ELECTROANALYTICAL STUDIES ON SOME ION SENSORS

Abstract

Analytical chemistry has contributed greatly to the development of newer methods for the analysis of many industrial products viz. drugs and pharmaceuticals, alloys and steels, cement and paint, textiles and polymers, ceramics and glasses, insecticides and fungicides etc. available to augment the quality of life. It is a paradox that the industries which made these products have also contributed greatly in polluting the environment causing detrimental effects to human and animal life. Thus, it has become important to determine contaminants in diverse samples. The aim of modern analytical techniques is to determine analytes with high sensitivity and selectivity. Several analytical techniques such as Atomic Absorption Spectrometry (AAS), Inductively Coupled Plasma with Mass Spectrometry (ICP-MS), Inductively Coupled Plasma Atomic Emission Spectroscopy (ICPAES), Fluorimetry, Gas Chromatography (GC), High performance liquid chromatography (HPLC), Cyclic Voltametery etc. are available. Although some of these methods are very precise and selective for the determination of a number of cations and anions in the solution, but their applications are limited by various factors such as cost, complex instrumentation and consumption of time. A technique that requires minimum chemical manipulation of the sample and provides rapid, accurate, low-cost, on-field determination is the most preferred requirement of analytical chemists. The above requirements are met to a great extent by ionselective electrodes (ISEs) or ion sensors. ISEs can be employed in the analysis of samples in various fields including clinical, environmental, industrial and agricultural studies. A number of commercially available ISEs' have been developed as convenient tools for analysis of cations and anions in food products, biological fluids, effluents, wastewater, soil, fertilizers etc. (i) Ion-selective electrode consists of a semipermeable membrane that separates two different solutions of an appropriate electrolyte and responds selectively to a particular ion in presence of other ions. The membrane constitutes an active ion-exchanger ingredient generally called an ionophore or electroactive material. Ionophore plays a key role in the sensitivity of an ISE. The creation of cavities and cleft in the ionophore are complementary to the size and charge of a particular ion leading to selective interactions. One of the most important feature of ISEs is the selectivity towards a specific analyte, which is generally limited by the interaction of ionophore within the membrane with other ions in solution. The ion-ionophore interactions based on their ion-exchange property or size-exclusion of the ionophore, determine selectivity of an ion sensor and its proper functioning towards a specific ion. The design and function of synthetic ionophores is based on diverseparameters viz. structure and cavity size of the ligand, stability and selectivity of its metal ion complex, its solubility and the ability to extract the metal ion into membrane phase. The wide use of ion-selective potentiometry in routine analysis is accompanied by a search for more selective membrane materials and also on theoretical studies of the mechanism of functioning of these sensors. The present work is aimed to synthesize new ligands and their ion-pair complexes for to use them as electroactive components (ionophore) in the preparation of membranes for determination of various cations and drugs. For the sake of convenience, simplicity and clarity, the work embodied in the thesis has been organized as follows: The First Chapter of the thesis 'General Introduction ' presents an historical review of all the literature on the previously reported ion selective membrane sensors of alkaline, alkali earth, transition and rare earth metal ions and also some extent too on drug selective membrane sensors. The problems of present research activities on membrane sensors have also been discussed to make a new challenge for future research. (ii) The Second Chapter of the thesis ''Theory and Methodology encompasses classification of ISEs, theory of membrane, its potentials and terms used in the study of ion selective electrode. The description of the selectivity of sensor membrane and method of its determination has also been described. The Third Chapter of the thesis 'Membranes of Setoff's Bases as Ion Selective Sensors' deals with synthesis and characterization of and Schiff bases and their analytical application in the preparation of ion-selective electrodes. In order to improve the