Activation, automated thermal

Air samples are usually collected to solid adsorbents such as Tenax, XAD resins, graphitized carbons (e.g. Carbopak), active charcoal, or porous polymers (e.g. Chromosorb). The chemicals are eluted from the adsorbent to a liquid or gas phase by liquid-solid elution or extraction or by thermal desorption. Extraction is the most common method. Thermal desorption can be applied when analysis is by GC (gas chromatography) method, and, recently, the use of automated thermal desorption has been proposed to provide increased sensitivity in GC/MS analysis of a wide range of CWC-related chemicals 8. ... 

A DuPont Model 990 Thermal Analysis Console with Model 910 DSC accessory was interfaced to a minicomputer system by means of a microcomputer for automated data collection. A program to provide the analysis of reaction kinetics data by the single dynamic scan method for DSC kinetics was developed. Features of this program include a fit of the data to a single equation by multiple regression techniques to yield the reaction order, the energy of activation and the Arrhenius frequency factor. The rate constant k(T) is then calculated and conversion data as a function of time and temperature can be generated at the operator s option. 

Thermal stability screens measure the increase in fluorescence intensity of a hydrophobic fluorescent probe that binds to proteins as they unfold during thermal denaturation. Automation of this assay in plate format has allowed rapid screening of libraries for compounds that improve the thermal stability profile of the target protein and has been particularly successful in identifying hits against active site pockets [152,153], and has recently been demonstrated in screening for inhibitors of Bel interactions and human MDM2/p53 [142, 154],... 

Slow LEMs can provide both negative and positive reactivity insertion with a moderate thermal response. Thirty-five slow LEMs provide the variation of reactivity between -2.79 and +2.88. The slow LEMs are used for automated bum-up reactivity compensation. In addition, slow LEMs partially realize the function of power control in accordance with the primary coolant flow rate. In nominal operation, the gas-liquid interface is placed in the active core region as shown in Fig. XVII-4. In case the core outlet temperature decreases, the gas-liquid interface goes up and positive reactivity is added, and vice-versa. To avoid quick positive reactivity addition, slow LEMs also have double-enveloped reservoirs (shells) with vacuum insulation. Therefore, only moderate thermal transients resulting from bum-up reactivity swing and primary flow rate variations affect slow LEMs. The design parameters of the LEMs are given in Table XVII-3. 

Among the most common methods to measure thermal and oxidative behavior of oils are the classical oxidative stability analysis used by industries, based on the active oxygen method (AOM), which determines the number of hours required for the oil to reach a peroxide value of 100 meq/kg O and the oxidative stability index (OSI), which can be considered as automated AOM with an apparatus that simulates the events under specific atmospheres, usually with the use of high temperatures. The OSI method measures the changes in water conductivity when the oxidation compounds are formed [17]. 

The elution of the organic compounds collected involves extraction by a solvent (displacement) or thermal desorption. Pentane, CS2 and benzyl alcohol are generally used as extraction solvents. CS2 is very suitable for activated charcoal, but cannot be used with polymeric materials, such as Tenax or Amberlite XAD, because decomposition occurs. As a result of displacement with solvents, the sample is extensively diluted, which can lead to problems with the detection limits on mass spectrometric detection. With solvents additional contamination can occur. The extracts are usually applied as solutions. The readily automated static headspace technique can also be used for sample injection. This procedure has also proved to be effective for desorption using polar solvents, such as benzyl alcohol or ethylene glycol monophenyl ether (1% solution in water, Krebs, 1991). 

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