A novel method for the determination of tiopronin by using potassium ferricyanide as spectroscopic probe reagent in pharmaceutical and urine samples

In this paper, a novel method has been established to determine tiopronin using potassium ferricyanide as spectroscopic probe reagent. It has been demonstrated that Fe(III) is reduced to Fe(II) by tiopronin, and the in situ formed Fe(II) reacts with potassium ferricyanide to form soluble Prussian blue. Beer’s law is obeyed in the range of tiopronin concentration of 0.040–9.00 μg/mL at the maximal absorption wavelength of 735 nm. The linear regression equation is A = 0.0153 + 0.1605c (μg/mL) with a correlation coefficient of 0.9997 and the apparent molar absorption coefficient of 2.6 × 10⁴ L/mol cm. The detection limit is 0.030 μg/mL and RSD is 1.3%. The parameters with regard to determination have been optimized and the reaction mechanism has been discussed. This method has been successfully applied to determine tiopronin in pharmaceutical and urine samples with satisfactory results.     

Selective spectrophotometric determination of paracetamol with sodium nitroprusside in pharmaceutical and biological samples

A novel simple method to determine paracetamol with good selectivity has been established by using sodium nitroprusside as the chromogenic reagent. The experiment indicates that sodium nitroprusside can react with paracetamol in a basic solution to form a product with colored O-nitrosamines. The maximal absorption wavelength (λ_max) and the apparent molar absorption coefficient of the product are 700 nm and 3.4 × 10³ L/mol cm, respectively. A Good linear relationship is obtained between the absorbance and the concentration of paracetamol in a wide range of 0.19–96 μg/mL. The linear regression equation is A = 0.01695 + 0.02240C (μg/mL), with a correlation coefficient of 0.9993. The detection limit (3σ/κ) is 0.10 μg/mL, and the relative standard deviation (RSD) is 0.90% (n = 11). The parameters with regard to determination are optimized, and the reaction mechanism is discussed. The method has been successfully applied to the selective determination of paracetamol in pharmaceutical and biological samples.     

The use of Chromazurol S in the presence of a mixture of cationic and non-ionic surfactants for the spectrophotometric determination of iron in cereals

Simple and sensitive methods for the spectrophotometric determination of iron(III) in food, based on the formation of coloured complexes of Fe(III) with Chromazurol S (CAS) in the presence of tetradecyltrimethylammonium bromide (TTA) or octadecyltrimethylammonium chloride (ODTA) and Triton X-100 (TX100), have been developed. Optimum pH and the concentrations of CAS, TTA, ODTA, and TX100 ensuring maximum absorbance have been determined. For the Fe-CAS-TTA-TX100 system the molar absorptivity is 1.12 × 10⁵ L/(mol cm) at 650 nm; for Fe-CAS-ODTA-TX100 it is 1.35 × 10⁵ L/(mol cm) at 659.5 nm. Beer’s law was obeyed for iron concentration in the range 0.08–0.56 μg/mL for the complex Fe-CAS-TTA-TX100 and 0.08–0.64 μg/mL for Fe-CAS-ODTA-TX100. The influence of several interfering ions has been discussed. The stoichiometry of the complexes was established by applying Job’s method. The more sensitive method, based on the Fe-CAS-ODTA-TX100 system, has been applied to the determination of iron in cereals. To evaluate the accuracy of the elaborated method, the determined content of Fe was compared to the declared value as well as to the result obtained by the reference ICP-OES method.     

