Catalytic Adsorptive Stripping Voltammetric Procedure Research Articles

A novel catalytic adsorptive stripping voltammetric method for the determination of germanium ultratraces in the presence of chloranilic acid and the V(IV)\xb7HEDTA complex

A novel, sensitive catalytic adsorptive stripping voltammetric procedure which can be used to determine trace amounts of germanium is described. The method is based on the interfacial accumulation of the complex formed by Ge(IV) and the product of the reduction of chloranilic acid on the hanging mercury drop electrode or the renewable silver amalgam film electrode, and its subsequent reduction from the adsorbed state followed by the catalytic action of the V(IV)·HEDTA complex. The presence of V(IV)·HEDTA greatly enhances the adsorptive stripping response of Ge. The reduction of the Ge(IV) in the presence of chloranilic acid and V(IV)·HEDTA was investigated in detail and the effects of pH, electrolyte composition, and instrumental parameters were studied. Under optimal conditions, the catalytic peak current of germanium exhibited good linearity for Ge(IV) concentrations in the range of 0.75–60 nM (for 60 s of accumulation at −0.1 V, r2 = 0.995) and a low limit of detection (LOD = 0.085 nM). The procedure was successfully applied to determine Ge in water samples.

Ultrasensitive catalytic-adsorptive stripping voltammetric determination of molybdenum using a Mo(VI)-chloranilic acid-chlorate system

A catalytic adsorptive stripping voltammetric procedure of the determination of ultratrace amounts of molybdenum using a novel catalytic system, Mo(VI)-chloranilic acid-chlorate was elaborated. In a supporting electrolyte containing 0.01M HCl (pH 2), 2.5×10−4M chloranilic acid and 0.4M KClO3, the catalytic adsorptive stripping response observed at −0.23V was proportional to the Mo(VI) concentration within the range of 0.16μgl−1 to 60μgl−1 for 60s of accumulation. The limit of detection was found to be 1.6×10−10M. The reproducibility of the blank signal was equal to 4.8%. The method was validated by quantifying Mo(VI) in certified reference surface water, and it was applied for the determination of Mo(VI) in extracts of fly ashes. The possible scheme of the catalytic reaction was suggested.

Ultra trace quantification of chromium(VI) in food and water samples by highly sensitive catalytic adsorptive stripping voltammetry with rubeanic acid

Abstract A simple and highly selective and sensitive catalytic adsorptive stripping voltammetric procedure for determination of ultra trace levels of chromium(VI) on hanging mercury drop electrode is reported. The method is based on the adsorptive preconcentration of the Cr(III)–dithiooxamide (rubeanic acid) complex and the utilization of the catalytic reaction in the presence of nitrate. At optimized conditions the calibration graph is linear from 0.01 to 6 ng/ml and detection limit is 0.002 ng/ml for accumulation time of 50 s. The interference of some common ions was studied and this method has been applied to the determination of chromium in food and waste water samples with satisfactory results.

Ultraselective and Sensitive Determination of Cr(VI) in the Presence of a High Excess of Cr(III) in Natural Waters with a Complicated Matrix

AbstractIn the present work, the catalytic adsorptive stripping voltammetric procedure for trace determination of Cr(VI) in the presence of a high excess of Cr(III) in natural waters with a complicated matrix has been developed. The influence from potentially interfering substances such as organic matter was successfully eliminated by exploiting adsorptive properties of polymeric resin. The detection limit estimated from 3 times the standard deviation for a low Cr(VI) concentration in the simultaneous presence of a 2×103 fold excess of Cr(III), 50 mg L−1 surfactants, 50 mg L−1 humic substances and the accumulation time of 30 s was about 5.3×10−10 mol L−1.

