Carrier techniques

Recent work153 with Zn(CH3)2 and Zn(CD3)2 using the toluene carrier technique (surface effects negligible) confirms the mechanism previously proposed46. Negligible yields of CD4 were observed. At infinite pressure... 

Protactinium (of mass number 231) is found in nature iu all uranium ores, since it is a long-lived member of the uranium series. It occurs in such ores to the extent of about part per million parts of uranium. An efficient method for the separation of protactinium is by a carrier technique using zirconium phosphate which, when precipitated from strongly acid solutions, coprecipitates protactinium nearly quantitatively. Then the protactinium is separated from the carrier by fractional crystallization of zirconium oxychloride. 

Kominar and coworkers115 used the toluene carrier technique for the pyrolysis of bromobenzene. The elimination process was found to be homogeneous and of first order. The Arrhenius expression for equation 26 is log kx (s-1) = (14.6 0.3) - [(317.000 5.4550)/19.157]. The result of this pyrolysis was discussed in terms of the following mechanism (equations 26-31) ... 

Years later, the same authors examined the decomposition of (bromomethyl)penta fluorobenzene, C6F5CH2Br, using the toluene carrier technique at 727-800 °C116. The reaction was shown to be first order and homogeneous. According to the products formed, the following mechanism of equations 32-37 was proposed ... 

This publication stimulated much discussion, particularly relating to the assumptions about the mechanism of decomposition of iodides. Especially contentious was the assumption of no secondary reactions. In the 1950s Szwarc developed the toluene carrier technique to try to ensure the complete... 

There are a few comments to be made in connection with the results obtained by the toluene carrier technique. Szwarc and Taylor observed the formation of... 

Szwarc et alP have studied the pyrolysis of biacetyl by the toluene carrier technique. For the CO formation, they gave the first-order rate coefficient as... 

Toluene carrier technique rates determined by acid titration. 

Kinetic results are given in Table 9. The toluene carrier technique often yields low values of the activation energies and 4-factors. Results for the benzyl esters, however, appear to be reasonably good. Note that the estimated reaction enthalpies compare favorably with the observed activation energies and that -factors are reasonable (AS 5 cal.deg mole ). Since only absolute decomposition rate coefficients were reported for the allyl esters, we have estimated the Arrhenius parameters on the assumption that the -factors were all 10 sec The activation energies so obtained are reasonable, since they compare quite favorably to those estimated by group additivities and the accepted heats of formation of the product radicals (Column 3, Table 9). 

Toluene carrier technique products in toluene were carbon dioxide and 1,2-diphenylethane with smaller amounts of carbon monoxide, hydrogen and methane intramolecular elimination of water was also thought to occur from phenyl acetic acid to give phenyl ketene and water. 

Toluene carrier technique rates were based on the disappearance of the reactant large surface effects were encountered. 

Three carboxylic acid bond fission reactions have been studied in the gas phase those of phenylacetic acid diphenylacetic acid , and peracetic acid . They were all studied by the toluene carrier technique and are therefore subject to the usual errors. In the phenyl and diphenylacetic acid decompositions, viz. 

Many bond fission reactions have been studied using the toluene carrier technique. 

The pyrolyses of benzylamine, iV-methylbenzylamine, and iV-methylaniline have been examined by the toluene carrier technique . They are all homogeneous, first order processes with a small heterogeneous contribution to the overall rate which produces H2 and CH4.. Rate parameters are collected in Table 25. 

The pyrolysis of methyl mercaptan was investigated by the toluene flow carrier technique in the range 732-829 °C . The reaction is first order and leads to the formation of CH4, HjS, Hj and bibenzyl in contrast to the photochemical case, the thermal decomposition is undoubtedly initiated by... 

The gas-phase pyrolysis of dimethyl disulfide in the range 316-373 °C is apparently homogeneous, first order, and characterized by a reproducible induction period . The overall rate coefiicient is fc = 2x 10 exp(—45,000/RT) sec". The main products found were H2S, CH3SH, CS2 and various sulfides which were not characterized. Using the toluene flow carrier technique only traces of dibenzyl were found, and in addition to H2S and CH3SH, CH4, H2, C2H4 and C2H6 were formed. The kinetic data are incomplete, but it is probable that dimethyl disulfide decomposes mainly by a molecular mechanism... 

WeiBhaar, H.-D., Carstensen, C.A., Vogel, P. and Koller, P.U. (1985). Evaluation of a reagent carrier technique for the quantitative determination of hemoglobin. Clin. Chem. 31, 921, Abstr. 97. 

The Pipsyl Method. Using radioactive isotopes Keston, Udenfriend and Cannan (1946, 1949 Keston and Udenfriend, 1949) have developed an accurate micro method, which theoretically could be applied to the estimation of any amino acid or peptide in a mixture. Two different techniques, the carrier technique and the indicator technique, have been worked out. In the former the peptide mixture to be analyzed is treated with p-iodophenylsulfonyl chloride (pipsyl chloride) containing radioactive which reacts quantitatively with the amino groups giving pipsyl... 

The effect of the method of product isolation on product distribution must always be considered. Carrier techniques are frequently used for purposes of collection and identification. It is apparent that when concentrations ranging from 10 to 10 mole fraction are involved, it is not always easy to recover the material in question. This problem has been dealt with in the reviews cited previously. The use of gas-liquid chromatography (GLC) has proved extremely useful in the assay of the products. Radioassay of the gas phase effluent from a GLC column was first described by Evans and Willard (1956). An excellent review of GLC-effluent counting techniques has been given by Cacace (1961). Indeed, commercial instruments in which GLC is combined with effluent radioassay equipment have appeared on the market in the last two years. Most of these use ionization chambers and lack the sensitivity of proportional counters, which can detect activities as low as 0-01 millimicrocuries of activity per emergent peak. 

The enzymes which catalyze the formation of GSH have been found in the livers of pigeons (1, 2) as well as of various mammals (3), and may be obtained in soluble form from acetone-dried tissue preparations. The presence of the GSH synthesizing system in extracts of E. coli has recently been demonstrated by Samuels (4). Synthesis of GSH can be followed either by the conventional glyoxalase assay (5), or, as in our experience, more conveniently by measuring the incorporation of radioactive amino acids into the tripeptide which is isolated by the carrier technique (1, 2). 

Provided that no pre-irradiation chemical manipulation is attempted, the technique is free from blank errors caused by the use of contaminated reagents. Post-irradiation chemical treatment is greatly facilitated by freedom to use carrier techniques, thus eliminating the necessity for rigorous microchemical procedures in the determination of trace constituents. 

Upon incubation of 2-methyl-C -butyrate, about 4% of the radioactivity appeared in the respiratory CO2 and about an equal amount in the acetone bodies. The major portion of the label was contained in propionate. This was isolated by the carrier technique and the identity of the compound demonstrated by conversion to the p-bromophenacyl ester. No labeled propionate is formed from the corresponding 2-methylbuty-rate-3-C ... 

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