Detector continuously measuring

The detector continuously measures the intensity ratio of the reference beam (7r) compared with the sample beam (7S). As the spectrometer scans the wavelengths in the UV region, a printer draws a graph (called a spectrum) of the absorbance of the sample as a function of the wavelength. 

As mentioned, the detector continually measures the conductivity of the buffer solution in the capillary. If an ionic component enters the detector cell, the local conductivity will change. At first glance, one would expect the conductivity to increase, because of additional ionic material. This is a simplified and incorrect approach, however. Suppose, in a buffer consisting of O.OIM potassium and 0.02M acetate (pH 4.7), a sodium solution is analyzed. Electroneutrality requires that with an increase of the sodium concentration from zero to, in this case, initially the... 

SS, 3 X 2nun). A Nal detector continuously measures the passing activity through the sample loop. A GC run is remotely started at the moment that the sample loop is filled with [ NJ-NHs. The GC is equipped with a Haysep P column (SS, mesh 80-100, O.D. 1/8). The GC run is started at 90°C, and after 1 minute, the temperature is increased with 10°C/min to 130°C. The products are analysed by a thermal conductivity detector (TCD). A Nal detector, directed at the TCD, monitors labelled products. Behind the TCD detector, a heated electrical 3-way valve selects a small part from the [ NJ-NHg peak. Depending on the experiment, a pulse time of 2-10 s is used to inject the labelled gaseous ammonia into the reactant stream. The required specific activity of the radioactive ammonia pulse is 0.1 MBq/ml minimum to meet the statistical requirements of the positron emission profiling experiments. 

As mentioned, the detector continually measures the conductivity of the buffer solution in the capillary. If an ionic component enters the detector cell, the local conductivity... 

As the vapor leaves the tube, the compounds in the sample are detected by a device such as a thermal conductivity detector. This instrument continuously measures the thermal conductivity (the ability to conduct heat) of the carrier gas, which changes when a solute is present. The detection techniques are very sensitive, allowing tiny amounts of solutes to be detected. Many environmental monitoring and forensic applications have been developed. 

Electrostatic Radon Monitor ERM flow rate 0.5 /min, electrode -3000 V applied, dehamidified, continuously measured, detector ZnS(Ag)... 

Flow-Type Ionization Chamber (PFC). The Flow -Type Ionization Chamber Method (PFC) has been developed for continuously measuring radon gas in the atmospheric air. The detail of the device has been described elsewhere (Shimo, 1985). Briefly, measurements are continuously carried out by drawing air through the detector at 1.0 2.0 /min. The ionization currentdue to alpha particles from radon and its daughters is detected with a vibrating reed electrometer (VRE) in the same manner as the DSC. The sensitivity... 

Other analysis methods dependent on multiple detectors can be implemented using this automated system. Two methods under development are the use of a continuous viscometer detector with a refractive index detector to yield absolute molecular weight and branching, utilizing the universal calibration curve concept (4), and the use of a UV or IR detector with the refractive index detector to measure compositional distribution as a function of molecular weight. 

A second advantage is that they can a be monitored in the field with inex- pensive equipment. More important,. they can be continuously measured through the pipe leading from the separator, without the need for gathering samples, by mounting a detector on the pipe. ... 

Sulfur Dioxide. Both flame photometric and pulsed fluorescence methods have been applied to the continuous measurement of S02 from aircraft. In the flame photometric detector (FPD), sulfur compounds are reduced in a hydrogen-rich flame to the S2 dimer. The emission resulting from the transition of the thermally excited dimer to its ground state at 394 nm is measured by using a narrow band-pass filter and a photomultiplier tube. 

Because the FPD responds to both aerosol and gaseous sulfur species, it has also been possible to modify these instruments to continuously measure aerosol sulfur by selectively removing gaseous sulfur compounds with a lead(II) oxide-glycerol coated denuder (55). Use of such an instrument for airborne measurements of aerosol sulfur in and around broken clouds has been reported (57). In principle, speciation between aerosol sulfate, disulfate, and sulfuric acid by selective thermal decomposition (58, 59) can also be achieved. Flame photometric detectors have also been used as selective detectors for gas chromatography. Thornton and Bandy (60) reported the use of a chromatographic system with a flame photometric detector for airborne measurement of S02 and OCS with a detection limit of 25 pptrv. 

Although spectroradiometers appear to have many advantages, their use in comparison to simpler broadband detectors in dense monitoring UV networks is not necessarily the best choice. First, because in general are unable to produce continuous measurements, since even the faster instruments would need a few minutes to complete a typical UV scan, while broadband detectors can be sampled easily once every a few seconds. The second reason is their purchase and operational cost, which can be 5-10 times higher than for a typical broadband detector. Finally, due to their extreme sensitivity their operation and maintenance requires special experimental support and experienced, well-trained personnel. Despite these disadvantages, their superior quality imposes the existence of at least on spectroradiometer to support each network and provide proper absolute calibration of the broadband detectors. 

