Single-channel detectors

Electrochemical detector Single channel electrochemical detector with a glassy carbon working electrode (Antec, Leiden, The Netherlands). Set the operating potential to 450 mV vs a Ag/AgCl reference electrode see Note 6) Use a 25-pm gasket to reduce the cell volume. 

A single-channel manifold also can be used for systems in which a chemical reaction generates the species responsible for the analytical signal. In this case the carrier stream both transports the sample to the detector and reacts with the sample. Because the sample must mix with the carrier stream, flow rates are lower than when no chemical reaction is involved. One example is the determination of chloride in water, which is based on the following sequence of reactions. ... 

Photomultipliers are used as detectors in the single-channel instruments. GaAs cathode tubes give a flat frequency response over the visible spectrum to 800 nm in the near IR. Contemporary Raman spectrometers use computers for instrument control, and data collection and storage, and permit versatile displays. 

The detector signal is conditioned through a single channel pulse height analyzer whose output pulses are fed to a scaler-timer in the single crystal controller. 

Working solutions (1 litre) which were 10 7 mol/1 in one of the elements to be studied were prepared by appropriate addition of the radioactive stock solutions to pH-adjusted artificial seawater. After the pH had been checked, 100 ml portions were transferred to the bottles to be tested. The filled bottles were shaken continuously and gently in an upright position, at room temperature and in the dark. At certain time intervals, ranging from 1 min to 28 d, 0.1 ml aliquots were taken. These aliquots were counted in a 3 x 3 in Nal (TI) well-type scintillation detector, coupled to a single-channel analyser with a window setting corresponding to the rays to be measured. 

A Princeton Gamma Tech Si (Li) solid state detector in conjunction with an EG G Ortec Model 673 Spectroscopy Amplifier and a Tennelec Model 450 Single Channel analyzer were employed to detect the characteristic Ru Ka... 

Dual-channel instruments are very similar to their single-channel counterparts and differ only in the fact that they analyse each sample for two constituents simultaneously. The sample stream is divided into two fractions, each one flowing independently through its own system of tubing with the appropriate reagents and detectors. 

Fig. 1.35 Multi-channel plate multiplier. Each hole corresponds to a single channel detector.

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