Hach DR/850, Procedures Manual, Page: 317 / 460

317
Table 1 Dilution Table (for use with Chloride Removal Procedure Only)
9.
Label each Mn III
COD vial and remove
the cap. Place the vial in
one of the numbered
holes in the Vacuum
Pretreatment Device
(VPD)* base.
Note: The VPD must be
attached to a vacuum pump
(not an aspirator-type
vacuum) that can create a
vacuum of 20 to 25 inches
of mercury.
* Patent Pending.
10.
Place the VPD top
on the base. Insert a
fresh Chloride Removal
Cartridge (CRC)**
directly above each
Mn III COD Reagent
Vial. Plug any open
holes in the VPD top
using the stoppers
provided.
** U.S. patents 5,667,754
and 5,683,914.
11.
Turn the vacuum
pump on and adjust the
vacuum regulator valve
on top of the VPD until
the internal gauge reads
20 inches of water.
Note: The optimum setting
allows the sample to flow
through the CRC in about
30 to 45 seconds.
12.
Pipet 0.60 mL of
acidified sample (made
in Steps 4-6) into the
CRC. Pipet 0.60 mL of
acidified blank into
another CRC.
Note: If the sample does
not flow through the CRC,
increase the vacuum until
flow starts, then reduce the
vacuum to 20 inches of
water. Proceed as usual.
All dilutions require that the ratio of sample to sulfuric acid remain at 9:1. For other dilutions that are not listed in Table 1,
simply add the sample deionized water and divide by the sample volume to obtain the multiplication factor.
Example:
Dilute the sample to a range of 90-4500 mg/L COD
Standard test range is 20-1000 mg/L COD.
It is best to use 0.5 mL or more of sample for diluting. If sample values exceed 18,000 mg/L COD, use a separate sample dilution
before the sample chloride removal procedure.
Sample (mL) Deionized Water (mL) Range (mg/L COD) Multiplication Factor
6.0 3.0 30-1500 1.5
3.0 6.0 60-3000 3
1.0 8.0 180-9000 9
0.5 8.5 360-18000 18
Sample Volume (2.0 mL) Deionized water (7.0 mL) + Total Volume (9.0 mL) =
Multiplication Factor
Total Volume
Sample Volume
--------------------------------------
9.0 mL
2.0 mL
----------------- 4.5 = = =
Example Test Range 4.5 (20) to 4.5 (1000) 90-4500 mg/L COD = =
OXYGEN DEMAND, CHEMICAL,
continued