Fiber optic pH sensing with long wavelength excitable Schiff bases in the pH range of 7.0-12.0

Anal Chim Acta. 2007 Apr 4;588(1):42-9. doi: 10.1016/j.aca.2007.01.070. Epub 2007 Feb 6.


Most of the fluorescent pH probes work near neutral or acidic regions of the pH scale. In this work, two different fluorescent Schiff bases, chloro phenyl imino propenyl aniline (CPIPA) and nitro phenyl imino propenyl aniline (NPIPA), have been investigated for pH sensing in the alkaline region. Absorption and emission based spectral data, quantum yield, fluorescence lifetime, photostability and acidity constant (pK(a)) of the Schiff bases were determined in conventional solvents and in PVC. The long wavelength excitable immobilized Schiff bases CPIPA (lambda(ex)=556 nm) and NPIPA (lambda(ex)=570 nm) exhibited absorption and emission based optical response to proton in the pH range of 8.0-12.0 and 7.0-12.0, respectively. Response of the CPIPA was fully reversible within the dynamic working range. The response times were between 3-13 min. A relative signal change of 95% and 96% have been achieved for sensor dyes of CPIPA and NPIPA, respectively. The CPIPA displayed better fluorescence quantum yield (varphi(F)=3.7 x 10(-1)) and higher matrix compatibility compared to NPIPA (varphi(F)=1.6 x 10(-1)) in immobilized PVC. The CPIPA and NPIPA exhibited a slight cross sensitivity to the ions of Hg(+) and Fe(3+), respectively.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Aniline Compounds / pharmacology
  • Cations
  • Chemistry Techniques, Analytical / methods*
  • Fiber Optic Technology*
  • Hydrogen-Ion Concentration
  • Imidazoles / pharmacology
  • Imines / pharmacology
  • Ions
  • Light
  • Models, Chemical
  • Optical Fibers
  • Protons
  • Pyridines / pharmacology
  • Schiff Bases
  • Solvents / chemistry*
  • Spectrometry, Fluorescence / instrumentation
  • Spectrometry, Fluorescence / methods
  • Spectrophotometry
  • Ultraviolet Rays


  • Aniline Compounds
  • Cations
  • Imidazoles
  • Imines
  • Ions
  • Protons
  • Pyridines
  • Schiff Bases
  • Solvents
  • nitrophenyl imino propenyl aniline
  • 2-(4-chlorophenyl)-3H-imidazo(4,5-b)pyridine-3-acetamide