Isotopic method

Hastorf, C.A. and DeNiro, MJ. 1985 Reconstruction of prehistoric plant production and cooking practices by a new isotopic method. Nature 315 489-491. 

Under conditions where the dismutation reaction is slow the exchange between Au(III) and Au(I) has been shown to proceed at a measurable rate at 0 °C in 0.09 M HCl, an exchange half-time of about 2 min was observed. The isotopic method ( Au) and a separation method based on the precipitation of dipyridine -chloroaurate(III) was used to obtain data. An acceleration in the exchange rate was observed as the HCl concentration was increased. ... 

The earliest reported studies on the exchange, by King, and Haissinsky and Cottin, utilised the isotopic method and showed the rapid nature... 

Peschanski, using the isotopic method ( ° Hg), has found complete exchange (0 °C) in methanol and various other non-aqueous media. The separation methods used were, (a) paper and column chromatography, (b) paper electrophoresis, and (c) precipitation of Hg(I) with chloride. In the presence of cyanide ions, however, less than complete exchange could be observed. Zero-time exchange was again found to vary in the same manner as for aqueous media. Similar effects were observed in the presence of chloride ions. 

Wilson and Dickenson observed no exchange, over a period of three hours at 100 °C, between arsenate and arsenite ions in media ranging from aqueous acid to aqueous alkali. Martin et al have found similar results for the exchange between arsenate and thioarsenite ions in aqueous media. However, in liquid ammonia exchange occurred between ammonium arsenate and arsenic trisulphide. The isotopic method was used -... 

Bonner, using the isotopic method ( Sb) and either precipitation of the oxinate of Sb(III) or an isopropyl ether extraction of Sb(V), obtained the first results on this exchange reaction. In media 6 M HCl a complex rate law, viz. 

King and Garner, using the isotopic method made an attempt to study... 

Anderson and Bonner made the first detailed kinetic study on the exchange using the isotopic method ( Cr) and a separation method based on the conversion of Cr(II) into Cr(IIl) oxalate and an ion-exchange treatment. To prevent oxidation of Cr(II) during exchange a hydrogen atmosphere was maintained over the reaction mixture. The rate law found to be obeyed for the concentration ratio range Cr(III)/Cr(II) of between 3.3 x 10 and 2.0 in perchlorate media was... 

The effect of chloride ion on the exchange was found by these workers to be very small, whereas Plane and Taube had estimated a rate coefficient about five times larger in the presence of 10 M chloride ion than in perchlorate solution. Van der Straaten and Aten have studied the exchange in media 1 M with respect to HCl and have estimated a rate coefficient 3.0 x 10 l.mole". sec . The isotopic method ( Cr) and a separation procedure based on the precipitation of Cr(II) as the acetate complex was used. 

The early studies on the exchange system, carried out by Muxart et al., Menker and Garner, and Burgus and Kennedy, showed the exchange to be slow in sulphate , perchlorate, nitrate, and hydroxide media -. The isotopic method ( Cr) was used with separation of the Cr(III) and Cr(VI) being achieved by the precipitation of chromic oxide and lead chromate. Some evidence was obtained for the retardation of the exchange by hydrogen ions. 

Altman and King made the first detailed study of this system, using Cr(ril) solutions containing only the monomeric species and Cr(VI) solutions which had been allowed to age. The isotopic method and lead chromate precipitation separation were used to obtain kinetic data at a temperature of 94.8 °C. Over the range of concentrations, Cr(VI) 2.3x10 to 8.4x10 A/, Cr(III) 1.8x10 to... 

The exchange of Mo between the anions Mo(CN)g and Mo(CN)g has been investigated by the isotopic method ( Mo) and the separation methods (a) precipitation of Mo(CN)g with either ethanol or cadmium ions, and (b) precipitation of Mo(CN) with tetraphenylarsonium chloride. Complete exchange was observed by Wolfgang even with reactant concentrations 5x10 M. An estimate of the rate coefficient at 2 °C of >10 l.mole . sec has been sug-geMd. 

Britt and Yen , using the pulsed nuclear resonance technique, have obtained exchange data comparable to those obtained by the isotopic method. An observed... 

