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The activation parameters of the V(II)--Fe(III) and U(III)--Fe(III) reactions were determined as a function of ionic strength in perchlorate media. Contrary to expectations, the values of ..delta..S/sup + +/ for these reactions were found to be independent of ionic strength, the changes in rate constant being reflected exclusively in the values of ..delta..H/sup + +/. Plausible explanations for these observations are discussed.

The kinetics and mechanisms of the reaction of U(III) with Tl(III) and Cr(III) have been examined in perchlorate media. The Tl(III) reaction was found to obey the rate law -d(U(III))/ dt = (U/sup 3 +/)(Tl/sup 3 +/) (k/sub -1/K/(H + K)) in which k/sub -1/ has a value of (3.6 +- 0.2) x 10/sup 5/ M/sup -1/ s/sup -1/ at 20/sup 0/C and an ionic strength of 2.0 M, whereas the Cr(III) reaction was found to exhibit a mechanism dominated by a reaction path having an inverse second-order concentration dependence. The rate constants are compared with those obtained for other similar systems; it is suggested, that the acid concentration independent and the inverse acid concentration dependent reaction paths of many electron-transfer reactions involving metal ions exhibit a limiting rate of 10/sup 6/ to 10/sup 7/ M/sup -1/ s/sup -1/. Plausible reasons for this limiting value are discussed.

The kinetics of the oxidation of U(III) by Co(III) was studied in perchlorate media. The rate law of the reaction was found to be given by the expression -d[Co(III)]/dt = k1 [Co(III)][U(III)]. The value of k1 was determined as (1.12 ± 0.1) x 106 M-1 sec-1 at 20°C and ionic strength of 2.00 and was found to be independent of acid concentration at constant ionic strength. The temperature dependence of the reaction was studied in the range 11 to 31°C, and the values of ΔH2+ and ΔS2+ were determined as 2.00 ± 0.25 kcal mole-1 and -25.6 ± 0.8 cal deg-1 mole-1, respectively. In common with many other reactions of Co(III), the rate constant of this reaction is much lower than expected from the very high ΔG0 value and plausible reasons for this observation are discussed.

Atomic emission of lithium in a small graphite furnace (CRA 63) was observed using a standard atomic absorption spectrometer with simple optical modifications. Improved diagnostic techniques facilitated a study of lithium atomic emission and atomic absorption signal profiles as a function of temperature. Low levels of lithium were measured relatively free from background emission with considerably improved signal-to-noise characteristics. Analytical growth curves plotted in logarithmic coordinates showed only a slight deviation from linearity over a concentration range of three orders.

The kinetics of the oxidation of U(III) by Co(III) was studied in perchlorate media. The rate law of the reaction was found to be given by the expression -d[Co(III)]/dt = k1 [Co(III)][U(III)]. The value of k1 was determined as (1.12 ± 0.1) x 106 M-1 sec-1 at 20°C and ionic strength of 2.00 and was found to be independent of acid concentration at constant ionic strength. The temperature dependence of the reaction was studied in the range 11 to 31°C, and the values of ΔH2+ and ΔS2+ were determined as 2.00 ± 0.25 kcal mole-1 and -25.6 ± 0.8 cal deg-1 mole-1, respectively. In common with many other reactions of Co(III), the rate constant of this reaction is much lower than expected from the very high ΔG0 value and plausible reasons for this observation are discussed.

Die Aktivierungsparameter der Reaktionen zwischen V(II) und Fe(III) sowie zwischen U(III) und Fe(III) werden als Funktionen der Ionenstarke (I) in C10; -haltigen Medien untersucht.

Molybdenum is extracted as the thiocyanate complex with the quaternary long-chain aliphatic amine Aliquat 336 in chloroform, followed by evaporation of the solvent, dissolution in MIBK, and atomic-absorption spectroscopy. The method is simple, rapid and sensitive, with few interference problems for the determination of the Mo content of soils and sediments in the range 0.1-1.0 ppm with a relative standard deviation better than 5% when 1-g samples are used. Quantitative extraction from large volumes of aqueous solution has also been confirmed, allowing the determination of Mo in natural waters in the ppM range.

In chemical analysis the most careful and skilled laboratory work, often using expensive physicochemical instrumentation, results in virtually worthless data unless the sample taken is representative of the material whose composition is to be determined. In a typical situation, for example, in water quality monitoring, the main steps and considerations can all influence the overall error. These are outlined in Table 1.

THE polarographic behaviour of some 2,2′-di-hydroxy azo dyes in the presence of the lanthanides has recently been a subject of study in this laboratory. The lanthanides were found to form coloured chelates in alkaline solution with erichrome violet B (5-sulpho-2-hydroxy benzene-azo-2-naphthol, C.I. No. 169), eriochrome black PV (5-sulpho-2-hydroxy benzene-azo-l,5-dihydroxy naphthalene, C.I. No. 170) and mordant blue 31 (5-sulpho-2-hydroxy benzene-azo-1,8-dihydroxy naphthalene 3,6-disulphonic acid, C.I. No. 16675). These dyes all exhibit well-defined single polarographic reduction waves. In ammonia, diethanolamine and piperidine buffers, the lanthanides cause a decrease in height of the dye step, and a second wave appears at a more negative potential. The height of the second wave is proportional to the concentration of lanthanide.

An introduction system for liquid micro-samples in inductively coupled plasma atomic-emission spectroscopy is described that allows the injection of 5–500-µl volumes into a rapidly flowing carrier reagent stream leading to the nebuliser. The effect on analyte signal was studied as a function of flow-rate, injection volume and sample concentration. It is shown that the carrier flow-rate determines the response time, sensitivity, precision and sample carry-over in the nebuliser. By the use of relatively rapid flow-rates of up to 7.5 ml min–1, fast injection of 10-µl samples is achieved at an injection rate of 240 h–1 with a relative standard deviation of 1.5% for a single-element analogue readout. Digital readout is used for multi-element determinations with similar or better precision. Detection limits of the order of 0.1 mg l–1 are obtained for 10-µl injections, limited by the volume injected, with a proportionate decrease in detection limit for increasing volumes.

A review is presented on current methods for beryllium determination. The methods range from gravimetric to radiochemical and spectrometric. Analysis of beryllium for impurities is treated. A bibliography of 159 references is included. (D.L.C.)

An improvement of the method previously presented for determination of oxygen in beryllium by the micro vacuum fusion method (Analyst 82, 57(1957)) is discussed. In this method a quantity of tin is added to the reaction to suppress beryllium evaporation. (J.R.D.)