Determination of Cr(VI) in the presence of Cr(III) and humic acid by cathodic stripping voltammetry

A voltammetric procedure in the flow system for determination of traces of Cr(VI) in the presence of Cr(III) and humic acid is presented. The calibration graph is linear from 5×10⁻¹⁰ to 1×10⁻⁷ mol l⁻¹ for an accumulation time of 120 s. The R.S.D. for 1×10⁻⁸ mol l⁻¹ Cr(VI) is 5.3% (n=5). The detection limit estimated from 3σ for a low concentration of Cr(VI) and accumulation time of 120 s is 2×10⁻¹⁰ mol l⁻¹. The method can be used for Cr(VI) determination in the presence of up to 50 mg l⁻¹ of humic acid. The validation of the method was carried out by studying the recovery of Cr(VI) from spiked river water and by the comparison of the results of determination of Cr(VI) in a soil sample. The method cannot be used for analysis of samples containing high concentrations of chloride ions such as seawater and estuarine water.     

Chemiluminescence system for automatic determination of chemical oxygen demand using flow injection analysis

A novel chemiluminescence (CL) system for automatic determination of chemical oxygen demand (COD) combined with flow injection analysis is proposed in this paper. In this system, potassium permanganate is reduced to Mn²⁺ which is first adsorbed on a strongly acid cation-exchange resin mini-column to be concentrated during chemical oxidation of the organic compounds at room temperature, while the excessive MnO₄⁻ passes through the mini-column to be waste, then the concentrated Mn²⁺ is eluted reversely and measured by the luminol-H₂O₂ CL system. The calibration graph is linear in the range of 4-4000 mg l⁻¹ and the detection limit is 2 mg l⁻¹. A complete analysis could be performed in 1.5 min including washing and sampling, giving a throughout of about 40 h⁻¹. The relative standard deviation was 4.4% for 10 mg l⁻¹ COD (n=11), 4.8% for 100 mg l⁻¹ COD (n=11). This CL flow system for determination of COD is very simple, rapid and suitable for automatic and continuous analysis. The presented system has been applied successfully to the determination of COD of water samples.     

Determination of Tiopronin in Pharmatceutical Preparations by Time Resolved Chemiluminescence Using the Stopped-Flow Technique

An analytical method for the determination of tiopronin in pharmaceuticals was developed. The method is based on measurements of the chemiluminescence (CL) produced by tiopronin upon reaction with sulfuric acid and potassium permanganate as the oxidant in the presence of formaldehyde as emission enhancer. This allows entire chemiluminescence intensity vs. time profiles to be recorded by using the stopped-flow technique in a continuous-flow system, which, in turn, enables the use of a new parameter (the rate of the light decay reaction) in addition to the maximum emission intensity and total emission area, which are proportional to the analyte concentration. The influence of chemical variables such as the type of acid used and its concentration, emission enhancer, and oxidant concentration on the chemiluminescence signal was examined. The calibration graph was linear from 0.05 to 3.00 mg L^?1. The limit of detection as determined according to Clayton ranged from 0.12 to 0.17 mg L^?1 and the relative standard deviation (RSD) for the analysis of 10 samples containing an analyte concentration of 1.50 mg L^?1 was 1.87%.     

Determination of trace amounts of chromium (VI) by flow injection analysis with chemiluminescence detection

A new sensitive chemiluminescence (CL) method combined with continuous flow injection analysis is described for the determination of Cr(VI). Strong CL signals were generated by Cr(VI)-catalysed oxidation of gallic acid in the presence of potassium permanganate and hydrogen peroxide. Effects of reagent concentrations, temperature, pH, flow rates, mixing coil length and mixing flow sequences on the chemiluminescence intensity were studied. Under the optimised experimental conditions, the relationship between the logarithm of concentration (log?C) of Cr(VI) and the logarithm of intensity (log?I) is linear over the range of 2?×?10^?11 – 5?×?10^?4?mol?L^?1, with the detection limit (3σ) of 4?×?10^?12?mol?L^?1. Relative standard deviation of ten measurements of 1?×?10^?9?mol?L^?1 Cr(VI) is 1.7%. This flow injection analysis (FIA) system proved to be able to analyse up to 40 samples h^?1. Effects of various interferences possibly present in the water samples were investigated. Most cations and anions, as well as organic compounds, did not interfere with the determination of Cr(VI) in water samples. The experimental results obtained for chromium in reference materials were also in good agreement with the certified values.     

