Determination of p-nitroaniline by the tartrate-acetone-Mn2+-KBrO3-H2SO4 double organic substrate oscillating system using non-equilibrium stationary state

This paper described the determination of p-nitroaniline in a double organic substrate oscillating system of tartrate-acetone-Mn²⁺-KBrO₃-H₂SO₄. Under the optimum conditions, temperature was chosen as a control parameter to design the bifurcation point and proposed a convenient method for determination of p-nitroaniline. Results showed that the system consisting of 3.5 mL 0.06 mol L⁻¹ tartrate, 4.0 mL 0.7 mol L⁻¹ H₂SO₄, 1.5 mL 1.5×10⁻⁴ mol L⁻¹ MnSO₄, 4.0 mL 0.4 mol L⁻¹ acetone and 7.0 mL 0.05 mol L⁻¹ KBrO₃ was very sensitive to the surrounding at 33.5°C. A good linear relationship between the potential difference and the negative logarithm concentration of p-nitroaniline was obtained to be in the range of 2.50×10⁻⁷∼3.75×10⁻⁵ mol L⁻¹ with a lower detection limit of 2.50×10⁻⁸ mol L⁻¹.      

Visual spectroscopy detection of triclosan

The azo coupling reaction with 2-aminonaphthalene-4,8-disulfonic acid (I) was used to develop a new cheap and rapid method of triclosan (II) determination in hygiene products. The calibration graph was linear in the range of 2.0−100 × 10⁻⁶ mol L⁻¹. The detection limit was 2.0 μmol L⁻¹.     

Electrochemical determination of ascorbic acid using the poly-cysteine film-modified electrode

A poly(L-cysteine) thin film was prepared onto electrode surface via electropolymerization. In pH 7.0 phosphate buffer, L-cysteine was oxidized during the cyclic potential sweep between −0.60 and 2.00 V, forming a thin film at the glassy carbon electrode (GCE) surface. The electrochemical behaviors of ascorbic acid at the bare GCE and the poly(L-cysteine) film-coated GCE were investigated. The oxidation peak potential of ascorbic acid shifts to more negative potential at the poly(L-cysteine) film-modified GCE. Moreover, the oxidation peak current significantly increases at the poly(L-cysteine) film-modified GCE. These phenomena indicate that poly(L-cysteine) film shows highly-efficient catalytic activity to the oxidation of ascorbic acid. Based on this, a sensitive and simple electrochemical method was proposed for the determination of ascorbic acid. The oxidation peak current of ascorbic acid is proportional to its concentration over the range from 1.0 × 10⁻⁶ to 5.0 × 10⁻⁴ mol l⁻¹. The limit of detection is evaluated to be 4.0 × 10⁻⁷ mol l⁻¹.     

Determination of vitamin B<Subscript>1</Subscript> in seawater and microalgal fermentation media by high-performance liquid chromatography with fluorescence detection

A highly sensitive high-performance liquid chromatographic method with fluorescence detection has been developed for determination of vitamin B₁. Vitamin B₁ was converted into a fluorescent compound by treatment with hydrogen peroxide–horseradish peroxidase and the derivative was subsequently analyzed by HPLC on a Waters Spherisorb ODS2 column (250 mm×4.6 mm ID, 5 μm) with 40:60 methanol–pH 8.5 acetate buffer solution as mobile phase and fluorescence detection at 440 nm (with excitation at 375 nm). The calibration graph was linear from 5.00×10⁻¹⁰ mol L⁻¹ to 5.00×10⁻⁷ mol L⁻¹ for vitamin B₁ with a correlation coefficient of 0.9991 (n=9). The detection limit was 1.0×10⁻¹⁰ mol L⁻¹. The method was successfully used for determination of vitamin B₁ at pg mL⁻¹ levels in microalgal fermentation media and seawater after solid-phase extraction. Recovery was from 89 to 110% and the relative standard deviation was in the range 1.1 to 4.3%.     

