Multianion analysis, applications of ion chromatography - Determination of Anions in Natural and Treated Waters - page 623

remainder passing to waste. The determination began with a freshly regenerated separator
column and proceeded sequentially through the sample series. Retention times of peaks
from the resulting chromatograms were compared with known synthetic standards
analysed under the same eluant strength and flow conditions. Measurements of anion
concentrations in each sample were obtained by
Fig. 12.6 Calibration chromatogram for a 250mm anion separator column using
standard 7b containing 0.1µg mL −1 F, 0.1µg mL −1 Cl, 0.1µg mL −1
PO 3− , 1.0µg mL −1 NO 3 − and 1.0µg mL −1 SO 4 2−
Source: Reproduced with permission from Elsevier Science [10]
comparing peak heights with a standard curve generated from peak heights of mixed
synthetic standard.
Two separator columns were studied by Smee et al. [10]—one 250mm and one
500mm in length. Examples of chromatograms obtained from standards injected into a
250mm column are shown in Fig. 12.6. Standard 7b used in the 250mm long column
(Fig. 12.6) does not contain nitrite and bromide but concentrations of fluoride, chloride,
phosphate, nitrate and sulphate are the same as for the 500mm column. Both columns
exhibit advantages and disadvantages. Better resolution of chromatographic peaks,
particularly those involving nitrate, nitrite, phosphate and bromide is obtained with the
500mm column. A depression of the baseline created by elution of the water portion of
the sample, thus lowering the background conductivity, occurs between the fluoride and
chloride peaks and can result in a depression of the chloride response. This depression is
negligible with the 500mm column. Disadvantages in using the 500mm column include a
longer elution time for each sample, a decrease in precision at moderate to high
concentrations created by broadening of chromatographic peaks (this may be
compensated for by integrating peak areas rather than measuring peak heights), and a
progressive deterioration of efficiency of the suppressor column caused by an increased
volume of eluant required for the longer elution time. This latter problem may be solved