Detectors response curves

Figure 2.6 Detector response curve showing (a) ideal behaviour, (b) real behaviour, (c) its linear range, (d) its dynamic range, (e) the noise level, and (f) the limit of detection at three times the noise level.

Calibration, in current Good Manufacturing Practices (cGMP) terminology, refers to instrument qualification or performance verification of the HPLC. Note that neither any internal instrumental adjustment nor detector response curve for quantitation is intended here as in the common usage of the terminology. In most pharmaceutical laboratories. 

Figure 3 Spectral power distributions of the two cool white lamps available overlaid with detector response curve. Source. Courtesy of Dr. R. Levin, Osram Sylvania.

The ideal quantum detector response curve is a square wave, i.e., equally sensitive over the entire wavelength range of measurement. These types of detectors should be used for all measurements of incident intensity, UV and VIS, if a spec-troradiometer is not available. While spectrally blind they will at least give a truer reading of the total amount of radiation actually being received by the samples. Figure 7 shows the response curves of two of these detectors. 

In Figure 3 are shown computer plots of the UV and LALLS detector response curves as a function of elution volume for a representative CTC. One obvious feature is the relative difference in the response of the two detectors as the sample molecular weight decreases with increasing elution volume. This is a consequence of the fact that the UV absorbance is a linear function of the solute concentration while R(9,c) is a function of both concentration and molecular weight. The molecular weight of solute eluting within a given volume element is calculated from a form of eq. t3)... 

Figure 3. Experimental VV(A) and LALLS (B)detector response curves for CTC...

Additional peak on the chromatogram Difficulties due to finding suitable internal standard sample application Nonlinearity of concentration vs. detector response curve Detector responses are function of chemical structures of analytes... 

Carrier gas was pure nitrogen with an inlet pressure of 1 atm. and a flow rate of about 30 ml/min. An additional stream of nitrogen at 150 ml/min is passed directly through the detector to reach the optimum value for the detector sensitivity. The response of the electron capture detector for the alkyl leads is greatly affected by the applied potential. In Figure 156 the detector current is plotted for various applied potentials (curve A), and the detector response (curve B) measured in arbitrary units from the peak areas for the same injected amount is also shown. 

In Figure 6 we show the number, surface area, and mass distributions calculated for the glass bead sample. Since the detector responds to the scattering of light at the particle surfaces, it produces a signal proportional to a fraction s particle surface area. Thus the area distribution is obtained directly from the detector response curve via a change of scales the number and mass... 

Modem NDT film systems (with Pb screens) are very linear X-ray detectors. This is shown in fig.l for different NDT film systems and a X-ray tube at 160 kV. Note that for histoncal reasons the film response curve is often plotted as film density versus log (radiation dose), which hides this linear relationship. The film density is the difference between the measured optical film density and the fog density Db of the film base. 

End Point vs Kinetic Methods. Samples may be assayed for enzymes, ie, biocatalysts, and for other substances, all of which are referred to as substrates. The assay reactions for substrates and enzymes differ in that substrates themselves are converted into some detectable product, whereas enzymes are detected indirectly through their conversion of a starting reagent A into a product B. The corresponding reaction curves, or plots of detector response vs time, differ for these two reaction systems, as shown in Eigure 2. Eigure 2a illustrates a typical substrate reaction curve Eigure 2b shows a typical enzyme reaction curve (see Enzyme applications). 

The actual analogue values we need to measure reflectance are given on the next page as 7.8.30. as follows. Note that the optical response curves of the measuring parts, i.e.- the non-linearity of the source and detector, are now corrected in the response of the overall instrument. 

The 1000 A column did not show any resolution between 312 nm and 57 nm particle sizes. Shown in Fig.2 are the calibration curves for the 2000 A and 3000 A columns and for their combination. The 57 nm particle standard appears to have been erroneously characterized by the supplier. This was subsequently confirmed by electron microscopy. The 2000 X column exhibited a sharp upturn in its calibration curve close to the exclusion limit. It is to be noted that while data points corresponding to 312 and 275 nm diameter particles appear on individual column calibration curves, they are not indicated for the calibration curve of the combination. This is because these larger diameter particles were completely retained in the packed colimms, generating no detector response. The percentage recovery for these particles from individual columns was considerably less than 100 resulting in their complete retention when the columns were combined in series. 

Generate a 4-5-point calibration curve with standards of concentrations within an order of magnitude of the estimated detection limit. For this purpose, the detection limit may be estimated as a concentration that would yield a signal three times Ap p. The calibration curve should be generated by plotting detector response (x) vs concentration (c). 

A new nonweighted linear calibration curve is to be generated with every set of samples analyzed. The calibration standards are interspersed among the analytical samples, preferably with a standard between every two analytical samples, and injected into the HPLC/OECD system. The calibration curve is generated by plotting peak height of the detector response against the concentration for each calibration standard of EMA and methylated HEMA. 

Detectors are usually conpued in terns of their operational characteristics defined by the nininvin detectable quantity of standards, the selectivity response ratio between standards of different conpositlon or structure, and the range of the linear portion of the detector-response calibration curve. These terns are wid. y used to neasure the perfomance of different chronatographic detectors and were fomally defined in section 1.8.1. 

Recently, Orosz et al. [136] reviewed and critically reevaluated some of the known mechanistic studies. Detailed mathematical expressions for rate constants were presented, and these are used to derive relationships, which can then be used as guidelines in the optimization procedure of the POCL response. A model based on the time-window concept, which assumes that only a fraction of the exponential light emission curve is captured and integrated by the detector, was presented. Existing data were used to simulate the detector response for different reagent concentrations and flow rates. 

In a typical pulse experiment, a pulse of known size, shape and composition is introduced to a reactor, preferably one with a simple flow pattern, either plug flow or well mixed. The response to the perturbation is then measured behind the reactor. A thermal conductivity detector can be used to compare the shape of the peaks before and after the reactor. This is usually done in the case of non-reacting systems, and moment analysis of the response curve can give information on diffusivities, mass transfer coefficients and adsorption constants. The typical pulse experiment in a reacting system traditionally uses GC analysis by leading the effluent from the reactor directly into a gas chromatographic column. This method yields conversions and selectivities for the total pulse, the time coordinate is lost. 

In Fig. 1.1 (d) the hydrodynamic behaviour is simplified in order to explain the mixing process. Let us assume that there is no axial dispersion and that radial dispersion is complete when the sampler reaches the detector. The volume of the sample zone is thus 200pl after the merging point (lOOpl sample+lOOpl-reagent as flow rates are equal). The total flow rate is 2.0ml min-1. Simple mathematics then gives a residence time of 6s for the sample in the detector flow cell. In reality, response curves reflect... 

Gas (GC) and Liquid (HPLC) Chromatographs These are similar to spectrophotometers in that they are calibrated via a detector response to some property of analyte. The analyte may either be in solution or, in the case of GC (Figure 5.9), in pure form. Again, a calibration (or "standard") curve of detector response vs. either concentration or amount of pure chemical used is plotted and unknowns determined by correlation with the known stan-... 

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