Determination Of Ultralow Concentrations Research Articles

Particle mass transport in impact electrochemistry

Impact electrochemistry is a set of methods in which individual micro- or nanoscale particles are detected and analyzed at a miniaturized electrode. Quantitative interpretation of the results, in particular the determination of ultralow concentrations, relies heavily on modeling the mass transport of the particles being analyzed. This is particularly subtle since, due to favorable scaling with increasing particle size, migration and convection play a disproportionate role in the transport of such particles compared to that of small molecules. Here we summarize the main governing principles in electrochemically-driven particle transport. We particularly emphasize the difference between particle electrophoresis and small-ion migration, which has led to inaccuracies in the recent literature.

New indicator reaction for the determination of ultralow concentrations of copper by the kinetic method

The optimum conditions of the oxidation of diphenylamine-4-sulfonate by peroxomonosulfate were studied, and a method for the catalytic determination of copper in aqueous solutions was developed on the basis of this reaction. The method is simple in implementation, highly sensitive (cl = 0.02 μg/L), and sufficiently selective in the direct determination of copper in different samples.

Atomic Absorption Determination of the Dissolved and Suspended Forms of Elements in Natural Water with Dynamic Sorption Preconcentration in Atomizers

* Institute of Fundamental Problems of Biology, Russian Academy of Sciences, Pushchino, Moscow oblast, Russia ** Department of Chemistry, Moscow State University, Vorob’evy gory, Moscow, 119899 Russia In natural water (river, sea, atmospheric, etc.) elements occur in dissolved and suspended forms. The data on the concentrations and ratio of these forms are important for geochemical and environmental studies. For the determination of ultralow concentrations of Ag, Bi, Cd, Pb, and Tl in dissolved (El diss ) and suspended (El susp ) forms and the total concentration (El diss + El susp ), we proposed a sorption–atomic-absorption method with the dynamic preconcentration of metals on the DETATA sorbent directly in a crucible electrothermal atomizer. A filtrate, unfiltered water sample, or solution obtained after the decomposition of a suspension (< 5– 50 mL) was pumped through a crucible microcolumn with holes of small diameter in the bottom and a graphite filter. The crucible microcolumn is a part (evaporation zone) of a two/three-chamber graphite electrothermal crucible–cell/crucible–cylinder–cell atomizer. The design of the atomizers provided independent programmed heating of the evaporation zone and the atomization zone for optimizing the processes and decreasing nonselective interferences and matrix effects. The cycle of the determination of elements in a solid matrix (concentrate, concentrate + suspension) commonly included drying, pyrolysis, and atomization ( 1800– 2600°e ) with the evaporation of elements to the isothermally heated zone. For the efficient suppression of interferences, we used the principles of element vapor filtration through graphite filters (between the evaporation and atomization zones) and fractional evaporation with the subsequent independent atomic-absorption analysis of the condensate.

Flow-injection chemiluminescence determination of ultra low concentrations of nitrite in water

A new flow chemiluminescence method for the determination of ultra low concentrations of nitrite in water is presented. Nitrite reacts with H2O2 in acid medium to form peroxynitrous acid that is subsequently detected as peroxynitrite by the chemiluminescence reaction with alkaline solution of luminol. The detection limit of nitrite is 1 × 10−9 mol 1−1 (for 50 μl samples) and the calibration graph is linear up to 1 × 10−5 M NO−2 The relative standard deviations for 1 × 10−6 M and 3 × 10−8 M NO-2 are 1.8% and 5.4%, respectively. The interferences of cations are eliminated by passing the sample through a cation-exchange column. Common anions do not interfere. Analysis time is 3 minutes. The results are in good agreement with a standard spectrophotometric method.

Radiochemical neutron activation determination of phosphorus in high pure germanium

A radiochemical procedure for determination of ultra low concentrations of phosphorus in germanium has been developed. The method involves application of multicells autoclaves for matrix distillation and extraction chromatography with dioctyltin diacetate for final phosphorus purification. The detection limit is 40 ppt for a 1-g sample.