Two-detector system

Gas chromatography (GC) is used to analyze the sample extracts. Two detector systems are used, one for quantitation and the other for analyte confirmation and quantitation. 

Penton, Z. (1991). Optimization of samples introduction parameters for determination of pesticides by capillary gas chromatography using a two column, two detector system. J. Assoc. Off. Anal. Chem., 74(5) 872-875. 

Another means of identification is a two-detector system. One detector should be nonspecific, such as the thermal conductivity cell in gas chromatography, or the refractive-index detector in liquid chromatography, while the other should have... 

The possibility of separation and analysis of enzymes by CZE has been explored. Banke, et al. separated alkahne proteases from crude fermentation broth, and collected fractions from CZE for enzyme analysis. CZE was also used to monitor the progress of an enzyme reaction [23]. Konse, et al. reported modification of a microtitre plate assembly which was used to coUect fractions on polyvinylidene difluoride (PVDF) membranes. Fractions blotted onto the PVDF membranes were then subsequently analyzed by a sequencer [24]. Emmer and Roeraade described an on-hne micro-post column reactor which they used in conjunction with on-column detection. By using the two detector system, they were able to rapidly monitor enzyme activity in samples. Through careful optimization of conditions in the reactor, the loss of efficiency at the point of detection through the reactor capiUary was minimal [25]. 

Similarly as collection, the identification methods vary enormously from one country to the next. Owing to similar density it is difficult to separate PVC from PET. At the same time, PVC has devastatingly large effect on de-polymerization of PET, thus not more than 15 ppm of PVC is permitted to enter PET recycles. Precise discriminating lines have been devised based on two detector systems, one able to identified crystalline PET,... 

Two detector systems, such as DAD plus fluorescence or MS detector, are often more important than an excellent measurement precision, = 0.8 % is often sufficient. 

The basic idea behind the RMC-system is to use a rotating modulator with two parallel grids in front of a non-imaging detector. In the WATCH detector the rear modulation grid and the monolithic detector of the classical RMC-system is replaced by a detector plane with interleaved stripes of two separate detectors - in WATCH the two detector systems are realized as alternating strips of Nal(Tl)- and CsI(Na)-scintillators. The period of the scintillator strip pattern is equal to the period in the modulation grid. 

The most recent development in CT scanners is dualsource technology. Two separate X-ray sources and two detector systems are arranged perpendicular to each other, and rotate around the body. Initially, the design was chosen to improve the temporal resolution for cardiac imaging. However, if these two tubes run at different kV levels, elements with different order numbers such as calcium and iodine may be separated by their different dual energy indices. As... 

The two-detector system also provides qualitative information about peak purity and sample pJCa. This information is gained by plotting the two detector outputs against each other. In addition to the usual ratio plots, it is suggested that multidimensional detection in any separation system is best served by plotting the raw detector outputs against each other. This type of implementation of single-column and suppressed 1C provides information beyond the sum total of that obtained with either approach alone. 

Several approaches have been considered so far in order to tackle this problem where the Co prompt-peak interferes with the physical part of the positron lifetime spectrum [145-147]. Aside from the PLEPS technique, one acceptable solution seems to be a triple-coincidence method using a Na source [145,147]. In this case, three y rays - one with an energy of 1274keV and two with energies of 511 keV - accompany each event of positron annihilation, while only two y-rays result from the °Co decay. However, compared to conventional two-detector systems, the requirement for triple coincidence drastically reduces the rate of accumulation of positron lifetime spectra [145,148]. In comparison, PLEPS reduces the measuring time by a factor of 500 and also enables the estimation of the defect concentration. 

To describe the X-ray imaging system the projection of 3D object points onto the 2D image plane, and nonlinear distortions inherent in the image detector system have to, be modelled. A parametric camera model based on a simple pinhole model to describe the projection in combination with a polynomal model of the nonlinear distortions is used to describe the X-ray imaging system. The parameters of the model are estimated using a two step approach. First the distortion parameters for fixed source and detector positions are calculated without any knowledge of the projection parameters. In a second step, the projection parameters are calculated for each image taken with the same source and detector positions but with different sample positions. 

The GAMMASCAN 1500 HR is a combined system for two-dimensional (2D-CT) and three-dimensional (3D-CT) computed tomography, as well as digital radiography (DR). The system is equipped with two separate detector systems for the fan-beam and cone-beam CT. The sire of the objects is limited to a height of four meters, maximum diameters of 1.5 meters and a weight of up to 15 tons. The turntable which carries the test samples can be moved along and across the beam direction ( X- and Y- direction). The radiation source and the detector systems can be moved in Z- direction, both, simultaneously and independently. 

Therefore it is reasonable to prepare already the data acquisition for a three dimensional evaluation in cone-beam-technique by means of two-dimensional detectors. The system is already prepared to integrate a second detector- system for this purpose. An array of up to four flat panel detectors is foreseen. The detector- elements are based on amorphous silicon. Because of the high photon energy and the high dose rates special attention was necessary to protect the read-out electronics. Details of the detector arrangement and the software for reconstruction, visualisation and comparison between the CT results and CAD data are part of a separate paper during this conference [2]. 

