Cyanide is a chemical compound consisting of a carbon atom and a nitrogen atom, bound by a triple bond. It is used by different types of industries, such as mining, pharmaceuticals, plastics, metal cleaning, electroplating, among others.
There are also a significant number of plant species that produce cyanide compounds naturally. Some of them are used for human and animal feed. For example, sorghum, cassava, almonds, bamboo shoots, sprouted potatoes, among others.
Cyanide can contaminate water resources through contaminated industrial waste, either directly or through leachates. It can also be released into the air from burning coal and plastics.
Is cyanide harmful to health?
Cyanide is toxic to humans due to its interaction with iron atoms in metalloenzymes, causing inhibition of biological processes linked to oxidative metabolism and cellular respiration.
The entry of cyanide into the body occurs by the consumption of contaminated water or food and raw or incorrectly processed cyanogenic plants. This can lead to death or permanent neurological problems.
According to the World Health Organization, if drinking water has a cyanide concentration above 0.5 mg/L, it should not be consumed by people for more than 5 days. This recommendation comes with the aim of protecting people’s health, in the short term.
The risk posed by the consumption of water or food contaminated with cyanide for human health requires effective methods that allow their detection in water and food samples.
Aspects of interest for cyanide determination
For cyanide analysis, we must consider the different presentations of this element. We can find it as free cyanide, in readily dissociable cyanide-metal complexes and in very stable cyanide-metal complexes.
Free cyanide includes cyanide ion and hydrogen cyanide, the easily dissociable complexes include those formed with cadmium, nickel, copper and zinc. Highly stable complexes include those formed from iron, gold, cobalt, and platinum.
Cyanide analysis can be performed for its free form or as total cyanide. The free form comprises the cyanide ion and hydrogen cyanide, while the total cyanide includes all free cyanide, all dissociable cyanide complexes and all stable complexes.
Several methodologies have been developed for cyanide detection. However, ion selective electrodes make up a versatile, affordable and advantageous measurement system, compared to other techniques.
How is total cyanide determined?
Ion-selective electrodes are highly efficient for detecting free cyanide but are less efficient for bound cyanide. The measurement will depend on the stability of the metal-cyanide complex. To perform the determination of total cyanide, we must perform some previous procedures, which ensure the release of metals that are forming complexes with cyanide.
For readily dissociable complexes, an ethylenediaminetetraacetic acid (EDTA) solution may be used, which will allow displacement of the bound metal. In the case of stable complexes, more laborious procedures are required to move the bound metal, such as distillation in an acid medium or the application of ultraviolet rays. After separating the metal-cyanide complexes, proceed with the measurement routine, which is generally as follows:
- Calibration of the electrode before use, with the calibration solutions of the equipment. Use a NaOH buffer solution (10 molar) in each calibration solution to prevent hydrogen cyanide vapors. Follow the instructions for measuring the solutions.
- For sample preparation, buffer solution should be added to each sample and well shaken before measurement.
- For sample measurement, follow the operating instructions. The electrodes should be washed and dried after each measurement. After immersion of the electrode, wait a reasonable time to take the reading.
- Record the reading of each sample.
Kalstein Silver Ion Meters
At Kalstein we offer a wide variety of cyanide ion meters, from the YR series. You can choose the one that best suits your needs. Kalstein ion meters, which offer the possibility to select the concentration units, e.g. ppm, mg/L and MOL/L, simplify the measurement process by performing direct ion concentration reading. In addition, they are designed with a backlit LCD screen and offer a set-up menu that allows the number of calibration points, stability criteria, temperature, unit, date and time, among others, to be set. For more information on Kalstein ion meters, visit the HERE