ABSTRACT
New far-visible absorbing anilino-cyanine dyes have been synthesised for future application as chromoionophores in integrated waveguide absorbance optodes based on bulk optodes. The effect of the heterocycle, of the substitution of the heterocyclic nitrogen and of the type of heptamethine central ring on the pKa values (4.3-8.2 in ethanol-water solutions and 9.5-11.0 in plasticised PVC membranes), on the spectroscopic characteristics of the dye and on photostability is discussed. pH-selective bulk optodes have been formulated as a first approach to develop ion-selective optodes, and sensitivity, repeatability, lifetime and response time have been determined. The dyes show good analytical behaviour for use as chromoionophores for the development of ion-selective optodes. Reversible (80-87%), fast (tr90%=0.94-2.28 min) and pH-sensitive membranes (slopes of 0.09-0.23 DeltaAbs.pHdec-1, absorbance range 0.19-0.53) have been obtained. Moreover, they exhibit good spectroscopic features for employment with integrated optochemical sensors: absorption maxima of the acidic species in plasticised PVC membranes matched those of 650-670-nm LEDs, high molar absorption coefficients (epsilonacidic=3.5x10(4)-9.3x10(4) L mol-1 cm-1 and epsilonbasic=1.9x10(4)-6.7x10(4) L mol-1 cm-1) and fluorescence.
Subject(s)
Aniline Compounds/chemistry , Carbocyanines/chemistry , Coloring Agents/chemistry , Carbocyanines/chemical synthesis , Coloring Agents/chemical synthesis , Hydrogen-Ion Concentration , Molecular Structure , Photochemistry , SolutionsABSTRACT
The optical and analytical characteristics of a series of neutral H+-selective chromoionophores in PVC membranes are described. Such indicators have been synthesized so that they can operate in bulk optode membranes as the chemically active region of integrated waveguide absorbance optodes (IWAOs), lambdamax near 780 nm. Their spectral characteristics, acid-base properties, chemical stability, and solubility in the membrane phase are given and discussed. The response characteristics are first tested in a conventional absorbance/transmittance flow cell. They offer a wide range of pKa's in PVC membranes, good sensitivity as a result of their high molar absortivities, excellent solubility in the plasticizer, and quick response times. They present good chemical stability in common laboratory conditions when stored in the dark, and the absence of leaching guarantees a long lifetime. Membranes have been finally applied as the sensing region of an integrated waveguide optode, demonstrating the extraordinary sensitivity improvement while preserving the remaining analytical features. Calibration curve slopes are multiplied by 3-28, and response times lower than 2 min are obtained.
