Response, detector

The size of the leakage was determined as follows. Radiation detectors were mounted on the inlet of the first side, and the outlet of the second side of the heat exchanger and at additional locations for control. A short pulse of Kr-85 tracer (<0.1 sec) was injected into the feed stream, which gave rise to detector responses shown in figure 3. 

Fig. XVII-5. Schematic detector response in a determination of nitrogen adsorption and desorption. A flow of He and N2 is passed through the sample until the detector reading is constant the sample is then cooled in a liquid nitrogen bath. For desorption, the bath is removed. (From Ref. 28. Reprinted with permission from John Wiley Sons, copyright 1995.)...

Typical chromatogram of detector response as a function of retention time. 

Further, peak overlap results in nonlinear detector response vs concentration. Therefore, some other detection method must be used in conjunction with either of these types of detection. Nevertheless, as can be seen from Figure Ilf, chiroptical detection can be advantageous if there is considerable overlap of the two peaks. In this case, chiroptical detection may reveal that the lea ding and tailing edges of the peak are enantiomerically enriched which may not be apparent from the chromatogram obtained with nonchiroptical detection (Fig. He). 

Essential features of an automated method are the specificity, ie, the assay should be free from interference by other semm or urine constituents, and the sensitivity, ie, the detector response for typical sample concentration of the species measured should be large enough compared to the noise level to ensure assay precision. Also important are the speed, ie, the reaction should occur within a convenient time interval (for fast analysis rates), and adequate range, the result for most samples should fall within the allowable range of the assay. 

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). 

Oxygen Transport. The most widely used methods for measuring oxygen transport are based upon the Ox-Tran instmment (Modem Controls, Inc.). Several models exist, but they all work on the same principle. The most common apphcation is to measure the permeabihty of a film sample. Typically, oxygen is introduced on one side of the film, and nitrogen gas sweeps the other side of the film to a coulometric detector. The detector measures the rate that oxygen comes through the film. The detector response at steady state can easily be converted to At (eq. 1). Simple... 

The algorithm is based both on a mathematical simulation of a spectmm of secondary radiation emitted by a sample to be studied and the detector response function. The detection limit is given by criteria 3s ... 

The two complicating factors that are encountered most frequently are the linearity of detector response and stray light scattering at low signal levels. DTGS... 

FIRE SIMULATOR predicts the effects of fire growth in a 1-room, 2-vent compartment with sprinkler and detector. It predicts temperature and smoke properties (Oj/CO/COj concentrations and optical densities), heat transfer through room walls and ceilings, sprinkler/heat and smoke detector activation time, heating history of sprinkler/heat detector links, smoke detector response, sprinkler activation, ceiling jet temperature and velocity history (at specified radius from the flre i, sprinkler suppression rate of fire, time to flashover, post-flashover burning rates and duration, doors and windows which open and close, forced ventilation, post-flashover ventilation-limited combustion, lower flammability limit, smoke emissivity, and generation rates of CO/CO, pro iri i post-flashover. 

These combined HDF and GPC separations require the use of detectors such as static light scattering or viscometers to help sort out the convoluted elution profiles seen in those type of experiments. It should also be remembered in these situations that the typical refractive index or ultraviolet detector responses may not be representative of the actual mass fraction of insolubles eluting from the column because of the significant light scattering that can occur with those large particles in the detector cell. 

Post-column on-line derivatisation is carried out in a special reactor situated between the column and detector. A feature of this technique is that the derivatisation reaction need not go to completion provided it can be made reproducible. The reaction, however, needs to be fairly rapid at moderate temperatures and there should be no detector response to any excess reagent present. Clearly an advantage of post-column derivatisation is that ideally the separation and detection processes can be optimised separately. A problem which may arise, however, is that the most suitable eluant for the chromatographic separation rarely provides an ideal reaction medium for derivatisation this is particularly true for electrochemical detectors which operate correctly only within a limited range of pH, ionic strength and aqueous solvent composition. 

Procedure. Inject 1 fiL of the sample solution and obtain a chromatogram. Under the above conditions the compounds are separated in about 3 minutes, the elution sequence being (1) aspirin (2) phenacetin (3) caffeine. Measure peak areas with an integrator and normalise the peak area for each compound (i.e. express each peak area as a percentage of the total peak area). Compare these results with the known composition of the mixture discrepancies arise because of different detector response to the same amount of each substance. 

Compared with the flame ionisation detector, however, the ECD is more specialised and tends to be chosen for its selectivity which can simplify chromatograms. The ECD requires careful attention to obtain reliable results. Cleanliness is essential and the carrier gases must be very pure and dry. The two most likely impurities in these gases are water and oxygen which are sufficiently electronegative to produce a detector response and so give a noisy baseline. 

To obtain an accurate quantitative analysis of the composition of a mixture, a knowledge of the response of the detector to each component is required. If the detector response is not the same for each component, then the areas under the peaks clearly cannot be used as a direct measure of the proportion of the components in the mixture. The experiment described illustrates the use of an internal normalisation method for the quantitative analysis of a mixture of the following three components ethyl acetate (ethanoate), octane, and ethyl n-propyl ketone (hexan-3-one). 

When the oven temperature has stabilised, inject a 0.3 pL sample of mixture B and decide from the peak areas whether the detector response is the same for each component. 

If the detector response differs, make up by weight a 1 1 mixture of each of the separate components (I, II, and III) with compound (IV). Inject a 0.1 pL sample of each mixture, measure the corresponding peak area, and hence deduce the factors which will correct the peak areas of components (I), (II), and (III) with respect to the internal standard (IV). 

With flame emission spectroscopy, the detector response E is given by the expression... 

When there is a possibility of significant variation in detector response t constant beam intensity, it is often better to carry out comparative absorptiometry with a single detector. In a slow and cumbersome way, this was done by using the stand (Figure 3-7) in conjunction with the laboratory photometer. 

Graph of Detector Response against Solute Concentration... 

Delta function response - Over most of the wavelengths of interest, optical and infrared detectors produce one photoelectron for every detected photon, which provides a one-to-one correspondence between detected photons and photoelectrons. This means that the detector response is exactly linear to the intensity incident on the detector - an attribute that allows astronomers to precisely remove sky background and electronic bias to accurately measure the intensity of the astronomical object. 

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