DETERMINATION OF LEAD(II) BY FLOW-INJECTION ANALYSIS USING LUMINOL-POTASSIUM PERIODATE POST-CHEMILUMINESCENCE REACTION

The post-chemiluminescence (PCL) phenomenon arising from the potassium periodate–luminol reaction induced by lead(II) was investigated. A strong PCL signal was observed when lead(II) was injected into the mixture of potassium periodate and luminol in a flow-cell. The influencing factors on the PCL intensity of the system were investigated. Under the optimum experimental conditions, the present method allowed the determination of lead(II) in the concentration range of 1.0 × 10^?8 to 1.0 × 10^?5 mol/L and the detection limit for lead(II) was 2.3 × 10^?10 mol/L. The relative standard deviation was 3.2% for 11 replicate analyses of 1.0 × 10^?6 mol/L lead(II). Combined with cotton cellulose xanthate for separation, the proposed method was applied to the determination of lead(II) in real water samples with satisfactory results.     

KINETIC SPECTROPHOTOMETRIC DETERMINATION OF TRACE AMOUNT OF EUROPIUM BASED ON ITS INHIBITORY EFFECT OF THE OXIDATION OF SWITZERLAND PIGMENT BY POTASSIUM BROMATE

In 4.0 × 10^?3 mol/L of hydrogen chloride medium, a trace of europium(III) plays a good inhibitory role in the fading reaction of Switzerland pigment oxidized by potassium bromate. Based on this principle, an inhibitory kinetic spectrophotometric method for the determination of trace europium was developed. A maximum absorption wavelength locates at 600 nm and a good linear range is presented over 0 – 0.18 µg/mL of europium(III) under the optimum conditions. The regression equation for the determination of europium(III) is ΔA = 4.495C(C:μg/mL) + 0.0278 with a correlation coefficient of 0.9965. The detection limit of the method was 19 ng/mL. The apparent activation energy of the inhibitory reaction and the reaction half-life period were 5.76 KJ/mol and 15.61 min, respectively. This method has been successfully used in the determination of europium in molecular sieve samples.     

INHIBITIVE KINETIC SPECTROPHOTOMETRIC DETERMINATION OF PROTEIN

A novel inhibitive kinetic spectrophotometric method for the determination of protein is proposed based on the principle that serum albumin (SA) has an inhibitive effect on the oxidation discoloring of p-acetylchlorophosphonazo (CPApA) by potassium periodate in the medium of 4.0 × 10^?4 mol/L H₂SO₄ at 100°C. The maximum absorption peak of SA – CPApA – KIO₄ system is located at 550 nm. The absorbance difference (ΔA) is linearly related with the concentration of SA over the range of 0.80–7.50 µg/mL at the wavelength and fitted the equation: ΔA = 0.064C (C: µg/mL) – 0.0173, with a correlation coefficient γ = 0.9973. The detection limit of the method was 0.30 μg/mL. The method was successfully used to determine protein content in milk and milk powder samples and the determined results were in good agreement with those of tribromoarsenazo spectrophotometry. The relative standard deviation for 13 replicate determinations of the method was 3.64–3.76%. The standard addition recovery of the method was 99.50–101.6%.     

Determination of polydatin by gold nanoparticle-enhanced chemiluminescence of silver nitrate and luminol

A novel flow injection method for the determination of polydatin is reported based on the inhibition of silver nitrate, luminol, and gold nanoparticles chemiluminescence. Under the optimum condition, the decrease in chemiluminescence was proportional to the concentration of polydatin from 1.0 × 10^?8 to 1.0 × 10^?5 mol/L. The detection limit was 2.1 × 10^?9 mo1/L and the relative standard deviation was 2.1% for the determination of 1.0 × 10^?6 mol/L polydatin. This method was successfully employed for the determination of polydatin in Polygonum cuspidatum roots and human urine.     

Spectrophotometric Determination of Silicon in Rice and Alloy Steel Samples

Abstract

In the medium of 0.128 mol/L nitric acid and 0.450 mol/L sulfuric acid, silicon(IV) and ammonium molybdate form molybdosilicate blue blue complex in the presence of ascorbic acid. The maximum absorption wavelength of the complex locates at 810 nm. The apparent molar absorptivity is ε_810 nm = 3.18 × 10⁴ L · mol^?1 · cm^?1. Beer's law is followed over the range of 0 ～ 1.0 µg/mLof silicon(IV). The present method has been successfully applied to the determination of silicon in rice and alloy steel samples.     

