Density detector

Findings with PDU. Work with the PDU largely paralleled the bench-scale reactor tests there was one important addition—extensive three-phase fluidization studies. As was mentioned, the PDU is equipped with a traversing gamma-ray density detector that is capable of measuring bed density to within dbO.Ol specific gravity units. Thus, we could measure and correlate fluidized bed expansion as a function of liquid and gas velocities and physical properties, and could also determine the... 

Figure 4.5. Mass chromatograph. (A) Carrier A inlet (S) sample inlet (B) carrier B inlet (V) valve/trap system (C) chromatographic column (D) gas density detector (R) recorder.

This detector was invented by Martin and James (1) and is a universal detector. The design was simplified and subsequently made available by the Gow-Mac Instrument Company. Use of two of these detectors in a dual column mode is the basis for the direct determination of molecular weight (the mass chromatograph). The hydrodynamics of the gas density detector as they apply to the mass chromatograph have been studied (36). 

Mass chromatography is a new form of gas chromatography that uses two gas density detectors operated in parallel and provides (a) mass of components within 1-2% relative without determination of response factors, (b) molecular weight of components within 0.25-1% in the mass range 2—400, and (c) a powerful identification tool by the combined use of retention time and molecular weight data. The theoretical basis of the technique and its scope as a molecular weight analyzer, a qualitative identification tool, and a quantitative analyzer in the polymer field are discussed. 

The predictable response of the gas density detector makes the overall method possible. The basic formula which describes its operation is... 

With the Chromalytics Model MC-2 mass chromatograph, a sample is introduced into the unit, split into two portions, collected onto traps, and then analyzed simultaneously with two gas density detectors as shown in Figure 1. The peak height or area ratios from each detector are measured and the molecular weights calculated from Equation 3. 

The gas density detector provides a predictable response as outlined in Equation 2 provided that the molecular weights of the various components in the sample are known. The detector has never achieved its full quantitative potential since molecular weight information is often not available. 

The large errors associated with the analysis using thermal conductivity (15.8%) and flame ionization (48.0%) detectors are understandable because of the diverse chemical nature of the solvents. Obvious good results could be achieved by individual calibration of response factors. The point being made is that the gas density detector gives excellent results without calibration even for unknown mixtures. 

One major aspect of quantitative analysis is sensitivity and dynamic range of linearity. Such data have been reviewed (2) for the gas density, thermal conductivity, and flame ionization detectors. Since response is a function of molecular weight in the gas density detector, it is difficult to make comparisons in a simple manner. In general, however, the sensitivity of the gas density cell is about twice that of comparable thermal conductivity cells and about one-tenth that of flame ionization detectors (when bleed of the column is limiting). 

Another variation using multiple detection is the molecular weight chromatograph,17 which is a GC with two gas density detectors and two... 

For polymer systems without UV activity the combination of a RI detector with a density (D) detector can be used. The working principle of the density detector is based on the mechanical oscillator method. Since this detector yields a signal for every polymer, provided that its density is different from the density of the mobile phase, this detector can be regarded as universal [29,30,36]. The separation of mixtures of polystyrene and polybutadiene by SEC with dual den-sity-RI detection is presented in Figs. 7 and 8. In a first set of experiments, the response factors of both polymers in both detectors have to be determined. Then from the intensity of each slice of the elution curves in both detectors, the mass distribution of both polymers across the elution volume axis can be calculated. As can be seen in Fig. 7, a separation into the component peaks is obtained due to the fact that the molar masses of PS and PB are sufficiently different. For both components the individual elution profiles can be determined and using corresponding calibration curves for PS and PB the individual MMDs can be calculated. The same information can be extracted from an experiment where the molar masses of the components are similar and SEC separation does not work (see Fig. 8). Again the individual mass distributions are obtained and the MMDs for PS and PB can be determined. 

An example of the separation of a mixture of tert-Boc-valine and phenylanaline methyl ester from a Sephadex LH-20 column monitored by the density detector is shown in figure 16. Each peak represents 50 mg of solute and thus the sensitivity is extremely low. Although it is a bulk property detector, and thus will detect all substances that have a density that differs from that of the mobile phase, it will obviously not tolerate gradient elution. Density measurement may be a basis for LC detection, and, in fact, this work has proved its validity. Nevertheless,... 

A continuous-density detector is working on the principles of a liquid flowing through a oscillating U-shaped glass tube where the oscillating frequency is found re-... 

There are many more design and control features to these facilities that aid in their management such as air circulators for mixing the contents, multiple-level and density detectors, temperature measuring devices, radiation alarms, etc. Although we do not take credit for these features as primary phases of confinement of the waste, we do rely on these control systems to ensure the primary barriers or phases are functional. 

For highly concentrated sugar solutions, e.g. in the separation of glucose and fructose, density detectors are often used. Again, these solvent sensitive detectors can only be used under isocratic conditions, as any change in mobile phase composition will also change the detector signal. 

Cs / Soil Density Detector (MC-1) / Radiation Dispersal Devices ... 

An identification of the ordinate scale in specific terms where possible. In general, increasing concentration of evolved gas should be plotted upward. For gas density detectors, increasing gas density should also be plotted upward. Deviations from these practices should be clearly marked. 

Thermal conductivity detectors have been discussed in detail by Ingraham (107), who also described their application to thermodynamic and kinetic measurements. In this same book. Lodding (4) describes the gas density detector as well as several ionization detectors, such as the argon ionization detector, the electron capture detector, and others. Flame ionization detectors have been described in detail by Brody and Chaney (108) and Johnson (109). The latter also discusses other types of detectors. Malone and McFad-den (110) described many different types of special identification detectors, such as those listed in Table 8.3. Numerous texts on gas chromatography describe a wide variety of detectors, many of them useful in EGD and EGA. 

PEG CR polymerization degree 2-75 Water / methanol 20/80wt. Silica gel Spherisorb ODS 2, 5 pm, 25x0.46cm 0.5ml/min 5 pi Rl, density detector... 

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