Oritron Dionex Ion Chromatography System ICS-2100 - Manual (Page 73)

3 • Operation and Maintenance
Doc. 065291-01 3/09
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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.
3.9.2 Pretreating Samples
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 Installation and Troubleshooting Guide for OnGuard
Cartridges (Document No. 032943) for instructions.
3.9.3 Diluting Samples
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 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.
To improve the accuracy of early eluting peak determinations, such as
fluoride, at concentrations below 50 ppb, dilute standards in eluent or
spike the samples with concentrated eluent to minimize the water dip. For
example, spike a 100 mL sample with 1.0 mL of a 100 X eluent
concentrate.