Clark probe

Electrochemical methods for NO determination offer several features that are not available with spectroscopic approaches. Perhaps the most important is the capability of microelectrodes to directly measure NO in single cells in situ, in close proximity to the source of NO generation. Figure 2 shows sensors that have been developed for the electrochemical measurement of NO. One is based on the electrochemical oxidation of NO on a platinum electrode (the classical Clark probe for detection of oxygen) and operates in the amperometric mode [17]. The other is based on the electrochemical oxidation of NO on conductive polymeric porphyrin (porphyrinic sensor) [24]. The Clark probe uses a platinum wire as a working electrode (anode) and a silver wire serves as the counterelectrode (cathode). The electrodes are mounted in a capillary tube filled with a sodium chlo-ride/hydrochloric acid solution separated from the analyte by a gas-permeable membrane. A constant potential of 0.9 V is applied, and direct current (analytical signal) is measured from the electrochemical oxidation of NO on the platinum anode. In the porphyrinic sensor, NO is catalytically oxidized on a polymeric metalloporphyrin... 

N03 in the chamber resulting from the reactions of NO with O2 and 02 the latter is an intermediate product of electrodic reduction of oxygen in the silver cathode. Accordingly, the concentration of NO measured with a Clark probe in a biological medium will usually be one to two orders of magnitude lower than the concentration measured with a porphyrinic sensor. The highest sensitivity for NO is obtained at a potential of approximately 0.9 V. 

Figure 7.40. Microbial biosensor Anode (Ag) on basis of Clark probe...

Plenary 18. Robin J FI Clark, e-mail address r.i.h.clark ucl.ac.uk (RS). Reports on recent diagnostic probing of art works ranging from illuminated manuscripts, paintings and pottery to papyri and icons. Nondestructive NIR microscopic RS is now realistic using CCD detection. Optimistic about new developments. 

FIGURE 6-18 Membrane-covered oxygen probe based on the Clark electrode. (Reproduced with permission from reference 60.)... 

Clarke RJ, Zouni A, Holzwarth JF (1995) Voltage sensitivity of the fluorescent probe RH421 in a model membrane system. Biophys J 68 1406-1415... 

Clark, N.D. and Berg, J.M. (1998) Zinc fingers in C. elegans finding families and probing pathways. Science 282, 2018-2022. 

Kenworthy, K.E., Bloomer, J.C., Clarke, S.E. and Houston, J.B. (1999) CYP3A4 drug interactions correlation of 10 in vitro probe substrates. British Journal of Clinical Pharmacology, 48 (5), 716-727. 

The first electron spectroscopic study of adsorbed hydrocarbons was that reported by Eastman and Demuth (78) who used He radiation to probe the valence electrons of benzene, acetylene, and ethylene. Figure 17 shows the difference spectrum of C2H4 adsorbed on Ni(lll) at 100 and 230 K compared with the results of Clarke et al. (79) for ethylene adsorption on Pt(lOO) at 290 K, propylene adsorption on Pt(lOO), and ethylene adsorption on Pt(lll). 

S. C. Park, M. Kim, J. Noh, H. Chung, Y. Woo, J. Lee and M.S. Kemper, Reliable and fast quantitative analysis of active ingredient in pharmaceutical suspension using Raman spechoscopy, Aruil. Chim. Acta, 593,46-53 (2007). P. Matousek, I.P. Clark, E.R.C. Draper, et al.. Subsurface probing in diffusely scattering media using spatially offset Raman spechoscopy, Appl. Spectrosc., 59, 393 00 (2005). 

A. A. Jones, Clark University, Mass. Could you summarize briefly those conditions under which rotating frame relaxation provides a good probe of molecular motion in the solid state Is this something that can be achieved with a good spectrometer and a rf large rf field ... 

We performed transient absorption measurements on BP(OH>2 with a spectrometer based on two noncollinearly phase matched optical parametric amplifiers (NOPAs) pumped by an homebuilt regenerative Ti Sapphire laser system or a CPA 2001 (Clark-MXR) [1,7]. The tunable UV pump pulses are generated by frequency doubling the output of one of the NOPAs. The other NOPA provides the visible probe pulses. The cross correlation between pump and probe pulses has a typical width (FWHM) of 40 fs. The sample is a cyclohexane solution of BP(OH)2 pumped through a flow cell with a 120 pm thick channel. 

The laser system consisted of a home-built Ti sapphire fs laser oscillator and regenerative amplifier (RGA). The pulse duration was 50 fs at 800 nm and 1 kHz repetition rate. The output of the RGA was split into two parts. One part was used as pump pulse. The other part served as a source for the generation of probe pulses with the help of a non-collinear optical parametric amplifier (NOPA, Clark). The sample preparation was explained elsewhere [7]. Briefly, sodium (Alfa Aesar) was used as received and sodium bromide (Alfa Aesar) was dried and re-crystallized under vacuum. The preparation of the samples was carried out in a glovebox under argon atmosphere. Localized electrons were generated by heating the metal-salt mixture to 800 °C, i.e. well above the melting point of the salt. 

The response time is between 15 and 20 s for both gases, and the precision is better than that obtained with the Clark electrode. A sterilizable oxygen probe based on this principle with performance characteristics equal to or better than the amperometric oxygen electrode has been constructed (Kroneis andMarsoner, 1983). 

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