A new chemosensor for cyanide in blood based on the Pd complex of 2-(5-bromo-2-pyridylazo)-5-[N-n-propyl-N-(3-sulfopropyl)amino]phenol

A new indirect chemosensor for the detection of cyanide is developed. 2-(5-Bromo-2-pyridylazo)-5-[N-n-propyl-N-(3-sulfopropyl)amino]phenol, a yellow dye, forms a blue-coloured complex with palladium ions. The yellow colour of this complex is regained upon reaction with cyanide ions. The complex shows high selectivity for detection of cyanide over 16 other anions. The system was applied to two different methods for the detection of cyanide in human whole blood. As a quantitative absorbance method, blood samples were mixed with acid and the resulting vaporised hydrogen cyanide was absorbed in an alkaline solution containing the complex in a Conway cell. The resulting absorbance response of the solution at 450 nm is linear over the range 4–40 µM (R2 = 1.000) and the limit of detection is 0.6 µM. Furthermore, the complex-soaked paper is applicable as a test strip for cyanide detection. When a test strip is used with 0.5 mL of blood, the limit of detection is 15 µM. The detection limits of these two methods are below the toxic blood cyanide concentration (19 µM). Therefore, both methods allow quantitation and screening of cyanide in blood samples. Furthermore, the test strip is low cost and enables on-site analysis.