Simultaneous kinetic–spectrophotometric determination of mycophenolate mofetil and mycophenolic acid based on complexation with Fe(III) using chemometric techniques

Determination of pharmaceutical analytes has been subjected to many investigations, especially in transplantations in which accurate and precise detection of drugs is of importance. In this study, a simple and fast complexation reaction has been employed for simultaneous kinetic–spectrophotometric determination of two immunosuppressant drugs, mycophenolate mofetil and its active metabolite mycophenolic acid, which is based on the reaction between drugs and Fe(III) ions in the presence of sodium dodecyl sulfate as anionic surfactant by standard addition method. The effect of influential parameters including type of surfactant, concentration of Fe(III) ions and pH of the solution on the complexation reaction has been studied, and SDS was chosen as suitable surfactant, while reaction proceeds with 0.1 M Fe(III) at pH 4. Multivariate curve resolution-alternating least squares has been employed for analyzing the multiset data obtained from augmentation of resulting standard addition matrices. Values for limit of detection of method have been calculated as 4.88 and 1.62 µg mL^?1 for mycophenolic acid and mycophenolate mofetil, respectively, and Beer’s law is obeyed over the concentration ranges 10–200 µg mL^?1 for MPM and 50–250 µg mL^?1 for MPA. The proposed method was successfully applied for determination of drugs in plasma serum samples. The accuracy and reliability of the method was further ascertained by recovery studies via standard addition procedure.     

Simple and sensitive fluorimetric method for determination of environmental hormone bisphenol A based on its inhibitory effect on the redox reaction between hydroxy radical and rhodamine 6G [corrected

Peroxyl radical produced by Fenton-like reagent (Fe(III) + H₂O₂) oxidizes Rhodamine 6G and produces the quenching of its fluorescence. It is also found that bisphenol A has an inhibitory effect on the redox reaction. Based on this observation, an inhibitory kinetic fluorimetric method is reported for the determination of trace bisphenol A. The fluorescent inhibition of rhodamine 6G is measured by fix-time method. Under the optimum experimental conditions, the detection limit and the quantification limit for bisphenol A is 2.0 and 6.7 ng mL⁻¹, respectively; and the linear range of the determination is 0.024-0.4 μg mL⁻¹. The proposed method has been used for the determination of bisphenol A in environmental waters, river bottom sediment, generic soil, polycarbonate products and teeth filling samples with recoveries of 92.5-110.0%. The possible mechanism of the reaction has also been discussed.     

Determination of As(III) and As(V) in water samples by flow injection online sorption preconcentration coupled to hydride generation atomic fluorescence spectrometry

A method was developed for the determination of arsenite [As(III)] and arsenate [As(V)] in water samples using flow injection online sorption coupled with hydride generation atomic fluorescence spectrometry (HG-AFS) using a cigarette filter as the sorbent. Selective determination of As(III) was achieved through online formation and retention of the pyrrolidine dithiocarbamate arsenic complex on the cigarette filter, but As(V) which did not form complexes was discarded. After reducing As(V) to As(III) using L-cysteine, total arsenic was determined by HG-AFS. The concentration of As(V) was calculated by the difference between As(III) and total arsenic. The analytes were eluted from the sorbent using 1.68 mol L^?1 HCl. With consumption of 22 mL of the sample solution, the enrichment factor of As(III) was 25.6. The detection limits (3σ/k) and the relative standard deviation for 11 replicate determinations of 1.0 ng mL^?1 As(III) were found to be 7.4 pg mL^?1 and 2.6%, respectively.     

Determination of Inorganic Arsenic Species by Electrochemical Hydride Generation Atomic Absorption Spectrometry with Selective Electrochemical Reduction