Simultaneous determination of phenylenediamine isomers and dihydroxybenzene isomers in hair dyes by capillary zone electrophoresis coupled with amperometric detection

The simultaneous determination of three isomers of phenylenediamines (o, m, and p-phenylenediamine) and two isomers of dihydroxybenzenes (catechol and resorcinol) in hair dyes was performed by capillary zone electrophoresis coupled with amperometric detection (CZE–AD). The effects of working electrode potential, pH and concentration of running buffer, separation voltage, and injection time on CZE–AD were investigated. Under the optimum conditions the five analytes could be perfectly separated in 0.30 mol L⁻¹ borate–0.40 mol L⁻¹ phosphate buffer (pH 5.8) within 15 min. A 300 μm diameter platinum electrode had good responses at +0.85 V (versus SCE) for the five analytes. Their linear ranges were from 1.0 × 10⁻⁶ to 1.0 × 10⁻⁴ mol L⁻¹ and the detection limits were as low as 10⁻⁷ mol L⁻¹ (S/N = 3). This working electrode was successfully used to analyze eight kinds of hair dye sample with recoveries in the range 91.0–108.0% and RSDs less than 5.0%. These results demonstrated that capillary zone electrophoresis coupled with electrochemical detection using a platinum working electrode as detector was convenient, highly sensitive, highly repeatable and could be used in the rapid determination of practical samples. Figure Electropherograms obtained from 10 mg mL⁻¹ hair dye sample solutions at a platinum working electrode under optimum CZE–AD conditions: (a) natural black (I), (b) golden: (1) p-phenylenediamine, (2) m-phenylenediamine, (3) o-phenylenediamine, (4) resorcinol, and (5) catechol     

Analysis of Terbumeton and its Major Metabolites by SPE and DAD-HPLC in Soil Bulk Water

A rapid and inexpensive method for simultaneous quantification of terbumeton (TER), and its major potential metabolites (TED; terbumeton-desethyl, TOH; terbumeton-2-hydroxy and TID; terbumeton-deisopropyl) in soil bulk water (SBW) samples is proposed. The analytical method involves extraction–concentration from SBW samples using a graphitized carbon black (GCB) cartridge followed by their separation–detection by reversed-phase high-performance liquid chromatography analysis using a C₁₈ column and a diode array detector. A mobile phase of acetonitrile−0.005 mol L⁻¹ phosphate buffer (pH 7.0) (35:65, v/v) at a flow rate of 0.8 mL min⁻¹ in isocratic elution mode has been used. After optimization of the extraction and separation conditions, this method can be used for the simultaneous determination of investigated compounds in the range of the international limits of 0.1 μg L⁻¹. For TER the detection limit was 0.009 μg L⁻¹ and it was 0.100, 0.550, and 0.480 μg L⁻¹ for TED, TOH, and TID, respectively. The recoveries of TER, TED, TOH, and TID from SBW samples, measured at three levels of concentration range, were found to be between 48.0 and 102.0%. The intra-day precision measured by relative standard deviation (RSD) was always lower than 9.0%.     

Determination of norfloxacin in human urine by capillary electrophoresis with electrochemiluminescence detection

A fast and sensitive approach that can be used to detect norfloxacin in human urine using capillary electrophoresis with end-column electrochemiluminescence (ECL) detection of is described. The separation column was a 75-μm i.d. capillary. The running buffer was 15 mmol L⁻¹ sodium phosphate (pH 8.2). The solution in the detection cell was 50 mmol L⁻¹ sodium phosphate (pH 8.0) and 5 mmol L⁻¹ The ECL intensity varied linearly with norfloxacin concentration from 0.05 to 10 μmol L⁻¹. The detection limit (S/N=3) was 0.0048 μmol L⁻¹, and the relative standard deviations of the ECL intensity and the migration time for eleven consecutive injections of 1.0 μmol L⁻¹ norfloxacin (n=11) were 2.6% and 0.8%, respectively. The method was successfully applied to the determination of norfloxacin spiked in human urine without sample pretreatment. The recoveries were 92.7–97.9%.      

Adsorptive anodic stripping voltammetry of zirconium(IV)-alizarin red S complex at a carbon paste electrode

A sensitive adsorptive anodic stripping procedure for the determination of trace zirconium at a carbon paste electrode (CPE) has been developed. The method is based on adsorptive accumulation of the Zr(IV)-alizarin red S(ARS) complex onto the surface of the CPE, followed by oxidation of adsorbed species. The optimal experimental conditions include the use of 0.10 mol · L⁻¹ ammonium acetate buffer (pH 4.3), ARS, an accumulation potential of 0.20 V (versus SCE), an accumulation time of 2 min, a scan rate of 200 mV · s⁻¹ and a second-order derivative linear scan mode. The oxidation peak for the complex appears at 0.69 V. The peak current is proportional to the concentration of Zr(IV) over the range of 1.0 × 10⁻⁹–2.0 × 10⁻⁷ mol · L⁻¹, and the detection limit is 3 × 10⁻¹⁰ mol · L⁻¹ for a 2 min adsorption time. The relative standard deviations (n = 8) for 5.0 × 10⁻⁸ and 5.0 × 10⁻⁹ mol · L⁻¹ Zr(IV) are 3.3 and 4.8%, respectively. The proposed method was applied to the determination of zirconium in ore samples with satisfactory results.     