Construction of an Optical Sensor for Cobalt Determination Based on Methyltrioctylammonium Chloride Immobilized on a Polymer Membrane

Abstract

An optical sensor has been designed for the determination of cobalt by spectrophotometry. The sensing membrane is made by immobilizing methyltrioctylammonium chloride on a triacetylcellulose membrane. In the presence of Co(II) and thiocyanate ions, the colorless membrane changes to blue. The response time of the optode was about 7 min. The sensor can readily be regenerated with 0.02 mol L^?1 sodium oxalate solution. This optode is stable and can be stored under water for more than a month without reagent leaching. The calibration curve was linear in the range of 8.5×10^?6–1.3×10^?4 mol L^?1 of Co(II) ion with a limit of detection 5.9×10^?6 mol L^?1. The relative standard deviations for seven replicate measurements of 3.4×10^?5 and 1×10^?4 mol L^?1 of Co(II) were 1.58 and 1.10%, respectively. The sensor was successfully applied to the determination of cobalt in food samples and vitamin B₁₂ ampoule.     

Batch and Flow‐Injection Determination of Catecholamines Using Ion Selective Electrodes

Abstract

New epinephrine (EP), dopamine (DA), and L‐Dopa (LD) ion selective PVC membrane electrodes based on ion‐pairs of catecholamines with tetraphenylborate (TPhB) are prepared. In the present work, plastic membrane selective electrodes have been constructed. They are based on the incorporation of EP‐TPhB, DA‐TPhB, or LD‐TPhB ion exchangers in poly(vinylchloride) (PVC) membranes plasticized with di(2‐ethylhexyl)sebacate (DES). The electrodes show a near – Nernstian response in the concentration ranges: 1.0×10^?4—1.0×10^?2 mol/L (epinephrine), 5.0×10^?5–1.0×10^?2 mol/L (dopamine), and 5.0×10^?4–1.0×10^?2 mol/L (L‐Dopa). The electrodes selective for epinephrine and L‐Dopa are used as detectors in the flow injection system. The proposed methods allow determination of catecholamines in pharmaceutical preparations.     

SENSITIVE L-CYSTEINE AMPEROMETRIC SENSOR BASED ON A GLASSY CARBON ELECTRODE MODIFIED BY MnO2 NANOPARTICLES

A sensitive amperometric sensor for the determination of L-cysteine was fabricated by electrodeposition of modified MnO₂ nanoparticles on a glassy carbon electrode. The morphology of the nanoparticles was characterized by scanning electron microscopy. Cyclic voltammetry was applied to investigate the mechanism of film formation and the electrochemical properties of the MnO₂ nanoparticle-modified electrode. The results of electrochemical experiments showed that the modified electrode had a favorable catalytic ability for the electrochemical oxidation of L-cysteine. Under optimized conditions, the MnO₂ nanoparticle-modified electrode exhibited a linear dependence on the concentration of L-cysteine from 1.0 × 10^?6 to 6.4 × 10^?4 M, and a detection limit of 8.0 × 10^?7 M (signal/noise = 3). The modified electrode was highly resistant towards typical inorganic salts and some biomolecules. In addition, the sensor was applied for the determination of L-cysteine in human serum with high accuracy, demonstrating its potential for practical applications.     

