Clark-type electrode

J.C. Millar, Real-time direct measurement of nitric oxide in bovine perfused eye trabecular meshwork using a Clark-type electrode. J. Ocular Pharmacol. Ther. 19, 299-313 (2003). 

Figure 13.10. Calibration curves for optical sensor and Clark-type oxygen electrode. The phase response of optical sensor and the voltage response of the Clark-type electrode is plotted against percent oxygen in the gas mixture (oxygen and nitrogen) sparged. While the Clark-type electrode shows a linear calibration the optical sensor shows a Siem-Volmer lype relationship (see Section 13.10.2).

Performance comparisons with a Clark-type sensor demonstrated the applicability of the optical sensor in monitoring dissolved oxygen (DO) levels in a bioreactor.<73) Figure 13.11 shows the response profiles of the optical sensor and Clark-type electrode... 

Figure 13.11. Dissolved oxygen profile during a typical Escherichia coli fermentation. Using a cubic spline interpolation of the data shown in Figure 13.3, the responses of the two sensors have been converted into percent oxygen and plotted as shown. The optical sensor closely tracks the response of the Clark-type electrode throughout the fermentation.

Amperometrically, using a Clark-type electrode. This is a platinnm electrode snr-rounded by a gas-permeable membrane. 

O2 evolution was measured with a Clark-type electrode. Specific activity of the untreated controls averaged 40 9 ymoles 0 evolved/mg Chi h. Data shown are arithmetic averages SD of determinations made with a minimum of three different isolations of chloroplasts. 

H20 served as the electron donor and methyl viologen as the electron acceptor. 0 consumption was measured with a Clark-type electrode and phosphorylation was measured colorimetrically. Data are presented as averaged I values SD obtained with three Isolations of thylakoids. Average specific activities were o9 3 ymoles 0, consumed and 171 16 ymoles Pi esterified/mg Chi h for the coupled reactions, and 223 i 5 ymoles 0 consumed/mg Chi h for the uncoupled reaction. 

Optimal oxygen detection by the Clark-type electrode is assured by a daily replacement of the membrane over the electrode. This can be very easily done with practice. 

If the depletion layer is completely inside the stagnant layer, the current is not affected by the change of flow. From (7.18), we know that this happens when the electrode radius becomes small. For Clark-type electrodes, the flow insensitivity is obtained even for larger diameters of the electrode, because of the additional confining effect of the membrane which has lower oxygen transmissivity, DmSm, than that of the solution. 

Heyman SN, Karmeli F, Rachmilewitz D, Haj-Yehia A, Brezis M Intrarenal nitric oxide monitoring with a Clark-type electrode potential pitfalls. Kidney Int 51 1619-23,1997... 

In the case of a single-phase laboratory reactor, shown schematically in Table 4, the reactor volume is totally occupied by liquid. The autoxidation of SO2 occius between reactants, including oxygen, pre-dissolved in the liquid. Thus, the only reaction rate limitations come from the properties of a measuring deviee (Clark-type electrode) and from... 

Amperometric sensors for hydrogen, nitrous oxides, and carbon dioxide have been developed by modification of the Clark-type electrode (Hanus et al., 1980 Albery and Barron, 1982). 

With a constant of K = 2.7640-5 mol/1 (pH 7.0, 25°C) the equilibrium of the LDH-catalyzed reaction lies far to the lactate side. This means that whereas for lactate sensors based on LDH the forward reaction has to be forced by alkaline buffer and pyruvate- or NADH-trapping agents, the reduction of pyruvate proceeds spontaneously under normal conditions. This direction of the reaction has been used in a sequence electrode for pyruvate assay (Weigelt et al., 1987b). In the presence of lactate monooxygenase (LMO) lactate formed from pyruvate by LDH is oxidized by molecular oxygen, the consumption of which was indicated at a Clark-type electrode. The enzymes were immobilized in a gelatin membrane. Of course such a sensor measures the concentration of lactate in the sample, too. Therefore it is suited to the determination of the lactate/pyruvate ratio, which is a clinically important parameter. Pro-... 

Oxygen-evolving PSII RC complexes were isolated as described in (3). Ion-exchange chromatography (FPLC) was used to remove the 10 and 22 kDa species and then the 28 kDa species. Oxygen evolution was measured with a Clark-type electrode in 50 mM MES-NaOH pH 6.0, 10 mM CaCl2 and 250 pM DCBQ or 2.5 mM Fe(CN)g as electron acceptors. Low-temperature EPR spectroscopy was performed with a Bruker 200D spectrometer operated at X-band and equipped with an Oxford cryostat. 

Oxygen evolution measurements were made with a Clark type electrode, using an assay buffer of 25 mM Mes/NaOH, 40 mM NaCl pH 6.3 at 18 C with additions as in the text. 

Photosystem II preparations isolated as per (15) oxidized water at rates of 700-850 pmol 02/mg Chi hr. The rate of O2 evolution was measured with a Clark-type electrode in a reaction mixture that contained 500 pM DCBQ, 400 mM sucrose and 50 mM MES buffered to pH 6.5 with TMA-OH. The concentration of Q" in the assay was held constant at 30 mM by the addition of TMA-Cl. Additions of Ca ", Sr and/or Na" to the assay were made from stock solutions prepared by buffering MES to pH 6.5 with Ca(OH)2, Sr(OH)2 and NaOH, respectively. 

O2 evolving activity was measured at 25 C using a Clark-type electrode with 1 mM PPBQ as acceptor. The Br - and N03 -treated samples were assayed in their own buffers. The activity of the Cl" control was 730 77 moles 02/mg chi-hr. 

PSII-enriched spinach thylakoid membranes were prepared as described previously (3) 02-evolving activity was 700 100 yumoles O2/(mg chl-hr) at 25 C using a Clark type electrode with phenyl-p-benzoquinone (PPBQ) as acceptor. EPR samples were prepared with sucrose as cryoprotectant. Oriented samples were prepared by partially dehydrating PSII-enriched membranes initially containing 290 3-(3, 4-dichlorophenyl)-1,1-dimethylurea (DCMU) and 3% ethanol onto mylar sheets under a stream of N2 gas at 4 C, as described previously (4). The S2-state was achieved by illumination of dark-adapted samples at 200 K for the times indicated. 

Oxygen evolution was measured in the presence of K3pe(CN) (2 mM) and phenyl-p-benzoquinone (Ph-p-BQ, 200 /iM) at a Chl-concentration of 25 /ig/ml using a Clark type electrode. The rate of DCIP photoreduction with diphenylcarbazide (DPC) as a donor was spectrophotometrically monitored at 590 nm. The reaction mixture contained 5 /xM Chi, 40 /xM DCIP and 600 /xM DPC. 

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