Proceedings of the International Cyanide Detection Testing Workshop

Ion-Selective Electrodes for Cyanide Detection:
Present Status and Future Possible Improvements
We all want a cyanide analytical technique that
is as simple and fast as possible, inexpensive,
capable of being done by minimally-trained
personnel; that will withstand judicial scrutiny.
Ultimately, it may be possible to meet all
of these requirements, but not within any
short-term time frame. Cyanide in fi sh, as in
other animals, is rarely present in the unbound
form, and requires pretreatment to free it
up for measurement. After digestion and
distillation, the sample consists of unbound
cyanide ion in an alkaline background and,
from the analyst’s point of view, is the
same whether it originated in fi sh tissue or
wastewater.
Round robin tests on cyanide “unknowns”
were conducted at different times by the
two recognized volunteer U.S. standards
organizations, using a method with a carefully
spelled-out distillation step and cyanide
ion-selective electrode (ISE) measurements.
Both tests had extremely good results,
Dr. Martin S. Frant
Chemotics Consulting
chemotics@gmail.com
147
including lower limits of detection on a linear
calibration plot to cyanide levels of 0.03 and
0.06 ppm. A more recent EPA-funded third
party evaluation had similar results. The
cyanide ion detection method, involving acid
digestion, distillation, and ISE measurement,
is approved by the U.S. Environmental
Protection Agency (EPA). This information
is all in the literature, and should give strong
backing against any legal challenges.
There are a number of interesting options
for modifying the present method, and these
will be discussed. They include techniques for
electrode measurements down to 0.003 ppm,
several possible changes in the distillation step,
and the use of other electrodes, such as the
silver ISE or an ISE for HCN. The problem
is that validating any changes will require
extensive testing, independent collaborative
data, and fi eld experience before they can be
used for enforcement.