Proceedings of the International Cyanide Detection Testing Workshop

measured using an ISE (Figure 3) linked to a
pH/ISE meter (Manipula et al. 2001c).
The ISE method for determination of CN -
concentrations has been evaluated through
two separate round-robin comparisons by
the ASTM and by the APHA (ASTM 1987,
1997, APHA-AWWA-WPCF 1998). Both the
ASTM round robin and the APHA round
robin evaluations were based on six operators
in fi ve laboratories (ASTM 1987, 1997).
But, the concentrations tested with water
samples and the sample sizes evaluated were
different.
With the ASTM (1987) round-robin
evaluation, samples of CN - in various water
matrices were sent as unknowns to fi ve
laboratories for analyses. The testing done
on samples with a known concentration
of 0.03 mg/L were determined to have an
average concentration of 0.029 ppm (ASTM
1987, 1997). The limit of detection must
be well below this level. In fact, Elsholz
et.al. (1990) found with a fi ve minute time
response that a CN - concentration of 0.003
mg/L (ppm) was detectable for two different
Figure 2. Distillation apparatus used by IMA chemists
to digest tissue samples in order to liberate hydrogen
cyanide gas, that is then captured as cyanide ion in an
absorber tube containing sodium hydroxide.
50
Figure 3. Ion Selective Electrodes (ISE) linked to a
Thermo-Orion pH/ISE meter used by the IMA to
measure cyanide ion concentrations in sodium hydroxide
after refl ux distillation.
cyanide ISEs. Hence, CN - is detectable below
0.03 mg/L, but the concentration may be
diffi cult to determine; since the calibration
on a semi-log plot deviates from a straightline
relationship, determined between known
CN - concentrations and the electric potential
readings obtained using the ISE apparatus.
There is no doubt by any of the organizations
(APHA, ASTM, US-EPA, USGS) that have
endorsed this method, that the ASTM ISE
method is a reliable method that can be
used to determine CN - concentrations in
solution (Ghosh et al. 2006). There are some
differences in the methods that have been
separately published by these organizations,
but they are minor.
The methods published by these agencies
involve an acid digestion and distillation of
samples, with addition of chemicals to help
remove interfering substances (Gosh et al.
2006). Cyanide ion can then be measured in
solution using a variety of methods (including
but not limited to colorimetric, ISE, HPLC,
and mass spectrometric methods).
The International Marinelife Alliance (IMA)
conducted cyanide detection testing (CDT)