Anions in wastewaters - Determination of Anions in Natural and Treated Waters - page 528

Table 8.5 Ion chromatographic conditions

0.003mol L −1 NaHCO 3 /0.004mol L −1 Na 2 CO 3

Eluent

Flow rate 138ml/h, 30%

Analytical column 3×500mm brine anion separator

Suppressor column 6×250mm anion suppressor

Detector sensitivity 3µmho full scale

Injection volume 100µL

Source: Reproduced with permission from the American Chemical Society [9]

8.1.2 Ion chromatography
Hill and Lash [9] have described an ion chromatographic method for the determination of
down to 0.05mg L −1 of borate in environmental waters, nuclear fuel dissolvent solutions
and effluents.
Borate is selectively concentrated on Amberlite XE-243 ion exchange resin and
converted to tetrafluoroborate using 10% hydrofluoric acid. Tetrafluoroborate is strongly
retained by the resin, thus allowing excess fluoride to be eluted without loss of boron.
The tetrafluoroborate is eluted with 1mol L −1 sodium hydroxide and is determined in the
eluent by ion chromatography. Boron is quantified to a lower limit of 0.05mg L −1 .
A Model 14 ion chromatograph (Dionex Corporation) was used in this work. Clear
polymethylpentane plastic ware (Nagel Company) was used in the preparation of all
reagents and standards. Separating columns; standard 3×150 and 3×500mm anion
separator columns, as well as a 3 ×500mm brine anion separator were used [10].
Suppressor column-standard; 6×250mm anion suppressor column, from Dionex
Corporation.
Samples and calibration standards containing between 1 and 20mg L −1
tetrafluoroborate are injected into the ion chromatograph using the conditions shown in
Table 8.5. Results are calculated on a peak height ratio basis.
The effects of the common anions on the standard procedure are shown in Table 8.6.
As can be seen, none of these ions interferes at a 100 to 1mole ratio to boron. In addition,
at least a 280 to 1mole ratio of fluoride to boron, as well as a 100 to 1mole ratio of
chloride to boron, can be tolerated. Fig. 8.2 shows an ion chromatogram of a sample
which initially contained all of the above anions at a 100 to 1mole ratio and which was
prepared according to the standard procedure. As shown, tetrafluoroborate peaks are well
resolved from all the residual amounts of those anions not completely removed by the
XE-243 column treatment.
Five water samples prepared to contain boron at levels ranging from 500 to 0.05mg
L −1 were analysed according to the standard procedure. Recoveries ranged from 99.3% to
94.6%.