Peak cleaning

Time or temperature (arb. units) Figure 1.6 Principle of the peak-cleaning technique. 

Figure 1.7 Principle of the peak-cleaning technique of Bucci et al. The dashed curves represent the TSDC peaks isolated during independent experiments by polarizing the sample from to the lowest available temperature (peak 1) and from to (peak 2).

On the other hand, the intensity of TSD (1 peaks is proportional to the volume concentration of ether groups in the polymer. Peak cleaning and partial heating procedures allow us to separate the (32 process from the total TSD spectrum. Probably, one of the (3 peaks corresponds to crankshaft-type motion. 

Poling and heating profiles used to measure thermally stimulated current. (1) Standard measurement, (11) partial heating method or peak cleaning method (111) thermal sampling method... 

However, in polymer systems there can be many internal relaxation modes and it is unreasonable to assume that a single relaxation process is responsible for the complex TSC curves typically recorded. In order to deconvolute complex TSC spectra into individual relaxation processes, where the Debye and Arrhenius relations are more applicable, two approaches are used. The first approach is called the partial heating method or peak cleaning method (Figure 6.29(H)). Following quenching and extinction of the applied electric field, the TSC curve of the polarized sample is measured as the sample is heated at a controlled rate to. The sample is requenched from to Tq, and the TSC curve is subsequently... 

The ECD is one of the most easily contaminated detectors and is adversely affected by oxygen and water. Ultrapure, dry gases, freedom from leaks, and clean samples are necessary. Evidence of contamination is usually a noisy baseline or peaks that have small negative dips before and after each peak. Cleaning can sometimes be accomplished by operation with hydrogen carrier gas at a high temperature to bum off impurities, but dismantling is often required. 

Care has to be taken in ir measurements to have the low-temperature tail of the measured TL peak clean from weak satellite TL peaks. This can be done by prewarming the sample up to a temperature on the tail of the measured peak, which bleaches away the satellite peaks in this region. One has also to make sure that no thermal decay of the emission takes place in the relevant temperature range. If such a decay takes place (at a thermal activation energy E ), this has to be added to the measured ir value of E. Similarly, if the frequency factor is temperature dependent, it will affect the measured E values. The lata- effect is, however, usually neglected. 

Figure 6.14. Application of peak cleaning techniques for the separation of overlapping relaxations (a) technique introduced by Creswell and Perlman (1970), with 7k = 10 °C and Tp = 47 °C (b) variation of TSC spectrum with changes in Tp (between -123 °C and +47 °C in 10° increments). Filled circles correspond to the spectrum recorded with the optimum polarization temperature (rp = -13°C) for p relaxation. [From Kalogeras (2004) reprinted with permission of John Wiley and Sons, Ltd.]...

The TSD spectra of polymer electrets are. in general, very complex, consisting of several relaxation peaks. Special techniques such as peak cleaning and partial heating (235) have been d eloped to analyze the complex TSD spectra of polymers. 

Figure Bl.23.6. TOF spectra of a Si 100] surface with chemisorbed H2O (left) and clean Si (right). Peaks...

Figure Bl.25.2 shows the XPS spectra of two organoplatinum complexes which contain different amounts of chlorine. The spectrum shows the peaks of all elements expected from the compounds, the Pt 4f and 4d doublets (the 4f doublet is iimesolved due to the low energy resolution employed for broad energy range scans). Cl 2p and Cl 2s, N Is and C Is. Flowever, the C Is caimot be taken as characteristic for the complex only. All surfaces that have not been cleaned by sputtermg or oxidation in the XPS spectrometer contain carbon. The reason is that adsorbed hydrocarbons from the atmosphere give the optimum lowering of the surface free energy and hence, all surfaces are covered by hydrocarbon fragments [9].

The AeroSizer, manufactured by Amherst Process Instmments Inc. (Hadley, Massachusetts), is equipped with a special device called the AeroDisperser for ensuring efficient dispersal of the powders to be inspected. The disperser and the measurement instmment are shown schematically in Figure 13. The aerosol particles to be characterized are sucked into the inspection zone which operates at a partial vacuum. As the air leaves the nozzle at near sonic velocities, the particles in the stream are accelerated across an inspection zone where they cross two laser beams. The time of flight between the two laser beams is used to deduce the size of the particles. The instmment is caUbrated with latex particles of known size. A stream of clean air confines the aerosol stream to the measurement zone. This technique is known as hydrodynamic focusing. A computer correlation estabUshes which peak in the second laser inspection matches the initiation of action from the first laser beam. The equipment can measure particles at a rate of 10,000/s. The output from the AeroSizer can either be displayed as a number count or a volume percentage count. 

