New chromoreactands for the detection of aldehydes, amines and alcohols

Two indicator dyes are presented that perform reversible chemical reactions with neutral analytes in thin layers of plasticised poly vinyl chloride (PVC). Since these dyes combine the properties of a selective ligand with those of a chemical reagent, they are termed chromoreactands. The lipophilic decyl derivative of α-Naphthyl Red (CR-418) reversibly reacts with formaldehyde shifting the absorbance maximum in plasticised PVC from 438 to 449 nm. The sensor membrane exhibits highest sensitivity to formaldehyde in the 1–100 mM range with a detection limit of 0.3 mM. A bisazo dye with a reactive trifluoroacetyl group (CR-573) reversibly forms a hemiaminal with amphetamine in thin layers of plasticised PVC and changes its colour from blue to red (corresponding to a shift in absorbance maximum from 575 to 548 nm). The sensitivity of the dye in the polymer layer covers the range from 0.3 to 30 mM amphetamine with a detection limit of 0.1 mM. The same dye also detects ethanol when the catalyst tridodecylmethylammonium chloride is used to accelerate the chemical reaction. The sensor layer exhibits a sensitive range from 1 to 40% ( v/v) ethanol and a detection limit of 0.8% (v/v). Maximum signal changes are observed at 630 nm making CR-573 compatible with cheap light sources and detectors.