• Universitat de València

• Ana María Costero Nieto
• Raúl Jesús Gotor Candel

Both cyanide anion in solution (CN-) and hydrogen cyanide in gaseous state (HCN) are polluting, toxic and extremely dangerous molecules, both in physiological systems and in the environment. A multitude of colourimetric sensors are currently available for the detection of CN-, but they generally do not offer adequate selectivity in the presence of other contaminant anions. As for the detection of HCN in the gas phase, the colourimetric systems marketed so far carry out the detection through an indirect route, making use of a pH indicator that detects the HCl generated by the reaction of HCN with HgCl2. The use of this type of mercury salts generates a significant pollution load, and it is interesting to look for efficient and more environmentally friendly alternatives.

Research staff at the Universitat de València have designed new CN- and HCN-colourimetric sensors, which have excellent selectivity characteristics and detection limits within the commonly accepted safety ranges. For both applications, the invention is based on the use of a diphenylmethane-quinone compound. In the specific case of gaseous HCN, the compound is deposited on a solid support of a basic nature.

The correct choice of the compound has made it possible to obtain a carbon centre with suitable electrophilicity for the cyanide anion which, unlike other similar commercial molecules, maintains its characteristics and reactivity once deposited on a suitable solid support. In this way, the researchers have designed the first direct-reaction colourimetric sensor for gaseous HCN.

The invention is applicable to the manufacture of detection devices, especially as personal protection systems. These systems are useful in various industrial sectors where HCN is generated (wood, plastics, steel, jewellery, mining, petrochemicals, etc.) and in public spaces susceptible to attacks (stations, airports, etc.).

The main benefits of the invention are:

• Detection limits: The direct reaction between the sensor and HCN results in a marked colour change with detection limits below 1 ppm.
• Selectivity: The sensor is selective in the presence of other gases such as CO, HCl, NH3, H2S, in concentrations up to 50 ppm.
• Respect for the environment: No heavy metals are used.
• Reversibility: The reaction is reversible by irradiation with UV light so that the sensor is regenerated and can be reused in successive cycles.
• Minimisation of false positives: Regeneration with UV radiation only occurs in case of reaction with HCN.

• Patent granted