Multianion analysis, applications of ion chromatography - Determination of Anions in Natural and Treated Waters - page 659

the chromatogram by the half value width method (width mm) in half value of peak
height× peak height (mm) and prepare a calibration curve.

Table 12.10 Anion determination conditions by ion chromatography

Separator column 3×500mm, filled with low-capacity anion exchange resin

Suppressor column 6×250nm, filled with high-capacity cation exchange resin

Mixture of 2m mol L −1 Na 2 CO 3 +5m mol L −1 NaOH

Eluent

156ml h −1

Pumping speed

Sample loop 100µL

Source: Reproduced with permission from Elsevier Science [59]

In the sodium carbonate-sodium bicarbonate eluent system, four kinds of eluent were
tested by Oikawa and Saitoh [59] 2m mol L −1 sodium carbonate, 2m mol L −1

sodium

carbonate, 2m mol L −1 sodium bicarbonate, and 3m mol L −1 sodium bicarbonate.
Fig. 12.27(a) shows the results. The higher the concentration of sodium bicarbonate,
the closer the peaks of fluoride, chloride and nitrite ions approach one another. This trend
was more significant in sulphite and sulphate and the elution time was shorter. When a
combination of 2m mol L −1 sodium carbonate/1m mol L −1 sodium bicarbonate was used,
the ions could not be determined because the peak of phosphate was not separated from
that of nitrate and sulphite. The ions also could not be determined when the peak of
sulphite overlapped when 2m mol L −1 sodium carbonate/1m mol L −1 sodium bicarbonate
and 2m mol L −1 sodium carbonate/3m mol L −1 sodium bicarbonate eluents were used.
These results show that the sodium carbonate-sodium bicarbonate eluent system is not
suitable when simultaneous determination of fluoride, chloride, nitrite, bromide,
phosphate, nitrate, sulphite and sulphate is required in samples containing all of these
ions.
Fig. 12.27(b) shows the results of ion determinations using the sodium carbonate
sodium hydroxide system. The pH of this eluent system was high, 10-12. When 2m mol
L −1 sodium carbonate alone (pH 10.12) and a mixture of 2m mol L −1
sodiumcarbonate/2.5m mol L −1 sodium hydroxide were used, the peak of nitrate
overlapped with that of sulphite and that of sulphate overlapped with that of phosphate.
Therefore these eluents are not suitable for determination of those ions.
When the 2m mol L −1 sodium carbonate (5m mol L −1 sodium hydroxide (pH 11.63)
was used, all the ions were well separated. When the pH was further increased, that is, the
2m mol L −1 sodium carbonate 10m mol L −1 sodium hydroxide eluent was used, the
elution time of ions other than phosphate decreased and the peaks approached one
another. Conversely, the elution time of phosphate increased; therefore, this eluent is also
not suitable.