A new direct procedure for the determination of inorganic arsenic species was developed by electrochemical hydride generation atomic absorption spectrometry （EcHG-AAS） with selective electrochemical reduction. The determination of inorganic arsenic species is based on the fact that As（Ⅲ） shows significantly higher absorbance at low electrolytic currents than As（Ⅴ） in 0.3 mol·L^-1 H2SO4. The electrolytic current used for the determination of As（Ⅲ） without considerable interferences of As（Ⅴ） was 0.4 A, whereas the current for the determination of As（Ⅲ） and As（Ⅴ） was 1.2 A. For equal concentrations of As（Ⅲ） and As（Ⅴ） in a sample, the interferences of As（Ⅴ） during the As（Ⅲ） determination were smaller than 5%. The absorbance for As（Ⅴ） could be calculated by subtracting that for As（Ⅲ） measured at 0.4 A from the total absorbance for As（Ⅲ） and As（Ⅴ） measured at 1.2 A, and then the concentration of As（Ⅴ） can be obtained by its calibration curve at 1.2 A. The methodology developed provided the detection limits of 0.3 and 0.6 ng·mL^-1 for As（Ⅲ） and As（Ⅴ）, respectively. The relative standard deviations were of 3.5% for 20 ng·mL^-1 As（Ⅲ） and 3.2% for 20 ng·mL^-1 As（Ⅴ）. The method was successfully applied to determination of soluble inorganic arsenic species in Chinese medicine.     

Selective extraction and determination of Au(III) by first-derivative spectrophotometry

The selective extraction of Au(III) in the presence of Zn(II) by salting-out of 2-propanol was investigated. The salting-out effect increased partitioning between water and 2-propanol in the presence of sodium chloride in aqueous–organic mixtures. This is observed through the distribution coefficient, which increases with salt addition. First-derivative spectrophotometry, which eliminates interference from overlapping spectral bands, was used for the determination of trace Au(III) in the presence of Zn(II). Absorption spectra were recorded and the first-derivative spectra were obtained using Δλ?=?10?nm. The calibration graph was linear for 0.857–5.142?µg?mL^?1 and the detection limit was 0.038–8?µg?mL^?1. The proposed method has been successfully applied to the determination of trace Au(III) in synthetic mixtures and Algerian low gold ore solutions. The results agree with those obtained by atomic absorption spectroscopy and the recoveries were >98%. The relative standard deviations were in all instances less than 3%.     

A New Spectrophotometric Method for the Determination of Arsenic in Environmental and Biological Samples

Abstract

A simple and selective spectrophotometric method has been developed for the determination of trace amounts of arsenic using azure B as a chromogenic reagent. The proposed method is based on the reaction of arsenic(III) with potassium iodate in acid medium to liberate iodine. The liberated iodine bleaches the violet color of azure B and is measured at 644 nm. This decrease in absorbance is directly proportional to the As(III) concentration, and Beer's law is obeyed in the range 0.2–10 µg ml^?1 of As(III). The molar absorptivity, Sandell's sensitivity, detection limit, and quantitation limit of the method were found to be 1.12×10⁴ l mol^?1cm^?1, 6.71×10^?3 µg cm^?2, 0.02 µg ml^?1 and 0.08 µg ml^?1, respectively. The optimum reaction conditions and other analytical parameters were evaluated. The proposed method has been successfully applied for the determination of arsenic in various environmental and biological samples.     

Catalytic-kinetic potentiometric determination of thyroxine

A kinetic method is described for the determination of thyroxine (0.4–4 μg ml^?1), based on its catalytic effect on the reduction of cerium(IV) by arsenic(III). The reaction is monitored potentiometrically; the time required for a 20-mV change in potential is inversely proportional to the thyroxine concentration. The method is applicable to tablets.     

Catalytic effect of iron(III) on the oxidation of 2-hydroxybenzaldehyde thiosemicarbazone by hydrogen peroxide : Kinetic Fluorimetric Determination of Iron

A kinetic method is described for the determination of nanogram amounts of iron(III) based on its catalysis of the oxidation of 2-hydroxybenzaldehyde thiosemicarbazone by hydrogen peroxide in an ammoniacal medium. In order to monitor the reaction, the appearance rate of fluorescence of the oxidation product (λ_ex=365 nm, λ_em=440 nm) is measured. The calibration graph is linear in the range 10–60 ng ml^?1 iron(III) with an r.s.d, of ± 1.3%. The proposed method has few interferences and has been applied satisfactorily to the determination of iron in several alloys and minerals. A mechanism for the catalyzed reaction is proposed.     

