Performance of a highly lipophilic Li+ lonophore in solvent polymeric membranes

Abstract

Ionophores based on non-cyclic triamides exhibiting Li § selectivity in solvent polymeric membranes are described. Their lipophilicity (water/1-noctanol partition coefficient) is up to 1013'8 so that they can be used in ionselective electrodes with a lifetime of up to 40 000 h even in permanent contact with whole blood or undiluted blood serum.Key words: ionophore for Li +, ion selective electrodes, high lipophilicity, solvent polymeric membranes.In view of the measurement of the lithium ion activity in whole blood, blood plasma or blood serum of patients suffering from manic depressive psychosis there are ongoing efforts to find ionophores which induce a high Li+/Na § selectivity in membranes [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19]. Assuming a therapeutic range between 0.7 and 1.5 mM Li § and an interference of less than 1% by Na + (worst case, 150 mM Na § a selectivity log rTPot -e /X.LiNa Ol at least --4.3 is required [20]. The most selective, analytically relevant Li § sensors exhibit values of -2.45 [5] and -2.8 [15], which are still far from the required level. Because of the high stability of the signal measured when contacting the ion selective electrode with undiluted blood, plasma or serum sensors with selectivities as low as log repot -1.9 [6] have found wide application in clinical aXLiNa = analyzers. This high signal stability is partly due to the high lipophilicity of the ionophore and plasticizer used [21]. Here we report on an Li + ionophore with increased lipophilicity related to the one described earlier and on the electromotive behaviour in solvent polymeric membranes of different composition. Experimental Regents and SynthesisThe synthesis of the ligands 1 and 2 ( Fig. 1) was described previously [1]. All electrolyte solutions were made from doubly quartz distilled water and salts of the highest purity available (Fluka AG, Buchs,

Voltammetric Mechanism of Multiion Detection with Thin Ionophore-Based Polymeric Membrane

“…Experimentally, we demonstrate the detection of primary and secondary ions based on IE and IT mechanisms by using single and double ionophores, respectively. Specifically, a thin poly­(vinyl chloride ) (PVC) membrane is doped with Na + -selective ionophore 1 or Li + -selective ionophore 2 (Figure ) to yield voltammetric responses not only to the primary ion, but also to the secondary alkaline earth ion based on the IE mechanism. The ratio of peak currents for the respective ions is assessed theoretically to confirm the formation of 1:1 complexes with both ions, which yields a net transferred charge, | z J |/ n J – | z I |/ n I , of +1.…”

Voltammetric Ion Selectivity of Thin Ionophore-Based Polymeric Membranes: Kinetic Effect of Ion Hydrophilicity

“…We found that voltammetric selectivity was improved kinetically not only by rigid cyclic ionophores 1 and 2 with slow ion-binding kinetics , but also by flexible noncyclic ionophore 3 . These results suggest that the kinetics of facilitated ion transfer is not controlled by ion–ionophore complexation.…”

“…19 These results suggest that the kinetics of facilitated ion transfer is not controlled by ion–ionophore complexation. Specifically, thin-layer CVs of o NPOE/PVC membranes doped with ionophore 3 were nearly reversible for lithium ion (Figure 6A) and nearly irreversible for magnesium ion (Figure 6B) in separate solutions.…”

“…We found that voltammetric selectivity was improved kinetically not only by rigid cyclic ionophores 1 and 2 with slow ion-binding kinetics 30,31 but also by flexible noncyclic ionophore 3. 19 These results suggest that the kinetics of facilitated ion transfer is not controlled by ion−ionophore complexation. Specifically, thin-layer CVs of oNPOE/PVC membranes doped with ionophore 3 were nearly reversible for lithium ion (Figure 6A) and nearly irreversible for magnesium ion (Figure 6B) in separate solutions.…”

“…14 Specifically, Na + -selective ionophore 1 16,17 gives irreversible CVs of calcium, strontium, and barium ions in separate solutions to kinetically improve voltammetric selectivity by 3, 2, and 1 order of magnitude, respectively. Moreover, the voltammetric Na + and Li + selectivity of ionophore 2 18 and 3 19 is improved by 4 and >7 orders of magnitude against calcium and magnesium ions, respectively, in mixed solutions owing to both thermodynamic and kinetic effects in comparison with thermodynamic selectivity in separate solutions. Mechanistically, we propose that the slower transfer of a more hydrophilic ion is controlled by its partial dehydration upon its attachment to a “water finger” as predicted theoretically.…”