Spectrophotometric flow injection determination of formetanate and m-aminophenol in water after reaction with p-aminophenol

An automated procedure has been developed for the determination of formetanate and its metabolite m-aminophenol (MAP) in water samples. MAP can be selectively determined in the presence of formetanate by direct on-line reaction with p-aminophenol and spectrophotometric measurement of the absorbance at 576 nm in the presence of KIO(4), as oxidizing agent. The method has a limit of detection of 5 x 10(-7)M, it provides a recovery percentage from 95 to 104% and permits one to carry out 120 measurements/hr. The spectrophotometric determination of formetanate must be carried out after a previous hydrolysis to MAP. To determine formetanate in the presence of MAP, two steps are necessary. Firstly, the MAP content is selectively determined as has been mentioned above. After that, the sample is treated with 0.05M NaOH at 90' degrees C, to hydrolyze the formetanate to MAP, and then the sum of both is determined spectrophotometrically. The difference between the results obtained in each step gives the formetanate concentration. The developed procedure for the determination of formetanate provides a sensitivity of 1070 absorbance units mol(-1) l and a limit of detection of 1.9 x 10(-7)M, which corresponds to 50 mug/l of formetanate hydrochloride. The method has been applied to the analysis of natural water samples fortified with formetanate and MAP, and formetanate has also been quantitatively recovered in irrigation waters at a concentration level of 1.9 x 10(-6)M which corresponds to 500 mug/l. On the other hand, working in the stopped-flow mode, for a reaction time of 100 sec, the sensitivity of the formetanate determination can be increased to 4642 absorbance units mol(-1) l but the limit of detection remains of the order of 44 mug/l.     

Catalytic Spectrophotometric Determination of Bromide Based on the Diphenylcarbazide–Chromium(VI)–Iodate Reaction

A new catalytic spectrophotometric method for the determination of bromide is proposed. Diphenylcarbazide reacts with chromium(VI) ions in an acid medium to give a violet complex. The method is based on the bromide-catalyzed oxidation of this violet complex by iodate followed by measuring the color change at = 542 nm spectrophotometrically. The reaction starts after an induction period. Bromide ions catalyze this reaction, so that the induction period is decreased by the addition of Br^–. The derivative of the absorbance with respect to time was calculated. The maximum absorbance difference (A _m) and thetime taken to reach the maximum difference (t _m) were measured from the derivative curve. These values are used as the measured parameters for bromide determination. Under optimum conditions bromide can be determined in the range of 0.5–8 g/mL. The detection limit is 0.25 g/mL, and the relative standard deviation for ten replicate measurements of 1 g/mL of bromide is 1.57%. The method was applied to the determination of bromide in the Persian Gulf water.     

Flow injection-spectrophotometric determination of cresol compounds in water by reaction withp-aminophenol

A spectrophotometric method has been developed for the simultaneous determination ofo-cresol andm-cresol in water by reaction withp-aminophenol (PAP). Three different methodologies have been assayed; (i) batch analysis, after reaction in an alkaline medium in the presence of dissolved molecular oxygen as oxidizing agent, (ii) a stopped-flow procedure, carried out in the presence of KIO₄ and (iii) a flow injection method based on the same approach. The batch procedure requires 22 min for the full development of colour witho-cresol and 12 min form-cresol. In the stopped-flow mode, using KIO₄ and a reaction time of 12 min, better sensitivity can be obtained for both compounds and limits of detection of 10 g 1^–1 foro-cresol and 30 g 1^–1 form-cresol were found. The flow injection method has a lower sensitivity but permits more than 80 injections per hour. Based on the different maximum absorbance wavelengths obtained for the reaction products of PAP witho-cresol (614 nm) andm-cresol (632 nm), both compounds can be simultaneously determined in water samples and recoveries of 90 to 115% were found in spiked water samples of different types.     