Catalytic kinetic spectrophotometric determination of iron with (dibromo-<Emphasis Type="Italic">p</Emphasis>-sulfonic acid arsenazo)-potassium bromate-ascorbic acid system

A new method for the determination of traces of iron was developed based on its catalytic effect on the oxidation reaction of dibromo-p-sulfonic acid-arsenazo (DBS-arsenazo, DBS-ASA) by potassium bromate in a 5.0 × 10⁻³ M sulfuric acid medium. The optimum experimental conditions for the determination of iron using iron(III)-dibromo-p-sulfonic acid-arsenazo, (DBS-ASA)-potassium bromate-ascorbic acid system and its kinetic spectrophotometric properties were studied. The absorbance difference (ΔA) is linearly related with the concentration of iron(III) over the range of 0.20–6.0 ng/mL at the maximum absorption wavelength of 520 nm and described by the equation: ΔA = 0.133c (ng/mL) — 0.0133 with a regression coefficient of 0.9966. The detection limit of the method is 0.17 ng/mL. The method has been successfully used in the determination of traces of iron in potato samples. The obtained results agree with those of atomic absorption spectrometry.     

Simultaneous separation and determination of Cu(II), Fe(III), and Pb(II) by reversed-phase ion-pair chromatography withN,N,N′, N′-ethylene-diaminetetrakis(methylenephosphonic Acid)

Summary A reversed-phase ion-pair chromatographic (RPIPC) method withN,N,N′, N′-ethylenediaminetetrakis(methylenephosphonic acid) (EDTMP) as coordinating agent has been developed for simultaneous separation and detection of Cu(II), Fe(III), and Pb(II) ions. Response is linearly dependent on amount of sample over the range 9.52–50.8 μg mL⁻¹ for Cu(II), 8.31–41.8 μg mL⁻¹ for Fe(III), and 37.3–51.8 μg mL⁻¹ for Pb(II). The method has been applied successfully to an artificial mixed-ore sample.     

Determination of Low-Level Ethylenediaminetetraacetic Acid in Water Samples by Ion Chromatography with Ultraviolet Detection

A convenient and sensitive ion chromatographic (IC) method for the analysis of ethylenediaminetetraacetic acid (EDTA) in water samples was proposed. Using a fast reversible reaction of free EDTA and metal–EDTA complexes into Fe(III)–EDTA complex in the presence of Fe(III) ions, sample solutions were applied to an ion-exchange column using a mobile phase (pH 2.3), which was composed of 100 μM Fe(III) chloride and 5 mM methanesulfonic acid. The addition of Fe(III) solution (100 μL) containing 10 mM Fe(III) chloride and 0.5 M methanesulfonic acid to the sample solution (10 mL) permitted the injection of a large volume (400 μL) of sample, which allowed for greater sensitivity. The proposed IC method gave a highly linear (r ² > 0.999) calibration curve ranging 0.005–1.0 μM EDTA and had a limit of detection of 1.5 nM. High repeatability (RSD < 2.1%) and recoveries (88–108%) were also obtained. With this method, total EDTA level in raw and drinking waters were analyzed successfully.     

Study on the interaction between diphenhydramine and erythrosin by absorption,fluorescence and resonance Rayleigh scattering spectra

In pH 4.5 Britton-Robinson(BR)buffer solution,erythrosin(ET)can react with diphenhydramine(DP)to form a 1:1 ion-association complex,which not only results in the change of the absorption spectra,but also results in the great enhancement of resonance Rayleigh scattering(RRS)and the quenching of fluorescence.Furthermore,a new RRS spectrum will appear,and the maximum RRS wavelength was located at about 580 nm.In this work,the spectral characteristics of the absorption,fluorescence and RRS,the optimum conditions of the reaction and the properties of an analytical chemistry were inves- tigated.A sensitive,simple and new method for the determination of DP by using erythrosin as a probe has been developed.The detection limits for DP were 0.0020μg/mL for RRS method,0.088μg/mL for absorption method and 0.094μg/mL for fluorophotometry.There was a linear relationship between the absorbance,RRS and fluorescence intensities and the drug concentration in the range of 0.0067-2.0, 0.29-6.4 and 0.31-3.2μg/mL,respectively.The effects of the interaction of diphenhydramine and erythrosin on the absorption,fluorescence and resonance Rayleigh scattering spectra were discussed. In light polarization experiment,the polarization of RRS at maximum wavelength was measured to be P =0.9779,and it revealed that the RRS spectrum of DP-ET complex consists mostly of resonance scat- tering and few resonance fluorescence.In this study,enthalpy of formation and mean polarizability were calculated by AM1 quantum chemistry method.In addition,the reaction mechanism and the rea- sons for the enhancement of scattering spectra and the energy transfer between absorption,fluores- cence and RRS were discussed.     