Tetrachloroethylene was first prepared ia 1821 by Faraday by thermal decomposition of hexachloroethane. Tetrachloroethylene is typically produced as a coproduct with either trichloroethylene or carbon tetrachloride from hydrocarbons, partially chloriaated hydrocarbons, and chlorine. Although production of tetrachloroethylene and trichloroethylene from acetylene was once the dominant process, it is now obsolete because of the high cost of acetylene. Demand for tetrachloroethylene peaked ia the 1980s. The decline ia demand can be attributed to use of tighter equipment and solvent recovery ia the dry-cleaning and metal cleaning iadustries and the phaseout of CFG 113 (trichlorotrifluoroethane) under the Montreal Protocol. 

A powerful tool now employed is that of diode array detection (DAD). This function allows peaks detected by UV to be scanned, and provides a spectral profile for each suspected microcystin. Microcystins have characteristic absorption profiles in the wavelength range 200-300 nm, and these can be used as an indication of identity without the concomitant use of purified microcystin standards for all variants. A HPLC-DAD analytical method has also been devised for measurement of intracellular and extracellular microcystins in water samples containing cyanobacteria. This method involves filtration of the cyanobacteria from the water sample. The cyanobacterial cells present on the filter are extracted with methanol and analysed by HPLC. The filtered water is subjected to solid-phase clean-up using C g cartridges, before elution with methanol and then HPLC analysis. 

With correct experimental procedure TDS is straightforward to use and has been applied extensively in basic experiments concerned with the nature of reactions between pure gases and clean solid surfaces. Most of these applications have been catalysis-related (i. e. performed on surfaces acting as models for catalysts) and TDS has always been used with other techniques, e.g. UPS, ELS, AES, and LEED. To a certain extent it is quantifiable, in that the area under a desorption peak is proportional to the number of ions of that species desorbed in that temperature range, but measurement of the area is not always easy if several processes overlap. 

Some limitations are associated with UV radiation for disinfection. These include (1) The process performance is highly dependent on the efficacy of upstream devices that remove suspended solids (2) Another key factor is that the UV lamps must be kept clean in order to maintain their peak radiation output (3) A further drawback is associated with the fact that a thin layer of water (< 0.5 cm) must pass within 5 cm of the lamps. 

Compound A undergoes hydrolysis of its acetal function in dilute sulfuric acid to yield 1,2-ethanediol and compound B (CgHg02), mp 54°C. Compound B exhibits a carbonyl stretching band in the infrared at 1690 cm and has two singlets in its H NMR spectrum, at 8 2.9 and 6.7, in the ratio 2 1. On standing in water or ethanol, compound B is converted cleanly to an isomeric substance, compound C, mp 172—173°C. Compound C has no peaks attributable to carbonyl groups in its infrared spectrum. Identify compounds B and C. 

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.

Figure 13.10 LC-LC chromatogram of a surface water sample spiked at 2 p.g 1 with ati azine, and its metabolites (registered at 220 nm). Conditions volume of sample injected, 2 ml clean-up time, 2.60 min ti ansfer time, 4.2 min The blank was subtracted. Peak identification is as follows 1, DIA 2, HA 3, DEA 4, atrazine. Reprinted from Journal of Chromatography, A 778, F. Hernandez et al, New method for the rapid detemiination of triazine herbicides and some of thek main metabolites in water by using coupled-column liquid cliromatography and large volume injection , pp. 171-181, copyright 1997, with permission from Elsevier Science.

Figure 14.19 Typical GC chromatogram of the separated di-aromatics fraction of a middle distillate sample Peak identification is as follows 1, naphthalene 2, 2-methylnaphthalene 3, 1-methylnaphthalene 4, biphenyl 5, C2-naphthalenes 6, C3-naphthalenes 7, C4-naph-thalenes 8, C5+-naphthalenes 9, benzothiophene 10, methylbenzothiophenes 11, C2-ben-zotliiopIrenes. Note the clean baseline between naphthalene and the methylnaphthalenes, which means that no overlap with the previous (mono-aromatics) fraction has occuned.

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