Determination of copper by its catalytic effect on the oxidation of hydroquinone by hydrogen peroxide on supports

The reaction of oxidation of hydroquinone by hydrogen peroxide catalyzed by copper(II) in the presence of 2,2’-dipyridyl is activated by hexamethylenediamino groups that are bonded to the surface of filter paper; additional activating effect is produced by 2,2′-dipyridyl. The introduction of malonic acid dinitrile into the indicator reaction improves the sensitivity of the determination of copper and the contrast of the reaction in solution because of the formation of a blue product. Differently colored compounds are formed on a paper support at different concentrations of copper, which makes it possible to visually distinguish the quantities of copper that differ by an order of magnitude in the range 1 × 10^-5-0.5 μg. Quantitative detection is possible in the range 5 × 10^-6-0.1 μg (c_min = 3 × 10^-6 μg). The concentration of copper (0.2-1.5 μg/mL) is determined in blood serum; the consumption of the sample per one determination is 3 μL     

Sorption-Catalytic Determination of Imazapyr on a Copper-Containing Sorbent

 Sorption of copper on filter-paper with chemically attached hexamethylenediamino-groups (HMDA-filter) allows to obtain the sorbent (Cu/HMDA-filter) stable in respect to desorption of copper. A nitrogen-containing herbicide imazapyr (imaz) is retained on Cu/HMDA-filters at pH 5.5–7.0 forming a relatively stable complex. Imazapyr is determined directly on the sorbent by its activating effect in the oxidation of hydroquinone with H₂O₂ catalyzed by Cu(II) with the formation of a product absorbing at 490 nm. The copper ions serve both to preconcentrate imazapyr and to catalyze the indicator reaction. The use of 1-μL sample aliquots pipetted onto the Cu/HMDA-filters allows to determine 1 × 10⁻³–0.03 μmol of imazapyr, whereas preconcentration of the analyte by pumping of its solution through the same sorbent expands the linear range to 1 × 10⁻⁴–1 × 10⁻¹ μmol of imazapyr. When the indicator reaction is carried out in solution, the range of activating action of imazapyr is narrower (0.06–0.1 μmol a for a solution volume of 10 mL). The determination is selective: 5–100-fold amounts of amines, aminoacids, carboxylic acid derivatives and other model compounds do not interfere. Soil extracts and carrot juice samples spiked with imazapyr have been analyzed. Received January 10, 2000. Revision July 28, 2000.     

Accelerating effect of silica on the indicator reaction o-dianisidine-H(2)O(2)

Reaction of oxidation of o-dianisidine (o-D) with H(2)O(2) which is widely used in catalytic methods of analysis in solution has been conducted on silica plates for thin-layer chromatography. The rate of the reaction catalyzed by model compounds (p-toluenesulphonyl chloride, methyl benzoate, benzoic acid, and acrylamide) is noticeably higher on silica than in solution in comparable conditions. The degree of acceleration varies depending on the catalyst and is more pronounced at its lower concentrations. By use of p-toluenesulphonyl chloride determination as an example it has been shown that the accelerating effect of silica enables to decrease the detection limit down to 0.07 nmol cm(-2) (as compared with 4 nmol.cm(-2) in solution); the accuracy is not diminished. It is concluded that catalytic indicator reactions on solid supports may represent high interest for analytical chemists.     

A Catalytic Method for Determining Cadmium(II), Nickel(II), and Zinc(II) Inhibitor Metals

The inhibitory effect of Cd(II), Ni(II), and Zn(II) on the oxidation of 3,3′,5,5′ -tetramethylbenzidine with periodate was detected. The optimum reaction conditions were found, and the procedures were developed for determining 1 × 10⁻² to 10 μg/mL Cd(II), Ni(II), and Zn(II) in solution. The indicator reaction was performed on a number of supports. The maximum inhibitory effect was observed on silica gel-based plates for TLC. Procedures for determining 6 × 10⁻³ to 0.4 μg of these metals were developed. Silica gel plates with the immobilized reagent for cadmium (bromobenzothiazo) were used to preconcentrate cadmium. A selective test procedure was developed for determining 1 × 10⁻⁴ −3 × 10⁻³ μg/mL cadmium with the visual detection of the process rate. Upon the introduction of dimethylglyoxime into the indicator reaction, the inhibitory effect of nickel changed to its promoting effect and the detection limit for nickel was lowered. A procedure was developed for determining 3 × 10⁻⁴ −3 × 10⁻³ μg/mL nickel in solution and 7 × 10⁻³−4 × 10⁻¹ μg nickel on the surface of Sorbfil plates. An assumption was made about the reasons for the inhibitory effect of metal ions on the oxidation of aryl diamines with periodate.__________Translated from Zhurnal Analiticheskoi Khimii, Vol. 60, No. 6, 2005, pp. 662–669.Original Russian Text Copyright © 2005 by Beklemishev, Kiryushchenkov, Stoyan, Dolmanova.     

Sorption-catalytic determination of cadmium using bromobenzothiazo noncovalently bound to silica and paper

Cadmium (along with Fe(II), Co(II), Zn(II), and Pb(II) ions) decreases the rate of oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB) with KIO₄ conducted either without or with Mn(II) as a catalyst. Cadmium(II) is preconcentrated from aqueous solutions on silica plates or paper filters physically modified with a reagent for selective determination of Cd(II), namely 1-[(6-bromo-2-benzothiazolyl)azo]-2-naphthol (bromobenzothiazo, or BBT). The modifier is strongly retained on the both supports at pH 6–10 and does not affect the inhibiting effect of Cd(II) in the indicator reaction. Cadmium is determined by its inhibiting action directly on the sorbents by measuring transmittance (BBT/paper) or reflectance (BBT/silica) with limits of detection of 2 × 10^–4 and 0.03 mg/L, respectively. The proposed hybrid combination of sorption with catalytic detection on the sorbent allows to increase the selectivity factors several times (up to 2 orders) relatively to the determination in solution. Tap water samples and soil extracts were analyzed.     

Enzymatic Methods for the Determination of Mercury(II)

Enzymatic methods for the determination of mercury(II) using native and immobilized enzymes from different classes and sources were considered. Enzymatic procedures were compared in sensitivity, selectivity, rapidity, and experimental techniques. The main approaches to controlling the performance characteristics of the enzymatic procedures were discussed. The application of these procedures to the determination of mercury(II) in particular samples (water and soils of different origin and biological fluids) was considered.