Multianion analysis, applications of ion chromatography - Determination of Anions in Natural and Treated Waters - page 679

exception of the use of the electrochemical detector after the anion suppressor. The
solutions were injected and the detector and chart recorder were adjusted to provide
peaks of appropriate height.
Simultaneous analysis of both anions and cations indicates that water samples from
various localities contain many of the same ions but in differing amounts.
A comparison of ion chromatography and a wet chemical method, EDTA titration, for
calcium and magnesium shows good correlation between the two methods. With ion
chromatography, the total calcium and magnesium is approximately 42mg L −1 while the

EDTA titration indicates a total hardness of approximately 49mg L −1 with calcium

assumed to be the major contributor.
The retention times and detection limits change according to the eluant selected but,
under normal daily operating conditions, detection limits will be less than 2mg L −1 and
retention times will range from 0.5 to 25min for most species.
Wagner et al. [65] and Rowland [66] have also determined chloride, nitrate and
sulphates in amounts down to 0.5mg L−1.
Rowland [66] pointed out that before the installation of the chromatograph, some of
the solutions might contain substances that could reduce the ion exchange efficiency of
the column. In particular, in the studies on the effects of acid rain on conifer species, rain
collected beneath the dense tree canopy (through-fall) and solutions running down the
tree stems (stemflow), was found to contain colourless soluble organic compounds that
gradually fouled the column. Such a sample may influence the chromatogram obtained
for the subsequent sample. The 'pseudo carry-over' was eliminated by passing these
sample types through a clean-up cartridge (Sep-pak C18, Waters Associates). It was
found that the guard column protects the separator column from long-term contamination
and an initial clean-up is not required. Leachates from the lower mineral soil horizons
may contain iron and aluminium colloidal complexes, but column efficiency does not
appear to be adversely affected by these solutions.
Despite some gradual deterioration in guard and separator efficiency with time, it is
possible to maintain analytical quality with careful monitoring and sample handling
techniques, and effective column cleanup procedures. Typically, within a 24h run,the
precision was of the order of 0.5%, whereas day to day precision ranged from 0.5 to
1.3%. To maintain good precision, the operating pressure and separating efficiency of the
guard column were monitored daily, and remedial action taken immediately when
required to minimise the contamination of the separator column. Several recommended
clean-up procedures were evaluated and 0.5M sodium nitrate was found to be the most
effective

Table 12.23 Determination of halide mixtures in non saline waters by ion
chromatography

Type of water Co-determined onions Ref.

Natural Cl, Br, F [10,11]

Natural F, Br [68]