Fiber Optic Probe Applications Using Near-Infrared Compounds: Determination of NaOH

Abstract

The development of a near-infrared fiber optic probe (FOPP) for the determination of caustic soda will be reported. The utility of the FOPP is demonstrated using an NIR non-commercially available tetrasubstituted chloroaluminum naphthalocyanine NIR dye which is susceptible to pH changes in solutions. The naphthalocyanine derivatives have been synthesized in our laboratories. The spectral characteristics of these NIR dyes, are above 700 nm and the absorbance maximum is a perfect match for the use of semiconductor laser diodes as the excitation source. The response of the Q-band against solution pHs and caustic soda will be reported. The FOPP consists of a semiconductor laser diode (λ_max=780 nm), an NIR dye and a detector. The probe made of poly(methyl methacrylate) serves as a support for a permeable polymer that is used for the entrapment of the NIR dye (about < 2mm in diameter). The permeable polymers used were Nafion and Gelatin. As hydrogen ions diffuse through the permeable polymer, a complex is formed with the dye, accompanied by changes in the spectral characteristics of the dye. Excitation of the complex is induced with a semiconductor laser diode at 780 nm. The probe shows good reproducibility of the data in NaOH measurements. Also the molar absorption coefficient of these dyes at different concentrations of polymer will be reported. The effect of Nafion on the spectral characteristics of the NIR dyes will be presented. The general procedure used for the attachment of the dye to the distal end of the probe can be used to construct compact non-invasive detectors. The use of photodiodes as detertors will be discussed. Use of smaller components shown here will allow for the manufacturing of portable instruments for applications in medicine and industry.