A new approach to the design and construction of an optical pH sensor
has been investigated by immobilizing a conductive polymer (polyanilin
e) onto the core of a silica optical fiber. An evanescent wave spectru
m 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 regre
ssion using a single wavelength. Correlation of the near-IR pH sensor
and a commercial electrode pH meter produced R2 values of >0.999 for b
oth 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.