Extraction-spectrophotometric determination of sulphide and sulphite in waters based on formation of the bis(2,9-dimethyl-1,10-phenanthroline) copper(I) ion

A spectrophotometric method is described for the determination of sulphide or sulphite. The bis(2,9-dimethyl-1,10-phenanthroline)copper(II) ion is reduced at pH 10 by sulphide in the presence of formaldehyde and by sulphide and sulphite in its absence. The resulting copper(I) complex is extracted into chloroform and measured. With any convenient sample volume between 1 and 100 ml, the limits of detection are 0.1 mg for sulphide and 0.25 μg for sulphite. The method is unaffected by iron(II) and nitrite, in concentrations of 100 and 1000 mg l^-1, respectively.     

Reagentless system for sulphite determination based on polyaniline

A new reagentless system for sulphite (or sulphur dioxide) determination is reported based on the use of an organic conducting polymer, polyaniline, and its absorbance variation at 550 nm, depending on the sulphite concentration. After chemical polymerisation of aniline a very thin film of polyaniline is obtained. Although the response is not fully reversible, each film can be used for at least 10 measurements for low analyte concentrations (up to 0.5 mg l⁻¹) and five measurements for higher sulphite concentrations. Moreover, the reproducibility, ease of preparation and low cost of the films, permit the use of a new disposable system for each measurement. When the change in absorbance at 550 nm was measured for 210 s (stabilisation time), the system showed a linear response, which ranged from 0.025 to 1.50 mg l⁻¹ of sulphite. A theory with regard to the reaction mechanism between the polyaniline films and sulphite is also proposed. The system was applied to sulphite determination in wine samples and the results were in agreement with those obtained by the Official Method of Analysis (iodometric titration).     

The Electrochemical Oxidation of Sulphite on Gold Electrodes

The electro‐oxidation of sulphite is studied in acid media on gold macroelectrodes and Au particle array modified boron doped diamond electrodes. The sulphite oxidation proceeds through a one‐electron transfer process followed by a chemical step of second order (EC₂ mechanism), as evidenced by experimental voltammetry and digital simulation for both gold macroelectrodes and gold particle modified substrates. The diffusion coefficient of sulphite is calculated consistently for both cases at about 4×10^?9 m² s^?1, with the reverse peak behaviour concentration dependent. The arrays are made by electrodeposition and show a morphological transition from a quasi‐spherical to a star shape as the growth time of the particles increases. Kinetic parameters inferred from the electro‐oxidation at the macroelectrode can be successfully applied to model the gold particle modified electrode data to confirm the EC₂ mechanism, whilst recognising the overlapping diffusion layers of adjacent gold particles.     

Determination of sulphite in wine by flow injection analysis with indirect electrochemical detection

A flow-injection method has been developed for the determination of total sulphite in wine samples. After hydrolysis of bound sulphite, sulphur dioxide is separated from the matrix by means of an in-line gas diffusion module. For detection indirect amperometry is used, with iodine as oxidizing reagent. The iodine can be generated in-line by merging and mixing iodate and iodide solutions, or alternatively, electrochemically from iodide. With the latter method the best results were obtained. The reproducibility of the peak heights is better than 2%. The linear range of the method can be regulated by adaptation of the current applied to generate the iodine reagent. Due to the low detection limits obtained (0.05 mg L^–1), wine samples can be strongly diluted before injection, which makes the sample pretreatment fast and simple. Good agreement has been found with the results obtained for the total sulphite concentration in different wine samples by titration.     

Separation and automatic spectrophotometric determination of low concentrations of cyanide in water

Semi-automatic methods are described for the routine determination of cyanide in water. Membrane diffusion and isothermal distillation are examined for the separation/concentration of cyanide; the isothermal distillation procedure is optimized for routine use. An air-segmented flow analyzer is used to quantify cyanide. Two classical spectrophotometric methods are adapted and compared. The method based on reaction with picric acid is applicable at cyanide concentrations exceeding 1 mg l^?1. A modified Aldridge method is far better for lower concentrations. Combination of isothermal distillation with the automatic version of the Aldridge method is suitable for the determination of cyanide in waters in the concentration range 0.01–10 mg l^?1. Interference by sulphide and sulphite and their removal are described.     

Chemical removal of humic substances interfering with the on-line solid-phase extraction—Liquid chromatographic determination of polar water pollutants

Summary Different methods for removing interference by humic substances in the analysis of polar pollutants have been compared in the analysis of environmental water by solid-phase extraction (SPE) with a chemically modified polymeric resin coupled on-line to liquid chromatography with UV detection. The methods were based on the use of chemical reagents. The best method was found to be addition of sodium sulphite to humic-containing water before SPE. The appropriate amount of sulphite depends on the amount of humic substances dissolved in the sample—for analysis of 50 mL tap and Ebro river water, respectively, 250 μL and 500 μL 10 % Na₂SO₃ solution had to be added. In both cases, the recovery values after chemical treatment were similar to those when a Milli-Q-quality water standard was analysed.     