Optimisation of an in-tube solid phase microextraction method coupled with HPLC for determination of some oestrogens in environmental liquid samples using different capillary columns

A simple on-line method for simultaneous determination of some oestrogens including oestriol (E3), norethisterone (NORE), ethynylestradiol (EE2), D-norgestrel (NORG) and bisphenol A (BPA), in environmental liquid samples was developed by coupling in-tube solid phase microextraction (in-tube SPME) to high-performance liquid chromatography with diode array (DAD) and fluorescence (FLD) detectors. Two capillary chromatographic columns (Supel-Q? and Carboxen? 1006 porous layer open tubular) were selected to develop this method. To achieve optimum extraction performance, several parameters were investigated including number of draw/eject cycles and the sample volume for each of the columns. Reproducibility was satisfactory for inter- and intra-day precision, yielding % RSDs of less than 10% and 7.6%, respectively. Limits of detection (LODs) and quantification (LOQs) for the proposed method using a DAD detector were achieved in the ranges of 0.04–0.63?ng?mL^?1 and 0.12–1.9?ng?mL^?1, depending of the capillary column used. Fluorescence detection improved these parameters for E3, BPA and EE2, obtaining LODs of 0.005–0.03?ng?mL^?1 and LOQs of 0.015–0.08?ng?mL^?1 using Supel-Q and LODs of 0.01–0.015?ng?mL^?1 and LOQs of 0.025–0.04?ng?mL^?1 using Carboxen. The proposed method was successfully applied to spiked environmental waters obtaining recoveries greater than 80%.     

Sensitive Quantification of Fe(III) in Food Samples at Screen Printed Carbon Electrode Modified with Graphene and Piroxicam by Catalytic Adsorptive Voltammetry

A new disposable sensitive voltammetric sensor for the determination of Fe(III) based on a graphene (G) and piroxicam (Pir) modified screen printed carbon electrode (Pir/G/SPCE) has been developed. The developed method is based on accumulation of Fe(III) on the surface of the prepared sensor strip, formation a complex with Pir and subsequent reduction the adsorbed chelated Fe(III) at ?0.03 V (vs. Ag/AgCl) coupled with the catalytic enhancement of bromate. Characterizations of the modified electrode surface were performed by field emission scanning electron microscopy (FE‐SEM), energy dispersive X‐ray spectroscopy (EDX) and electrochemical impedance spectroscopy (EIS). Electrochemical behavior of the modified SPCEs was investigated by cyclic voltammetry (CV) and differential pulse voltammetry (DPV). Under the optimum conditions, the catalytic voltammetric method exhibited linear calibration plot in the concentration ranges of 1–100 ng mL^?1 and 100–3500 ng mL^?1 Fe(III) with a limit of detection of 0.3 ng mL^?1. The sensor strip displayed good reproducibility with 1.7 % relative standard deviation (RSD%). The developed method was successfully applied for the determination of iron in food samples such as vegetables, fruit, and cereal.     

Second‐order Scattering and Frequency Doubling Scattering Spectra of Thallium(III)‐Methotrexate System and Its Analytical Application

In pH 4.9 Britton-Robinson buffer solution, methotrexate (MTX) reacted with thallium(III) to form a 3∶1 chelate. This resulted in great enhancement of second-order scattering (SOS) spectra and frequency doubling scattering (FDS) spectra and appearance of new SOS and FDS spectra. Their maximum wavelengths were located at 520 and 390 nm, respectively. The increments of scattering intensities (ΔI) were directly proportional to the concentrations of MTX in the ranges of 0.022—2.0 μg•mL－1 (SOS method) and 0.008—2.5 μg•mL－1 (FDS method). The methods exhibited high sensitivities. The detection limits for MTX were 7.4 ng•mL－1 (SOS method) and 2.3 ng•mL－1 (FDS method), respectively. The optimum conditions of the reaction, the influencing factors and the effects of coexisting substances were investigated. A highly sensitive, simple and fast method for the determination of MTX has been developed. The method can be applied satisfactorily to the determination of MTX in human serum samples. In this work, the charge distribution of MTX was calculated by a CNDO quantum chemistry method. In addition, the reaction mechanism was discussed.     

Spectrophotometric Determination of Selected Antibiotics Using Prussian Blue Reaction

A simple, sensitive and accurate spectrophotometric method has been described for the determination of ampicillin(I), amoxicillin trihydrate(II) and cefazolin sodium(III). The procedure is based on the formation of Prussian Blue (PB) complex. The reaction between the acidic hydrolysis products of antibiotics (T = 60 °C) with mixture of Fe³⁺ and hexacyanoferrate(III) ions was evaluated for the spectrophotometric determination of the mentioned drugs. The maximum absorbance of the colored complex occurs at λ = 700 nm and the molar absorptivity is 3.0 × 10⁴ 1 mol^?1cm^?1. The effect of various parameters such as concentration of K₃Fe(CN)₆ and Fe³⁺, nature and amount of acids used, temperature and time of heating were investigated. Under optimum conditions the linear range of calibration graph was 2.0–12.0, 5.0–13.5 and 3.0–12.0 μg mL^?1 for ampicillin, amoxicillin and cefazolin, respectively. The relative standard deviation for the determination of 10 μg mL^?1 of antibiotics was about 0.5–1.5%. The proposed method was successfully applied to the determination of selected antibiotics from pharmaceutical preparations. The validity of the method was tested by the official methods and by the recovery studies of standard addition to pharmaceuticals.     