A microcomputer-based peak-width method of extended calibration for flow-injection atomic absorption spectrometry

In the proposed method of extended calibration based on peak widths, all data collection and reduction are done by a microcomputer interfaced to the spectrometer. The method produces an estimate of concentration without dilution of the off-range samples. Calibrations covering the ranges 40/2-1000 mg l^?1, 1.0/2-50 mg l^?1 and 20/2-1000 mg l^?1 were obtained for chromium, magnesium and nickel, respectively.     

Flow injection-chemiluminescence determination of propranolol in pharmaceutical preparations

A rapid and precise continuous-flow method is described for the determination of propranolol based on the chemiluminescence (CL) produced by its reaction with potassium permanganate in a sulphuric acid medium. The optimum chemical conditions for the chemiluminescence emission were investigated. Two manifolds were tested and their characteristics such as the length of the reactor, injection volume and flow rate were compared. When using the selected manifold, propranolol gives a linear calibration graph over the concentration range 1.0-17.5 mg l⁻¹. The detection limit calculated as proposed by IUPAC was 70 ng ml⁻¹ and the detection limit calculated as proposed by Clayton was 0.87 mg l⁻¹. For analysis of 10 solutions of 10.0 mg l⁻¹ propranolol, if error propagation theory is assumed, the relative error was 0.1%. The standard deviation (S.D.) for 10 replicate samples was 0.07 mg l⁻¹. The method has been validated versus a published fluorimetric method.The present chemiluminescence procedure was applied to the determination of propranolol in simple British and Spanish pharmaceutical formulations, with excellent recoveries, as the determination is free from interference from common excipients. However, some drugs, such as hydralazine and bendroflumethizide which may also be present in the formulation, increase the emission intensity.     

Permanganate-based chemiluminescence analysis of ferulic acid using flow injection.

A simple, sensitive and rapid flow-injection chemiluminescence method has been developed for the determination of ferulic acid based on the chemiluminescence reaction of ferulic acid with potassium permanganate in a nitric acid medium. A strong chemiluminescence signal was observed when ferulic acid was injected into an acidic potassium permanganate solution in a flow-cell. The present method allowed the determination of ferulic acid in the concentration range of 6.0 x 10(-6) to 2.0 x 10(-4) mol l(-1); the detection limit (3sigma) for ferulic acid was 9.6 x 10(-8) mol l(-1). The relative standard deviation was 1.0% for 11 replicate analyses of 2.0 x 10(-4) mol l(-1) ferulic acid. The proposed method was applied to the determination of ferulic acid in real samples with satisfactory results. Moreover, the reaction mechanism of the chemiluminescence system was primarily considered.     

Effect of Cobalt(II) and Manganese(II) on the Chemiluminescent Reaction of Peroxymonosulfate with Humic Acid and Some Organic Compounds. Analytical Applications

Abstract

The intensity of the radiation emitted by humic acid (HA) in the presence of SO₅ ^2? in basic medium was used to determine HA in the range up to 20.0 mg l^?1. The detection limit was 0.24 mg l^?1. The addition to the sample of 50 mg l^?1 of Co(II) or Mn(II), as EDTA complexes or chloride salts, enhanced the radiation emission as a result of the formation of strong oxidant radicals such as SO₅ ^??, SO₄ ^??, and HO^?. In the presence of these metal ions, the oxidation of HA and the catalytic decomposition of SO₅ ^2? occur simultaneously. Low concentration of HA in natural waters can be detected. HA was replaced by some model organic compounds. The marked chemiluminescent (CL) signals followed the order: phloroglucinol>fulvic acid>humic acid>resorcinol>pyrogallol>cathecol>hydroquinone.     

