Please use this identifier to cite or link to this item: http://localhost:8081/xmlui/handle/123456789/1429
Title: ELECTROANALYTICAL INVESTIGATIONS AND APPLICATIONS OF SOME ION SELECTIVE SENSORS
Authors: Raisoni, Jitendra Rajendra
Keywords: CHEMISTRY;ELECTROANALYTICAL INVESTIGATIONS;ION SELECTIVE SENSORS;INDUCTIVE COUPLED PLASMA-MASS SPECTROMETRY
Issue Date: 2006
Abstract: The quantitative determination of target species is an area of paramount importance and research. Several analytical techniques such as Atomic Absorption Spectrometry, Inductive Coupled Plasma-Mass Spectrometry, Ion Chromatography, Flame Photometry, Cyclic Voltametry and so forth are available for the quantitative analysis of chemical species. However, maintenance and operational cost of these techniques is high and require adequate expertise. Therefore, the analysis is mostly limited to laboratory level only. A reliable, low cost, quick and portable analytical technique is the need ofthe day, especially for the analysis oflarge number ofsamples in the field and such requirements are greatly met with ion sensors. Analysis by ion sensors is often non-destructive and adaptable to small sample volume with possible applications in real-time analysis. Further, they provide accurate, reproducible, fast and often selective quantification of many chemical species. Thus, ion sensors have emerged as convenient tools for analysis of diverse samples. However, selective ion sensors are available only for some ions and for others, need to be developed. Ion sensors generally employ homogeneous/heterogeneous membranes of chemical compounds which have the property to allow a particular ion to diffuse through and restrict the diffusion of other ions substantially. The compounds whose membranes show such behaviour are normally called selective ionophores. Various types of ionophores such as solid electrolytes, inorganic and organic ion exchangers, insoluble salts of multivalent metals, macrocycles, cryptands, calixarenes, etc. have been explored for the fabrication of ion sensors for different ions. These investigations (0 have resulted in the commercial availability of highly selective sensors for H*, NH/, Na+, K+, Ca2+, Ag+, CN", N03", S2", S042', halide ions, etc. Sensors for many other heavy metals andanions have also been reported but they suffer from poor sensitivity and selectivity, long response time and limited pH range. Therefore, efforts are needed to prepare selective and sensitive sensors for other ions. It is obvious that the development of ion sensors require an ionophore which has high affinity for a particular cation/anion and very poor for others but such materials are not available in abundance. However, newer materials such as derivatized calixarenes, porphyrins, dendrimers, metal chelates and diamide receptors are being continually synthesized and some of them have shown high affinity for a particular ion and therefore possess the potential to provide selective membrane sensor for them. Thus, we have explored some newly synthesized and selective calixarenes, porphyrin and metal chelates for preparing Co +, Sr +, Pb +, Cu2+, Ni2+, QO42' -selective sensors and diamide receptors showing affinity towards anion, for preparing CO32" and HPO42" selective sensors. Calixarenes and porphyrins represent a unique class of macrocyclic molecular receptors having cavity which is able to encapsulate/complex a particular ion in it. It is reported that calixarenes and porphyrin viz., 4-tert-butylthiacalix[4]arene (I) and 4-tertbutylcalix[ 8]arene octaacetic acid octaethyl ester (H) show high affinity for Co2+ and Sr2+, respectively; 5,ll-dibromo-25,27-dipropoxycalix[4]arene (HI) and 2,12- dimethyl-7,17-diphenyl tetrapyrazole (IV) for Pb2+ and C-thiophenecalix[4] resorcinarene (V) for Cr042' ions. Thus, there is strong possibility that the membranes of(I-IV) may act as selective sensors for Co2+, Sr2* and Pb2+, respectively and of (V) for Cr042' ions. Thus, the membranes of these ionophores were investigated. Their homogeneous membranes could not be used as they were found to be mechanically 00 fragile. Therefore, PVC based membranes of the ionophores were prepared with and without plasticizers. The cells using these membranes were set up and their potential was determined as a function of activity of the ion under investigation. The results show that the potential response ofPVC based membrane (without plasticizer) of (I) is linear to logac02+ in the concentration range of3.2 x 10 '5 - 1.0 x 10_1 Mwith the near- Nernstian slope (30 mV decade"1 of activity). It is known that the addition of plasticizers to the PVC based membranes improves their performance characteristics. Thus, in order to improve performance characteristics of PVC based membranes of (I), the addition of various plasticizers viz., bis(2-ethylhexyl) sebacate (DOS), di-butylphosphate (DBP), tri-butyl phosphate (TBP), o-nitrophenyl octyl ether (NPOE), tris(2-ethylhexyl)phosphate (TEHP), di-butylbutylphosphate (DBBP), and chloronapthlene (CN) was tried and their potential response investigated. It was found that the performance of all plasticized membranes of (I) is better than its membrane without plasticizer. Of all the plasticized membranes, the one with NPOE plasticizer performs best. Therefore, the effect of amount of various ingredients on the membrane with NPOE plasticizer was also studied and the membrane with composition 2:1.5:80:140 mg (I:NaTPB:PVC:NPOE) exhibited widest working concentration range (5.3 x 10 *- 1.0 x 10 'l M) with near-Nernstian slope (30mV decade'1 ofactivity). This membrane also showed lowest response time of 10sand works satisfactorily in partially non-aqueous medium. The selectivity studies of this sensor, evaluated with Fixed Interference Method, show that the sensor under consideration possesses excellent selectivity for Co2+ over a large number of mono-, bi- and trivalent cations. This selectivity allowed its use as an indicator electrode in the potentiometric titration of Co2+ with EDTA and also for the determination ofCo2+ in presence of various ions by direct potentiometry. (iii) Similar studies were also carried out with PVC based membranes of (H) with and without plasticizer which were investigated as Sr2+ selective sensors because ionophore (II) shows high affinity for this ion. A large number of membranes of different compositionswere prepared and investigated. It was found that the membrane of composition 5:2:100:150 mg (H:NaTPB: PVC: TBP) performed best. The potential response ofthis membrane is linear to logasr2+ ions in the concentration range of3.2 x 10*5 - 1.0 x 10'1 Mwith near-Nernstian slope of30 mV decade"1 ofactivity. Further, selectivity studies indicated that this sensor is sufficiently selective towards Sr2* over a large number of ions and also performs satisfactorily in partially non-aqueous media. The sensor could be used as an indicator electrode in the quantification of Sr2+ by potentiometric titration against EDTA. As the ionophores (HI) and (IV) showed high affinity for Pb2+, their membranes were explored as Pb2+ selective sensors. Among several membranes prepared with and without plasticizer, the membranes having compositions 1.9:1.6:62.5:124 mg (HINaTPB: PVC:DBP) and of 1.9:1.6:62.5:124 mg (IV:NaTPB:PVC:TBP) performed best and showed maximum working concentration ranges 9.0 x 10"6 - 5.0 x 10"2 and 2.5 x 10"6 - 5.0 x 10"2MPb2+, respectively. These sensors showed near-Nernstian response (30 mV decade'1 of activity) and also worked satisfactorily in partially non-aqueous medium. The selectivity studies for the two sensors under consideration showed that the sensor based on ionophore (IV) is more selective for Pb2+ over a number ofions as compared to the sensor based on ionophore (HI). As the sensor based on (IV) showed better selectivity than (US), it was applied for the estimation of lead in real samples and could be used to determine Pb2+ in Eveready battery waste samples successfully. (iv) Calixarenes having structure similar to C-thiophenecalix[4]resorcinarene (V) have been reported to show high affinity for chromate and therefore, various membranes of (V) with and without plasticizers were investigated as chromate selective sensors. The results showed that the membrane with composition of 2:1.5:66:120 mg (V:TDDMAC1:PVC:DBP) is the best as it exhibits widest concentration range 5.2 x 10"6 -1.0 x 10'1Mwith Nernstian slope (29.0 mV decade'1 of activity) and a fast response time of 8s. The response of this sensor to chromate is independent of pH in the range 6.5-10. The studies further revealed that the sensor is highly selective towards chromate over a number of anions and therefore, could be used for its estimation in electroplating wastes. Thus, the membranes of calixarenes and porphyrin have provided sufficiently selective sensors for Co2+, Sr2*, Pb2+ and Cr042' ions. Metal chelates having high stability with a particular metal and poor stability with others have also been explored for developing selective and sensitive sensors. A survey of the literature reveals that metal chelates, bis[acetylacetonato] Cu(II) (VI), bis[ethylacetoacetate] Cu(II) (VH), and bis[salicyldehyde] Cu(II) (VHI) exhibit selective and rapid exchange for Cu2+ whereas N-(2-hydroxybenzyl)-N'-(2-hydroxybenzylidene) ethylene diamine Ni(II) (LX) and N-(2-Hydroxybenzylidene)-N'-(2-picolyl) ethylene diamine Ni(II) (X) exhibit selective exchange for Ni2+ ions. Thus, it was expected that membranes of these chelates might act as good sensors for the ions for which the chelates are selective. Therefore, a number of PVC based membranes (with and without plasticizer) of (VI), (VH) and (VHI) were prepared and investigated as Cu2+ selective sensors. The results show that the membranes of chelate (VI) perform best as compared to those of chelate (VH) and (VHI) in terms of selectivity, detection limit, response time and life time. Of (v) the various membranes of chelate (VI), the