Multianion analysis, applications of ion chromatography - Determination of Anions in Natural and Treated Waters - page 691

Softened 0.2 0.2 40 38 <05 0.4 0.2 <0.5

Nitrite
treated

<0.5 15 16 <2.5 <100 <10 <25

Nitrite
treated

5.0 13 16 <2.5 <100 0.6 0.55 <2.5

City
make-up

1.0 1.0 16 16 <0.5 <0.2 <0.05 <0.5

Well
water

0.6 0.6 2.2 3.0 <0.5 <0.2 <0.05 <0.5

Waste
effluent

<1 0.1 260 280 <5 16 16.1 150

Source: Reproduced with permission from the American Chemical Society [78]

Reproducibility of nitrite with relation to suppressor column capacity was investigated
by continuous analysis of a 20mg L −1 nitrite solution over a 6h period. During this period
a 24% increase in sensitivity was observed. However, it was noted that satisfactory
results (within 10% deviation) were obtained if calibration were re-established after every
six sample analyses. Partial exhaustion (after 2h of operation) of the suppressor column
was required to achieve sufficient sensitivity for measurement of the desired 0.5mg L −1
nitrite minimum reporting level. Since use of a strong eluent to exhaust partially the
suppressor column would also decrease operating time, it was decided that any sample
requiring nitrite quantitation would be analysed after the second calibration of the system
(calibration performed after every six samples). No nitrite data were reported for samples
analysed by using a freshly regenerated suppressor column.
Table 12.29 contains some examples of comparative data. Most results agreed within
experimental limits for the specific concentration range and test method used. Traditional
methods of analysis used for comparison purposes were as follows: fluoride, ion selective
electrode method; chloride, automated mercuric thiocyanate colorimetric method; nitrite,
permanganate titration method; orthophosphate, automated ascorbic acid reduction
colorimetric method; nitrate automated copper-cadmium reduction colorimetric method.
Sulphate was measured with a barium methylthymol blue colorimetric automated
method.

12.8.2 Cyanide, sulphide, iodide and bromide
Rocklin and Johnson [23] also used an electrochemical detector in the ion
chromatographic determination of cyanide and sulphide. They showed that by placing an
ion exchange column in front of an electrochemical detector, using a silver working
electrode, they were able to separate cyanide, sulphide, iodide and bromide and detect
them in water samples at concentrations of 2, 30, 10 and 10µg L −1 respectively. Cyanide
and sulphide could be determined simultaneously. The method has been applied to the
analysis of complexed cyanides and it is shown that cadmium and zinc cyanides can be