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it per unit time. A block diagram showing the essential elements of a data acquisition and processing system is given in figure 31. Figure 31. Data Acquisition and Processing System The Scaling Ampifier The output from the detector usually passes directly to a scaling amplifier that modifies the signal to a range that is appropriate for the analog-to-digital (A/D) converter. The output can alternatively pass to a potentiometric recorder and produce the chromatogram in real time. The computer system can also produce a real time chromatogram but, to do so, the data must be processed and the chromatogram presented on the printer. The output from most detectors ranges from 0 to 10 mV? whereas the input required by most A/D converters is considerably greater e.g. 0 to 1.0 V. For example, if the FSD of the signal is 10 mv, the instantaneous measurement of 2 mV (assumed from the detector) must be scaled up to 0.2 volt, which is carried out by a

column gave a quarter of a million theoretical plates. However, the chromatogram shown in figure 34 was obtained at a flow rate of 38 ml/min. and, thus, as it was operated well above its optimum velocity, the column only gave an efficiency of 160,000 theoretical plates. As the chromatographic data was acquired and processed by a computer portions of the chromatogram could be expanded and these are shown as inserts in the figure. It is seen that the apparently confused peaks at the start of the chromatogram are, in fact, well resolved into individual small peaks. It is also seen that the late small peak has retained its symmetry and is almost perfectly Gaussian in shape. Those familiar with cinnamon bark oil separated on GC capillary columns may wonder at the relatively few peaks that appear on the chromatogram. It should be pointed out that a UV detector was employed to monitor the separation and, thus, only, those substances that adsorb in the UV would be disclosed. As the

dispersive interactions from the fluctuating random charges and polar interactions from forces between the two dipoles. Examples of substances that contain permanent dipoles and can exhibit polar interactions with other molecules are alcohols, esters, ethers, amines, amides, nitriles, etc.  The retentive characteristics of a polar stationary phase are displayed in the lower chromatogram in figure 2 and can be compared with the retentive characteristics of a dispersive phase shown in the chromatogram above. The polar stationary phase is a cyanopropyl polymer that exhibits relatively weak dispersive interactions but strong polar interactions. The aliphatic hydrocarbons, that are well retained by the dispersive stationary phase, are rapidly eluted on the polar phase but the aromatics are strongly retained and well resolved from one another. On the dispersive stationary phase, all the solutes are spread along the chromatogram, roughly in order of their increasing molecular weights

at a pressure of 0.14 bar above atmospheric pressure, to force the decomposition gases and vapors through the conduit to the sampling device. The gasses vapors, produced during the thermogravimetric analysis are periodically sampled during the heating program. The components are separated on the capillary column and the column exit gas is split into two streams. One stream passes directly to the FTIR spectrometer and the other to the mass spectrometer. Thus, either a total ion current chromatogram and/or a total IR absorption chromatogram can be generated in real time. Alternatively, the chromatogram can be reconstructed after the analysis is complete. In addition, IR and MS spectra from any selected peak can be generated from disc for identification purposes. Identification can be achieved by direct comparison with reference spectra, or by elucidating the structure from the data provided by the complementary IR and MS spectra.     The Sampling Condition

nbsp; . An example of the chromatograms and spectra obtained are shown in figure 65. Figure 65A is the total ion current chromatogram from a sample of Rhine river water containing 200 ppt of the herbicides Atrazine and Simazine. The peaks are depicted somewhat enlarged in the insert. Figure 65 B shows a section of the same chromatogram presented in the selected ion mode. Atrazine (eluted at 16. 30 minutes) and Simazine (eluted at 16.36 min.) are shown. Figure 65. Chromatogram and Spectra from a Sample of River Water Containing 200 ppt of the Atrazine and Simazine (after. ref. 25

nbsp;   The Peak Capacity of a Chromatographic Column The peak capacity of a column has been defined as the number of peaks that can be fitted into a chromatogram between the dead point and the 'last peak', each peak being separated from its neighbor by 4s. The 'last peak' of  chromatogram is vague term because it depends somewhat on a number of unrelated factors such as the detector sensitivity and the column efficiency. As a result, the 'last peak' can be either arbitrarily specified or defined by the properties of the column and/or the chromatograph with which it is used. Limited peak capacity can be a serious problem in the analysis of multi-component mixtures if the capacity of the chromatogram is insufficient to contain all the peaks discretely. Isocratic