Using Pipets And Graduated Cylinders - Hach DR/850 Procedures Manual

CHEMICAL ANALYSIS INFORMATION
Sample Dilution and Interfering Substances

Using Pipets and Graduated Cylinders

Table 6 Multiplication Factors for Diluting to 100 mL
Sample Volume (mL)
1
2
5
10
25
50
Sample dilution may influence the level at which a substance may
interfere. The effect of the interferences decreases as the dilution
increases. In other words, higher levels of an interfering substance can be
present in the original sample if it is diluted before analysis.
An Example:
Copper does not interfere at or below 100 mg/L for a 25.00 mL sample in
a procedure. If the sample volume is diluted with an equal volume of
water, what is the level at which copper will not interfere?
Total volume
------------------------------------ - = Dilution factor
Sample volume
25
--------- - = 2
12.5
×
Interference Level Dilution Factor
×
100 2 = 200
The level at which copper will not interfere in the undiluted sample is at
or below 200 mg/L.
When small sample quantities are used, the accuracy of measurements is
important. Figure 3 illustrates the proper way of reading the sample level
or the meniscus formed when the liquid wets the cylinder or pipet walls.
, continued
= Interference level in sample
26
Multiplication Factor
100
50
20
10
4
2