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Lenar N, Piech R, Paczosa-Bator B. A New Planar Potentiometric Sensor for In Situ Measurements. SENSORS (BASEL, SWITZERLAND) 2024; 24:2492. [PMID: 38676109 PMCID: PMC11054197 DOI: 10.3390/s24082492] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/08/2024] [Revised: 04/02/2024] [Accepted: 04/10/2024] [Indexed: 04/28/2024]
Abstract
A new construction of a potentiometric sensor was introduced for the first time. It relies on the use of two membranes instead of one, as in the well-known coated-disc electrode. For this purpose, a new electrode body was constructed, including not one, but two glassy carbon discs covered with an ion-selective membrane. This solution allows for the sensor properties to be enhanced without using additional materials (layers or additives) on the membrane. The new construction is particularly useful for in situ measurements in environmental samples. Two ion-selective polymeric membranes were used, namely H+ and K+-selective membranes, to confirm the universality of the idea. The tests conducted included chronopotentiometric tests, electrochemical impedance spectroscopy, and potentiometric measurements. The electrical and analytical parameters of the sensors were evaluated and compared for all tested electrodes to evaluate the properties of the planar electrode versus previously known constructions. Research has shown that the application of two membranes instead of one allows for the resistance of an electrode to be lowered and for the electrical capacitance to be elevated. Improving the electrical properties of an electrode resulted in the enhancement of its analytical properties. The pH measurement range of the planar electrode is 2-11, which is much wider in contrast to that of the single-membrane electrode. The linear range of the K+-selective planar electrode is wider than that of the coated-disc electrode and equals 10-6 to 10-1 M. The response time turned out to be a few seconds shorter, and the potential drift was smaller due to the application of an additional membrane in the electrode construction. This research creates a new opportunity to design robust potentiometric sensors, as the presented construction is universal and can be used to obtain electrodes selective to various ions.
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Affiliation(s)
| | | | - Beata Paczosa-Bator
- Faculty of Materials Science and Ceramics, AGH University of Krakow, Mickiewicza 30, PL-30059 Krakow, Poland
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Li L, Tang J, Liu H, Qian Y. Highly Selective Potentiometric Sensing of Biologically Relevant Pyrophosphate and Lysophosphatidic Acid Using N-Alkyl/Aryl Ammonium Resorcinarenes/Extended-Resorcinarenes as Ionophores. Anal Chem 2022; 94:14854-14860. [PMID: 36260062 DOI: 10.1021/acs.analchem.2c01819] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The ionophore properties of four kinds of N-alkyl/aryl ammonium resorcinarenes and extended-resorcinarenes were inspected for the first time to fabricate polymeric membrane electrodes for determination of biologically relevant pyrophosphate (PPi) and lysophosphatidic acid (LPA). The proposed ion selective electrodes (ISEs) showed significant preference for PPi and LPA with significant selectivity pattern differences from the Hofmeister series. To gain further insight into the performances of the developed ISEs, the binding constants of ionophore-anion complexes in the plasticized membrane phase were investigated, along with the optimized geometries and calculated electrostatic potential. Nernstian potential responses with good reversibility to target anions can be observed when shifting the optimized membranes in aqueous solutions in the concentration range from 10-6.5 to 10-2.3/10-2.2 M. Moreover, potentiometric sensings of PPi and LPA in mineral water and artificial serum were achieved in low μM concentration range, demonstrating their promising real-world applications. These results provide a promising avenue for the development of polymeric membrane electrodes for biological relevant anions and will broaden the scope of potentiometric sensing.