Study and Application of Electrochemical Behavior of Calcium-ARS on a Mercury Film Electrode

A sensitive complex absorptive wave of Ca-ARS was obtained by using differential pulse voltammetry when a mercury film glass carbon electrode was immersed in 0.1 mol L⁻¹ KOH and 4.5×10⁻⁴ mol L⁻¹ ARS solution. The peak potential obtained was −1.17 V (vs Ag-AgCl). The peak current was proportional to the concentration of calcium in the range of 5.0×10⁻⁸−4.2×10⁻⁵ mol L⁻¹. The detection limit was 2.0×10⁻⁸ mol L⁻¹. This method was applied successfully to determining traces of calcium in blood serum. The electrochemical behavior of the system was also studied by cyclic voltammetry, and the experiment results showed that the electrode process was an irreversible absorptive with two electrons participating. Translated from Journal of Beijing Normal University (Natural Science Edition), 2005, 41(2) (in Chinese)     

Determination of sulfanilamide based on the Mn(II)-catalyzed oscillating chemical reaction

A convenient and sensitive method for determination of sulfanilamide (SNA) was described based on the Mn(II)-catalyzed oscillating chemical reaction. Under optimum conditions, a linear relationship existed between the changes of oscillating period or amplitude and the negative of logarithm of SNA concentration in the range of 4.27 × 10⁻⁸ mol ·L⁻¹ ∼ 7.41 × 10⁻⁶ mol ·L⁻¹ (RSD, 0.85%) and 9.33 × 10⁻⁸ mol ·L⁻¹ ∼ 3.02 × 10⁻⁶ mol ·L⁻1 (RSD, 1.08%), respectively. The lower limit of detection was found to be 2.69 × 10⁻⁸ mol ·L⁻¹ and 6.03 × 10⁻⁸ mol ·L⁻¹, respectively.      

Time-resolved chemiluminescent analysis of hydralazine in pharmaceuticals

A new analytical method is proposed for determination of hydralazine (HZ) in pharmaceuticals—measurement of the chemiluminescence (CL) emitted after reaction with phosphoric-acidified KMnO₄. The novelty of this method is the recording of the whole CL–time profile. Such a recording is possible by use of a CL-detector operating in tandem which enables the reactants to be mixed in the measurement cell only and, therefore, the CL is reaction monitored from beginning. At the precise time the pump is stopped signal recording is triggered and so CL evolution is recorded completely. The optimum chemical conditions for the determination were 0.8 mol L⁻¹ formaldehyde, 0.3 mmol L⁻¹ KMnO₄, 4.0 mol L⁻¹ H₃PO₄, and a total flow of 0.37 mL s⁻¹. Two calibration graphs were plotted, CL intensity and area under the profile curve against HZ concentration. Exhaustive statistical analysis provided very interesting results, for example, accordance with Clayton’s theory, detection limit below 0.2 μg mL⁻¹, and linear calibration ranges from 0.2 to 5.0 μg mL⁻¹. This method was successfully applied to the determination of HZ in pharmaceuticals. Because they are usually formulated in association with diuretics and β-blockers, the method was used for analysis of HZ in pharmaceuticals that contained either HZ only or HZ with other hypotensive substances. Obtained and nominal content were approximately the same and experimental Student t values indicated there were no significant differences between the values.     

