Multianion analysis, applications of ion chromatography - Determination of Anions in Natural and Treated Waters - page 620

both detectors. The iodate and bromate peaks monitored with the conductivity detector
(solid line chromatogram) were distorted by the so called carbonate dip. The size of the
carbonate dip is controlled by the eluant (both its concentration and composition), the
size of the injection loop and the size of the suppressor column. The peak distortion
caused by the carbonate dip makes both qualitative and quantitative analysis more
difficult. Little or no carbonate dip is observed in Fig. 12.2 (broken line chromatogram)
with the ultraviolet detector after the suppressor column.
Fig. 12.3(a) shows the ultraviolet and conductivity peaks from a 30mg L −1 nitrate
injection while Fig. 12.3(b) shows the ultraviolet and conductivity peaks from a 30mg
L −1 chlorate injection. Both species have the same retention time and peak shape (tailing)
and with just the information from the conductivity detector it would be impossible to
identify which species is present. With both detectors, it is possible to obtain a
ultraviolet/conductivity peak height ratio and this information can be used as an aid in
identifying unknown peaks. Additional ultraviolet/conductivity peak height ratios can be
obtained by varying
Fig. 12.4 Nitrite determination in the presence of 100-2000mg L −1 Cl −
ultraviolet detector (- - -) at 210nm position 1; conductivity detector
(--); peak 1, 1000-2000mg L −1