Detectors series coupled

The series coupling of detectors does not require an effluent splitter. This approach may be feasible when a nondestructive detector, such as the BCD or PID is used ahead of an FID, TID, HECD, etc. This technique has been demonstrated in a few Instances for ECD/FID [238,239] and PID/ECD detection [240]. 

The use of an atomic emission detector (AED) coupled to a GC may provide under ideal conditions information about the empirical formula of the analyte corresponding to a GC peak. However, it was found that the AED responses of C, Cl and O of a series of phenols is related to the working condition of the AED. The elemental response of Cl is independent of molecular structure, but those of C and O are not, probably due to formation of CO in the plasma. The O response is also affected in nitrophenols, probably due to NO2 formation. A novel detector, based upon hyperthermal negative surface ionization, shows up to 100-fold higher sensitivity than that of the FID for alcohols and phenolic compounds. ... 

The general use of series (or parallel) coupled detectors has been to record different channels of independent information as a method of qualitative identification [391,392]. The use of detector ratios for compound identification has declined with the development of low cost mass spectrometers that allow the use of more reliable identification methods. There are also practical problems related to long term stability of response ratios and their system dependence. Although rarely addressed in the literature, the chromatograms recorded with series coupled detectors often show greater peak shape deterioration than predicted from consideration of the additional coupled detector volume. 

The reliability of polymer characterization by SEC has been significantly advanced by new detection strategies based on series-coupled detectors with complementary response characteristics together with appropriate software for calculating molecular weights from the simultaneous detector inputs [518,522-526]. The three most popular detector combinations are refractive index and viscometry, light scattering and refractive... 

A typical chemiluminescence detector consists of a series-coupled thermal decomposition and ozone reaction chambers. The selective detection of nitrosamines is based on their facile low-temperature (275-300°C) catalytic pyrolysis to release nitric oxide. Thermal decomposition in the presence of oxygen at about 1000°C affords a mechanism for conversion of nitrogen-containing compounds to nitric oxide (catalytic oxidation at lower temperatures is also possible). Decomposition in a hydrogen-diffusion flame or thermal oxidation in a ceramic furnace is used to produce sulfur monoxide from sulfur-containing compounds. 

The chromatogram can finally be used as the series of bands or zones of components or the components can be eluted successively and then detected by various means (e.g. thermal conductivity, flame ionization, electron capture detectors, or the bands can be examined chemically). If the detection is non-destructive, preparative scale chromatography can separate measurable and useful quantities of components. The final detection stage can be coupled to a mass spectrometer (GCMS) and to a computer for final identification. 

Detector selectivity is much more important in LC than in GC since, in general, separations must be performed with a much smaller number of theoretical plates, and for complex mixtures both column separation and detector discrimination may be equally significant in obtaining an acceptable result. Sensitivity is important for trace analysis and for compatibility with the small sizes and miniaturised detector volumes associated with microcolumns in LC. The introduction of small bore packed columns in HPLC with reduced peak volume places an even greater strain on LC detector design. It is generally desirable to have a nondestructive detector this allows coupling several detectors in series (dual... 

To examine variation in the quality of methyl ketones expressed by females and newly-emerged males, we determined the number of unique methyl ketones expressed by individual snakes and compared the relative concentrations of individual methyl ketones comprising the overall pheromone profiles for the two groups. The methyl ketones present in the pheromone extracts were identified by gas chromatography / mass spectrometry (Hewlett Packard 5890 Series II gas chromatograph coupled with a Hewlett Packard 5971 Series mass selective detector— see LeMaster and Mason 2003 for full description of the GC/MS platform and methods). 

As the laser pulse is in the nanosecond range, a fast mass spectrometer has to be coupled in series. In most cases, MALDI is coimected to a time-of-flight (TOF) mass spectrometer with which m/z ratios are determined by precisely measuring the time an ion needs to pass from the ion source to the detector. Besides its abil-... 

FIGURE 7.10 Block diagram of a basic electrochemical detector. All three electrodes are controlled by a regulated power supply coupled to a potentiometer and a series of amplifiers. The output from the electrodes is fed into a data acquisition system. 

The derivatized samples were analyzed on a Hewlett-Packard 5890 series IIGC (helium carrier gas) coupled to a Hewlett-Packard 5971 mass-selective detector (MSD). A 60 m, 0.32 mm i d., 0.25-im film, SE-30 fused silica capillary column (J W Scientific, Folsom, CA) was installed in the GC, and an on-column injector (SGE model OCl-3) held at ambient temperature was fitted to the colunrn inlet. Samples (0.5 p,L) were injected directly into the column held at 105°C... 

Dual-electrode LCEC is very useful for the selective detection of chemically reversible redox couples. In this case, two electrodes are placed in series (Fig. 27.1 OB). The first electrode acts as a generator to produce an electroactive species that is detected more selectively downstream at the second electrode, which is set at a more analytically useful potential. One excellent example of the use of a dual-electrode detector for electrochemical derivatization is the detection of disulfides [34]. In this case, the first electrode is used to reduce the disulfide to the corresponding thiol. The thiol is then detected by the catalytic oxidation of mercury, described earlier. Because of the favorable potential employed at the second electrode, the selectivity and sensitivity of this method are extremely high. In addition, thiols can be distinguished from disulfides by simply turning off the generator electrode. 

Cadmium, copper and zinc associated with various proteins have been studied by means of an ion chromatograph coupled to a flame AAS (Ebdon et al., 1987). The design of the interface meant that the nebuliser of the AAS could be eliminated, thus avoiding the low efficiency of the nebulisation. Effluent from the HPLC was collected as discrete aliquots on a series of rotating platinum spirals that entered the flame atomiser. An atom trap (tube in flame) was included to increase the sensitivity of the detector by allowing the analyte to remain for a longer period in the optical path. 

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