Determination of alkaloids in Corydalis yanhusuo using hollow-fibre liquid phase microextraction and high performance liquid chromatography

Hollow fibre based liquid phase microextraction (HF-LPME) with high performance liquid chromatography (HPLC) was developed for the determination of alkaloids in Corydalis yanhusuo. Three alkaloids (protopine, tetrahydropalmatine, tetrahydroberberine) were extracted from a 10 mL alkaline sample (donor phase) to an organic phase impregnated in the pores of the hollow fibre, and then, they were extracted to an acidic solution (acceptor phase) in the lumen of the fibre. The extract was determined directly by HPLC. Parameters affecting the HF-LPME include the organic solvent, pH of the donor and the acceptor phase, the extraction time and the stirring speed were investigated systematically. To minimize the error of the injection, palmatine was added as an internal standard (I.S.). Under optimal conditions, calibration curves were obtained in the range of 0.1–1.0 mg L⁻¹ with a reasonable linearity (r ² > 0.993) and the limits of detection (LODs) ranged between 10.0 × 10⁻³ mg L⁻¹ and 13.7 × 10⁻³ mg L⁻¹. Additionally, enrichment factors with 100 to 184-fold were obtained. The method was then applied to the crude extract of Corydalis yanhusuo successfully.     

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°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 × 10⁻¹⁰ to 5 × 10⁻⁸ mol L⁻¹. The relative standard deviation for determination of Cr(VI) at a concentration of 1 × 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 × 10⁻¹⁰ mol L⁻¹. The proposed method was successfully applied to Cr(VI) determination at trace levels in soil samples.     

Development of a novel luminol chemiluminescent method catalyzed by gold nanoparticles for determination of estrogens

It has been found that gold nanoparticles (nano-Au) enhance the chemiluminescence (CL) of the luminol–hydrogen peroxide system and that estrogens inhibit these CL signals in alkaline solution. CL spectra, UV–visible spectra, X-ray photoelectron spectra (XPS), and transmission electron microscopy (TEM) were used to investigate the mechanism of the CL enhancement. On the basis of the inhibition, a flow-injection CL method has been established for determination of three natural estrogens. Under the optimized conditions, the linear range for determination of the estrogens was 0.07 to 7.0 μmol L⁻¹ for estrone, 0.04 to 10 μmol L⁻¹ for estradiol, and 0.1 to 10 μmol L⁻¹ for estriol. The detection limits were 3.2 nmol L⁻¹ for estrone, 7.7 nmol L⁻¹ for estradiol, and 49 nmol L⁻¹ for estriol, with RSD of 2.9, 2.6, and 1.8%, respectively. This method has been used for analysis of estrogens in commercial tablets and in urine samples from pregnant women.     

Flow injection spectrofluorimetric determination of iron(III) in water using salicylic acid

A simple and fast flow injection fluorescence quenching method for the determination of iron in water has been developed. Fluorimetric determination is based on the measurement of the quenching effect of iron on salicylic acid fluorescence. An emission peak of salicylic acid in aqueous solution occurs at 409 nm with excitation at 299 nm. The carrier solution used was 2 × 10⁻⁶ mol L⁻¹ salicylic acid in 0.1 mol L⁻¹ NH₄⁺/NH₃ buffer solution at pH 8.5. Linear calibration was obtained for 5–100 μg L⁻¹ iron(III) and the relative standard deviation was 1.25 % (n = 5) for a 20 μL injection volume iron(III). The limit of detection was 0.3 μg L⁻¹ and the sampling rate was 60 h⁻¹. The effect of interferences from various metals and anions commonly present in water was also studied. The method was successfully applied to the determination of low levels of iron in real samples (river, sea, and spring waters).     

Simultaneous determination of oxalate, thiosulfate, and thiocyanate in urine by ion-exclusion chromatography with electrochemical detection

Summary A sensitive ion-exclusion chromatographic method has been developed for determination of oxalate, thiosulfate, and thiocyanate. The method is based on separation of these anions on a polymethacrylate-based, weakly acidic cation-exchange resin (TSKgel OApak-A) and detection by means of a glassy carbon (GC) electrode electrochemically modified with polyvinylpyridine (PVP), palladium, and iridium oxide (PVP/Pd/IrO₂). The electrochemical behavior of oxalate, thiosulfate, and thiocyanate at this chemically modified electrode (CME) have been investigated by cyclic voltammetry. The results indicated that electrocatalytic oxidation of these anions by the electrode was efficient and that the sensitivity, stability, and lifetime of the electrode were relatively high. Combined with ion-exclusion chromatography the PVP/Pd/IrO₂ electrode was used as the working electrode for amperometric detection of these anions. All linear ranges were over two orders of magnitude and detection limits, defined asS/N=3, were 9.0×10⁻⁷ mol L⁻¹ for oxalate, 6.7×10⁻⁷ mol L⁻¹ for thiosulfate, and 5.6×10⁻⁷ mol L⁻¹ for thiocyanate. Correlation coefficients were all>0.998. Coupled with microdialysis sampling the method has been successfully applied to the determination of oxalate, thiosulfate, and thiocyanate in urine.     