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Affiliation(s)
- Long Li
- College of Environment and Safety Engineering, Qingdao University of Science and Technology, Qingdao 266042, China
| | - Jing Tang
- College of Environment and Safety Engineering, Qingdao University of Science and Technology, Qingdao 266042, China
| | - Haitao Liu
- College of Environment and Safety Engineering, Qingdao University of Science and Technology, Qingdao 266042, China
| | - Yi Qian
- College of Chemical Engineering, Qingdao University of Science and Technology, Qingdao 266042, China
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Li L, Liu H, Tang J, Du P, Zhang Y, Qian Y. Embedding of Functionalized Coordination Cages and a Molecular Knot in a Polymeric Membrane for Potentiometric Sensing of Environmentally Important Oxyanions and Halides. ACS Sens 2022; 7:1602-1611. [PMID: 35499166 DOI: 10.1021/acssensors.2c00782] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
Abstract
Three kinds of coordination cages and a molecular knot with inductively activated +P-H, N-H, or C-H hydrogen bond donors anchoring in the functionalized cavities were inspected as ionophores to develop polymeric membrane ISEs for potentiometric sensing of environmentally important oxyanions and halides. The proposed ISEs displayed significant preference for perrhenate, phosphate, or chloride with a selectivity pattern distinctively different from the sequence depending on the Gibbs free energy of hydration owing to the high degree of shape, charge, and size selectivity originating from the rigidity and complementarity of the binding cavities. To gain further insight into the response characters of the proposed ISEs, the binding constants of ionophore-anion complexes in the membrane phase were investigated, and the binding affinity, together with the Hofmeister series, correlates well with the determined selectivity pattern of the proposed ISEs. Optimizing the composition of the membrane such as lipophilic additives and plasticizers produced ISEs displaying Nernstian/near-Nernstian potentiometric responses to primary anions with a wide linear range, improved detection limits, good reversibility, and satisfying lifetime. Potentiometric determination of perrhenate, phosphate, and chloride in river water, mineral water, and artificial serum samples was achieved with good recovery and accuracy using the proposed ISEs, demonstrating their potential for real-life applications. These results will shed new light on how novel ionophores could be designed for potentiometric sensing and broaden the scope of host-guest chemistry of coordination cages and molecular knots.
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Affiliation(s)
- Long Li
- College of Environment and Safety Engineering, Qingdao University of Science and Technology, Qingdao 266042, P. R. China
| | - Haitao Liu
- College of Environment and Safety Engineering, Qingdao University of Science and Technology, Qingdao 266042, P. R. China
| | - Jing Tang
- College of Environment and Safety Engineering, Qingdao University of Science and Technology, Qingdao 266042, P. R. China
| | - Pengcheng Du
- College of Environment and Safety Engineering, Qingdao University of Science and Technology, Qingdao 266042, P. R. China
| | - Yihao Zhang
- College of Environment and Safety Engineering, Qingdao University of Science and Technology, Qingdao 266042, P. R. China
| | - Yi Qian
- College of Chemical Engineering, Qingdao University of Science and Technology, Qingdao 266042, P. R. China
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Shao Y, Ying Y, Ping J. Recent advances in solid-contact ion-selective electrodes: functional materials, transduction mechanisms, and development trends. Chem Soc Rev 2020; 49:4405-4465. [DOI: 10.1039/c9cs00587k] [Citation(s) in RCA: 143] [Impact Index Per Article: 35.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
This article presents a comprehensive overview of recent progress in the design and applications of solid-contact ion-selective electrodes (SC-ISEs).
