Trapping techniques

H. G. Dehmelt (University of Washington, Seattle) and W. Paul (Bonn) development of the ion trap technique. 

Chalfont ei a m were the first to apply the spin trapping technique in the study of radical polymerization. They studied radicals produced during S polymerization initiated by r-butoxy radicals with 108 as the radical trap. Since... 

There are several limitations on the use of the spin trapping technique when quantitative results are required. These are ... 

Major advantages of this method over other trapping techniques are that typical conditions for solution/bulk polymerization can be employed and that a very wide range of initiating systems can be examined. The application of the... 

Figure 15-12 is a schematic illustration of a technique known as acid volatile sulfides/ simultaneously extracted metals analysis (AVS/SEM). Briefly, a strong acid is added to a sediment sample to release the sediment-associated sulfides, acid volatile sulfides, which are analyzed by a cold-acid purge-and-trap technique (e.g., Allen et ai, 1993). The assumption shown in Fig. 15-12 is that the sulfides are present in the sediments in the form of either FeS or MeS (a metal sulfide). In a parallel analysis, metals simultaneously released with the sulfides (the simultaneously extracted metals) are also quantified, for example, by graphite furnace atomic absorption spectrometry. Metals released during the acid attack are considered to be associated with the phases operationally defined as "exchangeable," "carbonate," "Fe and Mn oxides," "FeS," and "MeS."... 

Zhang D-Q, Li C-U, Yang L-L, Sun H-W (1998) Determination of cadmium in vegetables by derivative flame atomic absorption spectrometry with atom trapping technique. J Anal At Spectrom 13 1155-1158. 

Gas phase stripping (purge-and-trap) techniques can iaq>rove the yield of organic volatiles from water or biological fluids by facilitating the transfer of volatiles from the liquid to the gas phase it is also more suitable than dynamic headspace sampling when the sample volume is restricted (320 23,347-351). Tbe technique is used routinely in many laboratorl B for the analysis... 

In general terss, the purge-and-trap technique is the nethod of choice Cor detemining organic volatiles in water because of its ease of operation. If greater sensitivity is required, the closed loop stripping apparatus should be used. 

Grab samples are usually returned to the laboratory for preconcentration, when required, and analysis [380-384]. Cold trapping techniques are used to Isolate and concentrate the analytes from air prior to separation. Since air contains relatively large volumes of water and carbon - di Bde compared to... 

Bourn (107) as 10.8 kcal mole-1 (AH4 temperature range 156—246 K solution of cyclohexane in carbon disulfide). By applying an interesting trapping technique Anet and coworkers (110) have recently measured a value of 5.3 kcal mole-1 for the barrier of the reverse twist/chair process (AH4 temperature range 72.5—74.0 K solid state). Our calculated (for the gas phase) activation enthalpies AH4 for the former process are at 73,... 

The instruments include an ionization chamber, the charcoal-trap technique, a flow-type ionization chamber (pulse-counting technique), a two-filter method, an electrostatic collection method and a passive integrating radon monitor. All instruments except for the passive radon monitor have been calibrated independently. Measurements were performed... 

On the other hand, microsomes may also directly oxidize or reduce various substrates. As already mentioned, microsomal oxidation of carbon tetrachloride results in the formation of trichloromethyl free radical and the initiation of lipid peroxidation. The effect of carbon tetrachloride on microsomes has been widely studied in connection with its cytotoxic activity in humans and animals. It has been shown that CCI4 is reduced by cytochrome P-450. For example, by the use of spin-trapping technique, Albani et al. [38] demonstrated the formation of the CCI3 radical in rat liver microsomal fractions and in vivo in rats. McCay et al. [39] found that carbon tetrachloride metabolism to CC13 by rat liver accompanied by the formation of lipid dienyl and lipid peroxydienyl radicals. The incubation of carbon tetrachloride with liver cells resulted in the formation of the C02 free radical (identified as the PBN-CO2 radical spin adduct) in addition to trichoromethyl radical [40]. It was found that glutathione rather than dioxygen is needed for the formation of this additional free radical. The formation of trichloromethyl radical caused the inactivation of hepatic microsomal calcium pump [41]. 

