Multianion analysis, applications of ion chromatography - Determination of Anions in Natural and Treated Waters - page 630

column is at least 3 months.
Determination of anions in non saline water is disturbed by the inevitable presence of
humic substances which are strongly adsorbed on the ion chromatographic column.

Table 12.3 Detection limits of chloride, nitrate and sulphate on the Zipax-SAX column
with 1.4×10 −3 mol L −1 Na 2 -succinate as eluent

Detection limit (µg L −1 )

Ion

200µL loop Concentrator column

Chloride 10 2

Nitrate 30 4

Sulphate 30 10

Source: Reproduced with permission from Elsevier Science [11]

Marko Varga et al. [14] found that a cleanup column prior to the separation column,
packed with a chemically bonded amine material (Nucleosil 5 HN 2 ) was found to be
effective in removing interfering humic substances. No influence was found from humic
substances in concentrations up to 45µg L −1 on ion chromatographic analysis of nitrate
and sulphate (10-100mg L −1 ) after passage through the cleanup column.
A short column packed with an amine bonded polymer (weak anion exchange
material) connected prior to the anion separation column was found to be very effective
for the selective removal of humic substances prior to anion separation by ion
chromatography. About 500 sample injections could be performed before breakthrough
of humic substances occurred as indicated by ultraviolet measurements made on the
eluate at 225nm.

Apparatus
Chromatographic system consisting of a pump (constametric III, LDC, Riviera Beach,
Florida) a loop (200 or, 500µL an injector) Model 7000 Rheodyne, Cotati, California) a
column (see below), two detectors in series (a conductometric detector
'Conductomonitor', LDC and a variable wavelength ultraviolet detector, 'Spectromonitor
III' 1.08), and a dual channel recorder (Model 2066, LKB, Bromma, Sweden).
For the adsorption of humic substances a stainless steel column (50mm ×4.9mm id)
was used, filled with 0.8g of Sum amine bonded polymer (Nucleosil 5NH 2 ). Anions were
separated by an anion exchange resin (Dionex, Sunnyvale, California) packed into a glass
column (5mm id bed length 50mm) (Pharmacia Fine Chemicals: Uppsala Sweden) which
permits the length of the resin bed to be easily adjusted.
P otassium hydrogen phthalate, 5×10 −4 mol L −1 , pH 5.5 was used as mobile phase. The
flow rate was 2ml min−1 and the conductometric detector was used in the 'absolute'
mode (10µS) full scale deflection. The conductance of the eluent was electronically
offset.
Under the chosen conditions, nitrate and sulphate were well resolved from other anions