PVC MATRIX MEMBRANE SENSORS FOR POTENTIOMETRIC DETERMINATION OF ARECOLINE

The construction and electrochemical response characteristics of Poly (vinyl chloride) (PVC) membrane sensors for arecoline HBr (AR) are described. The sensing membranes incorporate ion association complexes of (AR) cation and sodium tetraphenyl borate (NaTPB) (sensor 1) or phosphomolybdic acid (PMA) (sensor 2) or phosphotungstic acid (PTA) (sensor 3) as electroactive materials. The sensors display a fast, stable and near-Nernstian response over a relative wide AR concentration range (1 × 10^?2 – 4 × 10^?5 M) and (1 × 10^?2 to 5 × 10^?6 M), with cationic slopes of 52.5, 50.5 and 51.5 mV per concentration decade for sensor 1, 2, and 3, respectively over a pH range of 3.0–6.0. The sensors show good discrimination of AR from several inorganic and organic compounds. The direct determination of 1.5–2360.0 μg/ml of AR show an average recovery of 99.0, 98.5 and 99.5% and a mean relative standard deviation of 1.7, 1.6 and 1.5% at 200.0 μg/ml for sensor 1, 2 and 3 respectively. The proposed sensors have been applied for direct determination of AR in human saliva. The results obtained for determination of AR in saliva using the proposed method comparable favorably with those obtained using HPLC method.     

DESIGN OF A SENSITIVE MEMBRANE OPTODE FOR IRON DETERMINATION

An optical chemical sensor has been developed for the sensitive determination of Fe (III) ions by spectrophotometry. The optical membrane was constructed by immobilization of methyltrioctylammonium chloride on triacetylcellulose polymer. The exchange of thiocyanate as counter ion in the membrane sensitized this film to Fe (III). The sensing membrane is capable of determining Fe(III) reversibly over a dynamic range of 7.11 × 10^?7?8.88 × 10^?5 mol L^?1 with a limit of detection of 6.02 × 10^?7 mol L^?1 and a response time of 5 min. This optode can easily be regenerated by 0.1 mol L^?1 of sodium fluoride solution. The relative standard deviation for eight replicate measurements of 7.11 × 10^?6 and 5.33 × 10^?5 mol L^?1 of Fe (III) was 4.2 and 3.7%, respectively. The sensor was successfully applied for the determination of iron in tablet and water samples.     

DETERMINATION OF TRACE CADMIUM BY FLOW INJECTION ON-LINE MICROCOLUMN PRECONCENTRATION COUPLED WITH FLAME ATOMIC ABSORPTION SPECTROMETRY USING HUMAN HAIR AS A SORBENT

A novel method using a cone-shaped pipette tip packed with human hair as an adsorption material has been developed for the on-line flow injection preconcentration of trace Cd(II) ions based on its complex formation with the ammonium pyrrolidine dithiocarbamate (APDC) prior to flame atomic absorption spectrometric (FAAS) determination. Cd-PDC complex sorbed on the human hair was eluted by 4.0 mol L^?1 HNO₃. The enhancement factor is 19, and the detection limit (3σ) is 0.77 μg L^?1. The proposed method was successfully applied to the determination of trace cadmium in drinking water, beverage samples, and the certified reference materials.     

A HYDROGEN PEROXIDE SENSOR BASED ON PRUSSIAN BLUE AND DNA-MODIFIED ELECTRODE

The polyvinylpyrrolidone (PVP) protected Prussian blue (PB) nanoparticles were prepared for use as a sensor for the catalytic reduction of hydrogen peroxide. The nanoparticles were used to modify a gold electrode, which was applied to detect hydrogen peroxide. Impedance spectra and differential pulse voltammetry were applied to detect the performance of the novel electrode and its response to H₂O₂ and Ramos cell smash fluid. Under the optimized experimental conditions, hydrogen peroxide was detected in a linear range of 6.25 × 10^?7 to 1.0 × 10^?5 mol · L^?1, and the detection limit was 7.12 × 10^?8 mol · L^?1 according to 3σ rule. Under the same conditions, hydrogen peroxide was determined in Ramos cell smash fluid with a linear range from 400–80000 mol mL^?1, with a detection limit of 114 mL^?1 according to 3σ rule. The modified electrode with Prussian blue nanoparticles displayed high sensitivity, good reproducibility, and long-term stability to hydrogen peroxide.     

CERIUM(IV)-BASED CHEMILUMINESCENCE OF FELODIPINE SENSITIZED BY RHODAMINE 6G

A simple, rapid, and sensitive flow injection chemiluminescence (FI-CL) method was proposed for the determination of felodipine. The method was based on the CL-emitting reaction between the studied drug and cerium(IV) in a nitric acid medium and measurement of the CL intensity produced by rhodamine 6G used as a sensitizer. Under the optimum conditions, the proposed procedure had a linear range between 5.0 × 10^?9 and 7.0 × 10^?6 g mL^?1, with a detection limit of 2.0 × 10^?9 g mL^?1. The relative standard deviation was 2.3% for 1.0 × 10^?7 g mL^?1 felodipine solution (n = 11). It was applied to the determination of felodipine in pharmaceutical preparations and biological fluids with satisfactory results. The possible mechanism of the chemiluminescence reaction was also discussed briefly.     

