Ion-selective electrodes have many advantages in the ion activity determining process, i.e., direct and real-time monitoring of samples is possible. The key ingredient of plasticized PVC membranes is the incorporated ionophore, which defines the selectivity of the electrodes via selective complex formation with the cation of interest. The design and synthesis of neutral carriers/ionophores have become important in the field of host-guest chemistry. The most widely used ionselective electrode (ISE) for determining potassium is based on antibiotic valinomycin.1 Other carriers including crown ethers 2-5 substituted ethers of tetraethyleneglycol, 6 organo-phosphine ligands 7 and polymer supported liquid crystal membranes 8 have also been successfully applied as carriers for constructing potassium ISEs.The incorporation of crown ether groups into self-assembled monolayers (SAMs) and their potential use as metal-ion sensors was reported. 9,10 We recently prepared TEG (triethylene glycol monomethyl ether)-and PEG (polyethylene glycol monomethyl ether)-end-grafted carbosiloxane and carbosilane dendrimers and studied their ability to detect alkali metal-ion binding. 11 The general idea was to use the glycols to form ion binding domains at the periphery (similar to crown ethers) via self assembly. Apart from the ionophore topology, other membrane constituents, such as additive and plasticizers, also play a vital role in the performance of an ion sensor.Brodbelt et al. first described the use of electrospray ionization mass spectrometry (ESI-MS) as an easy way to obtain, in general, information about binding selectivities in host-guest compounds, such as crown ether or cryptand metal complexes.12,13 The minimal sample consumption and the rapid feedback are the advantages of this method. The obtained results could provide essential information regarding the use of compounds as potential ionophore in ion-selective electrodes (ISEs).In this publication, we describe the use of ESI-TOF mass spectrometry for preliminary screening a triethylene glycolfunctionalized carbosilane for the selective complexation of alkali metal ions.Based on information from mass spectrometric studies, we decided to use Si[CH2CH2CH2-Si(Me)2CH2CH2CH2(OCH2CH2)3Me]4 (1) as an ionophore in the fabrication of a PVC-based membrane electrode. We already reported on the synthesis and characterization of 1 in an earlier publication.11 Carbosilane dendrimers are expected to have high selectivity probably due to the fact that they are very stable towards hydrolysis, which makes them more suitable to be used as ionophores. The number of alkaline metal cations that can be coordinated depends on the number of peripheric TEG groups attached to the carbosilane. This paper reports on the cation selective properties and potentiometric response characteristics of 1 with various membrane components. The results indicate that the electrode offers a wide linear response range, and high selectivity and sensitivity to potassium.
ExperimentalReagents and equipment ESI-TOF exp...