Ascorbic acid as a new reductant in the thiocyanate method for the spectrophotometric determination of rhenium

Summary A spectrophotometric determination of rhenium is based on its reduction with ascorbic acid in the presence of thiocyanate. The orange-yellow complex is extracted into isoamyl alcohol and the absorbance measured at 430 nm. Various foreign ions do not interfere. Molar absorptivity and Sandell's sensitivity are 31162.79 l/mol/cm and 0.0059 g/cm², respectively.     

Spectrophotometric determination of traces of nitrite with rhodamine 6 G

A simple and highly selective spectrophotometric method is described for the determination of nitrite. The method is based on the measurement of decrease in absorbance at 525 nm of rhodamine 6 G in sulphuric acid medium. The decrease in absorbance is instantaneous on addition of nitrite and remains stable for 2 h. Linear calibration graph passing through the origin was obtained in the range 0.01–0.6 g/ml nitrite. The method is free from interference of Cu²⁺, Fe³⁺ and SO ₃ ^2– which normally interfere in other procedures. The method was applied successfully to the determination of nitrite in well and sea water samples and in KNO₃, NaNO₃, table salt, sugar and milk powder samples.     

A new cloud-point preconcentration approach for the spectrophotometric determination of p-aminophenol in the presence of paracetamol with 2-(2-Hydroxyphenyl)-1H-benzimidazole as a coupling reagent

A preconcentration and determination method for trace p-aminophenol (PAP) in paracetamol was developed. Cloud-point extraction (CPE) was employed for the preconcentration of p-aminophenol prior to spectrophotometric determination using Triton X-100 (TX-100) as an extractant. The determination is based on the reaction of p-aminophenol with 2-(2-hydroxyphenyl)-1H-benzimidazole (HPBI) at room temperature in the presence of an oxidant to produce indophenol blue dye. The dye formed is subsequently entrapped in micelles of the surfactant TX-100. The surfactant-rich phase shows maximum absorbance at 650 nm and the proposed method is linear in the 0.1 to 5.0 mg mL⁻¹ concentration range. By preconcentrating 10 mL of the sample solution, a detection limit as low as 55 ng/mL was obtained after a single-step extraction and the experimental concentration factor achieved for this method was found to be 10. The stoichiometric composition of the dye is 1: 1 (PAP: HPBI). Some parameters such as HPBI, KIO₄, Na₂CO₃, and TX-100 concentration, extraction temperature, incubation, and centrifugation time, and the sample volume were investigated in detail. The established procedure was successfully adopted for the determination of p-aminophenol in the presence of paracetamol in various pharmaceutical preparations. The text was submitted by the authors in English.     

Determination of clotiazepam by HPLC with spectrophotometric and amperometric detection

Summary Spectrophotometric and amperometric detectors were compared for the determination of clotiazepam by HPLC. Methanol-water (6040) containing 0.01 mol/l ammonium acetate and methanol-water (7030) containing 0.01 mol/l acetate buffer pH 4 were used as mobile phase in the spectrophotometric and amperometric detection, respectively. The minimum detectability for the spectrophotometric detection was 20 ng injected and the method was applied for the determination of clotiazepam in serum, whereas for the amperometric detection a limit of detection of 2.5 g injected was obtained, using this technique for clotizepam determination in tablets.

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Bestimmung von Clotiazepam durch HPLC mit spektralphotometrischer und amperometrischer Detektion

     

Determination of phenol, m-, o- and p-cresol, p-aminophenol and p-nitrophenol in urine by high-performance liquid chromatography