Determination of propyl gallate in edible oil by high-performance liquid chromatography with chemiluminescence detection

A novel and convenient method based on high-performance liquid chromatography coupled with chemiluminescence (HPLC) for the determination of propyl gallate in edible oil is reported. The detection was based on the inhibition of chemiluminescence between luminol and hydrogen peroxide in alkaline solution. The analysis was performed using a C₁₈ column with isocratic 60:40 methanol/water. Under the optimum conditions, the concentration of propyl gallate was linear from 9?×?10^?6?mol?L^?1 to 1?×?10^?4?mol?L^?1 with a detection limit of 2?×?10^?7?mol?L^?1. The method is simple, sensitive, and inexpensive and was used for the determination of propyl gallate in edible oil.     

CATALYTIC KINETIC SPECTROPHOTOMETRIC DETERMINATION OF SODIUM DODECYL SULPHONATE

A novel catalytic kinetic spectrophotometric method for the determination of trace sodium dodecyl sulphonate (SDS) is proposed using the principle that trace SDS catalyses the oxidation fading reaction of rhodamine B by potassium periodate. Under the optimum reaction conditions, a good linear relationship is presented between the reaction rate and the mass concentration of SDS over the range of 0.30–1.0 μg/mL at its maximum absorption wavelength of 552 nm. The detection limit of the method was 0.152 μg/mL. The method has been successfully used to determine SDS in scour and water samples.     

DETERMINATION AND SEPARATION MECHANISM OF ACRYLAMIDE BY HIGH-PERFORMANCE LIQUID CHROMATOGRAPHY

High-performance liquid chromatography using the negative peak method was developed for the determination and separation of acrylamide in food with methanol-water containing a background reagent of 0.01 mmol L^?1 5-sulfosalicylic acid (15/85, v/v) as the mobile phase with an ultraviolet-visible detector (λ_sig = 320 nm, λ_ref = 210 nm). The method was simple, the correlation coefficients exceeded 0.9990, and the limit of detection for acrylamide was 0.07 μg kg^?1. The concentrations of acrylamide in food were between 81 and 910 μg kg^?1. The recoveries were greater than 81.0% and the relative standard deviation was between 0.24 and 3.6%. The results showed that this method was suitable for the determination of acrylamide in food.     

DETERMINATION OF PICOMOLE CONCENTRATIONS OF ALUMINUM (III) IN HUMAN SALIVA AND URINE BY A LUMINOL-CARBOXYMETHYL CHITOSAN CHEMILUMINESCENCE SYSTEM

A luminol–carboxymethyl chitosan (CMCS) system was established using flow injection chemiluminescence (CL) based on the enhancing effect of CMCS on the luminol–dissolved oxygen reaction. The CL intensity was linear with the CMCS concentration ranging from 0.01–30.0 µM. Al(III) was shown to quench the CL of the luminol–CMCS reaction, and the decrease of CL intensity was linear with the logarithm of Al(III) concentration over the range from 10–1000 pM with a detection limit of 3.5 pM (3σ). At a flow rate of 2.0 mL min^?1, the analysis was performed within 30 s. The proposed CL method was successfully applied to the determination of picomole levels Al(III) in human saliva and urine after oral intake of two aluminum hydroxide tablets, with recoveries from 90.6–108.7% and relative standard deviations <3% (n = 5). The results indicated that the excreted Al(III) in saliva and urine reached its maximum values at 3 hr and 2 hr, and the total excretive ratio were 1.24 × 10^?3% and 3.45% in 6 hr and 12 hr, respectively. The elimination rate constant k and the half–life time t _1/2 in human saliva and urine were 0.3747 hr^?1, 1.8495 hr, 0.7132 hr^?1, and 0.9717 hr, respectively. The possible CL mechanism of the luminol–CMCS–Al(III) reaction is discussed.     