Development of a cloud point extraction and preconcentration method for chromium(III) and total chromium prior to flame atomic absorption spectrometry

A sensitive and selective method has been developed for the determination of chromium in water samples based on using cloud point extraction (CPE) preconcentration and determination by flame atomic absorption spectrometry (FAAS). The method is based on the complexation of Cr(III) ions with Brilliant Cresyl Blue (BCB) in the presence of non-ionic surfactant Triton X-114. Under the optimum conditions, the preconcentration of 50 mL of water sample in the presence of 0.5 g/L Triton X-114 and 1.2 × 10⁻⁵ M BCB permitted the detection of 0.42 μg/L chromium(III). The calibration graph was linear in the range of 1.5–70 μg/L, and the recovery of more than 99% was achieved. The proposed method was used in FAAS determination of Cr(III) in water samples and certified water samples. In addition, the developed CPE-FAAS method was also used for speciation of the inorganic chromium species after reduction of Cr(VI) to Cr(III) using a thiosulphate solution of 120 mg/L in the presence of Hg(II) ion as a stabilizer.     

Spectrophotometric determination of <Emphasis Type="Italic">L</Emphasis>-ascorbic acid in pharmaceuticals

A simple and sensitive spectrophotometric method for the determination of L-ascorbic acid with leuco crystal violet is proposed. The determination is based on the oxidation of analyte by potassium iodate. The colourless oxidation products were formed in the quantity equivalent to iodide ions. The iodide ions react with the excess of iodate ions in acidic medium, to form free iodine which oxidized leuco crystal violet (LCV) to the liberated crystal violet (CV ⁺) dye, showing maximum absorption at 588 nm. The absorbance was measured at pH of 4.1–4.2 in 1 cm cuvettes. Beer’s law was obeyed in the concentration range 0.5–4.0 μg/mL. The molar absorptivity of the coloured compound is 4.14 × 10⁴ L/mol cm for L-ascorbic acid. The analytical parameters were optimized and the method was successfully applied to the determination of L-ascorbic acid in pharmaceuticals. The results were compared with those obtained by methods proposed in Polish Standard.     

Determination of trace dimethoate in milk and river water by kinetic spectrophotometry using malachite green and potassium periodate

In the present study, a new sensitive and simple kinetic-spectrophotometric method for the determination of the insecticide dimethoate [O,O-dimethyl-S-(N-methyl-carbomoylmethyl)-phosphoro-dithioate] is developed. The method is based on the inhibition effect of dimethoate on the oxidation of malachite green (MG) by potassium periodate (KIO₄) in the presence of Mn(II) ions. Inhibition kinetics of this catalytic reaction was investigated in the presence of dimethoate and the possibility of its analytical application was evaluated. The important variables that affected the reaction rate were investigated and the optimum conditions giving maximum sensitivity were established. Dimethoate was determined with linear calibration graph in the interval from 4.58 to 41.22 μg/mL. The optimized conditions yielded a theoretical detection limit of 1.24 μg/mL based on the 3S _b criterion. The RSDs of the method (n = 5) were 1.2–4.9% for the concentration interval of dimethoate from 4.58 to 41.22 μg/mL. The reaction was monitored spectrophotometrically by measuring the change in absorbance over time at 615 nm. The method was applied to the determination of dimethoate in waters and milk, and was compared with the spectrophotometric method. The quantitive method developed on the basis of inhibition kinetics is practical, fast and economical. For this reason, it is open for new application fields.     