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Affiliation(s)
- Yuzhou Shao
- Laboratory of Agricultural Information Intelligent Sensing
- School of Biosystems Engineering and Food Science
- Zhejiang University
- Hangzhou
- China
| | - Yibin Ying
- Laboratory of Agricultural Information Intelligent Sensing
- School of Biosystems Engineering and Food Science
- Zhejiang University
- Hangzhou
- China
| | - Jianfeng Ping
- Laboratory of Agricultural Information Intelligent Sensing
- School of Biosystems Engineering and Food Science
- Zhejiang University
- Hangzhou
- China
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Simple and Efficient Synthesis of Gold Nanoclusters and Their Performance as Solid Contact of Ion Selective Electrode. Electrochim Acta 2016. [DOI: 10.1016/j.electacta.2016.11.069] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
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Makrlík E, Kvíčala J, Vaňura P. Complexation of the lithium cation with N,N,N’,N’-tetracyclohexyl-1,2-phenylenedioxydiacetamide: experimental and theoretical study. Mol Phys 2016. [DOI: 10.1080/00268976.2016.1177221] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
Affiliation(s)
- Emanuel Makrlík
- Faculty of Environmental Sciences, Czech University of Life Sciences, Prague, Czech Republic
| | | | - Petr Vaňura
- University of Chemistry and Technology, Prague, Czech Republic
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Makrlík E, Kvíčalová M, Vaňura P. Sodium Ionophore III as Very Effective Receptor for Trivalent Europium and Americium. J SOLUTION CHEM 2016. [DOI: 10.1007/s10953-016-0447-0] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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Szűcs J, Lindfors T, Bobacka J, Gyurcsányi RE. Ion-selective Electrodes with 3D Nanostructured Conducting Polymer Solid Contact. ELECTROANAL 2015. [DOI: 10.1002/elan.201500465] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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Sun Q, Li W, Su B. Highly hydrophobic solid contact based on graphene-hybrid nanocomposites for all solid state potentiometric sensors with well-formulated phase boundary potentials. J Electroanal Chem (Lausanne) 2015. [DOI: 10.1016/j.jelechem.2014.12.038] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
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10
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Extraction and DFT study on the complexation of the univalent silver cation with sodium ionophore III. MONATSHEFTE FUR CHEMIE 2014. [DOI: 10.1007/s00706-014-1219-4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
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Makrlík E, Kvíčala J, Vaňura P. Complexation of the sodium cation with sodium ionophore III: Experimental and theoretical study. J Mol Struct 2014. [DOI: 10.1016/j.molstruc.2014.03.020] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
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12
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Zhou M, Gan S, Cai B, Li F, Ma W, Han D, Niu L. Effective solid contact for ion-selective electrodes: tetrakis(4-chlorophenyl)borate (TB-) anions doped nanocluster films. Anal Chem 2012; 84:3480-3. [PMID: 22409283 DOI: 10.1021/ac300473a] [Citation(s) in RCA: 52] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
We report on a novel material, tetrakis(4-chlorophenyl)borate (TB(-)) anion doped nanocluster films, as the solid contact (SC) for producing well-defined, electrochemically reversible, and nonpolarizable double interfaces on it. Detailed studies have unambiguously revealed that, for the first time, the developed SC can fully overcome all the signal stability problems of ion-selective electrodes (ISEs), offering a reliable and universal platform for the development of high quality SC-ISEs. As an exemplification, the developed monolayer-protected cluster (MPC) based K(+)-ISEs have advantages of excellent analytical performances, e.g., the low potential drift (10.1 ± 0.3 μV h(-1) over 72 h measured in 0.1 M KCl and 10.8 ± 0.5 μV h(-1) over 96 h rechecked in 0.1 M KCl after 1 month) and the stable and reproducible linear range, sensitivity, and standard potential (few changes within the first 6 weeks). This evidence suggests that the developed MPC films are the most promising SC transducers among all the reported ones to the best of our knowledge.
