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Laboratory Practices
2.7.1 Sample Dilution with Interfering Substances
®
2.8 AccuVac
Ampuls
Laboratory Practices
Page 22
More accurate dilutions can be done with a pipet and a 100-mL volumetric flask
(see Table 5 for more information). Pipet the sample and dilute to volume with
deionized water. Swirl to mix.
Table 5 Multiplication Factors for Diluting to 100 mL
Sample Volume (mL)
Sample dilution may influence the level at which a substance interferes. The
effect of the interferences decreases as the dilution increases. In other words,
higher levels of an interfering substance can be tolerated 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 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 diluted sample is at or below
200 mg/L.
AccuVac Ampuls contain pre-measured powder or liquid vacuum-packed in
optical-quality glass ampules.
To use AccuVac Ampuls:
1. Collect the sample in a beaker or other open container.
2. Place the ampule tip well below the sample surface and break the tip off (see
Figure 5) against the beaker wall. The break must be far enough below the
surface to prevent air from being drawn in as the level of the sample drops
(the AccuVac Breaker may be used instead of breaking the ampule against the
beaker side).
Multiplication Factor
1
100
2
50
5
20
10
10
25
4
50
2
=
Interference level in sample
5940022LabPrac.fm
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