Multianion analysis, applications of ion chromatography - Determination of Anions in Natural and Treated Waters - page 614

Chapter 12
Multianion analysis, applications of ion
chromatography
Ion chromatography as originally developed by Small and co-workers in 1975 provided a
method for the separation and determination of inorganic anions and cations [1]. This
original method used two columns attached in series packed with ion exchange resins to
separate the ions of interest and suppress the conductance of the eluant, leaving only the
species of interest as the major conducting species in the solution. Once the ions were
separated and the eluant suppressed, the solution entered a conductivity cell where the
species of interest were detected. Since its introduction, ion chromatography has
advanced considerably and the technique is now routinely used for the analysis of organic
and inorganic anions and cations and substances, including organic acids and amines,
carbohydrates and alcohols. Ion chromatography is not restricted to the separate analysis
of only anions or cations. With the proper selection of eluant and separation columns, the
technique can be used for the simultaneous analysis of both anions and cations.
The simultaneous determinations of anions and cations using single injection ion
chromatography was introduced by Yamamoto and co-workers in 1984 [2]. This
technique determined cations and anions simultaneously using a complexing agent,
ethylenedinitrilotetraacetic acid, to complex the divalent metals. These divalent metals
were later separated and detected as anions along with the uncomplexed inorganic anions.
The technique has progressed rapidly since 1975 and in 1978 a topic was published on
ion chromatographic analysis of environmental pollutants [3]. Other early papers on the
application of ion chromatography cover the determination of selected ions in geothermal
well water [4], the determination of anions in potable water [5,6], and the separation of
metal ions and anions and anions and cations [7].
12.1 Ultraviolet versus conductivity detectors
Cochrane and Miller [8] state the sensitivity of an ultraviolet detector is about 10 times
greater than that of an electrical conductivity detector. Ultraviolet detection of anions is
not generally applicable except at very low wavelengths such as 215nm. An alternative
method of detection of non-ultraviolet absorbing species is to add a low level of
ultraviolet absorbing substances to the eluant. The emergence of a component is then
shown by a negative detector response.
The effect is easily achieved in the ion chromatography system where the preferred
buffer solution (potassium hydrogen phthalate (5×10 −3 M at pH 4.6) has a strong
ultraviolet response with λmax at 280nm. At this wavelength the excessively strong
absorbance will not allow adequate zero suppression and the wavelength was therefore