Semi-quantitative "spot-test" of cyanide

The use of tristimulus colorimetry for the determination of hydrogen cyanide in air by a modified König method

A simple visual and tristimulus colorimetric method (threedimensional system CIE-L*a*b*) for the determination of trace amounts of hydrogen cyanide in air has been developed. The method is based on the suction of hydrogen cyanide through a chlorinating cartridge where cyanogen chloride is formed, which is further driven to an indicator disc made of a modified cotton fabric. This indicator disc is placed into an adapter. Prior to analysis, the disc is saturated with a chromogenic reagent, a solution of 5,5-dimethyl-1,3-cyclohexanedione (dimedone) and 4-benzylpyridine in ethanol. In the presence of hydrogen cyanide (cyanogen chloride), a pink coloration emerges on the indicator disc, the intensity of which is evaluated either visually or by use of a tristimulus colorimeter. The detection limit is 0.1 mg m-3. The method is mainly suitable for mobile field analyses. It was applied for the CHP-5 chemical agent detector introduced into the equipment of the Czech Army corps.

Rapid colorimetric field test to determine levels of deltamethrin on PermaNet surfaces: association with mosquito bioactivity

OBJECTIVE

To evaluate a simple and inexpensive colorimetric test to measure the amount of cyanopyrethroid insecticide residue from filter paper exposed to mosquito net surfaces.

METHOD

The net sampling protocol and colorimetric test (NetTest) were evaluated for deltamethrin-impregnated PermaNet 2.0 by comparison with high-performance liquid chromatographic assays and mosquito mortality (WHO Cone Test).

CONCLUSION

The observed correlation between the amount of deltamethrin adsorbed onto the filter paper and the entire amount of deltamethrin per unit area of net material was good: 0.967, five assays. The relationship between the surface levels of deltamethrin determined by the colorimetric test and the 'gold standard' mosquito bioassay reveals a relatively accurate field test with a sensitivity of 91.4% and specificity if 85.4% (76 samplings from 19 nets).

Direct determination of free cyanide in drinking water by ion chromatography with pulsed amperometric detection

Cyanide is a regulated contaminant in drinking water in the United States. This paper describes an ion chromatography method with pulsed amperometric detection (PAD) that directly determines free cyanide in drinking water. Samples are treated with sodium hydroxide to stabilize cyanide and with a cation-exchange cartridge to remove transition metals. Cyanide is separated by anion-exchange chromatography and detected by PAD with a waveform optimized for cyanide and used with a disposable silver working electrode. The recovery of cyanide spiked into five water samples was >80%. With an MDL of 1.0 microg/L, this method determines cyanide concentrations well below the reporting limits for free cyanide in drinking water.

Enhanced fluorescence cyanide detection at physiologically lethal levels: reduced ICT-based signal transduction

Three water-soluble fluorescent probes have been specifically designed to determine free cyanide concentrations up to physiologically lethal levels, >20 microM. The probes have been designed in such a way as to afford many notable sensing features, which render them unique with regard to signal transduction, photophysical characteristics, and their application to physiological cyanide determination and safeguard. The probes are readily able to reversibly bind free aqueous cyanide with dissociation constants around 4 microM3. Subsequent cyanide binding modulates the intramolecular charge transfer within the probes, a change in the electronic properties within the probes, resulting in enhanced fluorescence optical signals as a function of increased solution cyanide concentration. The ground-state chelation with cyanide produces wavelength shifts, which also enable the probes to sense cyanide in both an excitation and emission ratiometric manner, in addition to enhanced fluorescence signaling. This has enabled a generic cyanide sensing platform to be realized that is not dependent on fluorescent probe concentration, probe photodegradation, or fluctuations in the intensity of any employed excitation sources, ideal for remote cyanide sensing applications. Further, the >600 nm fluorescence emission of the probes potentially allows for enhanced fluorescence ratiometric cyanide sensing in the optical window of tissues and blood, facilitating their use for the transdermal monitoring of cyanide for mammalian safeguard or postmortem in fire victims, both areas of active research.

Fluorescence intensity and lifetime-based cyanide sensitive probes for physiological safeguard

We characterize six new fluorescent probes that show both intensity and lifetime changes in the presence of free uncomplexed aqueous cyanide, allowing for fluorescence based cyanide sensing up to physiological safeguard levels, i.e. <30 µM. One of the probes, m-BMQBA, shows a ≈15-fold reduction in intensity and a ≈10% change in mean lifetime at this level. The response of the new probes is based on their ability to bind the cyanide anion through a boronic acid functional group, changing from the neutral form of the boronic acid group R-B(OH)2 to the anionic R-B-(CN)3 form, a new cyanide binding mechanism which we have recently reported. The presence of an electron deficient quaternary heterocyclic nitrogen nucleus, and the electron rich cyanide bound form, provides for the intensity changes observed. We have determined the disassociation constants of the probes to be in the range ≈ 15-84 µM3. In addition we have synthesized control compounds which do not contain the boronic acid moiety, allowing for a rationale of the cyanide responses between the probe isomers to be made. The lifetime of the cyanide bound probes are significantly shorter than the free R-B(OH)2 probe forms, providing for the opportunity of lifetime based cyanide sensing up to physiologically lethal levels. Finally, while fluorescent probes containing the boronic acid moiety have earned a well-deserved reputation for monosaccharide sensing, we show that strong bases such as CN- and OH- preferentially bind as compared to glucose, enabling the potential use of these probes for cyanide safeguard and determination in physiological fluids, especially given that physiologies do not experience any notable changes in pH.

Excitation and emission wavelength ratiometric cyanide-sensitive probes for physiological sensing

We characterize three new fluorescent probes that show both spectral shifts and intensity changes in the presence of aqueous cyanide, allowing for both excitation and fluorescence emission wavelength ratiometric and colorimetric sensing. The relatively high binding constants of the probes for cyanide enables a distinct colorimetric change to be visually observed with as little as 10 microM cyanide. The response of the new probes is based on the ability of the boronic acid group to interact with the CN(-) anion, changing from the neutral form of the boronic acid group R-B(OH)(2) to the anionic R-B(-)(OH)3 form, which is an electron-donating group. The presence of an electron-deficient quaternary heterocyclic nitrogen center and a strong electron-donating amino group in the 6 position on the quinolinium backbone provides for the spectral changes observed upon CN(-) complexation. We have determined the binding constants for the ortho-, meta-, and para-boronic acid probes to be 0.12, 0.17, and 0.14 microM(-3). In addition we have synthesized a control compound that does not contain the boronic acid moiety, allowing for structural comparisons and a rationale for the sensing mechanism to be made. Finally we show that the affinity for monosaccharides, such as glucose or fructose, is relatively low as compared to that for cyanide, enabling the potential detection of cyanide in physiologies up to lethal levels.