The values for the equilibrium constants (K2, K3) were estimated from the relevant Eo values. The simulated voltam-

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o-Xylylene bis(diisobuty1-and methyloctadecyl-dithiocarbamate) were synthesised and used as neutral carriers in membrane electrodes t o improve the selectivity for Cu2+. The electrodes based o n these ionophores, with o-nitrophenyl octyl ether as a plasticising solvent mediator and potassium tetrakis-(p-chloropheny1)borate as an anion excluder, exhibit a linearity range of 10-1-10-6 M and have a Nernstian slope of 28-29 mV per decade at 25°C. The highly selective electrode based o n o-xylylene bis(diisobuty1dithiocarbamate) rejected the interference of alkali, alkaline earth and transition metal cations by a factor in the range l O 2 -l O 4 and showed a high selectivity for Cu2+ even in chloride and bromide media. The properties of the electrodes are discussed and also compared with those of o-xylylene bis(diethy1dithiocarbamate) under similar measurement conditions.

A new thiocarbamate derivative is used in polymeric sensing films together with a lipophilic chromoionophore for determining Ag+ at submicromolar levels. The membrane composition has been optimized with a view to measuring concentrations of Ag+ added as a bacteriostatic agent to drinking water. The results compare well with those obtained by ICPMS.

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PVC membrane electrodes that are selective and sensitive to copper(l1) have been developed. The best electrode, based on 13,14-benzo-I ,5-tetrathiacyclopentadecane and 2-nitrophenyl octyl ether solvent mediator w i t h a potassium tetrakis(p-chloropheny1)borate anion excluder, exhibits a linear response in the range 10-1-10-6 M over the pH range 2.9-6.7 and has a Nernstian slope of 28-29 m V per decade at 25 "C. The response time is 10 s.

Samarium(III)-selective electrodes constructed on the basis of bis(alkylxanthato)alkanes and bis(thiaalkylxanthato)alkanes are described. As a class, both types of compounds showed quantitative responses toward Sm-(III) ion. Among the ionophores tested in this work, the neutral carrier, 1,4-bis(3-thiapentylxanthato)butane, provided an ion-selective electrode almost ideal for determination of Sm(III) in aqueous solution. This electrode exhibits a Nernstian slope of 20 mV per concentration decade, with a detection limit of 5.0 × 10 -7 M Sm(NO 3 ) 3 . Acceptable selectivity was obtained for Sm(III) determination against many of the transition, alkali, alkalineearth, and some of the lighter rare-earth metal ions. Only Cu(II) and Fe(III) interfere seriously.