ECD

The efficiency of gas turbines is limited by the maximum allowable turbine inlet temperature (TIT). The TIT may be increased by cooling of the blades and vanes of the high pressure turbine. Cooling channels can be casted into the components or may be drilled afterwards. Non-conventional processes like EDM, ECD or Laser are used for drilling. Radiographic examination of the drilled components is part of the inspection procedure. Traditional X-Ray film technique has been used. The consumable costs, the waste disposal and the limited capacity of the two film units lead to the decision to investigate the alternative of Real-Time X-Ray. 

Figure A2.3.3 P-Visothemis for van der Waals equation of state. Maxwell s equal areas mle (area ABE = area ECD) detemiines the volumes of the coexisting phases at subcritical temperatures.

Certain neutral technetium complexes can be used to image cerebral perfusion (Fig. 4). Those in Figure 4a and 4b have been approved for clinical use. Two other complexes (Fig. 4c and 4d) were tested in early clinical trials, but were not developed further. An effective cerebral perfusion agent must first cross the blood brain barrier and then be retained for the period necessary for image acquisition. Tc-bicisate is retained owing to a stereospecific hydrolysis in brain tissue of one of the ester groups to form the anionic complex TcO(ECD) , which does not cross the barrier. This mechanism of retention is termed metaboHc trapping. 

The sfe of chlorpyrifos methyl from wheat followed by on-line Ic/gc/ecd has been investigated (93). Extraction profiles were generated to determine the maximum analyte recovery and the minimum extraction time. Using pure CO2, a 65% recovery of chlorpyrifos methyl spiked onto wheat at 50 ppb was reported. When 2% methanol was added to the CO2, the recovery from a one gram sample averaged 97.8% (n = 10, 4.0% RSD). 

Chlorphenylid, Flucofuron and Sulcofuron Waters (Tentative Methods based on methylation and GC-ECD, ion-pair HPLC and hydrolysis of Sulcofuron to 4-chloro-3-trifluoromethylaniline by GC-ECD), 1993... 

D. Hainzl, J. Burhenne and H. Pariar, HRGC-ECD and HRGC-NICI SIM quantification of toxaphene residues in selected marine organism by envir onmentally relevant chloroboT nanes as standard , Chemosphere 2S 237-243 (1994). 

Figure 10.13 GC clrromatogram obtained after on-line LC-GC(ECD) of a human milk sample analysed for PCBs (attenuation X 64). Peak identification is as follows (1) PCB 28 (2) PCB 118 (3) PCB 153 (4) PCB 138 (5) PCB 180 (6) PCB 170 (7) PCB 207. Reprinted from Journal of High Resolution Chromatography, 20, G. R. van der Hoff et al, Determination of organochlorine compounds in fatty matiices application of normal-phase LC clean-up coupled on-line to GC/ECD , pp. 222-226, 1997, with permission from Wiley-VCH.

G. R. van der Hoff, R. A. Baumann, P. van Zoonen and U. A. Th. Brinkman, Determination of organocWoiine compounds in fatty matrices application of normal-phase PC clean-up coupled on-line to GC/ECD , 7. High Resolut. Chromatogr. 20 222-226(1997). 

The first bioanalytical application of LC-GC was presented by Grob et al. (119). These authors proposed this coupled system for the determination of diethylstilbe-strol in urine as a replacement for GC-MS. After hydrolysis, clean-up by solid-phase extraction and derivatization by pentafluorobenzyl bromide, the extract was separated with normal-phase LC by using cyclohexane/1 % tetrahydrofuran (THE) at a flow-rate of 260 p.l/min as the mobile phase. The result of LC-UV analysis of a urine sample and GC with electron-capture detection (ECD) of the LC fraction are shown in Ligures 11.8(a) and (b), respectively. The practical detection limits varied between about 0.1 and 0.3 ppb, depending on the urine being analysed. By use of... 

Figure 13.1 Monitor (FID) (a) and analytical (ECD) (b) channel responses for PCB congeners in Aroclor 1254, showing selection of the six heart-cut events Frr-st columns, HT8 second columns, BPX5. Reprinted from Journal of High Resolution Chromatography, 19, R. M. Kinghorn et al., Multidimensional capillar-y gas chr omatography of polychlorinated biphenyl marker compounds , pp. 622-626, 1996, with per-mission from Wiley-VCH.

Figure 13.2 MDGC-ECD chromatograms of PCB fractions from sediment samples, demonstrating the separation of the enantiomers of (a) PCB 95, (b) PCB 132, and (c) PCB 149 non-labelled peaks were not identified. Reprinted from Journal of Chromatography, A 723, A. Glausch et al, Enantioselective analysis of chiral polyclilorinated biphenyls in sediment samples by multidimensional gas cliromatography-electi on-capture detection after steam distillation-solvent exti action and sulfur removal , pp. 399-404, copyright 1996, with permission from Elsevier Science.

Figure 15.1 Separation of pesticides from butter by using LC-GC-ECD. Peak identification is as follows 1, HCB 2, lindane 5, aldrin 7, o,p -DDE 10, endrin 11, o,p -DDT 13, p,p -DDT peaks 3, 4, 6, 8, 9, 12, 14, 15 and 16 were not identified. Adapted from Journal of High Resolution Chromatography, 13, R. Barcarolo, Coupled EC-GC a new method for the on-line analysis of organchlorine pesticide residues in fat , pp. 465-469, 1990, with permission from Wiley-VCH.

Ionisation detectors. An important characteristic of the common carrier gases is that they behave as perfect insulators at normal temperatures and pressures. The increased conductivity due to the presence of a few charged molecules in the effluent from the column thus provides the high sensitivity which is a feature of the ionisation based detectors. Ionisation detectors in current use include the flame ionisation detector (FID), thermionic ionisation detector (TID), photoionisation detector (PID) and electron capture detector (ECD) each, of course, employing a different method to generate an ion current. The two most widely used ionisation detectors are, however, the FID and ECD and these are described below. 

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. 

Electron Capture Detector In the electron capture detector (ECD), a beta emitter such as tritium or 63Ni is used to ionize the carrier gas. Electrons from the ionization migrate to the anode and produce a steady current. If the GC effluent contains a compound that can capture electrons, the current is reduced because the resulting negative ions move more slowly than electrons. Thus, the signal measured is the loss of electrical current. The ECD is very sensitive to materials that readily capture electrons. These materials frequently have unsaturation and electronegative substituents. Because the ECD is sensitive to water, the carrier gas must be dry. 

In this core, concentrations of PCBs (determined as Aroclor 1254 and 1260, by high resolution gas chromatography, electron capture detection and high resolution gas chromatography-low resolution mass spectrometry) were <30 ng and those of total DDT (p,p DDT + p,p DDD + p,p DDE) <5 ng g Campesan et al. (21) in 11 sediment samples from Valle di Brenta, determined by GC-ECD the following mean concentrations (ng gd.w.) ... 

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