用铁氰化钾分光光度法测定头孢噻肟钠

建立了以铁氰化钾测定头孢噻肟钠的分光光度法。 在0.20 mol/L NaOH溶液中,头孢噻肟钠(CTX)于100 ℃水浴中降解生成的巯基化合物能将Fe(Ⅲ)(pH=3.0)还原为Fe(Ⅱ),根据Fe(Ⅱ)与K3[Fe(CN)6]反应生成可溶性普鲁士蓝(KFeⅢ[FeⅡ(CN)6])的吸光度,可以间接测定头孢噻肟钠的含量。 头孢噻肟钠在0.040~24 mg/L范围内与吸光度(A)呈线性关系,线性回归方程:A=0.05088+0.2166ρ(mg/L),相关系数R=0.9986,检出限为0.01 mg/L,相对标准偏差(RSD)为1.36%(n=11),表观摩尔吸光系数ε=2.3×105 L/(mol·cm)。 此方法可用于药物及血清中头孢噻肟钠含量的测定。     

Spectrophotometric determination of piroxicam

The possibility of the spectrophotometric determination of piroxicam based on the extraction of its ion associate (IA) with the polymethine dye, 5-thiocyanate-1,3,3-trimethyl-2[(1E)-3-[(2E)-1,3,3-trime-thyl-1-H-indol-2-ilidine]-propenyl]-3H-indolium chloride. The maximal recovery of IA with toluene is achieved when pH of the aqueous phase is 8.0–12.0 and the concentration of the dye is (1.0–2.0) × 10⁻⁴. The molar absorption coefficient of IA is 8 × 10⁴, the detection limit of piroxicam is 0.49 μg/mL. A procedure has been developed for the extraction-spectrophotometric determination of piroxicam in the concentration range 1.0–20.0 μg/mL.     

Effect of additives on the chemical vapour generation of bismuthane by tetrahydroborate(III) derivatization

The effect of mM concentrations of K₃[Fe(CN)₆], Fe(III), Mo(VI), KSCN and KMnO₄ on the generation of BiH₃ by the reaction of 0.2–10 μg ml⁻¹ Bi(III) with 0.2 M tetrahydroborate(III) at 1 M acidity (HCl or HNO₃) was investigated. Chemical vapour generation (CVG) of BiH₃ was investigated by atomic absorption spectrometry using a continuous flow reaction system (CF–CVG–AAS) and different mixing sequences and reagent reaction times. Gas chromatography–mass spectrometry (GC–MS) was employed in batch generation experiments with NaBD₄. In the absence of additives, the formation of Bi⁰ at high concentrations of Bi(III) caused rollover of calibration curves and limited the linear range to less than 1 μg ml⁻¹ Bi(III). In the presence of additives, the formation of Bi⁰ was not observed and the linear range was increased to 5 μg ml⁻¹ of Bi(III) while rollover was completely removed. GC–MS experiments indicated that the presence of additives did not affect the direct transfer of H from boron to bismuth. Experiments with CF–CVG–AAS and different mixing sequences and reagent reaction times suggest that additives act by preventing the formation of Bi⁰ through the formation of reaction intermediates which evolve towards the formation of BiH₃ at elevated Bi(III)/NaBH₄ ratios.      

