Detector on-line

The latest trend is to smaller beads in smaller columns, as this saves eluent and shortens the time for a chromatographic analysis. This argument can be correct if only one suitable detector is used. However, these modern small columns are not optimal for a combination of detectors. So-called multiple detection is a combination of some detectors with different measurement principles (differential refractometer, spectral photometer, light-scattering detector, on-line viscometer) behind the last column, mostly in series, seldom in a branched ( parallel ) order. In this way, the tedious preparative fractionation of a polymer sample can often be avoided. 

Morgan NY, Wellner E, Talbot T, Smith PD, Phillips TM. Development of a two-color laser finorescence detector—On-line detection of internal standards and nnknowns by capillary electrophoresis within the same sample. Journal of Chromatography A 1105, 213-219, 2006. 

Even if relatively new, HF FIFFF has been used to separate supramicrometer particles, proteins, water-soluble polymers, and synthetic organic-soluble polymers. Particle separation in HF FIFFF has recently been improved, reaching the level of efficiency normally achieved by conventional, rectangular FIFFF channels. With these channel-optimized HF FIFFF systems, separation speed and the resolution of nanosized particles have been increased. HF FIFFF has recently been examined as a means for off-line and on-line protein characterization by using the mass spectrometry (MS) through matrix-assisted laser desorption ionization time-of-flight mass spectrometry (M ALDl-TOF MS) and electrospray ionization (ESl)-TOF MS, as specific detectors. On-line HF FIFFF and ESl-TOF MS analysis has demonstrated the viability of fractionating proteins by HF FIFFF followed by direct analysis of the protein ions in MS [38]. 

GPC is a promising method for examination of template polymerization, especially copolymerization. Copolymerization of methacrylic acid with methyl methacrylate in the presence of polyCdimethylaminoethyl methacrylate) can be selected as an example of GPC application for examination of template processes. The process was carried out in tetrahydrofurane as solvent at 65°C. After proper time of polymerization, the samples were cooled, diluted by THF, filtered, and injected to GPC columns. Two detectors on line UV and differential refractometer, DRI, were applied. UV detector was used to measure concentration of two monomers, while the template was recorded by DRI detector (Figure 11.3) The decrease in concentration ofboth monomers can be measured separately. It was found that a big difference in the rate of polymerization between template process and blank polymerization exists. The rate measured separately for methacrylic acid (decrease of concentration of methacrylic acid in monomers mixture) was much higher in the template process. Furthermore, the ratio ofboth monomers changes in a different manner. Reactivity ratios for both monomers can be computed. Decrease in concentration during the process is shown in Figure 11.4. 

The traps should be dried at about 40°C in a mercury-free N2 flow for 5 min prior to analysis, after which they should be connected to the AFS detector on-line with the helium gas flow. The mercury is then thermally desorbed either directly into the detector or onto an analytical trap. If an analytical trap is used, a second heating step should be performed before the detection. The advantages of dual amalgamation are that the influence of any interfering substances adsorbed on the first trap may be reduced and that the mercury adsorbed on the second analytical trap will be more easily desorbed, thus yielding a sharper peak. 

From time to time in this chapter, mention has been made of procedures for the determination of particular chemical forms of elements. Sometimes this is achieved by a totally manual fractionation of an element into separate and distinct chemical fractions, and the fractions are then analysed one at a time by spectrometric procedures. However, by the 1980s there was a growing tendency to automate the fractionation procedures and to incorporate the spectrometric detector on-line . It is appropriate at this point to consider a few examples of this approach. 

The author is thankful to Dr. Ray Bakhtiar (Drug Metabolism of MRL at Rahway) for the preparation of Fig. 1, his support, encouragement in writing this manuscript, to Dr. Byron H. Arison (Drug Metabolism of MRL at Rahway) for his interest, support, encouragement, and constructive discussions during the course of this work, and David Knapp and Uresh Parikh (Medicinal Chemistry of MRL at Rahway) for technical help connecting the MS detector on-line to the LC-NMR system. 

Nondispersive infrared analyzer, on-line Flame ionization detector, on-line Chemiluminescence detector, on-line... 

Modern ECD detectors on line allow the recording of the complete CD trace, which can be used for the determination of the absolute configuration by comparison with calculated ECD spectra or application of empirical rules (01JA2703, 05JNP686,08OL1373). 

For their characterization, alginates must first be purified and isolated under their sodium form. NMR spectroscopy ( H and C) is the most powerful technique to characterize the chemical composition and the microstructure of alginates [46 9]. Purified alginates, isolated under the sodium salt form, were also characterized by steric exclusion chromatography (SEC)with three detectors on line. For commercial products, molecular weights may range between 32 000 and 400 000. A further means of characterization is their intrinsic viscosity using the Mark-Houwink relation ... 

If the signal from a detector is a factor of two properties, it is possible to use another detector on line to resolve the different properties, e.g., multiangle light scattering (MALS) in combination with differential refractive index (DRI), or continuous viscosimetry - - DRI. Alternatively, the two detectors may respond to two different properties of interest In either case, it is almost as simple to acquire multiple detector signals as a single one. Multiple detectors can be arranged either in series or in parallel. A parallel... 

The mobile phase reservoirs are generally screw-top plastic-coated glass bottles with inlet lines to allow for degassing of the solvents for 10-15 min either by vacuum or sparging with helium or both. A positive pressure of helium should be maintained in the solvent bottles. Degassing is important to prevent gas bubbles from lodging in the pump, column, or the detector. On-line degassing... 

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