The construction of a pH sensor, having the configuration of a probe, is described. The probe utilises a plastic-fibre bundle at the end of which is fabricated a sensitive tip consisting of a styrenedivinylbenzene copolymer supporting an adsorbed colorimetric pH indicator, which is retained in position by a membrane of polytetrafluoroethylene (PTFE). Changes in pH in the vicinity of the sensitive tip cause a variation in the attenuation of specific reflected visible radiation bands. Initial results and performance specifications using bromothymol blue as the colorimetric indicator are presented.

Results of studies using a flow-cell and immobilised indicator dye reagents for the development of a chemically sensitive fibre-optic system for measurement of pH are presented. The indicator dye reagents are immobilised on a cross-linked styrenedivinyl benzene polymer matrix and reflectance measurements are made as a function of pH using a bifurcated fibre-optic system.

In our review' we were in error in stating (page 796) that the infrared spectra of the optically active pair of amphetamine mandelates described by Heagy2 were mis-captioned. We had used a specimen described as D-mandelic acid, which is optically laevorotatory, and consequently obtained transposed spectra from those of Heagy who had used "d-mandelic acid," (which is dextrorotatory). Our error raises two points of emphasis.(i) It is regrettable that optically active substances continue to be described by the terms d and 1, particularly where the configuration based on the classical glyceraldehyde reference D or L structure may be of the opposite hand, i . e . , D-(!)and ~-( d ) -, as with mandelic acid. The preferred absolute description would be R( -)and S( +)for Iand d-mandelic acid, respectively.(ii) It also highlights the importance of using reference standards in (forensic) analysis. In this case the use1 of configuration labelled mandelic acid enantiomer unexpectedly gave the opposite spectra compared with those previously published .2 However, because authentic amphetamine enantiomer reference standard was simultaneously employed, the correct optical assignment was given to unknown amphetamine specimens.

No abstract