Highly sensitive spectrophotometric determination of olanzapine using cerium(IV) and iron(II) complexes of 1,10-phenanthroline and 2,2′-bipyridyl

Two highly sensitive spectrophotometric methods have been developed for the determination of olanzapine (OLP) in pharmaceuticals using cerium(IV) and iron(II) complexes of 1,10-phenanthroline and 2,2′-bipyridyl as reagents. The methods are based on the oxidation of OLP in acidic medium by a known excess of cerium(IV) followed by the determination of the unreacted oxidant by reacting with either ferroin and measuring the absorbance at 510 nm (method A) or iron(II)-2,2′-bipyridyl complex and measuring the absorbance at 525 nm (method B). The amount of cerium(IV) reacted corresponds to the amount of OLP. In both the methods, the absorbance is found to increase linearly with OLP concentration as shown by the correlation coefficient (r) of 0.9980 and 0.9958 for method A and method B, respectively. The calibration graphs are linear over the concentration range of 0.2–2.0 μg/mL in both the methods. The calculated molar absorptivity values are 1.00 × 10⁶ and 7.03 × 10⁵ L/mol cm, for method A and method B. The LOD and LOQ values for method A are calculated to be 0.04 and 0.13 μg/mL and the values are 0.07 and 0.22 μg/mL for method B, respectively. The methods were validated as per the current ICH guidelines. Both the methods gave similar results in terms of accuracy and precision. The RSD was less than 3% and the accuracy, obtained from recovery experiments, was 98.76–101.4%. The methods developed were applied to the determination of OLP in tablets and results agreed well with the label claim.     

Spectrophotometric determination of mefenamic acid in pharmaceutical preparations

The present paper describes an effective and low-cost spectrophotometric method for the determination of mefenamic acid in its pure form and pharmaceutical preparations. The method is based on the charge-transfer complexation between mefenamic acid as an n-electron donor and chloranil as a π-acceptor to form a violet chromogen measured at 540 nm. Under the optimum conditions, a linear relationship with a good correlation coefficient (0.9996) was found between the absorbance and concentration of the studied drug in the range of 10–60 μg/mL. The optimal reaction conditions such as reagent concentration, heating time, and stability of the reaction product were determined. The limit of detection (LOD) was 2.16 μg/mL and the limit of quantifycation (LOQ) was 7.15 μg/mL. The method was successfully applied to the determination of mefenamic acid in pharmaceutical preparations without any interference from common excipients. The text was submitted by the author in English.     

Spectrophotometric determination of furosemide in pharmaceutical dosage forms using complex formation with Cu(II)

A simple, sensitive, and accurate spectrophotometric method has been developed for the assay of furosemide (FUR), which is based on the complexation of the drug with copper(II) at pH 3.2 using Mclivaine buffer solution to produce a green adduct. The latter has maximum absorbance at 790 nm and obeys Beer’s law within the concentration range 5–30 μg/mL. Regression analysis of the calibration data showed a good correlation coefficient (r = 0.9997) with minimum detection limit of 0.23 μg/mL. The proposed procedure has been successfully applied to the determination of this drug in tablets. In addition, the spectral data and stability constant for the mononuclear copper(II) complex of furosemide (CuFUR₂(MeOH)₂) are reported. The text was submitted by the author in English.     

Extraction–thermal lens quantification of cobalt with Nitroso-R-Salt in two-phase aqueous systems with water-soluble polymer polyethylene glycol

A novel method is proposed for the extraction-thermal lens quantification of cobalt with Nitroso-R-Salt based on the distribution of the colored complex in a two-phase aqueous system on the basis of poly-ethylene glycol (PEG) and an ammonium sulfate solution followed by its thermal lens detection in the extract. The limit of detection is 0.3 μM (20 ng/mL); the lower limit of the analytical range is 0.7 μM (40 ng/mL); the relative standard deviation for the concentrations 1–50 μM makes 1–3% (n = 6, P = 0.95). In the determination of cobalt by spectrophotometry under the same conditions, the detection limit is 10 μM (0.6 μg/mL) and the lower limit of the analytical range is 40 μM (2.5 μg/mL). The precision of thermal lens measurements in PEG solutions is higher in comparison to that in aqueous ones because of the weaker interference of convection in aqueous solutions of PEG.     