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). 

To reduce the chance of false activation of the suppression system by vibration, a flexible pressure detector standoff is often used. Also, two detectors in series may be employed to reduce further the possi-bihty of false activation. 

Figure 4.1 Schematic diagram of a coupled column system. The first column (ID) is connected to the second column (2D) tlirough the interface or valve system. The interface can be a diiect coupling, a live T-union, a complex multiport valve, or a thermal or cryogenic modulation system. The stimulus can be the switching of the valve, abalancing pressure to divert flow towards 2D, an added flow that is used in pressure tuning, or the drive mechanism for the modulator. The line to detector 1 will normally be a non-retaining section of column. In a two-oven system, ID and 2D will be in different ovens the dotted line indicates separately heated zones.

The concrete block walls of the cell housing the generator tube and associated components are 1.7 meters thick. The facility also includes a Kaman Nuclear dual-axis rotator assembly for simultaneous transfer and irradiation of reference and unknown sample, and a dual Na iodide (Nal) scintillation detector system designed for simultaneous counting of activated samples. Automatic transfer of samples between load station to the rotator assembly in front of the target, and back to the count station, is accomplished pneumatically by means of two 1.2cm (i.d.) polyethylene tubes which loop down at both ends of the system and pass underneath the concrete shielding thru a pipe duct. Total one-way traverse distance for the samples is approx 9 meters. In performing quantitative analysis for a particular element by neutron activation, the usual approach is to compare the count rates of an unknown sample with that of a reference standard of known compn irradiated under identical conditions... 

CYCLOPS A four-step phase cycle that corrects dc imbalance in the two channels of a quadrature detector system. 

Another variation of the preceding method is to apply HPLC to fractionate the cleaned-up aliphatic-aromatic fraction from flash colurim separation of soluble organic matter as it is performed in the Chevron laboratory, for example, as described in Reference 2. A Waters HPLC system equipped with a preparative Whatman Partisil 10 silica column (9.4 X 500 mm), a HPLC pump, and two detectors for separation monitoring (a UV and refractive index detector) are used, giving three fractions of aliphatic hydrocarbons, mono-, di-, and triaromatics and polar compounds. The hrst two fractions are eluted with hexane, whereas polar compounds are eluted with... 

Cyanide and thiocyanate anions in aqueous solution can be determined as cyanogen bromide after reaction with bromine [686]. The thiocyanate anion can be quantitatively determined in the presence of cyanide by adding an excess of formaldehyde solution to the sample, which converts the cyanide ion to the unreactive cyanohydrin. The detection limits for the cyanide and thiocyanate anions were less than 0.01 ppm with an electron-capture detector. Iodine in acid solution reacts with acetone to form monoiodoacetone, which can be detected at high sensitivity with an electron-capture detector [687]. The reaction is specific for iodine, iodide being determined after oxidation with iodate. The nitrate anion can be determined in aqueous solution after conversion to nitrobenzene by reaction with benzene in the presence of sulfuric acid [688,689]. The detection limit for the nitrate anion was less than 0.1 ppm. The nitrite anion can be determined after oxidation to nitrate with potassium permanganate. Nitrite can be determined directly by alkylation with an alkaline solution of pentafluorobenzyl bromide [690]. The yield of derivative was about 80t.with a detection limit of 0.46 ng in 0.1 ml of aqueous sample. Pentafluorobenzyl p-toluenesulfonate has been used to derivatize carboxylate and phenolate anions and to simultaneously derivatize bromide, iodide, cyanide, thiocyanate, nitrite, nitrate and sulfide in a two-phase system using tetrapentylammonium cWoride as a phase transfer catalyst [691]. Detection limits wer Hi the ppm range. 

With the new VME/UNIX control system on the polarised hot-neutron normal-beam diffractometer D3 at ILL, each measurement cycle for both peak and background intensities lasts 2 s, and the (+)/(-) counting-time fractions are defined with a 1 MHz clock. There are two detector scalers and two monitor scalers ((+) and (-) states). In Table 1, we compare the flipping ratio measured for the strong 200 and the weak 600 Bragg peak reflections of a CoFe sample. As expected, the standard deviation cr (if) is improved in the case of the strong reflection (16%). 

Thus for an ideal two-phase system the total calibrated intensity that is scattered into the reciprocal space is the product of the square of the contrast between the phases and the product of the volume fractions of the phases, Vi (1 — Vi) = V1V2. V1V2 is the composition parameter66 of a two-phase system which is accessible in SAXS experiments. The total intensity of the photons scattered into space is thus independent from the arrangement and the shapes of the particles in the material (i.e., the topology). Moreover, Eq. (8.54) shows that in the raw data the intensity is as well proportional to the irradiated volume. From this fact a technical procedure to adjust the intensity that falls on the detector is readily established. If, for example, we do not receive a number of counts that is sufficient for good counting statistics, we may open the slits or increase the thickness of a thin sample. 

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