A catalytic adsorptive stripping voltammetric procedure for trace determination of Cr(VI) in natural samples containing high concentrations of humic substances

A simple and fast catalytic adsorptive stripping voltammetric procedure for trace determination of Cr(VI) in natural samples containing high concentrations of humic substances has been developed. The procedure for chromium determination in the presence of DTPA and nitrates was employed as the initial method. In order to enhance the selectivity vs. Cr(III) the measurements were performed at 40 degrees C. Interference from dissolved organic matter such as humic and fulvic acids was drastically decreased by adding Amberlite XAD-7 resin to the voltammetric cell before the deaeration step. The whole procedure was applied to a single cell, which allowed monitoring of the voltammetric scan. Optimum conditions for removing humic and fulvic acids due to their adsorption on XAD-7 resin were evaluated. The use of XAD-7 resin also minimize interferences from various cationic, anionic, and nonionic surfactants. The calibration graph for Cr(VI) for an accumulation time of 30 s was linear in the range 5 x 10(-10) to 5 x 10(-8) mol L(-1). The relative standard deviation for determination of Cr(VI) at a concentration of 1 x 10(-8) mol L(-1) was 3.5% (n = 5). The detection limit estimated from 3 times the standard deviation for low Cr(VI) concentrations and an accumulation time of 30 s was about 1.3 x 10(-10) mol L(-1). The proposed method was successfully applied to Cr(VI) determination at trace levels in soil samples.

Determination of Traces of Cobalt in Zinc Matrix by Catalytic Adsorptive Stripping Voltammetry at Bismuth Film Electrode

AbstractAn catalytic adsorptive stripping voltammetric procedure for the determination of cobalt in a zinc matrix at an in situ plated bismuth film electrode was described. The procedure exploits the enhancement effect of a cobalt peak observed in the system Co(II)–dimethylglyoxime–piperazine‐1,4‐bis(2‐ethanesulfonic acid)–cetyltrimethylammonium bromide. Using optimized conditions, in a solution containing 0.01 mol L−1 Zn(II) the calibration plot for Co(II) following accumulation time of 120 s was linear from 2×10−10 to 5×10−8 mol L−1. The detection limit (based on 3σ criterion) for Co(II) of 6×10−11 mol L−1 was achieved. The proposed procedure was applied for Co(II) determination in zinc reagent for analysis and in tap water.

Simple and Highly Selective Catalytic Adsorptive Voltammetric Method for Cr(VI) Determination

A simple and highly selective and sensitive catalytic adsorptive stripping voltammetric procedure for determination of traces of Cr(VI) in the presence of a large excess of Cr(III) in environmental water samples is reported. To obtain a low detection limit the voltammetric procedure of chromium determination in the presence of DTPA and nitrate was exploited. For elimination of interference of Cr(III) ethylenediaminedisuccinic acid was used as a masking agent. At optimized conditions the calibration graph is linear from 2×10−10 to 2×10−8 mol L−1 for accumulation time of 30 s. The validation of the procedure was performed by comparison of the results of analysis of river water samples with those obtained using other accepted voltammetric procedure.

Catalytic Adsorptive Stripping Voltammetric Procedure for Determination of Total Chromium in Environmental Materials

AbstractA sensitive catalytic adsorptive stripping voltammetric procedure for determination of traces of total chromium in environmental samples is reported. The method is based on the preconcentration of a Cr(III)H2DTPA complex by adsorption at the HMDE from an acetate buffer solution at the potential −1.0 V vs. Ag/AgCl. Total chromium was determined as Cr(III) after reduction of Cr(VI) to Cr(III) by NaHSO3. In order to stabilize the signal of Cr(III) the measurements were performed at 5 °C. The calibration graph for chromium for an accumulation time of 60 s was linear in the range from 5×10−10 to 5×10−8 mol L−1. The relative standard deviation for a chromium concentration of 1×10−8 mol L−1 was 3.9% (n=5). The detection limit for accumulation time of 60 s was about 8×10−11 mol L−1. The validation of the procedure was performed by the analysis of the certified reference materials.