performance characteristics of PVC based membrane sensors; different Schiffs bases have been synthesized and comparatively evaluated as ion-selective sensors. The addition of various plasticizers and ionic additives were tested for optimization of membrane composition and their potential responses were investigated. Therefore the membranes of 2,2'-(lZ, 1'Z)-(1E, l'E)-(l,2-phenylenebis (methan-1-yl-l-ylidene) bis(azaan-l-yl-l-ylidene) bis (methylene) bis (azan-1-yl-l-ylidene) bis(methan-l-ylylidene) diphenol (Li) and 4,4'-(lE,l'E)-(butane-l,4-diylbis(azan-l-yl-l-ylidene))bis (methan-1-yl-1 ylidene) dinaphthalen-1-ol (L2) have been comparatively investigated for quantification of cadmium ions. It has been observed that the membranes based on L, shows better performance in comparison to L2 based membranes. The membrane based on L| Schiff base of composition; w/w of (L,) (2.6%) : PVC (31.6%) : DOP (63.2%) : NaTPB (2.6%) exhibited Nernstian response in the concentration range 5.0 x 10" to 1.0 x 10" M Cd2+ with detection limit of 3.1 x 10"9 and performs satisfactorily over wide pH range (2.0 - 8.5) with a fast response time (11 s). The Li based sensor has also been tested in partial non aqueous medium and it was observed that it works satisfactorily in partially non-aqueous media up to 40% (v/v) content of methanol, ethanol and acetonitrile and could be used for a period of 2.5 months. The analytical application of Li based membrane has been evaluated (iii) by determining the cadmium concentration in Cigarette samples. The practical utility of the membrane electrode has also been observed in the presence of surfactants. Similarly Praseodymium ion (Pr3+) selective polyvinyl chloride (PVC) membrane sensors, based on two newly synthesized schiffs bases; l,3-diphenylpropane-l,3- diylidenebis(azan-l-ylidene) diphenol (L3) and N,N'-bis(pyridoxylideneiminato)ethylene (L4) have been developed and comparatively studied. It was found that among two schiff s base (L3 & L4) based membrane sensors; the L3 based membrane sensor shows better performances with composition (w/w,mg) (L3) (8) : PVC (150) : o-NPOE(300) : NaTPB (5). The L3 based membrane sensor exhibits working concentration rangel.O x 10 8 to 1.0 x 10"2 Mwith a detection limit of 5.0 x 10"9 Mand a Nernstian slope 20.0 ± 0.3 mV decade of activity. It exhibited a quick response time as < 8 s and performs satisfactorily over pH range of 3.5 to 8.5. The sensor's performance has been also checked in non aqueous medium and it was found that L3 based sensor work satisfactorily in partially non aqueous media up to 15 % (v/v) content of methanol, ethanol or acetonitrile and could be used for a period of 3 months. To assess its analytical applicability the prepared sensor was successfully applied for determination of praseodymium (III) in spiked water samples. At last The two nickel chelates of Schiff bases, 3-Hydroxy-N- {2-[(3-hydroxy-Nphenylbutyrimidoyl)- amino]-phenyl}-N'-Phenylbutyramidine (Mi) and 4-(E) -2-(E)-(4- hydroxynaphthalen-lyl) methyleneamino ethylimino methyl naphthalene-1-ol (M2), have been synthesized and explored as ionophores for preparing PVC-based membrane sensors selective to nickel ion. The influences of membrane compositions on the potentiometric response of the electrodes have been found to substantially improve the performance characteristics. The best performance was obtained with the sensor no.2, having a membrane composition (w/w; mg) of (Mi): PVC: NaTPB : CN in the ratio 5: 150: 5: 150. (iv) The sensor no. 2 shows a linear potential response for Ni~ over a wide concentration range 1.6 x 10"7 to 1.0 x 10"2 Mwith Nernstian compliance (30.0 ± 0.2 mVdecade"' of activity) within pH range 2.5 to 9.5 and a fast response time of 10 s. The sensor no. 2 has been found to work satisfactorily in partially non-aqueous media up to 20% (v/v) content of methanol, ethanol, and acetone and could be used for a period of 4 months. The analytical usefulness of the proposed electrode has been evaluated by its application in the determination of nickel in real samples. The practical utility of the membrane electrode has also been observed in the presence of surfactants. Fourth Chapter of thesis 'Membranes of Macrocyclic Schiffs Bases as Ion Selective Sensors' deals with the synthesis, characterization and applications of macrocyclic Schiff bases's as ion-selective sensors. In this regard, six different macrocyclic Schiff 4- bases's (Ls-Lio) derivatives of 4,13-Diaza-18-crown ether have been synthesized and explored as Silver(I) selective poly(vinyl chloride) membrane sensors. The addition of Potassium