one having composition of 2:2:66:130 mg (VI:NaTPB:PVC:TBP) was found to be the best as it responded to Cu2+ in the widest concentration range of2.0 x 10"6 -1.0 x 10'1 Mwith Nernstian slope (29.3 mV decade"1 of activity) and exhibited high selectivity for Cu2+ over a large number of ions. The sensor could also be used as an indicator electrode in the potentiometric titration of Cu2+ with EDTA and for the determination of Cu2+ in vegetable foliar and multivitamin capsule by direct potentiometry. Similarly, the membranes of two nickel chelates viz., N-(2-hydroxybenzyl)-N'-(2-hydroxybenzylidene) ethylenediamine Ni(II) (IX) and N-(2-Hydroxybenzylidene)-N'-(2-picolyl)ethylenediamine Ni(II) (X) were investigated as Ni2+ selective sensors. The studies carried out on these membranes show that membranes of chelate (X) performed better than those of chelate (IX) in terms of all parameters. The optimumcomposition of the membrane of chelate (X) performing best was found to be 2:1:66:131 mg (X:NaTPB:PVC:CN). The sensor based on the membrane of this composition exhibits Nernstian response in the concentration range of3.2 x 10'6 - 5.0 x 10"2Mand shows high selectivity towards Ni2+ over large number of interfering ions and therefore, could be employed for Ni2+ determination at trace level in biological and environmental samples. Recent studies have shown that amide receptors can also be potential source for use as electroactive component in the membranes of anion selective sensors as they are able to bind specific anions through hydrogen bonds. We have, therefore, synthesized neutral hydrogen bonding diamide receptors viz., N, j^-bis^henytysophthalohydrazide, (XI), N,A^-bis(2,4-dinitrophenyl)isophthalohydrazide (XII) and bis(dithioxamide) (XIII) showing strong binding affinity towards carbonate and phosphate ions, respectively and explored them for developing CO32' and HPO ]~ selective sensors. Of (vi) the various membranes prepared with (XI) or (XH) and different plasticizers, the membranes based on (XH) performed better than those of membranes based on (XI) in terms of all parameters. The optimum composition of the membrane of (XH) performing best was found to be 4:3:66:120 mg (XH:TDDMAC1:PVC:CN). This sensor showed linear potential response to logaco2- in the concentration range of 1.3 x 10' - 1.0 x 10'3M with Nernstian compliance (29.0 mV decade'1 ofactivity) at pH 8.6. It showed good selectivity for carbonate over all common anions. The sensor was successfully applied for the quantification of total inorganic carbon in water samples. Cyclic bis(dithioxamide) (XIH) has been investigated as a sensing material for HP042". The sensor with membrane of composition 2:1.5:66:127 mg (XHI:TDDMACl:PVC:NPOE) showed Nernstian response (29.6 mV decade"1 of activity) in the concentration range of1.7 x 10"6 - 1.0 x 10'2M at pH 8.0. The response ofthe sensor was highly selective to HPO42' over a large number ofanions. As a result of good selectivity, the sensor could be successfully used for HPO42" determination in presence of other ions by direct potentiometry and also as an indicator electrode in the quantification ofHP042'by potentiometric titration against Ba2+. Thus, the present investigations on the membranes of some calixarenes, porphyrin, metal chelates and diamide receptors have resulted in the development of selective and sensitive sensors for Co2+, St2*, Pb2+ , Cu2+, Ni2+ cations and Cr042' , C03 ', HPO4 ' anions. All these sensors are mechanically as well as chemically stable, have long life ofabout 2-4 months, low response time ofabout 7-15s, reasonably wide working concentration range with Nernstian or near-Nernstian slope and exhibit good selectivity. A comparison of their performance with reported sensors show that the sensors developed for Sr2+, Pb2+ and Cu2+ are comparable to the reported sensors. (vii) However, the prepared sensors for Co2+ and Ni2+ are better in terms of selectivity compared to reported sensors as Cu2+, Ni2+ and Ag+, Hg2+ do not interfere, respectively, in their functioning whereas reported sensors show interference to these ions. All the three anion sensors have been found to be better than reported anion sensors in that (i) the Cr042* selective sensor shows low detection limit compared to available sensors, (ii) the prepared CO32" sensor shows high selectivity for CO32" over Sal", CIO4' and SCN" whereas the reported sensors exhibit interference to these ions and (iii) the HPO42' sensor shows excellent selectivity for HPO42' over Sal", CIO4', SCN" and I" while the reported sensors do not. Thus, the present work on ion sensor has resulted in the availability of some improved ion sensors which can be used successfully for analytical purposes.
URI: http://hdl.handle.net/123456789/1429
Other Identifiers: Ph.D
Research Supervisor/ Guide: Gupta, V. K.
Jain, A. K.
metadata.dc.type: Doctoral Thesis
Appears in Collections:DOCTORAL THESES (chemistry)

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