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Which recent cyanide measuring methods do we have on the market and how CyanoGuard’s method works.
We can find cyanides in many different forms in nature, as well as being used in many industries in today’s world. One of the most popular uses of cyanide is within the mining industry. The mining industry has been using cyanide for metal extraction for more than 150 years.
Cyanide should be handled with care as it can be potentially poisonous for humans and wildlife. Therefore, we have to make sure to properly manage, measure, and dispose of cyanide after its use.
That is why there are so many cyanide measuring methods used for the mining industry, the food industry, and medical uses. Some methods have been developed recently or have been re-examined and improved.
Official methods for the determination of cyanides include titration, spectrophotometry, potentiometry with cyanide-selective electrodes, and flow injection (FI) – amperometry.
In this post, we will go through some of the newest emerging cyanide measuring methods and how they work:
1. Naked eye detection
2. Colorimetry and spectrophotometry
3. Fluorometry
4. Chemiluminescence (CL)
5. Near-infrared cavity ring-down spectroscopy (NI-CRDS)
6. Electrochemical methods: Potentiometry and amperometry
7. Mass Spectrometry
8. Gas chromatography-mass spectrometry
9. Gas chromatography
10. GC-NPD
11. GC-ECD
12. Quartz crystal mass monitor (QCMM)
Naked eye detection
Since ancient times, people have been detecting poisons (mostly in food) with the usage of different chemicals to get a colored reaction. Colorimetric detection kits for poisons in foods are today one of the commercially most used tests.
Most new methods and reagents introduced in the last few years for cyanide detection were the ones that react with cyanide with a visible color change.
For some methods, it is required to use a large amount of organic solvents, like methanol or acetonitrile, or other solvents such as dimethylsulfoxide reducing their attractiveness.
Prof. Zelder proposed using Vitamin B12 with cyanide. The use of Vitamin B12 allows for the visual detection of mM levels of cyanide in water.
Some vitamin B12-based methods have shown very accurate measurements of cyanide in biological samples including CyanoGuard’s method.
Colorimetry and spectrophotometry
All the methods which use reagents that create a visual reaction with cyanides can use quantitative measurements using colorimeters.
Zelder classified colorimetric sensing into 4 categories: sensors that rely on hydrogen bonding, sensors based on coordination to boron, sensors based on transition metal coordination, and sensors that rely on an organic binding reaction that does not fit into the above categories
Colorimetry usually involves simple and mostly inexpensive instruments. Because of usually their inexpensive economical traits, colorimetric techniques are generally popular.
Fluorometry
Many cyanine dyes are both colored and fluorescent. They contain two nitrogen centers (one of which is positively charged) connected by a polymethine bridge containing an odd number of carbons. They have large extinction coefficients and strong fluorescence in the near infrared.
Chemiluminescence (CL)
Gavrilov found that alkaline solutions of luminol containing p-nitrobenzaldehyde and hemin exhibit enhanced CL when cyanide is present. The p-nitrobenzaldehyde cyanohydrin likely reduces dissolved oxygen to superoxide which activates chemiluminescence at a high rate.
Near-infrared cavity ring-down spectroscopy
A particular transition of gaseous HCN (the first H-C stretching overtone) is at 1.5374192 μm that is accessible by a tunable diode laser. This absorption was used, through a cavity ring-down spectroscopy arrangement to monitor HCN in exhaled breath. Exhaled breath HCN has been suggested as a diagnostic tool for cyanide poisoning and for cyanide-producing bacterial infections.
Electrochemical methods: Potentiometry and amperometry
Ion-selective electrodes are convenient, they involve no chemistry, offer a fast response time and hence are widely used. commercial ion-selective electrodes for cyanide which are available on the market have numerous interferences.
Amperometry is also very popular and can be very sensitive. Taheri developed a novel cyanide sensor. A silver-doped silica nanocomposite was synthesized by self-assembly of a sol-gel network and silver nanoparticles.
Different industrial electroplating waste waters were analysed, and the results were statistically indistinguishable from those obtained by accepted standard methods.
Amperometric detection of cyanide is not free of interferences and the electrode response changes over time. The electrode must be often recalibrated. The first problem is ameliorated by carrying out an actual chromatographic separation prior to amperometric detection. The second problem is solved by rapidly cycling the electrode through pre-measurement, measurement and cleaning potentials. The two techniques together have come to be used as ion chromatography with pulsed amperometric detection (IC-PAD) which is particularly popular.