Horne has studied the kinetics of exchange in aqueous perchlorate media at temperatures down to —78 °C by the isotopic method ( Fe) and dipyridyl separation. The same rate law in these ice media as in aqueous solution was observed, although the acid dependence was small. Horne concluded that the same exchange mechanism occurs in solid and liquid solvent. Evidence for a Grotthus-type mechanism has been summarised. ... 

The effect of the addition of inorganic ions has been investigated using the isotopic method ( Fe or Fe) and the 2,2 -dipyridyl separation. The rate law in the presence of inorganic anions is given by... 

The isotopic method has been used in conjunction with a flow apparatus by Stranks, to measure the exchange between the cyclopentadienyl complexes of iron (III) and iron (II) in methanol. Separation was based on the insolubility of Fe(C5H5) in petroleum ether at —80 °C. Using Fe(II) and Fe(III) 10 M and short reaction times ( msec), a rate coefficient 8.7 x 10 l.mole .sec at — 75 °C was obtained. The rate of exchange in the presence of chloride ions and inert electrolytes was found to be more rapid. Calculations using Marcus Theory showed reasonable agreement with the experimental observations. In deuterated acetone, line broadening measurements have led to an estimate of this rate coefficient of > 10 l.mole . sec at 26 °C. 

The exchange between the ruthenium anions RuO and RuO " in aqueous hydroxide media has been found rapid. A limit for the rate coefficient at 0 °C of > 1.7x10 l.mole . sec has been proposed by Luoma and Brubaker. The isotopic method ( ° Ru), and separation procedures based on the precipitation of the Ru04 or RuOJ species with barium or tetraphenylarsonium ions, respectively, were used. Attempts to use an esr technique failed. 

The earliest investigation of the exchange reaction between the aquated ions of Co(III) and Co(II) was carried out by Hoshowsky et al., using the isotopic method ( Co). When sulphate salts ( 10 M) were employed, complete exchange was observed between the two oxidation states of cobalt, in a time of less than two min. Two separation methods were employed (a) adsorption on an alumina column, and (b) precipitation of the Co(III) as the cobaltinitrite. 

Stranks has also studied the exchange between tris- and bis-ethylenediamine complexes of Co(III) and Co(II). The isotopic method was used. At low ionic strengths (CIO4 ) a rate law... 

Baker et al, have obtained some kinetic data on the exchange reactions between the 1,10-phenanthroline, 2,2 -dipyridine and 2,2, 2"-tripyridine complexes of Co(III) and Co(ll) in both H2O and D2O solution. The isotopic method ( Co) and separations involving either extraction of Co(II) with organic solvents (n-hexanol-ether or saturated sodium acetate in n-hexanol) or precipitation of Co(III) as Co(phen)3(l3)3 were used. For the 1,10-phenanthroline system, a rate law... 

The isotopic method has been used to investigate the exchanges between... 

In dimethylformamide solution, platinum exchange between Pt(en)Br2 and Pt(en)Br4 has been found to be light-sensitive and catalysed by bromide ions. In the absence of light, a value < 1.33 x 10" l.mole . sec was obtained for the observed rate coefficient (25 °C) from data obtained by the isotopic method (i95pt) separation using an ether precipitation of Pt(en)Br2. The bridge mechanism was thought to occur... 

Ion migration and diffusion separation techniques, in conjunction with the isotopic method ( Ce and have led to complete exchange being observed... 

The exchange reaction between Np(VI) and Np(V) has been investigated using the isotopic method ( Np) and an extraction separation (Np(VI) with tri-butylphosphate or thenoyltrifluoroacetone in toluene) Cohen et al. have found, for the exchange in perchlorate media, a rate law... 

Keenan has made an investigation of the exchange reaction between Pu(IV) and Pu(in) in perchlorate media. The isotopic method was used with an a energy analyser to separate the tracer activity ( Pu) from that normally present from the major constituent ( Pu). Tributylphosphate extraction of the Pu(IV) formed the basis of the separation method. It was shown that the rate law has the approximate form... 

In perchlorate media the latter reaction was found to be rapid (100 % exchange in < 60 sec) and the former reaction slow (half times of > 200 hours at 100 °C). The isotopic method was used ( Am). 

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