Sample Dilution Techniques - Hach DR/700 Procedures Manual

accuracy and precision, sample cells should be matched prior to use.
Refer to Matching Sample Cells in the instrument manual supplied with
the colorimeter.

Sample Dilution Techniques

Ten and Twenty-five milliliter (mL) are the specified volumes for most
colorimetric tests. However, in some tests, the color developed in the
sample may be too intense to be measured. Unexpected colors may
develop in other tests. In both cases, it is necessary to dilute the sample
or determine if interfering substances are present.
For example, when performing the chromium tests, the colorimeter may
detect a concentration above the maximum range limit. This results in a
flashing maximum concentration value in the display. A sample
solution is necessary. The test can be repeated, for example, with a 25-
mL graduated cylinder filled to the 5-mL mark with the sample and then
to the 10-mL mark with deionized water. Because the sample was
diluted to twice its original volume (5 mL to 10 mL), the test result
should be multiplied by 2 to give the correct concentration of chromium.
To accomplish the sample dilution conveniently, pipet the chosen sample
portion into a clean graduated cylinder (or clean volumetric flask for
more accurate work) and fill the cylinder (or flask) to the desired volume
with deionized water. Mix well. Use the diluted sample when running
the test.
As an aid, Table 5 shows the amount of sample taken, the amount of
deionized water used to bring the volume up to 25 mL and the
multiplication factor.
Table 5. Sample Dilutions
Sample
Volume
(mL)
25.0
12.5
10.0*
5.0*
2.5*
1.0*
0.250*
*For sample sizes of 10 mL or less, a pipet should be used to measure the sample into the
graduated cylinder or volumetric flask.
Deionized Water Used
to Bring the Volume
to 25 mL (mL)
0.0
12.5
15.0
20.0
22.5
24.0
24.75
1-24
Multiplication
Factor
1
2
2.5
5
10
25
100