Flow-injection chemiluminescence determinations for human blood lead using controlled reagent release technology

A flow-through CL method for the determination of lead combined with controlled-reagent-release technology has been developed. Chemiluminescence (CL) reagents luminol and potassium permanganate were immobilized on anion exchange resin by electrostatic interaction. Lead ion was determined by its enhancing effect on the CL reaction between luminol and potassium permanganate. Both luminol and potassium permanganate were eluted from the anion exchange resin column by sodium phosphate solution. The linear range of the system was 10 μg mL^?1, and the detection limit was 5?×?10^–9 g mL^?1 lead (3σ). A complete analysis could be performed in 1 min with a relative SD 3.2% (1.0?×?10^–7 g mL^?1, n?=?9). The column shows remarkable stability and can be reused over 350 times and 21 days. The method has been applied to determine lead in human blood samples.     

Application of dispersive liquid–liquid microextraction for the determination of donepezil in urine by HPLC using a core–shell column

A rapid and novel method combining dispersive liquid–liquid microextraction and high-performance liquid chromatography coupled with fluorescence detection was developed for the determination of donepezil in human urine. Parameters affecting extraction efficiency and chromatographic determination, such as the type and volume of the extraction and disperser solvent, pH of sample for dispersive liquid–liquid microextraction, mobile-phase composition, pH, column oven temperature, and flow rate for chromatographic determination, were evaluated and optimized. Using a C₁₈ core–shell column (7.5 × 4.6?mm, 2.7?μm), the determination of donepezil was accomplished within 5?min. Under optimum conditions, developed method was linear in the range of 0.5–25?ng?mL^?1 with the correlation coefficient >0.99. Limit of detection was 0.15?ng?mL^?1. The relative standard deviation at three concentration levels (2, 12.5, and 20?ng?mL^?1) was less than 11% with accuracy in the range of 96.9–102.8%. The results of this study demonstrate that the use of dispersive liquid–liquid microextraction and core–shell column can be considered as a powerful tool for the analysis of donepezil in human urine.     

Spectrophotometric Study of Isoniazid by Using 1,2‐Naphthoquinone‐4‐Sulfonic Acid Sodium as the Chemical Derivative Chromogenic Reagent

A new method for the determination of isoniazid by using 1,2‐naphthoquinone‐4‐sulfonic sodium as the chemical derivative chromogenic reagent is established. The method is based on a condensation reaction to measure the pink compound produced by the reaction of isoniazid with 1,2‐naphthoquinone‐4‐sulfonic sodium in pH 13.00 buffer solution. The stoichiometric ratio of the compound is 1:1, and its maximum absorption wavelength is at 460 nm, ? = 1.18 × 10⁴ L·mol^?1 cm^?1. Beer's law is perfectly obeyed in the range of 0.50?30 μg.mL^?1 of isoniazid. The linear regression equation is A = 0.0185 + 0.11056C (mol.L^?1), with 0.9994 of a linear regression correlation. The detection limit is 0.40 μg.mL^?1, RSD is 0.48%, and average recovery is over 99.3%. This paper further optimizes the determination of isoniazid compared to the previous methods, and the kinetic property and reaction mechanism are studied intensively. This proposed method has been successfully applied to the determination of isoniazid in tablets of isoniazid with satisfactory results.     

