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PubMed2000

Rapid 90Sr/90Y determination in water samples using a sequential injection method

We have developed a semiautomatic procedure based on a sequential injection method for 90Sr/90Y determination that allows their radiochemical separation in about 30 min. The method has been tested using 90Sr/90Y solutions with activities lower than 12 Bq. The source is eluted in a pH = 6.5 medium through a MnO2-impregnated cotton filter, where 9OY is preconcentrated in preference by adsorption. 90Y is extracted from the column with hydroxylamine, some 90Sr in the leached solution has also been found. After the radiochemical separation, the total beta-activity of the leached solution has been determined using a low background alpha-beta proportional counter and, assuming the presence of 90Sr and 90Y at t = 0, the solution of the Bateman equations allows the initial concentration of both isotopes to be obtained. We have verified that the addition of some ions usually found in water samples (Cl-, HCO3-, NO3-, SO4(2-), Ca2+, Mg2+) does not interfere with the yield of the radiochemical process, (90 +/- 10)%. The method has been applied to 90Sr/90Y determination in mineral waters, and even in thermal waters, where the salt concentration can be about 3500 mg/l, the radiochemical yield remains greater than 80%.

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PubMed2000

A robust multisyringe system for process flow analysis. Part II. A multi-commuted injection system applied to the photometric determination of free acidity and iron(III) in metallurgical solutions.

A new software-controlled volume-based system for sample introduction in process flow injection analysis was developed. By using a multi-syringe burette coupled with one or two additional commutation valves, the multi-commuted injection of precise sample volumes was accomplished. Characteristics and performance of the injection system were studied by injecting an indicator in a buffered carrier. Three configurations were implemented in order to achieve two different tasks: the single injection of a sample in a two- or three-channels manifold, and the dual injection into different streams. The two channel flow system using the single injection was applied to the determination of free acidity in diluted samples containing high levels of iron(III), by employing the single point titration methodology. The precipitation of ferric hydroxide was prevented using the ammonium and sodium salts of oxalate and acetate as buffer titrant. Methyl Red was employed as indicator. The procedure allows determination of acid concentration in solutions with a Fe(III)/H+ molar ratio up to 0.2. Samples with higher Fe(III)/H+ molar ratios were spiked with a known strong acid at dilution. The three-channel configuration was applied to the determination of ferric ions, using, as reagent, a merging mixture of sulfuric acid and potassium thiocyanate. The double injection system was implemented in series in a single (three-channel) manifold in such a way that a different injection volume and a changed reagent were used for each analyte. It was applied to the separated or sequential determination of free acidity and ferric ions. In this configuration, iron(III) was determined using 0.5-0.7% (w/v) sodium salicylate solution as reagent. The systems can operate at up to 100, 84 and 78 injections per hour, respectively. Determinations on synthetic and process samples compared well with the reference values and procedures. Recoveries of 95-102% with a maximum RSD value of 5.4% were found for acidity. The respective values obtained for iron determinations were 96-105% and 4.3%.

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