Here is a description of the method used with the ISE test. This is from a post on RDO by Dr. Peter Rubec who conducted this particular type of testing in the Philippines while with the IMA.
"Briefly, the tissue is mascerated in a blender with sodium hydroxide. The slurry is added to a distillaton flask and magnesium chloride and another chemical is added (two chemicals one to deal with inteference by nitrates and the other to act as a catalyst). Then the flask is heated to near boiling and hydrogen cyanide (HCN) gas is released.The HCN passes through a reflux condenser at a measured rate (about 1 ml per second). Then the gas is recaptured in an absorber tube containing concentrated sodium hydroxide solution at pH 12-13. Then, lead carbonate is added to precipitate sulfides (that can interfer with cyanide readings with the ISE electrode). The cyanide ion selective electrode is used with a known volume of sodium hydroxide to measure the cyanide ion concentration while linked to an ISE meter. Corrections are made to determine the concentration of cyanide ion based on the original weight of the tissue sample in order to determine the concentration in milligrams per killigram (ppm). The concentration in ppm determined with the ISE meter is done against a four point calibration with known cyanide ion concentrations. Calibrations are done daily. The apparatus can not be used in the field (but can be done regionally at field laboratories). A fume hood and space is needed for the apparatus. Tests should be done by chemists. Short of having a mobile trailer with the equipment, this is not a field test.
Peter Rubec"
Here is another post by Dr. Rubec which briefly explains the length of time cyanide will remain in a fish prior to it being expelled.
"Question-Please explain how long cyanide ion can be expected to remain in the fish being tested.
Answer-A common belief (misconception) is that cyanide ion is rapidly excreted and hence not detectable a short time after the fish were collected...Cyanide uptake and clearance studies have been conducted on freshwater fish, but not on marine fish. Cyanide ion is transformed to thiocyanate ion (mainly in the liver) by an enzyme called rhodanese. This process is slower than one might predict based on enzyme kinetics, since the conversion process is limited by the availability of sulfur in the fish.
Another factor which may influence this, and allow cyanide and/or thiocyanate to be retained in marine fish longer than with freshwater fish is the difference in osmoregulatory physiology. Marine fish excrete urine at a much lower rate than freshwater fish in order to retain fresh fluids in their blood. Hence, they can be expected to excrete cyanide at a much slower rate than freshwater fish.
A proposal to look at cyanide enzyme kinetics (uptake and release) was submitted (twice) to the Pet Industry Joint Advisory Council (PIJAC) by myself on behalf of IMA and the New England Aquarium in 1989 and 1990. PIJAC chose not to fund the proposed research. The IMA recently received a grant to look into these questions.
The quick answer to your question is that the IMA routinely was able to detect cyanide ion in marine fish tested by the 6 CDT laboratories in the Philippines at least 2 to 3 weeks after the fish were collected. "
It's my understanding that this is the most reliable method for CN detection and there are no reliable testing methods on this side of the water. There are studies ongoing in an attempt to establish a North American based testing method for cyanide detection. Not to be critical Kyle, but if the testing was just as easy as you have said, wouldn't there be testing being currently done for cyanide detection in fish? Or is there a conspiracy?
Cheers,
Kyle
CMA
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