We have confirmed the dissociation manner of these compounds by means of the spin-trapping technique [167]. The radicals produced from 7 and 2-phenylethyl N,N-diethyldithiocarbamate (41) were trapped with 2,4,6-tri-ferf-butylnitrosobenzene (BNB) as a spin-trapping agent (Eq.44) [168] ... 

The dissociation of model compounds for co-chain ends of polymers obtained using iniferters with the DC group was examined by the spin-trapping technique, similar to the disso dation of 7 and 8 previously mentioned [174,175]. From the results of the trapping experiments, it was concluded that 46,47, and 48 as model compounds for poly(MA), poly(MMA), and poly(VAc), respectively, dissociated at the appropriate position to produce a reactive carbon-centered radical and a stable DC radical. In fact, these compounds were found to induce the living radical polymerization of St when they were used as photoiniferters. 

Special spin-trapping techniques are also available for the detection of short-lived radicals in both homogeneous and heterogeneous systems. For instance, a-phenyl A-ferf-butyl nitrone (PBN), ferf-nitrosobutanc (f-NB), -(4-pyridyl A-oxidc) A-ferf-butyl nitrone (4-POBN), or 5,5-dimethyl-l-pyrroline A-oxidc (DMPO) can be made to react with catalytic intermediates to form stable paramagnetic adducts detectable by ESR [135], Radicals evolving into the gas phase can also be trapped directly by condensation or by using matrix isolation techniques [139],... 

Askari et al. [15] have compared purge and trap, methanol immersion and hot solvent extraction methods for the determination of volatile organic compound in aged soil. These workers found that hot solvent extraction is much more effective than the US Environmental Protection Agency approved purge and trap technique [7, 8]. 

Britigan, B. E., Cohen, M. S., Rosen, G. M. (1987). Detection of the production of oxygen-centered free radicals by human neutrophils using spin trapping techniques A critical perspective. J. Leuk. Biol. 41, 349-62. 

Despite these interesting diversions, the vast majority of reports of investigations or applications of the spin-trapping technique depend on the use of C-nitroso-compounds or of nitrones the remainder of this review will be concerned exclusively with these two classes of scavenger. 

Spin-adduct spectra often reveal splittings to substituent atoms other than hydrogen. Indeed, since the spin-trapping technique provides a convenient route to many nitroxides containing structural features likely to be of spectroscopic interest, it has frequently been used to this end. Chlorine and bromine splittings, as well as those from fluorine, have been encountered and many nitroxide spectra have been reported in which there is splitting from a second nitrogen, from phosphorus, or even from a metal atom. 

A final note of caution regarding rate comparisons by the spin-trapping technique might be that, despite the apparent simplicity of the procedure outlined here, great care has to be taken with sample preparation in order to achieve the expected reproducibility of ca. 5-10%. Nevertheless, an early prediction that spin trapping would have little quantitative value has proved to be without foundation. 

Burlaka et al. (2004) used pristine C60 at 10 pM with visible light from a mercury lamp to produce some phototoxicity in Ehrlich carcinoma cells or rat thymocytes and used EPR spin-trapping techniques to demonstrate the formation of ROS. 

Second, no work has yet been done on the application of the transpiration method to the preparation of samples for chemical analysis. In this area the same strictures on odour sampling apply, even where sub-ambient-temperature trapping techniques are used. Especially where cryogenic trapping is proposed, preparation of the odour sample in the laboratory is a considerable advantage. 

First attempts have now been made using a trapping technique to trace the formation of the more advanced intermediates of lignification. 

A number of reports on the thermal decomposition of peroxides have been published. The thermal decompositions of f-butyl peroxyacetate and f-butyl peroxypivalate, of HCOH and a kinetic study of the acid-induced decomposition of di-f-butyl peroxide in n-heptane at high temperatures and pressures have been reported. Thermolysis of substituted f-butyl (2-phenylprop-2-yl) peroxides gave acetophenone as the major product, formed via fragmentation of intermediate alkoxy radicals RCH2C(Ph)(Me)0. A study of the thermolysis mechanism of di-f-butyl and di-f-amyl peroxide by ESR and spin-trapping techniques has been reported. The di-f-amyloxy radical has been trapped for the first time. jS-Scission reaction is much faster in di-f-amyloxyl radicals than in r-butoxyl radicals. The radicals derived from di-f-butyl peroxide are more reactive towards hydrogen abstraction from toluene than those derived from di-f-amyl peroxide. 

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