High detector

Detectability High-detector response Good signal-to-noise ratio... 

Another technique that has been used in CE format for chiral drug-protein interactions is the Hummel-Dreyer method (52). In this technique, the solute is dissolved in the run buffer at varying concentrations, creating a high detector background response. After equilibration of the system, mixtures of the ligand and protein in various ratios are injected into this system as a sample. 

Laser power too high Detector voltage too high Laser power too low Detector voltage too low Instrument is not calibrated... 

There are a few complications to this simple picture. First it has been assumed the conduction band is normally empty of electrons. This is never entirely true, and for many semiconductor materials used in photoconductive devices with reasonably large values of Aj, it is not even approximately true. Where kT is an appreciable fraction of AEg there will be significant thermal promotion of electrons into the conduction band, and a consequently high detector dark current. For this reason, many photoconductive detectors are cooled, often using thermo-electric devices (for easy packaging) in order to reduce kT, and hence the dark current. 

It is seen that a typical integral chromatogram is obtained that is quite suitable for quantitative analysis. As the total mass of each solute eluted from the column is, in effect, diluted to 500 ml by the mobile phase in the reservoir, high detector sensitivities are required. 

Images formed using a high detector positioned in the lens. 

The pulse height distribution at high detector gain often shows a structure, probably due to the discrete numbers of secondary electrons emitted at the first dynode. An example for an H7422P-40 module is shown in Fig. 6.14. 

Low detector temperatures apparently encourage the attachment process and high detector temperatures the dissociative process. The presence of molecules capable of either process will diminish the electron flux within the detector and consequently the standing current, and it is this reduction in the standing current which is amplified and measured to produce the detector signal. For practical purposes it is, however, enough to know that the sensitivity of detection increases in the order ... 

Most of the applications of these detectors require detection of small signals at relatively high detector operating temperatures and in substantial back-... 

Peaks generated by fast GC are no different to measure than other chromatographic peaks, except that they are narrower, and a high detector sampling frequency will be required to measure very narrow peaks accurately. Data points from 10 to 20 per cat is generally considered a sufficient number however, it has been suggested that this number should be far greater to reduce measurement uncertainty for asymmetric peaks. 

The use of the differential mode of detector operation can be extremely useful in cases where the normal chromatographic development gives very poor separation resulting from peak tailing. However, the technique does require significantly more sample for frontal analysis than with normal elution development so that sufficient sample must be available. Furthermore, the response of the detector operation in its differential mode is two orders of magnitude less sensitive than when operated normally and thus high detector sensitivities have to be employed. 

Air dissolved in the sample will usually be eluted close to the dead volume and will change the refractive index of the mobile phase. This change in refractive index will produce a peak on both the refractive index detector and the UV detector, particularly when using high detector sensitivities. To eliminate this effect the sample should also be degassed provided the components of interest used are involatile. As already stated desolved air will be a particular problem when using the electrochemical detector. 

Figure 3.4. Two Gaussian spots separated to be near the Rayleigh resolution limit are shown with very high detector resolution in (A) and (B) and with pixels one half the spot separation in (C) and (D). When the spots are centered on the large pixels, they are still resolved (C) displaced to the pixel edge, they are not (D).

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