Titrimetric and spectrophotometric assay of pantoprazole in pharmaceuticals using cerium(IV) sulphate as oxidimetric agent

Titrimetric and spectrophotometric assay of pantoprazole sodium sesquihydrate (PSS) using cerium(IV) sulphate as the oxidimetric reagent is described. The methods are based on the oxidation of PSS with a measured excess of Ce(IV) sulphate followed by the determination of unreacted oxidant using different reaction schemes. In titrimetry, the unreacted oxidant was determined by back titration with ferrous ammonium sulphate (FAS) in sulphuric acid medium. Spectrophotometry involves the reduction of unreacted Ce(IV) sulphate with a fixed quantity of Fe(II). The resulting Fe(III) is complexed with thiocyanate and the absorbance is measured at 470 nm. In both the methods, the amount of Ce(lV) sulphate reacted corresponds to PSS concentration. Titrimetry is applicable over 1–10 mg range whereas in spectrophotometry, the calibration graph is linear in the range of 0.5–7.0 μg/mL and the calculated molar absorptivity value is 1.58 × 10⁵ L/mol cm. The validity of the proposed methods was tested by analyzing pure and dosage forms containing PSS. Statistical treatment of the results reflects that the proposed procedures are precise, accurate and easily applicable to the determination of PSS in pure form and in pharmaceutical formulations.     

Sorption-fluorimetric determination of zinc

The sorption of ions of zinc on carriers modified by 8-oxychinoline and its derivative is investigated. The optimum parameters of sorption are revealed, based on which silochrome S-60 with immobilized 8-oxychinoline (pH 7.1, time of contact 30 min, weight of sorbent 0.3 g, capacity of sorbent on the modifier 60 μmol/g) is chosen. A yellow-green fluorescence sorbate arises on irradiation by ultra-violet light in a phase sorbent. The spectrum of fluorescence represents a wide unstructured strip with a maximum at 505 nm. In the construction of a calibrated graph, Cu(II), Cd(II), Pb (II), Bi(III), and Fe(III) do not prevent the determination of 5–50 μg of zinc; however, equal amounts of Al(III) (50–100 μg) do prevent it. The technique is applied for the sorption-fluorimetric determination of zinc in river and waste water. The relative standard deviation does not exceed 0.05 (n = 5).     

Development and validation of an HPLC-UV method for the simultaneous quantification of carbamazepine, oxcarbazepine, eslicarbazepine acetate and their main metabolites in human plasma

For the first time, a simple, selective and accurate high-performance liquid chromatography method with ultraviolet detection was developed and validated to quantify simultaneously three structurally related antiepileptic drugs; carbamazepine, oxcarbazepine, and the recently launched eslicarbazepine acetate and their main metabolites, carbamazepine-10,11-epoxide, 10,11-trans-dihydroxy-10,11-dihydro-carbamazepine, and licarbazepine. The method involves a solid-phase extraction and a reverse-phase C18 column with 5 cm length. The mobile phase consisting of water, methanol, and acetonitrile in the ratio 64:30:6 was selected as the best one and pumped at 1 mL/min at 40 °C. The use of this recent column and an aqueous mobile phase instead of buffers gives several advantages over the method herein developed; namely the fact that the chromatographic analysis takes only 9 min. The method was validated according to the guidelines of the Food and Drug Administration, showing to be accurate (bias within ±12%), precise (coefficient variation <9%), selective and linear (r ² > 0.997) over the concentration range of 0.05–30 μg/mL for carbamazepine; 0.05–20 μg/mL for oxcarbazepine; 0.15–4 μg/mL for eslicarbazepine acetate; 0.1–30 μg/mL for carbamazepine-10,11-epoxide; 0.1–10 μg/mL for 10,11-trans-dihydroxy-10,11-dihydro-carbamazepine, and 0.1–60 μg/mL for licarbazepine. It was also shown that this method can adequately be used for the therapeutic drug monitoring of the considered antiepileptic drugs, carbamazepine, oxcarbazepine, eslicarazepine acetate, and their metabolites.