The application of 2,4,6-trinitrobenzene-1-sulphonic acid in the differential pulse polarographic determination of amines

The differential pulse polarographic behaviour of 2,4,6-trinitrophenyl (TNP) derivatives of several primary amines and amino acids was investigated in the presence of sulphite ion. All the derivatives produced a polarographic peak for their complexes with sulphite (1 × 10^?2 M) in pH 8.0 phosphate buffer (0.05 M)/0.1 M potassium chloride. The derivatives of proteins and peptides did not give such a peak. A 5-min reaction time at room temperature (or 50°C for lysine) and pH 10.5 using 1 × 10^?4 M 2,4,6-trinitrobenzene-1-sulphonic acid provides the optimal conditions for the determination of 5 × 10^?6?2.5 × 10^?5 M amines. The relative standard deviation for determining 1 × 10^?5 M glycine (n = 5) was 1%.     

Lead dioxide-coated carbon paste electrodes

Lead dioxide electrodeposited under optimized conditions on carbon paste provides an electroanalytically useful electrode, with an anodic working range extending to 1.9 V. Voltammograms for sulphite are used to study electrode lifetime and reproducibility; calibration graphs are linear up to 10^-3M sulphite in 0.5 M sulphuric acid.     

Flow-Injection Chemiluminescence Determination of Fluoroquinolones

ABSTRACT

A new flow-injection CL method was developed for the determination of fluoroquinolones including ofloxacin, norfloxacin, ciprofloxacin and lomefloxacin in pharmaceutical preparations, based on the chemiluminescence reaction of sulphite with cerium(IV) sensitized by these compounds. The linear ranges are 0.04 to 4.0 μg ml^?1 for ofloxacin and 0.4 to 40.0 μg ml^?1 for norfloxacin, ciprofloxacin and lomefloxacin, respectively. The detection limits are 0.016 μg ml^?1 for ofloxacin and 0.16 μg ml ^?1 for norfloxacin, ciprofloxacin and lomefloxacin, respectively. The relative standard deviations (RSD) are 2.1 to 2.6% (n=10) for these fluoroquinolones. The analytical procedure has been applied to the determination of the fluoroquinolones in pharmaceutical commercial formulations. The results are in agreement with those obtained by the official methods.     

Flow-injection determination of sulphite and assay of sulphite oxidase

Sulphite (1–80 × 10^?5 M) in formaldehyde-stabilized solutions is determined by injection into a flowing stream of pH 8.5 phosphate buffer, passing through a mini-column of sulphite oxidase immobilized on controlled-pore glass, with amperometric detection of the hydrogen peroxide produced. Sulphite oxidase (5–100 U l^?) is determined by injection into a flowing stream of formaldehyde-stabilized 2 × 10^?3 M sodium sulphite in pH 8.0 phosphate buffer; hydrogen peroxide is again monitored.     

Flow injection on-line sorption preconcentration of platinum in a knotted reactor coupled with electrothermal atomic absorption spectrometry

A flow injection on-line sorption preconcentration method for the electrothermal AAS determination of platinum has been developed. The pyrrolidine dithiocarbamate complexes of either Pt⁴⁺ or Pt²⁺, formed in 0.7 mol L^–1 HNO₃, are on-line adsorbed on the inner walls of a PTFE knotted reactor and subsequently eluted with methanol. An enhancement factor of 112 and a detection limit (3 σ) of 10 ng L^–1 along with a sampling frequency of 21 h^–1 are achieved with a 90 s preconcentration time at a sample flow rate of 8.8 mL min^–1. The relative standard deviation is 2.5% for 0.4 μg L^–1 Pt. The method has been applied to the determination of platinum in blood samples.     

Flow-injection fluorimetric assay of nitrogen-containing substrates by on-line enzymatic generation of ammonia

A fluorimetric flow-injection method for the determination of nitrogen-containing substrates, which can be enzymatically degraded to ammonium/ammonia is described. The generated ammonia is detected fluorimetrically after on-line derivatization with o-phthaldialdehyde (OPA) and sulphite. The derivatization procedure is optimized by a fractional factorial design at two levels and by a super modified simplex procedure to obtain a high sensitivity and a low detection limit for ammonia in the micromolar concentration range. Under the given flow conditions the detection limit is 1 μM, and considerable selectivity for ammonia over primary amines such as unconverted substrate and amino acids is achieved. Two enzymatic systems, incorporating immobilized creatinine iminohydrolase (CIH) and L-aspartase column reactors, respectively, are tested as model systems. The feasibility of the CIH system for the practical assay of creatinine in serum samples is demonstrated.     

Determination of Arsenic and Phosphorus in Doped Polysilicon Layers

Abstract

The method is based on polysilicon dissolution with a water-hydrofluoric-nitric acid etchant mixture followed by matrix volatilization as hexafluorosilicic acid. Losses of arsenic through volatilization are avoided by its oxidation with permanganate. Phosphorus is determined by the molybdenum blue method with direct addition of a mixed reagent to the residue. Spectrophotometric evaluation at 882 nm provides a detection limit of 10 ng P ml^?1 with a precision better than 3%. Arsenic is determined by reducing As(V) to electroactive As(III) on addition of sulphite in 2 M hydrochloric acid. Differential-pulse polarography of this solution provides a precision of 2% and a detection limit of 20 ng As ml^?1.     