Catalytic adsorptive stripping voltammetric determination of Cr(VI) in EDTA extracts from solid samples

A catalytic adsorptive stripping voltammetric procedure which allows for Cr(VI) determination in EDTA extracts is presented. EDTA used for extraction can be exploited as a masking agent for Cr(III). The calibration graph for Cr(VI) for an accumulation time of 60 s was linear in the range from 2 × 10 −10 to 3 × 10 −8 mol L −1. The relative standard deviation for a Cr(VI) concentration of 2 × 10 −9 mol L −1 was 5.1% ( n = 5). The detection limit estimated from three times the standard deviation of low Cr(VI) concentration and accumulation time of 60 s was about 7 × 10 −11 mol L −1. The influence of foreign ions commonly present in extracts from solid samples is presented. The proposed voltammetric procedure was applied to determine Cr(VI) in EDTA extractable chromium from soil certified reference materials CRM 483 and CRM 041. The performance of the method was also verified by studying the recovery of Cr(VI) from spiked river water.

Simultaneous ultratrace determination of platinum and rhodium by cathodic stripping voltammetry

A highly sensitive, catalytic adsorptive stripping voltammetric procedure at the hanging mercury drop electrode for the simultaneous determination of ultratraces of platinum and rhodium in electrolyte solutions has been evaluated. Optimal conditions were found to be: first accumulation potential 0 V (vs. Ag/AgCl), second accumulation potential −0.8 V, first preconcentration time 90 s, second preconcentration time 120 s, scan rate 20 mV s −1. The response of the system was found to be linear in a range of platinum concentrations up to 6 ng l −1 and for rhodium up to 0.5 ng l −1. The detection limit was 21 pg l −1 for platinum and 5.6 pg l −1 for rhodium. The effect of various possible interferences from other metal ions was also studied. With the exception of zinc (whose influence was studied in more detail), no significant interferences were observed. The method was successfully applied to the determination of traces of Pt and Rh in real environmental samples (spruce shoots) after high pressure digestion.

Catalytic-adsorptive stripping voltammetric determination of molybdenum in plant foodstuffs

In acetate buffer solution (pH 3.5) containing oxine and chlorate, ultratrace amounts of molybdenum can be determined after adsorptive accumulation of the Mo(VI)-oxine complex on a hanging mercury drop electrode, coupled with the catalytic effect on the reduction of chlorate. Under optimized conditions, the catalytic-adsorptive stripping voltammetric procedure gives excellent selectivity and an extremely low detection limit of 1.7 pM molybdenum (60 s accumulation). The stripping peak current increases linearly with molybdenum concentration between 10 pM and 5.0 nM. The procedure is applied to determine traces of molybdenum in plant foodstuffs.

Ultrasensitive adsorptive-catalytic stripping voltammetry of iron in the presence of hydroxamic acids and hydrogen peroxide

An ultratrace catalytic–adsorptive stripping voltammetric procedure for the determination of trace amounts of iron is reported. The method is based on the interfacial accumulation of the iron-N-benzoyl-N-phenylhydroxylamine complex on the hanging mercury drop electrode, followed by catalytic reduction of the adsorbed complex in the presence of hydrogen peroxide. The presence of hydrogen peroxide greatly amplifies the adsorptive stripping response. Optimum experimental conditions have been explored to give an extremely low detection limit of 1.8 × 10−10M (10 ng/L) iron following 10min accumulation. Analogous improvements are reported for other hydroxamic acid complexes of iron. Such acids hold great promise for developing additional adsorptive stripping procedures.

Catalytic—adsorptive stripping voltammetric measurements of ultratrace levels of tungsten

An ultrasensitive catalytic—adsorptive stripping voltammetric procedure for trace measurements of tungsten, based on a chlorate catalytic reduction peak in a 3-methoxy-4-hydroxymandelic acid (VMA)-oxine-sulfuric acid medium is reported. Optimum experimental conditions (particularly the solution composition) are explored to give an extremely low detection limit of 5 ng/l. (2.5 × 1O −11 M) tungsten following 5-min accumulation. The relative standard deviation (at 1 μg/l.) is 1.0%. The high sensitivity and precision are coupled to high selectivity. Simultaneous trace quantitation of tungsten and molybdenum is also illustrated.