V. V. Chernysh

Investigation of the reaction of copper(I) with 2,9-dimethyl-1,10-phenanthroline at trace level by thermal lensing

The stability constants for copper(I) chelate with 2,9-dimethyl-1,10-phenanthroline are determined by thermal lensing, and the advantages over spectrophotometric determination of stability constants are shown. Changes in the photometric reaction when moving from the microgram to the nanogram level of reactants are discussed. The conditions for the thermal-lens determination of copper are optimized. The limit of detection of copper is 3x10(-8) mol dm(-3), and the linear calibration range 1x10(-7)-1x10(-5) mol dm(-3).

Determination of Stability Constants of Copper(I) Chelates with 1,10-Phenanthroline by Thermal Lensing

Using investigations of the copper(I)–1,10-phenanthroline system as an example, it is shown that thermal lensing can be used for determining stability constants at a level of concentrations one–two orders of magnitude lower compared to conventional spectrophotometry, with better precision of measurements. The values of stability constants are logβ2= 11.7 ± 0.7 without regard for stepwise chelation, and logK1= 5.9 ± 0.3, logK2= 5.4 ± 0.3, and logβ2= 11.3 ± 0.6 taking into account stepwise chelation. It is shown that, when shifting from microgram to nanogram amounts of reactants in the determination of stability constants by thermal lensing, changes in the kinetic parameters of the reaction studied should be taken into account. The thermal-lens limit of detection of copper(I) is 2 × 10–8M; the linear calibration range is 4 × 10–8–2 × 10–5M (488.0 nm, pump power 120 mW). The data obtained were used for determining copper(I) in the hydrogen sulfide layer of the Baltic Sea.

Investigation of adsorption of nanogram quantities of iron(II) tris-(1,10-phenanthrolinate) on glasses and silica by thermal lens spectrometry

Thermal lens spectrometry is used for studying adsorption equilibria in aqueous solutions at the level of nanogram quantities of iron(II) tris-(1,10-phenanthrolinate) as a model system. The kinetics of the sorption of the chelate on silica is studied and adsorption isotherms are built. Thermal lensing is used as a method for direct determination of the chelate concentration adsorbed on a quartz surface. The detected amount is 4.1x10(-15) mol at the area irradiated by the excitation beam. The adsorption of iron(II) tris-(1,10-phenanthrolinate) on laboratory glassware at the nanogram level is characterised by measuring the residual concentration of the sorbate in solution. A procedure for handling and cleaning the laboratory glassware for determining nanogram amounts of iron in aqueous solutions is proposed. The sensitivity of thermal lensing both in measuring adsorption on silica and glass and quartz surfaces is 100-fold higher than diffuse-reflectance measurements under the same conditions.

Potentialities of thermal lens spectrometry in studying peculiarities of reactions at the trace level

It was shown that thermal lensing can be used for studying peculiarities of the reactions at the nanogram reactant concentrations. Examples of determining molar absorptivities, dissociation constants of acids, cumulative and stepwise stability constants of complexes, characteristic rate constants, solubility constants, and other parameters using the data of thermal-lens experiments are presented. In a number of cases, taking into account reaction conditions at the nanogram level improves the performance characteristics of the determination.

Determination of Microamounts of Phenols by Thermal Lens Spectrometry

The conditions for unified spectrophotometric determination of phenols (using phenol, resorcinol, and pyrogallol as model substances) in batch mode by their azo coupling with p-nitrophenyldiazonium were optimised. The detection limits are 50–120 ng ml–1. The data were used in the search for the optimum conditions for thermal lens determination of the test phenols. The main disadvantage of thermal lens determination of phenols by this procedure is a high blank signal. To decrease the blank signals, the concentration of the reagent was decreased by a factor of 40. The detection limits of the test phenols are 2–9 ng ml–1, the linear calibration range is two orders of magnitude. The relative standard deviation (3–8%) is similar to that of spectrophotometric determination.

