Mercury detector cells

Marcott, C., Reeder, R. C., Paschalis, E. P., Talakis, D. N., Boskey, A. L. and Mendelsohn, R. (1998) Infrared microspectroscopic imaging of biomineralized tissues using a mercury-cadmium-telluride focal-plane array detector. Cell. Mol. Biol. 44, 109-115. 

Dithiocarbamates and thioureas are included in this section because of their useful electrochemical behavior at mercury and mercury amalgam electrodes. The formation of mercury complexes results in an easy oxidation at the mercury electrode. On the other hand, carbon electrodes are not well suited for the detection of these compounds because the oxidation occurs beyond the usual scope of carbon detector cells. 

A. G. Fogg and A. M. Summan, Simple Wall-Jet Detector Cell Holding Either a Solid Electrode or a Sessile Mercury-Drop Electrode and an Illustration of Its Use in the Oxidative and Reductive Flow Injection Voltammetric Determination of Food Colouring Matters. Analyst, 109 (1984) 1029. 

Bioanalytical Systems were the first to manufacture metal electrodes that would interchange with their standard GCE blocks in their amperometric detector cell. Thiols could be detected by forming an amalgam on a gold electrode. The static electrode had increased sensitivity relative to the mercury-pool electrode requiring similar low potentials but importantly was easier to operate. Nobel metal electrodes work at potentials intermediate between those of mercury-based electrodes and those required by a GCE (Figure 5.1). With the development of these metal electrodes the availability and the applicability of the methods described above were extended. 

Hydrogen Mercury-mercuric oxide detector cell Exhaled hydrogen monitor Palladium metal oxide semiconductors Thermistor thermal conductivity Mathiot et al. (1992), and Pauss et al. (1990) Collins and Paskins (1987) Pauss et al. (1990) Bjomsson et al. (2001)... 

A diagram of their detector is shown in figure 21. The UV adsorption system consists of a low pressure mercury lamp emitting light at 254 nm and a solid state photo cell with quartz windows allowing the photo cell to respond to light in the UV region. 

Elements such as As, Se and Te can be determined by AFS with hydride sample introduction into a flame or heated cell followed by atomization of the hydride. Mercury has been determined by cold-vapour AFS. A non-dispersive system for the determination of Hg in liquid and gas samples using AFS has been developed commercially (Fig. 6.4). Mercury ions in an aqueous solution are reduced to mercury using tin(II) chloride solution. The mercury vapour is continuously swept out of the solution by a carrier gas and fed to the fluorescence detector, where the fluorescence radiation is measured at 253.7 nm after excitation of the mercury vapour with a high-intensity mercury lamp (detection limit 0.9 ng I l). Gaseous mercury in gas samples (e.g. air) can be measured directly or after preconcentration on an absorber consisting of, for example, gold-coated sand. By heating the absorber, mercury is desorbed and transferred to the fluorescence detector. 

FTIR Microspectroscopy.3 A microscope accessory coupled to a liquid-nitrogen-cooled mercury-cadmium-telluride (MCT) detector can be used to obtain an IR spectrum. This is possible in both the transmission and reflectance modes. Several beads are spread on an IR-transparent window (NaCl, KBr, diamond) and possibly flattened via a hand-press or a compression cell. The IR beam is focused on a single bead using the view mode of the microscope. The blank area surrounding the bead is isolated using an adjustable aperture, and a spectrum is recorded using 32 scans (<1 min). A nearby blank area of the same size on the IR transparent window is recorded as the background. 

Monochromatic detection. A schematic of a monochromatic absorbance detector is given in Fig. 3.12. It is composed of a mercury or deuterium light source, a monochromator used to isolate a narrow bandwidth (10 nm) or spectral line (i.e. 254 nm for Hg), a flow cell with a volume of a few pi (optical path 0.1 to 1 cm) and a means of optical detection. This system is an example of a selective detector the intensity of absorption depends on the analyte molar absorption coefficient (see Fig. 3.13). It is thus possible to calculate the concentration of the analytes by measuring directly the peak areas without taking into account the specific absorption coefficients. For compounds that do not possess a significant absorption spectrum, it is possible to perform derivatisation of the analytes prior to detection. 

An ultraviolet detector using a flow cell such as that. in Figure 25-19 is the most common HPLC detector, because many solutes absorb ultraviolet light. Simple systems employ the intense 254-nm emission of a mercury lamp. More versatile instruments have deuterium, xenon, or tungsten lamps and a monochromator, so you can choose the optimum ultraviolet... 

Two UV detectors are also available from Laboratory Data Control, the UV Monitor and the Duo Monitor. The UV Monitor (Fig.3.45) consists of an optical unit anda control unit. The optical unit contains the UV source (low-pressure mercury lamp), sample, reference cells and photodetector. The control unit is connected by cable to the optical unit and may be located at a distance of up to 25 ft. The dual quartz flow cells (path-length, 10 mm diameter, 1 mm) each have a capacity of 8 (i 1. Double-beam linear-absorbance measurements may be made at either 254 nm or 280 nm. The absorbance ranges vary from 0.01 to 0.64 optical density units full scale (ODFS). The minimum detectable absorbance (equivalent to the noise) is 0.001 optical density units (OD). The drift of the photometer is usually less than 0.002 OD/h. With this system, it is possible to monitor continuously and quantitatively the absorbance at 254 or 280 nm of one liquid stream or the differential absorbance between two streams. The absorbance readout is linear and is directly related to the concentration in accordance with Beer s law. In the 280 nm mode, the 254-nm light is converted by a phosphor into a band with a maximum at 280 nm. This light is then passed to a photodetector which is sensitized for a response at 280 nm. The Duo Monitor (Fig.3.46) is a dual-wavelength continuous-flow detector with which effluents can be monitored simultaneously at 254 nm and 280 nm. The system consists of two modules, and the principle of operation is based on a modification of the 280-nm conversion kit for the UV Monitor. Light of 254-nm wavelength from a low-pressure mercury lamp is partially converted by the phosphor into a band at 280 nm. 

The Laboratory Data Control Fluoro Monitor (Fig.3.52) is a modular fluorescence detector similar in appearance to their UV detectors. With this detector, measurements may be made of the fluorescence of one stream or the differential fluorescence of two streams. The single-wavelength excitation source (a hot-cathode mercury lamp with a phosphor coating) emits a band of light with a maximum at 360 nm. The cell assembly is... 

The Aminco Fluoro-Microphotometer (Fig.3.56) is a filter instrument which is easily adaptable to liquid chromatography. The microflow cell has a capacity of 10 jul. A full range of excitation and emission filters are available. This detector has been adapted for use with the Technicon AutoAnalyser. The system uses a mercury lamp as the source and solid-state electronics. 

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