A method for the biological monitoring of human exposure to aromatic hydrocarbons, nitrocompounds, amines and phenols has been developed. Phenol, cresols, p-aminophenol, p-nitrophenol and their glucorono- or sulpho-conjugates, were quantified by HPLC; 4-chlorphenol was added as internal standard. After enzymatic hydrolysis, the free compounds were extracted with an organic solvent and analyzed by an isocratic HPLC Perkin Elmer system at ambient temperature and at a flow-rate of 1 ml/min. The column was a reversed-phase Pecosphere 3 x 3 C18 Perkin Elmer; the mobile phase was a 30:70:0.1 (v/v/v) methanol-water-orthophosphoric acid mixture and the chromatogram was monitored at 215 nm. Identification was based on retention time and quantification was performed by automatic peak height determination, corrected for the internal standard. The recovery was ca. 95% for phenol and cresols; 90% for p-nitrophenol; 85% for p-aminophenol; the coefficients of variance were less than 6% within analysis (n = 20) and less than 10% between analysis (n = 20). The detection limits, at a signal/noise ratio of 2, were 0.5 mg/l for phenol and cresols and 1 mg/l for p-aminophenol and p-nitrophenol.     

Flow-injection spectrophotometric determination of dipyrone in pharmaceutical formulations using a solid-phase reactor with copper(II) phosphate

In this work, a flow-injection spectrophotometric method for dipyrone determination in pharmaceutical formulations was developed. Dipyrone sample solutions were injected into a carrier stream of deionized water and the reaction was carried out in a solid-phase reactor (12 cm, 2.0 mm i.d.) packed with Cu₃(PO₄)_2(s) entrapped in a matrix of polyester resin. The Cu(II) ions were released from the solid phase reactor by the formation of Cu(II)-(dipyrone)_n complex. When the complex is released, it reacts with 0.02% m/v alizarin red S in deionized water to produce a Cu(VABO₃)₃ complex whose absorbance was monitored at 540 nm. The calibration graph was linear over the range 5.0×10^?5–4.0×10^?4 mol L^?1 with a detection limit of 2.0×10^?5 mol L^?1 and relative standard deviation for 10 successive determinations of 1.5% (2.0×10^?4 mol L^?1 dipyrone solution). The calculated sample throughput was 60 h^?1. The column was stable for at least 8 h of continuous use (500 injections) at 25°C. Pharmaceutical formulations were analyzed and the results from an official procedure measurement were compared with those from the proposed FIA method in order to validate the latter method.      

Bestimmung von Alkali- und Erdalkaliionen in Regenwasserproben mit der Ionen-Chromatographie

Summary Alkali and alkaline earth ions in rain water can be determined by ion chromatography (IC) without preconcentration. The detection limits for alkali ions are between about 0.05 and 0.15 mol/l and those for alkaline earth ions between about 0.2 and 0.6 mol/l. The main advantages of IC are: very small sample volumes are sufficient; the simultaneous determination of the alkali ions or the alkaline earth ions requires less than 30 min; NH ₄ ⁺ ions can also be determined. The results are compared with those obtained by flame AAS and AES-ICP.     

m-Aminophenylarsonic Acid as an Analytical Form for the Photometric Determination of Phenol in Water

The azocoupling reaction of diazonium salts of o- and m-aminophenylarsonic acids with phenol was studied. On the basis of quantum-chemical calculations of the reagents, conformation analysis of resulting azo compounds, and experimental data, it was found that the meta isomer of aminophenylarsonic acid is of practical interest as an analytical reagent for the determination of phenol. The advantage of the proposed reagent is a high stability of the diazonium salt. A procedure was developed for the spectrophotometric determination of phenol in water at a level of 0.06 g/mL. The error in the determination is no higher than 5.5%.     

Amperometrische Biosensoren zur Bestimmung von Cholin und Acetylcholin

Summary Amperometric biosensors for the determination of choline and acetylcholine were constructed by coupling immobilized choline oxidase or choline oxidase and acetylcholinesterase membrane with an electrode. H₂O₂ which results from the oxidase reaction is anodically monitored. The sensors' response is linear in the concentration range of 1 to 300 mol/l choline and 1 to at least 660 mol/l acetylcholine. The sample frequency is 60 h^–1 with an imprecision of less than 2% for both choline and acetylcholine. The longtime-stability of the sensors was tested to be more than 22 days. The influence of the reversible inhibitor NaF on the bienzyme-electrode response was investigated.     