Investigations of Cobalt, Nickel, and Copper Diethyldithiocarbamates Using Thermal Lens Spectrometry

Thermal lens spectrometry was used to study the dissociation kinetics of diethyldithiocarbamate complexes of copper(II), cobalt(III), and nickel(II) as a function of pH in the presence of chloride and sulfate ions. It is shown that, as distinct from conventional spectrophotometric and potentiometric measurements, the reversible dissociation of the test complexes and the irreversible oxidation of the ligand can be studied separately (at a level of n × 10–8–n × 10–6 M) using thermal lens spectrometry. Because of work in more dilute solutions and due account of the kinetic features of the systems in question, thermal lens spectrometry provides a higher accuracy of the determination of stability constants for diethyldithiocarbamate complexes of copper(II), cobalt(III), and nickel(II). The adsorption of the diethyldithiocarbamate complexes in question from water–ethanol solutions (1 : 3) on Silasorb C18 silica is studied, and the adsorption constants are determined. The limits of detection of copper(II), cobalt(III), and nickel(II) diethyldithiocarbamates obtained in extraction–thermal-lens determination are n × 10–8 M.

Application of Thermal-Lens Spectrometry to a Study of the Interaction of Trace Nickel(II) with Dimethylglyoxime

Thermal-lens spectrometry was applied to a study of the properties of a nickel(II) complex with dimethylglyoxime at a concentration level of n × 10–8–n × 10–6 mol/L. The possibility of determining the solubility of the complex and the characteristics of its adsorption on the glass surface of laboratory ware was demonstrated. The stability constants of the complex in water–ethanol mixtures (9 : 1) were determined. The found data made it possible to optimize the conditions for the photometric determination of nanomolar concentrations of nickel. The optimized procedure was used for a thermal-lens determination of nickel(II) traces in heteropoly compounds and high-purity water.

The studies of the reaction of bismuth(III) with iodide at nanogram level by thermal lensing.

By the example of the analytical system based on the reaction of bismuth with iodide, it is shown that thermal lens spectrometry can be used for studying changes in analytical reactions at the nanogram level of reactants. The stability constants of bismuth(III) iodides at the concentration level are found. The solubility constants of iodides of metals interfering with bismuth determination are estimated. It is shown that the due regard to the new conditions could enhance the sensitivity and selectivity of determination.

Flow Analysis of Transition Metals by Thermal Lensing

The conditions for the flow determination of Al(III), Bi(III), Cd(II), Co(II), Cr(III), Cu(II), Fe(III), Mn(II), Nd(III), Ni(II), Pb(II), Pr(III), and Zn(II) by reaction with Xylenol Orange in aqueous solutions at pH 4.5 and the determination of Cd(II), Co(II), Cu(II), Fe(II), Ni(II), Pb(II), and Zn(II) by reaction with 4-(2-thiazolylazo)resorcinol in water–ethanol mixtures (5 : 1) at pH 5.0 using an injected sample volume of 80 μL were proposed. The limits of detection were n × 10–8–n × 10–7 mol/L; the linearity ranges in the calibration graphs were of about three orders of magnitude; the relative standard deviation was of 3–7%.

Determination of copper with neocuproine by thermal-lens spectrometry

Conditions for the spectrophotometric determination of copper with 2,9-dimethyl-l,10-phenan-throline (neocuproine) in the presence of ascorbic acid in a water-ethanol solution (9 : 1) at pH 4.5–5.0 have been found. The detection limit is 3 x 10-6 M. The concentration range is from 4.4 x 10-6 to 3 x 10-4 M. Conditions for the determination of copper(I) with neocuproine by thermal lens spectrometry have been proposed. The detection limit is 4 x 10-7 M. The concentration range is from 7 x 10-7 to 6 x 10-5 M. Iron(II) at concentrations as high asn x 10-4 M does not interfere with the determination of copper. Changes in the conditions for the photometric reaction associated with passing from spectrophotometric measurements to thermal lensing are discussed.