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Affiliation(s)
- Min Zhou
- State Key Laboratory of Electroanalytical Chemistry, c/o Engineering Laboratory for Modern Analytical Techniques, Changchun Institute of Applied Chemistry and Graduate University of the Chinese Academy of Sciences, Chinese Academy of Sciences, Changchun 130022, P. R. China
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Sundfors F, Höfler L, Gyurcsányi RE, Lindfors T. Influence of Poly(3-octylthiophene) on the Water Transport Through Methacrylic-Acrylic Based Polymer Membranes. ELECTROANAL 2011. [DOI: 10.1002/elan.201100076] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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14
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Lindner E, Tóth K. To the Memory of Ernő Pungor: A Subjective View on the History of Ion-Selective Electrodes. ELECTROANAL 2009. [DOI: 10.1002/elan.200904624] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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15
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Borowitz IJ, Li VS, Gross I. CONVENIENT ONE-STEP CONVERSIONS OF ALCOHOLS OR PHENOLS TO N,N-DIPROPYL ALKOXYACETAMIDES. ORG PREP PROCED INT 2009. [DOI: 10.1080/00304947709356084] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
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16
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Lindner E, Gyurcsányi RE. Quality control criteria for solid-contact, solvent polymeric membrane ion-selective electrodes. J Solid State Electrochem 2008. [DOI: 10.1007/s10008-008-0608-1] [Citation(s) in RCA: 243] [Impact Index Per Article: 15.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
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17
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Güggi M, Oehme M, Pretsch E, Simon W. Neutraler Ionophor für Flüssigmembranelektroden mit hoher Selektivität für Natrium- gegenüber Kalium-Ionen. Helv Chim Acta 2004. [DOI: 10.1002/hlca.19760590716] [Citation(s) in RCA: 73] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
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18
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Bongardt F, Vögtle F, Wegmann D, Ammann D, Maruizumi T, Simon W. Herstellung und Charakterisierung in Membranen von Ionophoren mit Selektivität fü Natrium-Ionen. Helv Chim Acta 2004. [DOI: 10.1002/hlca.19870700119] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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19
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Bissig R, Pretsch E, Morf WE, Simon W. Makrocyclische und acyclische neutrale Ionophore. Einfluss des Ringschlusses auf die Kationenselektivität. Helv Chim Acta 2004. [DOI: 10.1002/hlca.19780610503] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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Kirsch NNL, Funck RJJ, Simon W. Extraktion von Alkali- und Erdalkalimetallpikraten aus wässerigen Lösungen in Methylenchlorid durch ungeladene azyklische Ionophoren. Quantitative Interpretation. Helv Chim Acta 2004. [DOI: 10.1002/hlca.19780610610] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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Ha TK, Wild UP, Kühne RO, Loesch C, Schaffhauser T, Stachel J, Wokaun A. A Theoretical Study of Complex Formation between Formaldehyde and Lithium. Helv Chim Acta 2004. [DOI: 10.1002/hlca.19780610335] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
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22
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Hamilton C, Murphy S, Tighe B. Synthetic hydrogels (10): anomalous transport behaviour in crown ether-containing hydrogel membranes. POLYMER 2000. [DOI: 10.1016/s0032-3861(99)00599-6] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/17/2022]
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23
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Photocured polymers in ion-selective electrode membranes. Part 5: Photopolymerised sodium sensitive ion-selective electrodes for flow injection potentiometry. Anal Chim Acta 1996. [DOI: 10.1016/s0003-2670(96)00340-6] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
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24
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Hauser PC, Chiang DW, Wright GA. A potassium-ion selective electrode with valinomycin based poly(vinyl chloride) membrane and a poly(vinyl ferrocene) solid contact. Anal Chim Acta 1995. [DOI: 10.1016/0003-2670(94)00472-x] [Citation(s) in RCA: 72] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
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25
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Duro JA, Torres T. Synthesis and Aggregation Properties in Solution of a New Octasubstituted Copper Phthalocyanine: {2,3,9,10,16,17,23,24-Octakis-[(dioctylaminocarbonyl)methoxy]phthalocyaninato}copper(II). ACTA ACUST UNITED AC 1993. [DOI: 10.1002/cber.19931260137] [Citation(s) in RCA: 46] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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26
