Chemical Analysis
Chemical Analysis
Page 28
5940022ChemAnal.fm
d. Rinse well with deionized water. For chromium, 12–15 rinses may be
necessary. When determining ammonia and Kjeldahl nitrogen, the rinse
water must be ammonia-free.
e. Air dry. Protect the glassware from fumes and other sources of
contamination when storing.
Use chromic acid or chromium-free substitutes to remove organic deposits from
glass containers. Afterward, rinse thoroughly with water to remove all traces
of chromium.
Avoid introducing metal contaminants from containers, distilled water, or
membrane filters.
3.1.1.5 Sample Splits
Samples must often be split or divided into separate containers for intra- or
inter-laboratory use in studies, confirmation, alternative techniques, or
maintaining additional sample for reference, or stability studies. It is very
important that sample splits be done correctly.
• Collect a large volume of sample in a single container and transfer to smaller
containers; do not fill the smaller containers individually from the
water source.
• Thoroughly mix samples containing particulates or solids before splitting so
that all the splits are homogeneous.
• If the sample requires filtering before analysis or storage, filter the entire
sample before splitting.
• Use the same kind of container for all the splits.
• Analyze biologically active splits on the same day, or as close to the same day
as is possible.
• Preserve all splits in the same way; if this is not done, the differing methods
must be fully documented.
• When testing for volatile contaminants, fill containers samples to
overflowing and cap carefully. Do not leave any headspace or air in the
container.
3.1.2 Storage and Preservation
Because chemical and biological processes continue after collection, analyze the
sample as soon as possible. This also reduces the chance for error and minimizes
labor. When immediate analysis is not possible, the sample must be preserved.
Preservation methods include pH control, chemical addition, refrigeration,
and freezing.
Table 8 presents an overview of preservation methods and holding times for
specific procedures.
You can preserve aluminum, cadmium, chromium, cobalt, copper, iron, lead,
nickel, potassium, silver, and zinc samples for at least 24 hours by adding one
Nitric Acid Solution Pillow 1:1 (Cat. No. 2540-98) per liter of sample. Check the
pH with pH indicator paper or a pH meter to assure the pH is 2 or less. Add
additional pillows if necessary. Adjust the sample pH prior to analysis by raising
the pH to 4.5 with Sodium Hydroxide Standard Solution, 1 N or 5 N.
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