Trl-n-octyltln chlorlde acts as a neutral carrler for anlons. Llquld membranes contalnlng thls carrler, ( R ,R )-2,3dlmeth-oxysuccinic acld bls( 1-butylpentyl) ester as plastlclzer, and poly(vlny1 chlorlde) as membrane malrlx show selectlvlly patterns whlch are not In accordance with the sequence obtained for classlcal anlon exchangers. These neutral carrler membranes dlsplay Nernstian electrode functlons for dlfferenl anlons In the I O 9 M to IO-' M concentratlon range. NMR and vapor pressure osmometry studles lndlcate an lnteractlon of the tln organlc compound wlth the chlorlde anlon. The expected mlgrallon of the tin organic compound In the dlrectlon of the anode is demonstrated with an electrodlalytlc transport experlment.A large number of anion-selective liquid membrane electrodes based on classical ion exchangers such as quaternary ammonium salts, phosphonium salts, complexes of 0-phenanthroline, and of other complexing agents have been described (1-4). Electrodes have been proposed for the analysis of Cl-(5-9), NO, (3,9, IO), SCN-(11-13) and other inorganic as well as organic anions. For electrodes based on tetraalkylammonium salts, 35 different detectable anions have been mentioned in ref 1. Usually all these electrodes exhibit roughly the same selectivity sequence with a preference of lipophilic and a rejection of hydrophilic anions (14, 15). In these cases, the free energy of transfer of the anions from the aqueous sample phase to the membrane phase-and therefore the membrane selectivity-is controlled by the free energy of hydration of these ions (4,16-20). This is in contrast to neutral carrier based systems for cations, where the ion selectivity highly depends on the free energy of the interaction of the ions with the ligand (14,21). In the latter case, a wide variety of ion selectivities is made accessible (22).Tin organic compounds have been used as components in anion selective electrodes with response t o C1-(23), HAs0,2-IH2As04-(N), NO, (W), and other species. Although tripropyl tin chloride (26) and other triorgano tin compounds (27) have been found to influence anion transport, it has not yet been properly proved that such tin organic compounds may act as neutral carriers for anions. In this paper, we show that trioctyltin chloride displays anion carrier properties if incorporated in solvent polymeric membranes. EXPERIMENTAL SECTIONCell Assemblies for EMF Studies. For all EMF measurements, cells of the following type were used: Hg, Hg2C12; KC1 (satd)llM LiOAclsample solution llmembrane 110.01 M NaC1; AgC1, Ag The external reference electrode was a double junction saturated calomel electrode with a ceramic diaphragm (for details see ref 28). Measurements were performed with four different membranes of the following compositions: (a) 6 wt % methyltri-ndodecylammonium chloride (MTDDACl), 65 wt % di-n-butyl phthalate (DBP), 29 wt % poly(viny1 chloride) (PVC); (b) 3 wt % MTDDACI, 49 wt % (R,R)-2,3-dimethoxysuccinic acid bis(1-butylpentyl) ester (DMSNE), 48 wt % PVC; (c) 3 wt % tri-noctyltin chloride...

Requirements for the applicability of anion-selective electrodes in clinical analysis are discussed in terms of selectivity, response time, lifetime and stability. Basically, classical anion-exchangers, electrically charged carriers and electrically neutral carriers may be used as anion-selective components in solvent polymeric membranes. While classical ion-exchanger-based membrane electrodes are only of limited practical relevance, sensors containing ion carriers seem to bear a broad potential with regard to the feasibility of realizing the required properties. The control of the selectivity determining properties of electrically neutral tin organic anion carriers probably allows the development of sufficiently selective membranes for the assay of clinically relevant anions. Furthermore, the incorporation of membrane technology into the design of such carrier membranes may lead to fully optimized sensors.

A series of triorganyltin compounds of the type R,SnY and R:R2SnY has been studied in view of their anion selectivities exhibited in solvent polymeric membranes. A large variety of selectivity patterns has been observed first by varying the concentration of a given ionophore in the membrane phase, and second by using ionophores which differ in the organic substituents R on the Sn centre. With more space consuming substituents R, the observed selectivity patterns become more and more similar to that of a blank membrane, suggesting steric hindrance for the pentacoordination of the corresponding ionophores by sample anions.Introduction. -Certain organotin compounds induce anion selectivity in membranes [l-61 and act as electrically neutral carriers for anions [4] [6] (see also [7]). They are attractive candidates for anion sensors with a selectivity sequence deviating from the one observed with classical anion-exchanger membranes [5] [6] (Hofmeister lyotropic anion selectivity sequence:

A series of distannyl derivatives (2,2-bis(trimethylstannyl)-1,3-dithiane, 2,2-bis(tributylstannyl)-l,3-dithiane, hexamethyldistannane, hexabutyldistannane, hexaphenyldistannane, bis(triphenylstannyl)sulfide, o-bis(trime-thylstanny1)benzene) has been studied in view of their applicability as anion-selective ionophores in solvent polymeric membranes. None of these compounds induces significant changes in the anion-selectivity pattern as compared with the membranes containing no organotin compound. Representatives with tributylstdnnyl groups, however, undergo chemical reactions leading to highly active anion ionophores of the type Bu,SnX, several of which (e.g. Bu,SnCI and Bu,SnOH) may be present in equilibrium in the membrane phase depending on the measuring conditions.

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