22
CHEMICAL ANALYSIS INFORMATION, continued
Acid Washing Bottles
If a procedure suggests acid-washing, use the following instructions:
a) Clean the glassware or plasticware with laboratory detergent
(phosphate-free detergent is recommended).
b) Rinse well with tap water.
c) Rinse with a 1:1 Hydrochloric Acid Solution or 1:1 Nitric Acid
Solution.
d) Rinse well with deionized water at least four times. Up to 12-15
rinses may be necessary if chromium is being determined.
e) Air dry.
Use chromic acid or chromium-free substitutes to remove organic
deposits from glass containers. Rinse containers thoroughly with water to
remove traces of chromium.
Wash glassware for phosphate determinations with phosphate-free
detergents and acid-wash with 1:1 HCl. Thoroughly rinse the glassware
with deionized water. For ammonia and Kjeldahl nitrogen, rinse with
ammonia-free water.
Correcting for Volume Additions
If you use a large volume of preservative, correct for the volume of
preservative added. This accounts for dilution due to the acid added to
preserve the sample and the base used to adjust the pH to the range of the
procedure. This correction is made as follows:
1. Determine the volume of initial sample, the volume of acid and base
added, and the total or final volume of the sample.
2. Divide the total volume by the initial volume of sample.
3. Multiply the test result by this factor.
Example:
A one-liter sample was preserved with 2 mL of nitric acid. It was
neutralized with 5 mL of 5 N sodium hydroxide. The result of the analysis
procedure was 10.00 mg/L. What is the volume correction factor and
correct result?
1.
2.
3.
Total Volume 1000 mL 2 mL 5 mL+ + 1007 mL==
1007
1000
------------ 1.007 volume correction factor==
10.0 mg/L 1.007× 10.07 mg/L correct result==
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