1-51
glassware must be rinsed thoroughly with distilled water. For ammonia
and Kjeldahl nitrogen, the glassware must be rinsed with ammonia-free
water.
Storage and Preservation
The most cost-effective sample containers are made of polypropylene or
polyethylene. The best and most expensive containers are made of
quartz or TFE (tetrafluoroethylene, Teflon). Avoid soft glass containers
for metals in the microgram-per-liter range. Store samples for silver
determination in light-absorbing containers.
Avoid introducing contaminating metals from containers, distilled water
or membrane filters. Thoroughly clean sample containers as described
under Acid Washing Bottles.
Preservation techniques retard the chemical and biological changes
continuing after sample is taken. These changes may change the amount
of a chemical species available for analysis. As a general rule, it is best
to analyze the samples as soon as possible after collection. This is
especially true when the concentration is expected to be low. Analyzing
immediately reduces the potential for error and minimizes labor.
Preservation methods are limited generally to pH control, chemical
addition, refrigeration and freezing. The recommended preservation for
various constituents is given in Table 9. Other information provided in
the table is the suggested type of container and the maximum
recommended holding times for properly preserved samples.
Aluminum, cadmium, chromium, cobalt, copper, iron, lead, nickel,
phosphorus, potassium, silver and zinc samples can be preserved for at
least 24 hours by the addition of one Nitric Acid Solution Powder 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 adding an equal number of Sodium Carbonate Anhydrous Powder
Pillows (Cat. No. 179-98). Or, raise the pH to 4-5 with Sodium
Hydroxide Standard Solution, 1 N or 5 N.
To Next Page
Loading...
