Anions in wastewaters - Determination of Anions in Natural and Treated Waters - page 542

sampling capillary, 15s; pressurisation of sample vial, 60s; sample withdrawal from
headspace, 5s; 20ml vials thermostated at 80°C for 10min were used. Under these
conditions the retention time of hydrogen cyanide was 5min.

Table 8.14 Influence of sodium chloride concentration on the HCN response

Amount of CN−(mg L−1) NaCl added (%) Peak height (cm) Increase(%)

1.00 0 7.4 -

1.00 10 8.2 11

1.00 20 8.8 19

1.00 30 9.4 27

Source: Reproduced with permission from Elsevier Science [43]

Table 8.15 Standard additions method applied to a 2mg L −1 CN − sample

Aliquot
No.

Amount of CN− present
(µg)

Sample volume
(ml)

CN− added
(µg)

Peak height
(cm)

1 10 5.00 0.00 5.5

2 10 5.00 1.00 6.1

3 10 5.00 2.00 6.5

4 10 5.00 4.00 7.7

5 10 5.00 5.00 8.3

Source: Reproduced with permission from Elsevier Science [43]

A F42 gas chromatograph (Perkin Elmer) equipped with a headspace device or equivalent
and a nitrogen phosphorus detector were employed. The column (2m×0.3cm id) was
made of borosilicate glass and packed with Poropak Q. Methods were developed to
determine cyanide alone, thiocyanate in the absence of cyanide and thiocyanate in the
presence of thiocyanate.
Table 8.14 shows the effect of the salt concentration on the response for hydrogen
cyanide. The matrix effect can be avoided by making use of the method of standard
additions, as illustrated by the results in Table 8.15 for a solution containing 2mg L −1 of
cyanide. The presence of iron(II), iron(III) and copper(II) in the sampl e decreases the
response for hydrogen cyanide. The greatest effect is caused by copper(II). Reducing
agents do not interfere in the analysis of cyanide but oxidising substances have to be
reduced prior to heating of the sample. Oxidants and reducing agents do not interfere in
the determination of thiocyanate.
Typical results for the analysis of cyanide in some coke oven waste waters and coke