Microelectrodes glass

Squid axons Lollgo pealii) H sealed-end all-glass microelectrode pH 7.3 144)... 

Giant neuron of Aplysia californica Nj closed-end all-glass microelectrode Na- 40.3 mM 146)... 

Sheep heart Purkinje fibers closed end, recessed up—all-glass microelectrode Na- 7.3mM 147)... 

For the sake of completeness, glass microelectrodes [48, 59, 184] will first be mentioned. Two types of these electrodes are used, spear-shaped microelectrodes [59] and recessed-tip microelectrodes [165] (see fig. 4.5). In the former case, the microelectrode is drawn from a capillary of an ion-exchanger glass and is insulated on the outside, except for the tip, by inserting the microelectrode into a micropipette made of an inactive glass. In the latter case, the outer micropipette extends over the microelectrode tip. The two capillaries are sealed together and the ISM is in contact with the liquid between the two capillaries. 

Fig. 4.5. Two types of ion-sensitive glass microelectrodes (a) Hinke s spear type (b) recessed-tip type. (After J. L. Walker [1841.)...

N. Khuri, Glass Microelectrodes and their Uses in Biological Systems, in Glass Electrodes for Hydrogen and other Cations (ed. G. Eisenman),... 

Bis(crown) ethers [208] have been used for the T1(I) ISE. Where glass microelectrodes cannot be used for pH determination because of their fragility, microelectrodes with ligand XXXI can be used for [118],... 

Acetylcholineesterase (AChE) Glass microelectrode with AChE immobilized on active surface. Nernstian response. Detection limit is pH-dependent. At pH 8.5 detection limit was 10 pM. In cerebrospinal fluids it was 0.1 mM. [63]... 

Fibers electrically paced via bipolar silver electrodes and impaled with 3M KC1-filled glass microelectrodes Action potentials continuously monitored... 

Microelectrodes based on closed-end pH glass membranes were the first to be described in the literature (Cl). Hinke (H2) fiuther developed glass membrane microelectrodes with tip diameters of 10 im for the measurement of sodium and potassium. Various designs and approaches to the fiibri-cation of these all-glass microelectrodes have been taken over the years, and specific fabrication procedures may be found in the literature (H3, K3). Similarly, solid-state type electrodes based on pressed pellets of Ag2S with tip diameters on the order of 100 fim have been reported for the determination of Ag" ", S , I, Cl , Cu +, Br , etc. (C13). We have already discussed that such solid-state electrodes can foul when applied for direct measurements in biological systems, so the fabrication of these will not be discussed here. 

Giant neuron of Aplysia califomica Na closed-end all-glass microelectrode Na+ 40.3 mM El... 

Sheep heart Purkmje fibers Na closed end, recessed tip—all-glass microelectrode Na 7.3 mM E4... 

When short response times and short sampling depths are needed, reversed tip glass microelectrodes can be made by introducing the pointed end of an active sealed-end measuring tip into the narrow open end of the electrode body pipette. The pointed end of the active tip ends up inside the body and the narrow tip of the body is sealed together with the wide part of the measuring tip. 

This relation was proved by Nyquist (10) to be a consequence of basic thermodynamics laws and, except for quantum corrections, was never really challenged. Studies performed with glass microelectrodes (II) and heterogeneous ionic systems (12) showed that for zero ionic gradients and zero applied currents, the measured levels of noise were in agreement with noise levels calculated from the impedance according to eq 1. Hence, a study of electrical noise of a system under equilibrium conditions can be initiated for only two reasons. First, if there is some a priori information that the system is in equilibrium, then measurements of the system impedance or temperature can be performed without external perturbations (quantum effects are not considered here). Second, if impedance and temperature are measured independently by some other techniques, noise measurements can verify that the system under study is in an equilibrium state. 

Volumetric Absorption Cells. Often the amount of sample available for trace analysis is rather limited also, it is often desirable to make the final volume as small as possible, so that absorbance is maximized. This may be accomplished by calibrating an absorption cell to a definite volume by putting a mark on the side and using it as a volumetric flask. Color development may be carried out in the cell, in order to keep the final volume at a minimum. If pH adjustment is required, a glass microelectrode may be used. For an ordinary 1-cm cell, volumes of about 3 ml may be used. 

Ion-selective electrodes are really a subgroup of glass microelectrodes because the electrodes are identical in many respects. Conventional glass micropipets and filling solutions are used, but in addition, an ion-selective barrier is interposed between filling solution and external solution. 

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