Hach DR/850, Procedures Manual, Page: 32 / 460

32
CHEMICAL ANALYSIS INFORMATION
, continued
a substantial error in the result. For instance, a 0.1-mL mistake in the
dilution of a 1.0-mL final volume produces a 10% error in the test result.
Volumes for standard additions can be measured using the 25-mL mark,
but it is not recommended for the 10-mL mark due to a potentially
excessive relative error. An error of 0.5 mL in 25 mL is only 2%, while
0.5 mL error in 10 mL is 5%.
For 10 mL standard additions, follow this procedure:
1. Transfer 10.0 mL of sample into a clean, dry sample cell (the
unspiked sample).
2. Add the standard (spike) to a 25 mL portion of sample in a 25-mL
mixing cylinder. Stopper and mix thoroughly.
3. Transfer 10 mL to another sample cell (use fill mark) for analysis.
Using AccuVac Ampuls
AccuVac ampuls contain pre-measured powder or liquid in optical-quality
glass ampuls.
1. Collect the sample in a beaker or other open container.
2. Place the ampul tip well below the sample surface and break the tip
off (see
Figure 6 ) 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 lowers (the AccuVac Breaker may be used instead
of breaking the ampul against the beaker side).
3. Invert the ampul several times to dissolve the reagent. Do not place
your finger over the broken end; the liquid will stay in the ampul when
inverted. Wipe the ampul with a towel to remove fingerprints, etc.
4. Insert the ampul into the instrument and read the results directly.
Figure 6 Using AccuVac Ampuls
2. 3. 4. 1.