The spectrophotometric determination of arsenic in sea water,potable water and effluents

Procedures are described for the determination of arsenic in sea water, potable waters and effluents. The sample is treated with sodium borohydride added at a controlled rate. The arsine evolved is absorbed in a solution of iodine and the resultant arsenate ion is determined photometrically by a molybdenum blue method. The time required for a complete analysis is about 90 min, but of this only 15 min is operator time. For sea water the range, standard deviation, and detection limit are 1–4 μgl^-1, 1.4 % and O.14 μg l^-1, respectively; for potable waters they are 0–800 μg l^-1, about 1 % (at 20μg l^-1 level) and 0.5μg l^-1, respectively. Silver and copper cause serious interference at levels of 0.5 mgl^-1, and nickel, cadmium and bismuth interfere at concentrations of a few tens of mg l^-1; however, these elements can be removed either by preliminary extraction with a solution of dithizone in chloroform or by ion exchange. Arsenic present in organo-arsenic compounds is not directly determinable, but can be rendered reactive either by photolysis with ultraviolet radiation or by oxidation with permanganate or nitric—sulphuric acid mixture. Arsenic(V) can be determined separately from total inorganic arsenic after extracting arsenic(III) as its pyrrolidine dithiocarbamate into chloroform.     

KMnO4-OP Chemiluminescence system for FIA determination of hydrogen peroxide

A fast and simple KMnO₄-OP chemiluminescence system for flow-injection analysis of hydrogen peroxide is described. When a mixture of sample and OP is injected into acidic KMnO₄, solution in a flow-cell, strong chemiluminescence occurs. The response is linear to the concentration of hydrogen peroxide in the range of 1.0 × 10^–8 to 6.0 × 10^–5 mol/l with 0.1 mol/l permanganate, and the upper limit of linear response could be extended to 6 × 10^–3 mol/l by increasing the permanganate concentration. The relative standard deviation of the method is between 1.6 and 2.3%. The detection limit is 6.0 × 10^–9 mol/l. This method is suitable for automatic and continuous analysis and has been successfully tested for determination of hydrogen peroxide in rain water. The chemiluminescence intensity was found to be remarkably enhanced in the presence of the OP micellar system.     

Flow injection chemiluminescence determination of medazepam

A new flow injection chemiluminescence method for the assay of medazepam is explored. The method involves the use of permanganate in sulfuric acid for the oxidation of medazepam with the emission of chemiluminescence detected by a photomultiplier tube. A simplex procedure was employed for optimising the conditions for high sensitivity detection, which were found to be 1.03 × 10^–3 mol L^–1 permanganate, 0.153 mol L^–1 sulfuric acid and 3.43 mL min^–1 flow rate. The linear calibration range was 3.7 × 10^–5 to 1.7 × 10^–3 mol L^–1. The detection limit (3σ) and the sample throughput were 1.85 × 10^–5 mol L^–1 and 100 per hour, respectively. The relative standard deviation for 5 replicate determinations of 1.9 × 10^–4 mol L^–1 medazepam was 0.15%. Common excipients (starch, glucose, maltose, lactose) used in pharmaceutical preparations had no effect. Received: 2 February 1998 / Revised: 20 May 1998 / Accepted: 25 May 1998     

Continuous flow extraction of indium with bis(2-ethylhexyl)phosphoric acid in 4-methylpentane-2-one coupled on-line with flame atomic absorption spectrometry

Extraction in liquid-liquid segmented flow is used for preconcentration of indium from dilute nitric acid solutions into bis(2-ethylhexyl)phosphoric acid dissolved in 4-methylpentane-2-one. The extraction setup is coupled on-line with flame spectrometry to give a fully mechanized system. The detection limit of the method is 0.03 mg l^?1, the calibration plot is linear up to 1.75 mg l^?1. Repeatability is 1.5% RSD measured at 1 mg l^?1. Sample throughput is 60 h^?1.     