Room-temperature,phosphorimetric determination of the beta-blocking agent pindolol in pharmaceutical tablets,urine and blood serum

It is already recognised that heavy-atom-induced, room-temperature phosphorescence can be used to determine pindolol in pharmaceutical samples and biological fluids. We describe here a new, simple, rapid and selective development of this technique. The phosphorescence signals derive from the interaction of pindolol with a relatively high concentration of heavy-atom salts in the presence of sodium sulphite as oxygen scavenger. Phosphorescence was registered in the presence of 1.2 M potassium iodide, 15 mM sodium sulphite and 30% v/v methanol at 450 nm, exciting at 285 nm. The detection limit was 21.1 ng mL⁻¹. The method has been successfully applied to the determination of pindolol in commercial pharmaceutical tablets, urine and blood serum.     

Determination of hydrogen sulphide and sulphur dioxide in a mixture

A method has been proposed for the determination of hydrogen sulphide and sulphur dioxide in a mixture. The method is based upon the quantitative oxidation of sulphide and sulphite with an excess of radiochloramine-T in alkaline medium /0.1N NaOH/. The released chloride activity is proportional to the total amount of sulphide and sulphite present. Addition of 1% CdSO₄ solution to the mixture of sulphide and sulphite precipitates sulphide, and sulphite in the filtrate determined by the reagent. From the difference in activities, the amount of sulphide can be calculated. This method can be employed for the determination of hydrogen sulphide and sulphur dioxide in air samples.     

Flow-injection chemiluminometric analysis of some steroids by their sensitizing effect on the bromate-sulphite reaction

The chemiluminescent oxidation of sulphite by bromate was investigated and compared with that by cerium(IV). The reaction is sensitized by various steroid hormones which can thus be determined in the ranges 0.50–20.0μg ml ¹ for cortisone; 0.50–5.00 μg ml^?1 for hydrocortisone and progesterone and 0.50–6.00 μg ml^?1 for testosterone and corticosterone.     

Flow injection on-line sorption preconcentration of platinum in a knotted reactor coupled with electrothermal atomic absorption spectrometry

A flow injection on-line sorption preconcentration method for the electrothermal AAS determination of platinum has been developed. The pyrrolidine dithiocarbamate complexes of either Pt⁴⁺ or Pt²⁺, formed in 0.7 mol L^–1 HNO₃, are on-line adsorbed on the inner walls of a PTFE knotted reactor and subsequently eluted with methanol. An enhancement factor of 112 and a detection limit (3 σ) of 10 ng L^–1 along with a sampling frequency of 21 h^–1 are achieved with a 90 s preconcentration time at a sample flow rate of 8.8 mL min^–1. The relative standard deviation is 2.5% for 0.4 μg L^–1 Pt. The method has been applied to the determination of platinum in blood samples. Received: 6 October 1997 / Revised: 26 November 1997 / Accepted: 3 December 1997     

Determination of quinine and quinidine by continuous-flow chemiluminescence

A rapid and precise continuous-flow method is described for the determination of quinine and quinidine (5.00–500 μg ml^?1) which is based on the sensitizing effect of the compounds on the chemiluminescent oxidation of sulphite by cerium(IV). When applied to tablets, the procedure is relatively free from interferences from common excipients. The results obtained for the assay of commercial formulations compared well with those obtained by an official method and demonstrated good accuracy and precision.     

Photometric titration of total iodine at trace levels in concetrated chloride solutions

The method is based on reduction of total iodine (10^?7?10^?5 M), to iodide with sulphite in acidic solution. The excess of sulphur dioxide is removed by bubbling with nitrogen, and the resulting solution is titrated spectrophotometrically with a standard solution of iodate, the absorbance being measured at 230 nm. Some Italian table salts, iodized or common, were analyzed for their iodide and total iodine content.     

Determination of formaldehyde by flow injection analysis with spectrophotometric detection exploiting brilliant green-sulphite reaction

A method for the determination of formaldehyde by flow injection analysis with spectrophotometric detection is proposed, based on retarding the reaction between brilliant green and sulphite by the addition of formaldehyde; this was investigated for formaldehyde quantification in extracts from wood-based panels. For the first time, a heating step was explored, providing a sample throughput of 50 analyses per hour, with a limit of detection of 0.02 mg L^?1 and linearity of 0.20–3.0 mg L^?1, which was adequate for the expected range of formaldehyde concentration in the extracts. The mean recovery observed for actual samples was in the range of 92–106 %, with a maximum relative standard deviation of 6.0 %. The paired t-test revealed no significant difference between this method and the official Nash method, demonstrating an appropriate accuracy and precision; the method is proposed as a simple, fast and inexpensive alternative for the routine determination of formaldehyde in an aqueous medium.