Optimization of analytical procedures for the simultaneous voltammetric determination of total Hg(II) in presence of Cu(II) in environmental matrices

The present work reports the critical comparison about the employment of three different supporting electrolytes (0.1 mol L⁻¹ HClO₄, 0.01 mol L⁻¹ EDTA-Na² + 0.06 mol L⁻¹ NaCl + 2.0 mol L⁻¹ HClO₄ and 0.1 mol L⁻¹ KSCN + 0.001 mol L⁻¹ HClO₄) and their instrumental and chemical optimisation for the simultaneous voltammetric determination of total mercury(II) and copper(II) in sediments and sea water at gold electrode, especially discussing the reciprocal interference problems.     

Design of a field flow system for the on-line spectrophotometric determination of phosphate, nitrite and nitrate in natural water and wastewater

This study describes the design and optimisation of a field flow system for the in-situ collection and on-line determination of phosphate, nitrate and nitrite by flow injection analysis-spectrophotometry. The method is based on the initial determination of phosphate as its phosphoantimonylmolybdenum blue complex which is then oxidized on-line by nitrite and the decrease in absorbance is monitored at 880 nm. Nitrate is determined as the difference between total and initial nitrite content in a separate flow after reduction to nitrite in a cadmium reductive column. The calibration curves were linear in the range 0–2.00 mg L⁻¹ P-phosphate, 0–10.00 mg L⁻¹ nitrite and 0–7.00 mg L⁻¹ nitrate with correlation coefficients of 0.9979, 0.9993 and 0.9995, respectively. The detection limits, calculated as 3S/N, were 0.15 mg L⁻¹ for P-phosphate, 0.17 mg L⁻¹ for nitrite and 0.09 mg L⁻¹ for nitrate. The reproducibility was below 3.0% (n = 7). Method validation in the analysis of natural water and wastewater samples revealed that it can efficiently be applied to the determination of the target analytes, with recoveries in the range of 92–108%. Correspondence: Athanasios G. Vlessidis, Laboratory of Analytical Chemistry, Department of Chemistry, University of Ioannina, Ioannina 45110, Greece     

A novel kinetic-spectrophotometric method for determination of nitrites in water

A simple, selective and sensitive kinetic method for the determination of nitrite in water was developed. The method is based on the catalytic effect of nitrite on the oxidation of methylene blue (MB) with bromate in a sulfuric acid medium. During the oxidation process, absorbance of the reaction mixture decreases with the increasing time, inversely proportional to the nitrite concentration. The reaction rate was monitored spectrophotometrically at λ = 666 nm within 30 s of mixing. Linear calibration graph was obtained in the range of 0.005–0.5 μg mL⁻¹ with a relative standard deviation of 2.09 % for six measurements at 0.5 μg mL⁻¹. The detection limit was found to be 0.0015 μg mL⁻¹. The effect of different factors such as acidity, time, bromate concentration, MB concentration, ionic strength, and order of reactants additions is reported. Interference of the most common foreign ions was also investigated. The optimum experimental conditions were: 0.38 mol L⁻¹ H₂SO₄, 5 × 10.4 mol L⁻¹ KBrO₃, 1.25 × 10.5 mol L⁻¹ MB, 0.3 mol L⁻¹ sodium nitrate, and 25°C. The proposed method was conveniently applied for the determination of nitrite in spiked drinking water samples.     

Highly sensitive spectrofluorimetric determination of trace amounts of lecithin

A new spectrofluorimetric method was developed for the determination of trace amounts of lecithin using the ciprofloxacin (CIP)–terbium (Tb³⁺) ion complex as a fluorescent probe. In a buffer solution at pH=5.60, lecithin can remarkably reduce the fluorescence intensity of the CIP–Tb³⁺ complex at λ=545 nm. The reduced fluorescence intensity of the Tb³⁺ ion is proportional to the concentration of lecithin. Optimum conditions for the determination of lecithin were also investigated. The linear range and detection limit for the determination of lecithin were 1.0×10⁻⁶–3.0×10⁻⁵ mol L⁻¹ and 3.44×10⁻⁷ mol L⁻¹, respectively. This method is simple, practical, and relatively free of interference from coexisting substances. Furthermore, it has been successfully applied to assess lecithin in serum samples.