.................48189-00
Pipet, TenSette, 0.1 to 1.0 mL ..............................................................1 ....................... each.................19700-01
Pipet Tips, for 19700-01 TenSette Pipet ..............................................1 ................. 50/pkg*.................21856-96
Pipet, volumetric, Class A, 2 mL .........................................................1 ....................... each.................14515-36
Pipet Filler, safety bulb.........................................................................1 ....................... each.................14651-00
Test Tube Rack ............................................................................ 1 to 2 racks ............... each.................18641-00
OPTIONAL REAGENTS AND STANDARDS
COD Digestion Reagent Vials, 0 to 150 mg/L COD ............................................... 150/pkg.................21258-15
COD Digestion Reagent Vials, 0 to 1,500 mg/L COD ............................................ 150/pkg.................21259-15
COD Standard Solution, 300-mg/L...........................................................................200 mL.................12186-29
COD Standard Solution, 1000-mg/L.........................................................................200 mL.................22539-29
COD2 Reagent Vials, High Range, 0–1500 mg/L ..................................................... 25/pkg.................25651-25
COD2 Reagent Vials, High Range, 0–1500 mg/L ................................................... 150/pkg.................25651-15
COD2 Reagent Vials, Ultra High Range, 0–15,000 mg/L ......................................... 25/pkg.................28343-25
Mercuric Sulfate, ACS ................................................................................................. 28 g*...................1915-20
Potassium Acid Phthalate, ACS ................................................................................... 500 g.....................315-34
Sulfuric Acid, ACS, concentrated ...........................................................................500 mL*.....................979-49
OPTIONAL EQUIPMENT AND SUPPLIES
Description
Unit
Cat. No.
Beaker, 250-mL.............................................................................................................. each..................500-46H
Culture Tube, 16 x 100 mm.......................................................................................... 6/pkg.................22758-06
Culture Tube Cap (for 22758-06)................................................................................. 6/pkg.................22411-06
Cylinder, graduated, 5-mL ............................................................................................. each.....................508-37
Flask, volumetric, Class A, 100-mL .............................................................................. each.................14574-42
Flask, volumetric, Class A, 250-mL .............................................................................. each.................14574-46
Flask, volumetric, Class A, 1000-mL ............................................................................ each.................14574-53
pH -Paper, pH 1.0 to 11.0..................................................................................... 5 rolls/pkg.....................391-33
Pipet, serological, 5-mL ................................................................................................. each.....................532-37
Pipet, volumetric, Class A, 2.00-mL .............................................................................. each.................14515-04
Pipet, volumetric, Class A, 6.00-mL .............................................................................. each.................14515-06
Pipet, volumetric, Class A, 8.00-mL .............................................................................. each.................14515-08
Pipet, volumetric, Class A, 10.00-mL ............................................................................ each.................14515-38
Pipet, volumetric, Class A, 20.00-mL ............................................................................ each.................14515-20
Safety shield, for COD reactor....................................................................................... each.................50030-00
Spoon, measuring, 0.5-g................................................................................................. each.....................907-00
RELATED LITERATURE—Ask for your copy by literature code number.
Title
Literature Code No.
COD Disposal Information Brochure ............................................................................................................ 4144
COD2 Reagent Vials Information Brochure .................................................................................................. 1356
* Contact Hach for larger sizes.
OxygenCOD_None_High_RCD_Eng_4000.fm
OXYGEN DEMAND, Chemical
Page 7 of 8
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On the Worldwide Web – www.hach.com; E-mail – techhelp@hach.com
© Hach Company, 1997-2003. All rights reserved. Printed in the U.S.A.
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WORLD HEADQUARTERS
Telephone: (970) 669-3050
FAX: (970) 669-2932
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OxygenCOD_None_High_RCD_Eng_4000.fm