Multianion analysis, miscellaneous methods - Determination of Anions in Natural and Treated Waters - page 724

ammonium, alkali metals and alkaline earth metals).
Reijnders et al. [33] have also used this technique to determine chloride, nitrate
sulphate and phosphate in rainwater.
14.6 Column coupling isotachoelectrophoresis
14.6.1 Non saline waters
14.6.1.1 Chloride, fluoride, nitrite, nitrate, sulphate and phosphate
At present, ion chromatography has a dominant position among the separation methods
used for the analysis of inorganic anions [35-38]. However, when the separation
efficiencies typically achieved by ion chromatography are compared to characterising
capillary zone electrophoresis for analysis of a group of analytes, it is apparent that the
latter technique has advantages. As the effective mobilities of inorganic anions are
sufficiently due to differences in their ionic mobilities they can be influenced in a desired
way via appropriately selecting (differences in pK, values) and/or via the use of suitable
additives [39], the selectivity factors [40] are also favourable leading to rapid resolutions
of the analytes by capillary zone electrophoresis.
Although in some instances it is possible to determine low concentrations of inorganic
anions by capillary zone electrophoresis [41], problems arise when the concentrations of
the sample constituents vary considerably. This is due to the fact that the determination of
microconstituents may require the sample load to have an impact on both the migration
velocities and the resolution of analytes [42]. The use of indirect detection, as preferred in
the case of inorganic anions [41,43] is also less capable of achieving adequate load
capacities.
Of the inorganic anions which are currently monitored chloride, sulphate, and in many
instances also nitrate, are considered anionic macroconstituents. These are often
accompanied by nitrite, fluoride, and phosphate present in samples at 10 2 -10 5 -fold lower
concentrations. Such a concentration span probably cannot be covered by capillary zone
electrophoresis.
This technique offers very similar advantages to ion chromatography in the
determination of anions in water, namely multipleion analysis, little or no sample
pretreatment, speed, sensitivity and automation. Very similar advantages are offered by
capillary isotachophoresis [44,45]. However, with the exception of the work by Bocek et
al. [46] in which the determinations of chloride and sulphate in mineral water were
demonstrated, little attention has been paid to this subject.
Zelenski et al. [47] applied the technique to the determination of 0.02-0.1mg L −1
quantities of chloride, nitrate, sulphate, nitrite, fluoride and phosphate in river water.
Approximately 25min was required for a full analysis. These workers used a column
coupling technique which, by dividing the analysis into two stages, enables a high load
capacity and a low detection limit to be achieved simultaneously without an appreciable
increase in the analysis time.
The separation unit of the home made capillary isotachophoresis instrument used is