Spectrophotometric and titrimetric determination of gallium in minerals and ores using semimethylthymol blue

The composition, overall stability constant and molar absorptivity of the chelate of gallium(III) ion with semimethylthymol blue, SMTB, were determined spectrophotometrically in acetate buffer (pH 4.5–5). A violet Ga(SMTB) chelate was formed with logarithmic overall stability constant of 18.0±0.1 (I=0.1) and molar absorptivity of 4.25×10⁴l mol^–1cm^–1 (_max 580 nm). SMTB is proposed as a new reagent for the spectrophotometric determination of micro-molar amounts of gallium(III). The colour development depends on time, temperature, pH and buffer species. The interference of different cations, anions and organic acids on gallium(III) determination was also investigated. Beer's law was obeyed for 3.5–31.3 gGa(III)/25ml (0.14–1.25 g ml^–1). SMTB was used for the spectrophotometric determination of gallium in different grade minerals and ores and the results were of acceptable error and relative standard deviation. Comparison between the two suggested methods and atomic absorption spectrometry for Ga(III) determination was carried out.     

Extraction of palladium from nitric acid medium and its spectrophotometric determination using arsenazo III

Summary Di-octyl sulphoxide in xylene was successfully employed for extracting palladium from 0.5 to 1.5 mol/l nitric acid medium. The extracted species was found to be Pd(NO₃)₂·2DOSO. The palladium was back extracted into a mixture of 2 mol/l sodium carbonate and 0.05 mol/l ammonia. The recovery was found to be quantitative. A spectrophotometric method using Arsenazo III was developed in nitric acid medium for the determination of palladium. The colour development was found to be maximum in the acid range of 2.5 to 5 mol/l. Beer's law was found to be obeyed in 1 to 100 g range of palladium. The molar extinction coefficient was found to be 2.26×10⁴ l/mol/cm. The RSD obtained at 16 g of palladium was 5%.     

Rapid method for the spectrophotometric determination of sulphate in surface water using ion-exchange separation and the sulphate and chlorophosphonazo III (CPA III)-Ba2+ complex reaction

Summary A rapid spectrophotometric method for the determination of SO ₄ ^2– in surface water is reported. It is based on the reaction of CPA III-Ba²⁺ complex with SO ₄ ^2– in acidic medium in the presence of ethanol. Beer's law is obeyed up to 120 g of SO ₄ ^2– in 25 ml solution. The molar absorptivity is 6.3×10³ l · mol^–1 · cm^–1 at 500 nm, and the coefficient of variation varies from 1.85% to 3.10%. The absorbance remains stable for at least 24 h and interfering ions are separated by strongly acidic cation-exchange resin.Among the methods for determining micro amounts of sulphate in water, the following can be mentioned: An indirect method using a suspension of barium chloranilate [1–3] or barium chromate [4–6] and the classical turbidimetric (BaSO₄) method [7, 8]. It is well known that the latter is more convenient, but of rather low precision and sensitivity. The formers are tedious and time-consuming, because they require to separate the precipitation of BaSO₄.In 1985, we have used CPA III for the indirect spectrophotometric determination of sulphate in soils, but the procedure is not fast [9]. It is the purpose of this work to propose a more convenient method for the spectrophotometric determination of sulphate in water.