Kinetics of radioeuropium sorption on Gorleben sand from aqueous solutions and ground water

Kinetics of Eu sorption on sandy sediment from Gorleben, Germany, containing humic substances, was studied by radiotracer method in batch experiments at very low europium concentration (3.4^.10^-8 mol/l), with the aim to find kinetic parameters suitable for modeling Eu migration in bed of the sediment and to elucidate the mechanism of the sorption. Experiments were evaluated using a new simplified method taking into account simultaneous sorption/desorption of Eu on the walls of sorption vessel. Five kinetic functions were tested, of which that describing diffusion in inert surface layer of sorbent proved most suitable. The effects of pH (3.0-8.8) by addition of Aldrich humic acid (10 mg/l), addition of hydrogencarbonates (5^.10^-3 mol/l) and preequilibration of the sediment with solution or of Eu with solution were examined. From the results it has been concluded that the kinetics and mechanism of the sorption strongly depend on pH. At pH 4.8 Eu is sorbed mainly as humate complex from the solution of humic acid. The addition of humic acid accelerates the sorption. Carbonate complexes of Eu are the probable forms sorbed at pH 8.8. The presence of humic substances in the slightly alkaline solutions suppresses the rate of the sorption due to slow dissociation of Eu-humate complexes.     

Determination of ethamsylate in pharmaceutical preparations by irreversible biamperometry

A novel flow-injection irreversible biamperometric method is described for the determination of ethamsylate. The proposed method is based on the oxidation of ethamsylate at one platinum electrode and the reduction of permanganate at another to form an irreversible biamperometric detection system. Ethamsylate can be determined over the range 1.0×10⁻⁶-1.0×10⁻⁴ mol l⁻¹ with a sample measurement frequency of 180 samples h⁻¹. The detection limit for ethamsylate is 4.0×10⁻⁷ mol l⁻¹. The stability of the proposed method is shown by a RSD of 0.52% for 11 replicate determinations of 2.0×10⁻⁵ mol l⁻¹ ethamsylate. The proposed method was applied to the determination of ethamsylate in pharmaceutical preparations.     

Determination of pipemidic acid based on flow-injection chemiluminescence due to energy transfer from peroxynitrous acid synthesized on-line

A flow-injection chemiluminescence (CL) method for the determination of pipemidic acid is described. It is based on energy transfer from excited state peroxynitrous acid to pipemidic acid, in which the excited state peroxynitrous acid is synthesized on-line by the mixing of acid hydrogen peroxide with nitrite in a flow system and the CL is from two excited states of pipemidic acid. The proposed method allows the measurement of pipemidic acid over the range of 2.0×10^–7–2.0×10^–5 mol l^–1 . The detection limit is 6.3×10^–8 mol l^–1, and the relative standard deviation for 2.0×10^–6 mol l^–1 pipemidic acid (n= 9) is 0.9%. This method was evaluated by the analysis of pipemidic acid in pharmaceutical preparations.     

An atomic absorption spectrometric method for the determination of non-ionic surfactants

A method is described for the determination of non-ionic surfactants in the concentration range 0.05–2 mg l^-1.Surfactant molecules are extracted into 1,2-dichlorobenzene as a neutral adduct with potassium tetrathiocyanatozincate(II) and the determination is completed by atomic absorption spectrometry. With a 150-ml water sample, the limit of detection is 0.03 mg l^-1(as Triton X-100).The method requires a single phase separation step, is applicable, without modification, to fresh, estuarine and sea-water samples and is relatively free from interference by anionic surfactants; the presence of up to 5 mg l^-1 of anionic surfactant (as LAS) introduces an error of no more than 0.07 mg l^-1 (as Triton X-100) in the apparent non-ionic surfactant concentration.     

