FIBEROPTIC PH SENSOR-BASED ON EVANESCENT-WAVE ABSORPTION-SPECTROSCOPY

A new approach to the design and construction of an optical pH sensor has been investigated by immobilizing a conductive polymer (polyaniline) onto the core of a silica optical fiber. An evanescent wave spectrum of the conductive polymer was used to monitor the effect of pH. The spectrum was measured on a holographic grating monochromator with a Ge diode array detector and on a Fourier transform near-IR spectrometer equipped with an InSb detector in the near-IR region from 1100 to 1450 nm. Models expressing pH were developed with nonlinear P-matrix regression using a single wavelength. Correlation of the near-IR pH sensor and a commercial electrode pH meter produced R2 values of >0.999 for both the training and validation sets. The standard error of prediction (SEP) for cross validation of the training set was 0.084 and that for a validation set was 0.067 over a pH range of 3-12.