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Effect of a catechol segment in a polyether chain on the complexing ability of some phosphonate and quinoline monopodands. ACTA ACUST UNITED AC 1989. [DOI: 10.1007/bf01168097] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
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27
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Dror M, Bergs E, Rhodes R. Potassium ion-selective electrodes based on valinomycin/PVC overlayered solid substrates. ACTA ACUST UNITED AC 1987. [DOI: 10.1016/0250-6874(87)85002-3] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
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28
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Dawson WD, Smith TC. Intracellular Na+, K+ and Cl- activities in Ehrlich ascites tumor cells. BIOCHIMICA ET BIOPHYSICA ACTA 1986; 860:293-300. [PMID: 3741854 DOI: 10.1016/0005-2736(86)90526-2] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
Ehrlich ascites tumor cell membrane potential (Vm) and intracellular Na+, K+ and Cl- activities were measured under steady-state conditions in normal saline medium (Na+ = 154, K+ = 6, Cl- 150 mequiv./l). Membrane potential was estimated to be -23.3 +/- 0.8 mV using glass microelectrodes. Intracellular ion activities were estimated with similar glass electrodes rendered ion-selective by incorporation of ion-specific ionophores. Measurements of Vm and ion-activity differences were made in the same populations of cells. Under these conditions the intracellular Na+, K+ and Cl- activities are 4.6 +/- 0.5; 68.3 +/- 8.0; and 43.6 +/- 2.1 mequiv./l, respectively. The apparent activity coefficients for Na+ and K+ are 0.18 +/- 0.02 and 0.41 +/- 0.05 respectively. These are significantly lower than the activity coefficients expected for the ions in physiological salt solutions (0.71 and 0.73, respectively). The activity coefficient for intracellular Cl- (0.67 +/- 0.03), however, is close to that of the medium (0.73), and the transmembrane electrochemical potential difference for Cl- is not different from zero. The results establish that the energy available from the Na+ electrochemical gradient is much greater than previously estimated from chemical measurements.
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Khalil MM, Anghel DF, Luca C. Poly(Vinyl Chloride) Containing Dibenzo-18-crown-6 as an Ion-Selective Membrane for Hyamine 1622. ANAL LETT 1986. [DOI: 10.1080/00032718608066264] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/17/2022]
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30
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Zhujun Z, Mullin J, Seitz W. Optical sensor for sodium based on ion-pair extraction and fluorescence. Anal Chim Acta 1986. [DOI: 10.1016/s0003-2670(00)86489-2] [Citation(s) in RCA: 26] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/17/2022]
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Decorte E, Toso R, Sega A, ?unji� V, Ru?i?-Toro? ?, Koji?-Prodi? B, Bresciani-Pahor N, Nardin G, Randaccio L. Chiral 1, 4-Benzodiazepin-2-one, template for enantioselective synthesis of ?-amino acids and their ?-deuterio congeners. Preliminary communication. Helv Chim Acta 1981. [DOI: 10.1002/hlca.19810640420] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
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Crowe W, Mayevsky A, Mela L. Application of a solid membrane ion-selective electrode to in vivo measurements. THE AMERICAN JOURNAL OF PHYSIOLOGY 1977; 233:C56-60. [PMID: 879313 DOI: 10.1152/ajpcell.1977.233.1.c56] [Citation(s) in RCA: 45] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
A solid membrane electrode containing a highly selective ion-complexing agent immobilized in a polymer membrane is applied to measurements in vivo from the surface of an organ. For the measurements reported here, an ion-complexing agent selective for potassium is incorporated in a silicone rubber membrane and applied to measure ion changes in the brain. Comparison is made to the measurements recorded with an ion-selective microelectrode in the cortical tissue. The surface electrode compares favorably with the microelectrode in terms of amplitude of response and response time for the changes seen in the phenomenon of cortical spreading depression of Leao. The methods reported here are amenable to a selection of ion measurements by incorporation of a suitable ion exchanger in a polymer membrane. Extracellular ion activity is monitored in the anesthetized animal by holding the electrode in a balanced suspension which provides a light, flexible contact to the organ of interest. In the unanesthetized animal, when recording from the brain, the electrode is fixed in a skull-implanted cannula.
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