A chemiluminescence-based continuous flow aqueous ozone analyzer using photoactivated chromotropic acid

Ozone has become the oxidant of choice for water disinfection, especially in large water treatment facilities. This paper describes a fast and sensitive method for the determination of ozone content by reaction with photoactivated chromotropic acid (CA, 4,5-dihydroxynaphthalene-2,7-disulfonic acid), which results in intense chemiluminescence (CL). Freshly ozonated water from a recirculating ozonizer/reservoir is injected into a carrier stream of deionized water in the flow-injection mode. This flow mixes with a stream of photoactivated CA solution in a spiral cell placed directly on top of an inexpensive miniature (8 mm diameter active area) photomultiplier tube (PMT). Alkaline CA is photoactivated by passing it through a FEP-Teflon^® coil (residence time ∼ 50 s) wrapped around a 1 W UV lamp emitting at 254 nm; without photoactivation, the signal is ∼70-fold lower. The S/N = 3 limit of detection for aqueous ozone is 3 μg l⁻¹ and good response slope is obtained up to an ozone concentration of 1.4 mg l⁻¹, the highest that could be made in this study. The response obeyed a quadratic equation with r² = 0.9984. No interference from permanganate ion is observed. The proposed system was applied to the monitoring of ozonation status of a playa lake water that exhibited significant ozone demand.     

Spectrophotometric determination of trace uranium in geological samples by flow injection analysis with on-line levextrel resin separation and preconcentration

A flow-injection system with on-line separation and preconcentration is described for the spectrophotometric determination of trace uranium in geological samples. Uranium is selctively adsorbed from 0.7 mol l^?1 nitric acid on a microcolumn (40 mm long, 4.4 mm i.d.) containing levextrel CL-5209 resin (120–200 mesh) and separated from the sample matrix and most of the co-existing ions; 10-fold concentration is obtained. Eluted uranium is determined spectrophotometrically with arsenazo-III. The detection limit is μg l^?1 uranium and calibration is linear up to 0.3 mg l^?1 uranium With dual columns operated alternately for adsorption and elution, 30 samples can be analyzed per hour. Masking agents are added to eliminate interferences from thorium and iron. The method is sensitive and highly selective, easy to operate and suitable for routine analysis of geological samples for uranium.     

Determination of Phenols In Natural Waters with A Flow-Analysis Method and Chemiluminescence Detection

ABSTRACT

A simple flow-manifold with time based sample introduction system was elaborated and used to determine phenols in natural waters. Use of computer controlled solenoid valves and direct chemiluminescence detection enables very low reagent consumption. A quantity of less than 1.5 μmol of potassium permanganate and 600μmol of sulphuric acid per determination is used. The use of on-line preconcentration column filled with XAD-4 resin enables determination with the detection limit of 5 ng-ml^?. The sample throughput is 12-h^? when the column is used and 60-h^? without a column.     

U(VI) mono-hydroxo humate complexation

The complexation of the uranyl ion with humic acid is investigated. The humic acid ligand concentration is described as the concentration of reactive humic acid molecules based on the number of humic acid molecules, taking protonation of functional groups into account. Excess amounts of U(VI) are used and the concentration of the humic acid complex is determined by the solubility enhancement over the solid phase. pH is varied between 7.5 to 7.9 in 0.1M NaClO₄ under normal atmosphere and room temperature. The solubility of U(VI) in absence of humic acid is determined over amorphous solid phase between pH 4.45 and 8.62. With humic acid, only a limited range of data can be used for the determination of the complexation constant because of flocculation or sorption of the humic acid upon progressive complexation. Analysis of the complex formation dependency with pH shows that the dominant uranyl species in the concerned pH range are UO₂(OH)⁺ and (UO₂)₃(OH)₅ ⁺. The complexation constant is evaluated for the humate interaction with the to UO₂(OH)⁺ ion. The stability constant is found to be logβ = 6.94±0.3 l/mol. The humate complexation constant of the uranyl mono-hydroxo species thus is significantly higher than that of the nonhydrolyzed uranyl ion (6.2 l/mol). Published data on the Cm³⁺, CmOH²⁺ and Cm(OH)₂ ⁺ humate complexation are reevaluated by the present approach. The higher stability of the hydrolysis complex is also found for Cm(III) humate complexation.