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e.g. sulfur compounds, are expected to be detected well by either waveform. Results from a comparison of the waveformrs in Figure 1B and Figure 1D are shown in Figure 10 for detection of glucose (Al, A2) and thiourea (Bl,B2) in 0.2 M NaOH. For the comparison, the total period of detection was the same in the two waveforms (lo00 Ms). Numerical values for the base-line signal (microcoulombs) are indicated in parentheses. Glucose shows a substantially higher sensitivity for the waveform in Figure 1B as compared to that in Figure lD, as predicted. Thiourea is detected with similar sensitivity, also as predicted.
CONCLUSION The design of the waveform for PS-PCD at a Au electrode can result in virtual elimination of base-line signals for oxide-catalyzed detection processes, and the techkque is recommended for liquid chromatographic separations that utilize pH-gradient elution over a limited pH range.
LITERATURE CITED Hughes, S.; Johnson, D. C. Anal. Chlm. Acta 1981, 132, 11. Hughes, S.; Johnson, D. C. Anal. Chlm. Acta 1983, 149, 1. Edwards, P.; k a k , K. Am. Lab. 1983, April, 78. Rockiln, R. D.; Pohl, C. A. J . Uq. Chfomatcgr. 1983, 6(8), 1577. Neuburger, G. G.; Johnson, D. C. Anal. Chem. 1987, 5 9 , 150. Neuburger, G. G.; Johnson, D. C. Anal. Chem. 1987, 5 9 , 203. Polta, J. A.; Johnson, D. C. J . Liq. chrometcgr. 1983, 6, 1727. Polta, J. A.; Johnson. D. C.; Merkel, K. E. J . Chromatogr. 1985, 324, 407. Pdta, T. 2.;Johnson, D. C. J . Elecbwnal. Chem. Intwfac&l€kctro& e m . 1980, 209, 159. Polta, T. 2.; Luecke, G. R.; Johnson, D. C. J . Electroanal. Chem. Interfacial Electrochem. 1986, 209, 171. Thomas, M. 0.; Sturrock, P. E. J . Chromatogr. 1988. 357, 318. Neuburger, G. 0.; Johnson, D. C. Anal. Chim. Acta 1987, 192, 205. Polta, J. A.; Yeo, I. H.; Johnson, D. C. Anal. Chem. 1985. 5 7 , 563. Mead. D. A. M.S. Dissertation, Iowa State Unlverslty, Ames, IA, 1008.
RECEIVED for review April 20,1988. Accepted June 24,1988. This work was supported by the National Science Foundation through Contract CHE-8312032.
Response Properties of Ion-Selective Polymeric Membrane Electrodes Prepared with Aminated and Carboxylated Poly(viny1 c hIoride) S. C. Ma, N. A. Chaniotakis, and M. E. MeyerhofP Department of Chemistry, University of Michigan, Ann Arbor, Michigan 48109
The potentlometrlc response characterlstlcs of several lonselectlve polymer membranes prepared with aminated and carboxylated poly(vlnyl chlorlde) (PVC) are examined and compared to those observed with the underivatlzed polymer. Three lonaelectlve reagents, trkiodecylamlne (H'), nonactln (NH,'), and (5,10,15,20-tetraphenylporphyrlnato)tln( I V ) dlchloride (salicylate) serve as models for these lnvestlgatlons. the presence of carboxyl or amine functional groups wlthln the membranes, even In mole excess to the ion carriers, Is shown to have little effect on the response and selectlvlty of the neutraltarrler-based membranes (nonactln and tridodecylamlne). However, anlon response of membranes doped with the Sn( IV) porphyrin complex is completely ellmlnated when excess carboxyl groups are Introduced Into the polymer matrix. Blank aminated PVC membranes respond to pH In a manner analogous to that of underlvatlzed PVC membranes containing trldodecylamlne, while blank carboxylated PVC membranes exhibit little or no proton response. The impllcations of these flndlngs are discussed in terms of the charged or uncharged nature of the functional groups within the membrane phase as well as the potential advantages of using functionallzed PVC to fabrlcate blosensors.
For nearly two decades, neutral and charged carrier molecules have been incorporated into solvent/ polymeric membranes to devise a variety of ion-selective eIectrodes (ISEs) (1-4). While several polymeric matrices have been examined (5-IO),poly(viny1 chloride) (PVC) has emerged as the most widely used membrane support material. However, ISEs prepared with alternate matrices, particularly ones containing functional groups, could offer attractive advantages. These may include the following: (a) providing membrane sites to 0003-2700/88/0360-2293$01.50/0
covalently attach more water soluble ion-selective carriers for the purpose of developing new ISEs; (b) reducing the electrical resistances of the polymer membranes (if the sites are charged); (c) improving the adhesive properties of the ionselective membranes when cast on solid substrates to prepare disposable thin-film electrodes; and (d) providing surface sites that should enable the direct attachment of enzymes, antibodies, antithrombin compounds, and other bioreagents for the purpose of fabricating new biosensors. Given these advantages and potential applications envisioned, we now report on the potentiometric properties of several ion carrier systems when incorporated into aminated and carboxylated PVC based membranes. It is well-known that the presence of even trace levels of soluble additives (other than the ion carrier) within the polymer membrane phase can have a profound effect on the response and selectivity of ISEs (11). The addition of lipophilic charged anions (e.g., tetraphenylborate) or cations (e.g., quaternary ammonium compounds) to neutral-carrier-based membranes can decrease resistances and eliminate counterion interferences (12-16). However, in certain instances, if the level of the additive approaches or becomes greater than the concentration of carrier in the membrane, carrier-mediated selectivity is lost. In the case of aminated or carboxylated PVC, such behavior should occur only if excess functional groups (relative to the carrier) are ionized or if the functional groups directly interact with the carrier within the membrane phase. Carboxylated PVC has been used previously to devise ion-selective devices. Satchwill and Harrison (17)examined the use of this derivatized polymer to improve the adhesion of potassium-selective membranes to silica surfaces, while Pace (18)found that a cross-linked layer of urease adhered tightly to an ammonium-sensitive membrane prepared with nonactin, plasticizer, and carboxylated PVC. Similarly, Anzai et al. (19) 0 1988 American Chemical Society
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Table I. Potentiometric Response Characteristics, Selectivity, and Resistances of Nonactin-Based Membranes Prepared in Various Matrices" resistancesd
mol ratio of nonactin to
10sn
log KNQ+JPt Mg2+ Ca2+ Me4N+
H+
-5.0 -4.8 -5.0