Mass Spectrometry
Several types of mass spectrometry have been used for the measurement of cyanide.
Selected ion flow tube mass spectrometry (SIFT-MS) has been used particularly for the measurement of exhaled breath constituents, including HCN. SIFT-MS uses three selected reagent ions, H3O+, NO+ and O2+, and utilizes fast-flow tube technology along with accurate quantitative mass spectrometry.
Electrospray ionization tandem mass spectrometry (ESI-MS-MS) is one of the most commonly used forms of mass spectrometry.
Gas chromatography-mass spectrometry
While mass spectrometry (MS) is one of the most sensitive analytical methods, quantitation accuracy often leaves much to be desired; this is particularly true for complex samples where co-elution is possible. While there may not be a qualitative interference by the co-elution on the analyte peak of interest, quantitation will almost certainly be affected because the ionization of the desired molecule will be affected by the presence of the other molecules.
The great sensitivity with which analytes can be detected often hides this Achilles heel of quantitation. This problem is most easily solved by the use of isotopically labeled versions of the analyte which are chemically the same as the analyte but produce different and distinct signatures on the mass spectrometer. They cannot be significantly present in the sample initially and thus can act as internal standards. Isotope dilution mass spectrometry (IDMS) as it is called, is particularly easy to practice for cyanide, as instead of the common isotopic variety of cyanide, 12C14N, one can use singly labeled tracers e.g., 13C14N or 12C15N, or preferably the doubly labeled standard 13C15N. This is of particular value in the analysis of cyanide in complex biological samples.
Gas chromatography
Chromatography, notably gas chromatography, has been particularly important in the measurement of cyanide in complex, especially biological samples. Uses with MS detectors have already been discussed in the foregoing; here we discuss use with two selective detectors, the nitrogen-phosphorus detector (NPD), and the ECD.
GC-NPD
Matrix isolation of analyte cyanide is typically achieved by acidification of the sample to produce HCN. The headspace can then be sampled either directly or via an SPME fiber. NPD approach has been widely used for cyanide determination in clinical and forensic needs. Many methods based on this principle and incremental improvements thereof have been published in the past.
GC-ECD
The ECD is more sensitive to appropriately derivatized analytes and tends to be more robust and stable than the NPD. HCN does not directly respond to the ECD and must be derivatized. While there was no dramatic new development, there were some important application papers. Zhang applied headspace GC-ECD to measure cyanide and reported on cyanide distribution in various in human blood, kidney, brain, urine, and stomach content.
Quartz crystal mass monitor (QCMM)
QCMMs are typically quartz crystals cut with certain facets. They vibrate naturally and the resonant frequency can be readily determined by appropriate electrical excitation. The exact resonant frequency is acutely dependent on the total mass of the crystal, decreasing with the increasing mass of the crystal. If such a crystal is metalized by gold or silver for example, and cyanide in a toxic solution contacts the crystal, the metal will dissolve to form a cyano complex, the mass will decrease and the resonant frequency will increase.
Sun developed a sensitive and inexpensive QCMM-based cyanide sensor. The sensing layer consisted of photochemically generated nano-sized silver particles on a titanium dioxide film at the electrode surface of the QCMM. The fresh nanoparticulate silver is easily attacked by cyanide, leading to improved sensor performance with a LOD of 85 nM.
Conclusion:
There are many cyanide detection methods out there, but the main question is which method is reliable, fast and meets market standards.
There are three main criteria that testing methods should have, these are: sensitivity, selectivity and straightforwardness.
There are very few methods that actually meet these criteria. The new colorimetric reagents have so far shown as very convenient because they don’t require complex procedures, economical and simple to use.
As companies are trying to follow more strictly Cyanide Code rules and increase their ESG scores in order to win over investors it will be of crucial importance to switch to and develop better, faster, safer and more reliable cyanide measuring methods.
It is crucial to rapidly analyze cyanide samples, if possible, on-site and affordable. Techniques that involve complicated procedures before measuring won’t be able to meet the market needs.
Find more in-depth information about the cyanide measuring methods in the source material here: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2911244/
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