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Schnelle spektralphotometrische Sulfatbestimmung in OberflÄchenwasser aufgrund von Ionenaustausch und der Reaktion von Sulfat mit dem Chlorophosphonazo(III)-Ba-Komplex

     

One-step solid-phase UV spectrophotometric method for phenol determination in vaccines: Development and quality assessment

A solid-phase spectrophotometric technique was used to develop very sensitive, inexpensive, onestep procedure for determination of phenol (UV-SPS procedure). The proposed procedure is based on simultaneous sorption of phenol on an anion exchanger QAE Sephadex A-25 (40 mg), within 10 min at pH 11 and measurement of the intrinsic absorbance of the solid phase in a 1-mm cell at 289 and 500 nm, without previous derivatization. The optimum experimental conditions were investigated and comprehensive quality control of the new procedure was carried out using a prevalidation strategy accompanied by a very informative system of diagnosis. The UV-SPS procedure is characterized with both ideal calibration and analytical evaluation function within analyte working range from 0.3 to 3.0 μmol (6.0 to 60.0 nmol/mL). Random deviations (from ±0.3 to ±5.0%) and systematic deviations (from ?3.0 to +4.9%) confirmed the favourable precision and accuracy of the UV-SPS method. Evaluated limiting values (L _D = 1.0 μM, L _Q = 6.0 μM) showed that this method enables determination of very low levels of phenol. The sensitivity of UV-SPS procedure is 50 times higher than that provided by the corresponding method in solution. The UV-SPS method was successfully applied to the determination of phenol in vaccines (recovery 95.6–103.4%).     

Ionic Strength Dependence of Formation Constants and Complexation of Glutamine with Dioxovanadium(V)

The dependence of L-glutamine protonation and its complexation with dioxovanadium(V) on ionic strength (I) is reported in sodium perchlorate solution as a background salt. The measurements have been performed at 25 ± 0.1°C and various ionic strengths in the range 0.1 to 1.0 mol/l, using a combination of potentiometric and spectrophotometric techniques. The overall analysis of the present and the previous data dealing with the determination of stability constants at different ionic strengths allowed us to obtain a general equation, by which a formation constant determined at a fixed ionic strength can be calculated, with a good approximation, at another ionic strength, if 0.1 I 1.0 mol/l (NaClO₄).     

Spectrophotometric determination of chromium(VI) with ferron

Chromium(VI) gives a pink coloured solution in chloroform in the presence of ferron when extracted from slightly acidic medium. This reaction is used for the spectrophotometric determination of chromium by measuring the absorbance at 510 nm. Beers law is obeyed in the range of 5–70 g/ml. Most of the important metal ions do not interfere. The relative standard deviation is 2.78%.     

Broadening and shift of Ν(AH)IR bands in a series of H complexes of one base with various acids

The parameters of the IR bands for the (AH) stretching vibration (the frequencies, the widths, and partly the intensities) were measured in a series of AH ... B H complexes between one base B (ethylene oxide) and 17 various OH, NH, and CH acids in carbon tetrachloride solutions. The width _1/2 and shift =₀ ⁰– (from the frequency ₀ ⁰ of the gaseous AH) of the investigated bands amount to 530 and 740 cm^–1. A relationship close to direct proportionality between the broadening and the shift of the band for the H bond was found for all the H complexes. The relationship was insensitive to the medium and was preserved for the gaseous complex and in the undiluted ethylene oxide; it did not change greatly when was calculated from the free AH in carbon tetrachloride. This partial (with constant B) proportionality is not observed in the traditional series of acids (phenol, alcohol) with various bases, where agreement is only observed for _1/2 and . cThe electric-donating power of ethylene oxide (0.79±0.03) on the E scale (with reference to diethyl ether, E=1) was determined from the increase and shift of (AH).Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 24, No. 4, pp. 461–466, July–August, 1988.     

Simultaneous differential pulse-polarographic determination of CS2 and COS gases and its application in the analysis of dithiocarbamate fungicide residues in foods

The differential pulse-polarographic (DPP) determination of both CS₂ and COS gases, after their absorption in a methanolic piperidine reagent and the subsequent application of this technique to the residue analysis of dithiocarbamate fungicides is described. Rectilinear calibration curves for both CS₂ and COS in the respective regions of 1.5–9.2 and 2.1–12.6 mol/l were obtained. The DPP method has been successfully applied to the determination of thiram residues on apples after a hot acid hydrolysis of the fruits.