Irradiation physical method

A physical method of desorption is, for example, the desorption stimulated by the impact of ions or electrons 3-8). Another method is desorption by a strong electrostatic field (9). Irradiation by a current of photons can lead to a photodesorption process (10-14). Even desorption by means of phonic energy has been described (15), Finally, the desorption by thermal energy falls into this group of desorption techniques. 

Photolysis of the sulphinyl-3H-pyrazole 587 in ether or methylene chloride leads to the formation of a relatively stable carbene 588 that can be identified by physical methods. When the irradiation is performed in ethyl vinyl ether or in furan, the expected cyclopropanes are formed smoothly and stereospecifically683 (equation 374). 

Sterilization by physical methods such as irradiation (gamma or UV) for disinfection of materials and environments.64... 

Physical methods include plasma treatments, UV irradiation, corona discharge, and flame treatment. Among these, plasma treatment is widely used for the surface modification of synthetic polymers. Plasma can be obtained by exciting gases into an energetic state by radio frequency, microwave, or electrons from a hot filament discharge. Generation of plasma requires a vacuum, which normally poses several... 

Inactivation of mycotoxins. When removal or elimination of mycotoxins is not possible, mycotoxins can be inactivated by (a) physical methods such as thermal inactivation, photochemical or gamma irradiation (b) chemical methods such as treatment of commodities with acids, alkalis, aldehydes, oxidizing agents, and gases like chlorine, sulfur dioxide, ozone and ammonia [201] and (c) biological methods such as fermentations or enzymatic digestions that cause the breakdown of mycotoxins [202]. 

In addition to chemical methods variety of physical methods has been employed for the synthesis of AuNPs. UV irradiation is used to improve the quality of the AuNPs when it is used in synergy with micelles or seeds [32,33], Near-IR laser irradiation provokes an enormous size growth of thiol-stabilized AuNPs [34], The presence of an ultrasonic field (200 kHz) allowed the control of the rate of AuC14" reduction in an aqueous solution containing only a small amount of 2-propanol and the sizes of the formed AuNPs are controlled by varying the parameters such as the temperature of the solution, the intensity of the ultrasound, and the positioning of the reactor [35,36], Sonochemistry was also used for the synthesis of AuNPs within the pores of silica and for the synthesis of Au/Pd bimetallic particles [37,38], Radiolysis has been used to control the size of AuNPs [39], Laser photolysis has been used to form AuNPs in block copolymer micelles. Laser ablation is another technique of AuNP synthesis that has been used under various conditions whereby size control can be induced by the laser [40,41],... 

Physical or chemical separation of the analyte from its matrix avoids interelemental effects but is time-consuming, expensive, or tedious. Physical methods have the general advantage that interelement effect can be calculated. In x-ray fluorescence spectroscopy this is performed by taking the absorption of the primary beam and of the secondary fluorescence radiation into account. Figure 6.27 shows a profile of a sample during irradiation. 

Because it is impossible to completely avoid some degree of aflatoxin contamination, a variety of strategies for their detoxification in foodstuffs have been proposed. These strategies have included physical methods of separation, thermal inactivation, irradiation, solvent extraction, adsorption from solution, microbial inactivation, chemical methods of inactivation and fermentation. Two of these strategies are described in more detail below. 

Irradiation of PPD (4 mM) with unsymmetrical olefins (EVE and AN) in deaerated solutions yields site selective and regioselective [2+2] type 1 1 photoadducts (19 and 20) and 1 2 photoadducts (21-26) [47]. The structure of these adducts was determined by various physical methods, including C-NMR spectroscopy, which is vital for the determination of the reaction site. The C-NMR spectra for all of these adducts show two sp hybridized carbon peaks indicating that one of the carbon-carbon triple bonds remains intact. The existence of ethynyl benzene moiety (120-125 ppm) in all the adducts indicates that C3-C4 triple bond is the reactive site. The 1 2 adducts (21-23) rearranged to give ring opened 1,5-diene products (27 and 28) on warming to 101 °C (in methylcyclohexane). 

FIGURE 32-9 Estimated sensitivities of neutron activation methods. Numbers in blue correspond to (S sensitivities in micrograms numbers in black to y sensitivities in micrograms. In each case samples were irradiated for 1 h or less in a thermal neutron flux of 1.8 x n/cm Vs. (From V, P. Guinn and H. R. Lukens Jr., in Trace Analysis Physical Methods, G, H. Morrison, ed., p. 345, New York Wiley, 1965.)... 

Since the absolute intensity of an irradiation source is difficult to determine by physical methods, photochemists prefer the use of a simple photochemical reaction for the measurement of intensity. Any photoreaction for which the mechanism is known to be simple can be used as a chemical actinometer. It requires that the photochemical quantum yield is determined and independent of intensity or other effects. 

Proper definition of quantum yields (cp) requires the cai eful assessment of photons absorbed by the photocatalyst. Methods based on chemical actinometry ai e limited as they provide only the total rate of photons entering the reactor and do not account for various light scattering losses. The use of physical methods involving spec-trophotoradiometers and collimators (Salaices et al., 2001), as described in chapter IV, enables macroscopic energy balances, the proper assessment of irradiation energy absorbed by the photocatalyst and, consequently, an adequate definition of quantum efficiencies. 

Many pretreatment techniques are used in practice (Table 8.2). The normal physical method used to improve the adhesive strength of the coating to the substrate is to slightly roughen the surface by solvent treatment, abrasion, or blasting. Some plastics (e.g., polyolefins) require special pretreatment methods processes that modify the surface molecular layers of the plastic to increase their polarity have proved suitable (e.g., flaming, immersion in an oxidizing acid, immersion in a benzophenone solution with UV irradiation, corona treatment, plasma treatment). 

Alternative physical methods for decontamination including electrostatic precipitation, ultraviolet irradiation, heat, etc., are reviewed below. 

A major handicap of chemical crosslinking agents is the potential toxic effect of residual molecules and/or compounds formed during in-vivo degradation. Therefore, alternative physical methods are pursued, including dry heat, exposure to ultraviolet or y-irradiation [55],... 

---