Simultaneous Determination of Six Trace Elements in Plant Medicines by Derivative Adsorption Waves in Conjunction with a Microwave Technique

Abstract

Complex adsorption waves of Cu(II), Pb(II), Cd(II), Ni(II), Co(II), and Zn(II) in substrate solution (pH=9.26) of diacetyldioxime‐ammonia‐ammonium chloride‐sodium citrate‐gelatin‐sodium sulfite were studied and a new method for determination of the six trace elements in aqueous solutions was developed. The results show that there are sensitive adsorption waves of Cu(II), Pb(II), Cd(II), Ni(II), Co(II), and Zn(II) complexes at about ?0.45, ?0.61,?0.78, ?1.07, ?1.23, and ?1.38 V, respectively. The method is easy to operate and is able to determine these trace elements in aqueous solutions rapidly and simultaneously. When the signal‐to‐noise ratio equals 3, the detection limits of copper, lead, cadmium, nickel, cobalt, and zinc are 3.2×10^?4, 4.8×10^?3, 1.9×10^?3, 1.7×10^?5, 2.1×10^?6, and 1.0×10^?3 µg/cm³. Good linear relationships exist between the concentrations and the current peaks when copper, lead, cadmium, nickel, cobalt, and zinc concentrations are within 6.5×10^?4～10⁰, 9.3×10^?3～10, 4.1×10^?3～10, 3.2×10^?5～10^?1, 4.0×10^?6～10^?2, and 2.1×10^?3～10 µg/cm³, respectively. In conjunction with a microwave assimilation technique, the method has been used in the rapid and simultaneous determination of these trace elements in some plant medicines with satisfactory results.     

Resonance Rayleigh Scattering of K2Zn3[Fe(CN)6]2 Nanoparticles and its Application for the Determination of Vitamin C

Abstract

In Britton-Robinson buffer medium, (pH 4.43), potassium ferricyanide (K₃[Fe(CN)₆]) could react with vitamin C (VC) to produce potassium ferrocyanide (K₄[Fe(CN)₆]), which further reacted with Zn²⁺ to form potassium zinc hexacyanoferate K₂Zn₃[Fe(CN)₆]₂ nanoparticles. The shapes and diameters of the K₂Zn₃[Fe(CN)₆]₂ nanoparticles have been observed with transmission electron microscopy, which showed the shapes of these nanoparticles was cubic and their average sizes were about 50 nm in the presence of 2.0 × 10^?5 mol L^?1 VC. The characteristics of resonance Rayleigh scattering (RRS) spectra of this reaction have been studied. The optimum reaction condition for the determination of VC has been investigated. It was found that the RRS intensity of the system at the RRS peak of 363.4 nm was proportional to the VC concentration in the range of 4.0?80.0 µmol L^?1, and the detection limit (3σ) for VC was 0.075 µmol L^?1. A novel and simple RRS method for the determination of VC based on the formation of K₂Zn₃[Fe(CN)₆]₂ nanoparticles has been established.     

PVC Membrane Sensor for Potentiometric Determination of Fluoxetine in Some Pharmaceutical Formulations

Abstract

The construction and general performance of a novel potentiometric membrane sensor for determination of fluoxetine has been developed. It is based on the formation of the ion association complex of fluoxetine with picrolonic acid as electroactive material, dispersed in a PVC matrix and o‐nitrophenyl octyl ether as a plasticizer. The sensor shows a fast, stable, and near Nernstian response for 1×10^?2 M to 8×10^?6 M fluoxetine at 25°C over the pH range of 1–5 with a cationic slope of 51±0.5 mV/decade. The lower detection limit is 6×10^?6 M and the response time 20–35 sec. Selectivity coefficients for fluoxetine, related to number of interfering substances, were investigated. There are negligible interferences from the studied cations, anions, and pharmaceutical excipients. The determination of fluoxetine in aqueous solution shows an average recovery of 98.6% and a mean relative standard deviation (RSD) of 1.5% at 100 µg/mL. The direct determination of fluoxetine in some formulations gave results that compare favorably with those obtained by a spectrophotometric method. The developed membrane electrode has been used as an end point indicator electrode, e.g., potentiometric titration of fluoxetine with sodium tetraphenylborate as a titrant has been monitored.