ICS-90 Ion Chromatography System
3-4 Doc. 031851-05 12/04
with strong acids or detergents because these will leave traces of ions on
the container walls. The ions may interfere with the analysis.
If samples will not be analyzed on the day they are collected, filter them
through clean 0.45 µm filters immediately after collection; otherwise,
bacteria in the samples may cause the ionic concentrations to change over
time. Refrigerating the samples at 4
° C (39° F) will reduce, but not
eliminate, bacterial growth.
Analyze samples containing nitrite or sulfite as soon as possible. Nitrite
oxidizes to nitrate, and sulfite to sulfate, thus increasing the measured
concentrations of these ions in the sample. In general, samples that do not
contain nitrite or sulfite can be refrigerated for at least one week with no
significant changes in anion concentrations.
3.4.2 Pretreating
Analyze rainwater, drinking water, and air particulate leach solutions
directly with no sample preparation (other than filtering and possibly
diluting).
Filter groundwater and wastewater samples through 0.45 µm filters
before injection, unless samples were filtered after collection.
Before injection, pretreat samples that may contain high concentrations of
interfering substances by putting them through Dionex OnGuard™
cartridges. Refer to the Installation and Troubleshooting Guide for
OnGuard Cartridges (Document No. 032943) for instructions.
3.4.3 Diluting
Because the concentrations of ionic species in different samples can vary
widely from sample to sample, no single dilution factor can be
recommended for all samples of one type. In some cases (for example,
many water samples), concentrations are so low that dilution is not
necessary.
Use eluent or ASTM filtered, Type I (18-megohm) deionized (DI) water
to dilute the sample. When using carbonate eluents, diluting with eluent
minimizes the effect of the water dip at the beginning of the
chromatogram. If you dilute the sample with eluent, also use eluent from
the same lot to prepare the calibration standards. This is most important
for fluoride and chloride, which elute near the water dip.
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