Two different arrangements are illustrated in Fig. 6.32. Figure 6.32a shows a typical installation where a high level limit alarm is required. In this case the intensity of the radiation g reaching the detector would be determined by equation 6.54. If a continuous measurement of level is necessary, then the radioactive source and detector would be positioned as in Fig. 6.326 and o is then given by equation 6.55. 

The use of sensors and detectors to continuously measure important chemical properties has significant analytical advantages. By providing a fast return of analytical information in a timely, safe, and cost-effective fashion, such devices offer direct and reliable monitoring of explosive compounds while greatly reducing the huge analytical costs and... 

Helium or nitrogen were used as carrier gas and methane was the tracer gas. A pulse of tracer gas was injected through a six-way valve into the carrier gas flow. The concentration of the tracer in the effluent was continuously measured by means of a thermal conductivity detector and recorded. 

Finally, several attempts have been made to develop an absolute molar mass detector based on osmotic pressure measurements. Commercially available membrane osmometers are designed for static measurements, and the cell design with a flat membrane is not suited for continuous flow operation. Different from the conventional design, Yau developed a detector which measures the flow resistance of a column caused by osmotic swelling and deswelling of soft gel particles used for the packing (see Fig. 12) [65,78]. With a microbore gel column, a... 

Detectors capable of continuously measuring the density of the flowing liquid have been designed by Kratky et al. [146]. They are based on the measurement of frequency oscillations of a quartz tube through which the eluate flows. The oscillation frequency depends on the tube mass and, thus, for the given eluent, on the concentration and density of the solute. Their application to size exclusion chromatography has been described by Trathnigg and Jorde [147]. Kirkland applied such a detector for FFF [148]. 

The heat of adsorption detector, devised by Claxton, consists of a small plug of adsorbent, usually silica gel, through which the chromatographic eluent passes subsequent to leaving the column. Embedded in the silica gel is either a thermocouple or a thermistor that continuously measures the temperature of the adsorbent and mobile phase. 

The schematics of the instrument installation are shown in Fig. 9.13. The RADAIR instrument develops readouts on 4 continuous measuring channels of activity concentrations of artificial a, P, emitters and natural radon in Bq m and of the ambient y dose in pGy h. These activity concentration readouts are divided from countings in 1000 s cycles, of the activity deposited on the filter taken from samples of the surrounding air. The filter automatically advances after remaining 24 hours in front of the stack of two semiconductor detectors. The first detector located above the filter, delivers a net counting rate in proportion to the activity deposited on the filter. The... 

The necessary conditions for application of the universal calibration method and for calculation of molecular weights through Eq. (6) is the knowledge of the [r]]i values, which are obtained from the Mark-Houwink equations when the pertinent values of K and a constants are known. An alternative way is to make a continuous measurement of [t]]i at the different elution volumes with an on-line viscometer detector coupled to the usual concentration detector system. 

In contrast to component-specific detectors, such as ultraviolet (UV) absorbance and fluorescence, conductivity detection is a universal detection method. This means that a bulk property (conductivity) of the buffer solution is continuously measured. A migrating ionic component locally changes the conductivity and this change is monitored. As such, conductivity detection is universally sensitive because, in principle, all migrating ionic compounds show detector response, although not to the same extent. 

From that point, the necessity of continuously measuring viscosity, in addition to polymer concentration, became obvious. Several attempts were made to adapt existing viscometers as GPC detectors, but the problem of internal volume was critical. Ouano [2] published the first design of a single-capillary viscometer which was based on pressure measurement. Several similar designs [3-6] were pubfished and a commercially available instrument, the Waters Model 150CV (Waters Associates, Milford, MA, U.S.A.), based on a design described in Ref. 4, became commercially available. 

A Mossbauer spectrometer consists of a radioactive Co source on a transducer that continuously scans the desired velocity range, an absorber consisting of the catalyst and a detector to measure the intensity of the gamma radiation transmitted by the absorber as a function of the source velocity. This is the common mode of operation, called Mossbauer absorption spectroscopy, sometimes abbreviated as MAS. It is also possible to fix the Co containing source and move a single-line Fe absorber, in order to investigate Co-containing catalysts. This technique, called Mossbauer emission spectroscopy (MES), has successfully been applied to study Co-Mo hydrodesulphurization catalysts [42]. 

Detectors contain measuring cells that exhibit a backmixing behavior that dominates the influence of the pipe system behind the chromatographic column. Therefore, the whole system behind the column is modeled as an ideal continuously stirred tank (C.S.T.). 

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