Anions in wastewaters - Determination of Anions in Natural and Treated Waters - page 540

Funazo et al. [42] analysed several wastewater samples from various factories using
cyanide, such as metal refining and plating factories by the gas chromatographic and by
the spectrophotometric pyridine pyrazolene

Table 8.12 Comparison of spectrophotometric and gas chromatographic methods for the
analysis of waste water samples

Cyanide concentration (mg L −1 )

Sample

Spectrophotometric
method a

Gas chromatographic
method b

A 0.48 0.51±0.015

B 0.20 0.20±0.006

C 0.13 0.16±0.002

D 0.08 0.03±<0.0005

E 0.08 0.09±0.002

a Pyridine-pyrazolone method
b Mean=S.D. of five replicate analyses
Source: Reproduced with permission from Elsevier Science [42]

methods. Instantly after collection, sodium hydroxide was added to the samples and the
solution was adjusted to pH 12-13 in order to prevent the evolution of hydrogen cyanide.
The results show that the values measured by the two methods agree well (Table 8.12).
Nota and Improta [43] determined cyanide in coke oven waste water by gas
chromatography. The method is based on treatment of the sample with bromine and
direct selective determination of the cyanogen bromide by gas-solid chromatography
using a BrCN − selective electron capture detector. No preliminary treatment of the
sample to remove interferences is necessary in this method, and in this sense it has
distinct advantages over many of the earlier procedures. Bromine also oxidises
thiocyanate to cyanogen bromide. Previous treatment of the sample with aqueous
formaldehyde destroys thiocyanate and prevents its interference.
Some typical results of cyanide analysis of coke oven water and coke oven water
effluents are reported in Table 8.13, and are compared with the results obtained following
the procedure suggested by the Standard Methods [44].
Generally, results obtained by the APHA standard method [44] are some 15% lower
than those obtained by gas chromatography.
Nota et al. [45] have made the cyanogen bromide technique for determining cyanides
and thiocyanate more sensitive and reproducible by adopting the headspace technique.
This technique lends itself to automation.
Nota et al. [46] have also described a gas chromatographic headspace method based on
different principles for the determination of 0.01-100mg L −1 of cyanide and thiocyanate
in coke oven waters and waste effluents. This method involves first transforming the