Variation of salivary calcium, phosphate and buffering capacity in adolescents.

Calcium, phosphate and buffering capacity were measured in children's (n=43) unstimulated saliva between September 1990 and June 1991 inclusive. Saliva samples were collected in the afternoon, once a month, on 10 consecutive occasions. Buffering capacity was assessed immediately after sample collection using the Dentobuff strip method.

Symmetrical, unsymmetrical and bridged calix[4]arene derivatives as neutral carrier ionophores in poly (vinyl chloride) membrane sodium selective electrodes.

The complexing ability of a range of 19 symmetrical, unsymmetrical and bridged calix[4]arene derivatives having ester, ketone, amide, amine and thioether functionalities were determined by the picrate extraction method. On incorporating these calix[4]arene derivatives as neutral carrier ionophores in sodium-selective poly (vinyl chloride) membrane electrodes the performance was assessed on the basis of the sensitivity and selectivity over the alkali, alkaline earth metals and hydrogen and ammonium ions. The temperature dependence, response times and lifetimes were also determined.

Calixarene-based potentiometric ion-selective electrodes for silver.

Four lipophilic sulphur and/or nitrogen containing calixarene derivatives have been tested as ionophores in Ag(I)-selective poly (vinyl chloride) membrane electrodes. All gave acceptable linear responses with one giving a response of 50 mV/dec in the Ag(I) ion activity range 10(-4)-10(-1)M and high selectivity towards other transition metals and sodium and potassium ions. This ionophore was also tested as a membrane coated glassy-carbon electrode where the sensitivity and selectivity of the conventional membrane electrode was found to be repeated.

A computer-assisted metal analyser using flow injection coupled with direct current plasma-optical emission spectroscopy.

An automated routine method was developed for the determination of trace metals using a flow injection system into a direct current plasma spectrometer. The characteristic emission in the 'Spectra- Metrics' three-electrode jet is channelled through an echelle grating to the detector of the instrument. The emission signal is continuously recorded, and, after digitalization, calculated and recorded by a Touchstone software package and interface card.

Determination of traces of osmium by the catalysed hydrogen peroxide-cyanocuprate(I) reaction.

The reaction between hydrogen peroxide and a mixture of cyanocuprate(I) species at pH 11.2 is selectively catalysed by traces of osmium. With potentiometric or amperometric monitoring, osmium concentrations up to 1 ng ml can be determined, with a lowest determinable concentration of 0.