Multianion analysis, applications of ion chromatography - Determination of Anions in Natural and Treated Waters - page 625

obtained by colorimetry. Furthermore, the 500mm column yields higher values than the
250mm column. Values above 0.2mg L −1 generally agree well. The limit of detection
(0.02mg L −1 ) reported for the 250mm column is below that reported for the 500mm
column (0.05mg L −1 ) because of the sharper peaks obtained with the shorter column.
Chloride contents of the non saline waters varied from 0.5 to 312mg L −1 by the
spectrophotometric method. A comparison of the chloride determinations reveal an
excellent correlation between the chloride values obtained from the 500mm column and
the expected values. The 250mm column exhibits a gradational increase in the difference
between the ion chromatograph and the expected results with increasing chloride
concentration. This difference is probably caused by a progressive overlap of the chloride
peak with the fluoride peak. Minimum reported concentrations for chloride using the
250mm column is 0.02mg L −1 and for the 500mm column, 0.01mg L −1

against 0.5mg

L −1 for spectrophotometric methods.
Estimates of precision based on five analyses of the replicate non saline water samples
are presented in Table 12.2. The 250mm column is more precise than the 500mm column
for all anions analysed, mainly because the peak height of a response was measured
rather than peak area, the shorter column producing the more narrow peaks. Fluoride
determinations using the 500mm column exhibit a progressive upward increase in
fluoride content caused by the aging of the column during the analytical run. This
apparent increase in fluoride content may occur at the expense of the chloride ion, the
next anion through the column, as there appears to be a gradual decrease in chloride
content with time. No data on nitrate was obtained from the replicate sample. Precision
for sulphate through both columns is excellent, although the 250mm column consistently
produces the higher analytical values.
Van Os et al. [11] achieved complete separations in 6min of 1-30mg L −1
concentrations of bromide, chloride, nitrite, nitrate and sulphate using a Zipax. SAX
separation column, with eluent suppression and electrical conductivity detection. The
necessary high pressure packing techniques for packing the separation column is
described in detail. With sample preconcentration, detection limits were reduced to about
5µg L −1 but calibration graphs for chloride and nitrate were not linear.

Reagents
Adipate and succinate solutions were prepared by adjusting the corresponding acid
solutions to the desired pH with sodium hydroxide.

Apparatus
Separator column Zipax SAX beads (particle diameter 25-37µm, Du Pont de Nemours,
Den Bosch, The Netherlands). (Zipax SAX is a strong

Table 12.2 Dionex replicate samples, non saline waters

Sample
no.

F (250mm) (µg
L −1 )

F (500mm) (µg
L −1 )

Cl (250mm) (mg
L −1 )

Cl (500mm) (mg
L −1 )

7 852 860 20.0 14.5