tetrakis(4-chlorophenyl) borate and various plasticizers, viz., o-NPOE, DBP, DBBP, DOP and CN has been found to substantially improve the performance of the sensors. The best performance was obtained with the sensor having membrane of macrocyclic Schiff bases's (Li0) with composition (w/w); Lio (2.8%) : PVC (45.7%) : o-NPOE (48.6%) : KTpClPB (2.8%). This sensor exhibits Nernstian response with slope 59.3 mV/ decade of activity in the concentration range 5.6 x 10"8 - 1.0 x 10"'M Ag(I), performs satisfactorily over wide pH range of (3.0-8.0) with a fast response time (12 s). The sensor was also found to work satisfactorily in partially non-aqueous media up to 25% (v/v) content of acetonitrile, methanol or ethanol and can tolerate the concentration 1.0 x 10" M of ionic (SDS, TBC) and nonionic (TritonX-100) surfactants. The analytical application of proposed silver selective sensor is evidence by determining the silver content in blood of occupationally exposed persons. (v) Similarly Three more macrocyclic schiff bases's (Ln-Ln) derivatives of Bis (5- formyl-2-thienyl) methane Schiff s base have been synthesized and explored as a neutral ionophores for comparative evaluation of poly(vinyl chloride ) based membrane sensors selective to Dy +. The different membranes have been optimized by using sodium tetraphenyl borate as an anion excluder with different plasticizers: o-NPOE, DBP, DBBP, DOP and CN. It has been found that best performance observed with L,| containing membrane sensor with composition; (w/w) Ln (4.5%) : PVC (30.5%) : o-NPOE (59.5%) : NaTPB(5.5%). This sensor exhibits Nernstian response with slope 19.4 mV/ decade of activity in the concentration range 5.4 x 10"8 - 1.0 x 10"2 MDy3-, performs satisfactorily over wide pH range of (2.8-7.2) with a fast response time (10s). The sensor was also found to work satisfactorily in partially non-aqueous media up to 20% (v/v) content of acetonitrile, methanol or ethanol. The proposed sensor can be used over a period of 1.5 months without significant drift in potentials. The sensor has been applied in determination of Dy3+ level in different soil samples. Fifth Chapter of thesis 'Drug Selective PVC Based Membrane Sensors ' deals with the synthesis, characterization and applications of ion-pair complexes of Quaternary ammonium drugs as a PVCbased membrane sensors. In this view two novel ion-pairs (PBTPB & NB-TPB) of quaternary ammonium drugs; Propantheline bromide (PB), N,N-Diisopropyl-N-methyl-N-[2-(xanthen-9ylcarbonyloxy)ethyl] ammonium bromide and Neostigmine bromide (NB), 3-(dimethylcarbamoyloxy) phenyl]- trimethylazanium have been synthesized respectively and explored as poly (vinyl chloride)-based membrane sensors for the quantification of Propantheline bromide and Neostigmine bromide in different pharmaceutical preparations. The influences of membrane compositions on the potentiometric responses of membrane sensors have been found to substantially improve the (Vi) performance characteristics. The best performance was reported with membrane having composition (w/w) of PB-TPB or NB-TPB (6%) : PVC (34%) : o-NPOE (60%). The proposed sensors exhibit nernstian responses in the concentration range of 2.1 x 10" M - 1.0 x 10"2 M and 4.4 x 10"7 M - 1.0 x 10"2 M with detection limit of 1.5 x 10"7 M and 3.3 x 10"7Mrespectively. The both membrane sensors perform satisfactorily over pH ranges of (3.5 - 7.5 and 4.0 - 7.0) with fast response times (11 & 13) seconds respectively. These drugs (PB & NB) were further utilized as a Prostaglandin Ei (PGE|) and Deoxycholate (DOC) selective poly (vinyl chloride)-based membrane sensors for the determination of prostaglandin Ei and Deoxycholate in blood samples of different patients. The Desipramine hydrochloride (DH) 3-(5,6-dihydrobenz [b] [1] benzazepin-1 1-yl) -N-methyl propan-1-amine selective PVC membrane sensor has been developed by synthesizing novel ion-pair ([TPB]" [DH]+). Similarly the effect of membrane composition on potentiometric responses by using different plasticizers has been analyzed and It was observed that best responses were expressed by membrane having composition (w/w,mg) of ([TPB]" [DH]+) (5) : PVC (150) : o-NPOE (150). The proposed sensor exhibits nernstian response in the concentration range of 2.2 x 10"6- 1.0 x 10"2 Mwith detection limit of 1.2 x 10"6 M. The membrane sensor performs satisfactorily over pH range of (2.8 - 7.4) with fast response time 12 seconds. The proposed sensor can tolerate the non-aqueous content up to 20% and utilized for the determination of drug concentration in pharmaceutical preparation and in body fluids like urine and blood samples.