A Spectrophotometric Study of Streptomycin Effect on the Clinical Urea Determination

The results of studying inhibitory effect of streptomycin on the modified Berthelot reaction were presented in this paper and a new kinetic method for determining streptomycin in pharmaceutical preparations and human urine was developed on the basis of the obtained results. The rates of catalytic and catalytic‐inhibitory reaction were monitored at 700 nm (t=25±0.1°C) using UV/vis spectrophotometer. By analyzing the spectra and experimental dependences of the catalytic and catalytic‐inhibitory reaction rates on the reactant concentrations, it was noticed that streptomycin attacked nitroprusside and hypochlorite causing the inhibition of the production of 2,2′‐dicarboxylindophenol. According to this effect, an analytical decrease for determination of urea by modified Berthelot reaction appeared in the presence of small amounts of streptomycin. Beer's law was obeyed in the interval of streptomycin sulfate concentration from 18.2 to 182 µg·mL^?1. The detection limit calculated by two methods was obtained at 11.75 µg·mL^?1 and 8.54 µg·mL^?1. The relative standard deviation of 0.55%–8.83% and the recovery of 109.10% were determined. The obtained results were validated using the referent HPLC method.     

钯（II）-克林霉素-卤代荧光素体系的共振瑞丽散射光谱及其分析应用

在pH为5.0-5.4的乙酸-乙酸钠缓冲溶液中,克林霉素（Clin）与钯(Ⅱ)形成螯合阳离子,它能进一步与二碘荧光素（DIF）,赤藓红（Ery）,曙红Y（EY）等卤代荧光素类染料反应形成1：1：1的三元离子缔合物,此时将引起吸收光谱变化和荧光猝灭,同时还导致共振瑞利散射(RRS)的急剧增强并产生新的RRS光谱,钯(Ⅱ)-克林霉素与DIF,Ery和EY形成产物的最大散射波长分别位于285,287,32 1nm处,另外还有些较弱的散射峰存在。散射增强（ΔI）与克林霉素浓度在一定范围内成正比,可用于克林霉素的定量测定。对于DIF,Ery和EY体系的线性范围和检出限分别为0.025-2.1μg•mL-1和7.8 ng•mL-1,0.053-2.4μg•mL-1和16.0 ng•mL-1;以及0.038-2.4μg•mL-1和11.0 ng•mL-1。本文研究了适宜的反应条件,考察了共存物质的影响,表明方法有较好的选择性,基于三元离子缔合物的RRS光谱,发展了一种高灵敏、简便快速测定克林霉素的新方法。文中还对离子缔合物的组成,结构和反应机理,以及离子缔合物对吸收,荧光和RRS光谱的影响进行了讨论。     

Determination of Poisonous Trace Element Thallium(I) by Kinetic Catalytic Reaction

Abstract

A effective and simple determination of poisonous trace element thallium(I) by means of kinetic catalytic reaction is proposed. The method is based on a catalytic effect of thallium(I) on a luminol-hydrogen peroxide system. Three different kinds of surfactants, cetrimonium bromide (CTMAB), sodium dodecyl sulphate (SDS), and Tween-80, are also investigated to improve the detection sensitivity. In optimum conditions, a highly selective and sensitive method for detecting trace thallium(I) has been established. The detection limit is 0.0073 µg · mL^?1, the relative standard deviation for six determinations of 0.04 µg · mL^?1 thallium(I) is less than 4.0%, and the linear range of determination is 0.02–0.1 µg · mL^?1.     

Cloud-point extraction,preconcentration, and spectrophotometric determination of palladium in water samples

The possibility of using Thio-Michler's Ketone (TMK), 4,4′-bis(dimethylamino) thiobenzophenone, for palladium(II) concentrated by micellar extraction at the cloud-point temperature, and later spectrophotometric determination, was investigated. Under the optimum conditions, preconcentration of 50?mL of water samples in the presence of 0.1% (w/v) octylphenoxy polyethoxy ethanol (Triton X-114), 2?×?10^?6?mol?L^?1?TMK and 1?×?10^–3?mol?L^?1 buffer solution (pH?=?3.0) gave the limit of detection of 0.47?ng?mL^?1, and the calibration graph was linear in the range of 2–50?ng?mL^–1. The recovery under optimum working conditions was higher than 97%. The proposed method has been applied to the spectrophotometric determination of palladium(II) in natural water samples after cloud-point extraction with satisfactory results.     

Determination of Ultratrace Silver Using Surfactant as Sensitizer by Catalytic Near Field Laser Thermal Lens Spectrometry

Introduction Thermal lens spectrometry (TLS) is an excellent method for trace analysis.1-3 Methods classified as TLS are based upon a thermal change in the optical proper-ties of a sample on the absorption of laser energy which leads to a temperature rise in the sample and conse-quently to the formation of an inhomogeneous spatial profile of the refractive index. The change in the diver-gence of a laser beam on the resulting optical element (thermal lens) is proportional to the amount of abs…