Kinetic Spectrophotometric Determination of Traces of Iron by its Catalytic Effect on the Oxidation of m-Acetylchlorophosphonazo by Hydrogen Peroxide

Abstract

In the buffer medium of KHC₈H₄O₄–HCl at pH 3.2, a catalytic kinetic spectrophotometric method for the determination of iron was developed by use of the catalytic effect of iron(III) on the oxidation of m-acetylchlorophosphonazo by hydrogen peroxide. At the wavelength of 544 nm, the difference of absorbance(?A) is well linearly related with the concentration of iron(III) in the range of 0–2.5 µg/25 mL and fitted the equation: ?A = 0.1469 C(µg/25 mL) + 0.0037, with a regression coefficient of 0.9979.The detection limit of the method is 1.34 ng/mL. The present method was successfully applied to determine iron in rice samples.     

Polarographic Reduction Wave of Hemoglobin and its Application to Micro‐Determination

Abstract

An adsorptive reduction wave of hemoglobin at about ?1.43 V (vs. SCE), in phosphate buffer solution, pH 6.8, was found by using single sweep polarography. Based on this wave, a simple, rapid, and reliable polarographic method for hemoglobin determination was developed. The wave height is linearly proportional to the concentration of hemoglobin in the range of 1.0–28 mg/L (correlation coefficient 0.997). The detection limit is 0.5 mg/L. Serum albumin, common amino acids, and metal ions present no interference with the hemoglobin determination.

The proposed method was applied to the determination of hemoglobin in human blood samples with satisfactory results. The polarographic wave is attributed to the direct reduction of hemoglobin at the dropping mercury electrode. The new method could be useful in biochemical, clinical, and pharmaceutical analysis.     

Accurate Calibration of Mercury Vapour Indicators for Occupational Exposure Measurements using a Dynamic Mercury Vapour Generator

Abstract

An accurate and rapid calibration procedure for mercury vapour indicators used for occupational exposure measurements is described, using a dynamic mercury vapour generator traceable to the standard bell-jar calibration apparatus. The method provides greater flexibility, accuracy, and trace ability than the usual methods for the calibration of mercury vapour indicators used for occupational exposure measurements. The calibration procedure allows a correction to be applied to the mass concentration value displayed by the mercury vapour indicator. Measurement results from the mercury vapour indicator at the occupational exposure limit of 25 µg ·m^?3, following calibration, have been estimated to have an expanded uncertainty of 8%.     

A MINIATURE SURFACE PLASMON RESONANCE BIOANALYTICAL SYSTEM FOR FIELD DETECTION OF MICROCYSTIN-LR IN SURFACE WATER

A miniature surface plasmon resonance (SPR)–based immunoassay system for analyzing microcystin-LR (MC-LR) in surface water has been developed. A Spreeta biosensor was adopted in the SPR flow injection analysis (FIA) system. An optional biofilm immobilization method was exploited using covalent-coupling between a bioconjugate of microcystin-LR and bovine serum albumin [(MC-LR)-BSA] and the golden surface. An acceptable relative standard deviation of repeatability, 1.29% (n = 20), was achieved. An analysis of the calibration curve showed that this method has a detection limit of 0.55 ng/mL, a half-maximal inhibitory concentration (IC₅₀) of 5.6 ng/mL, and a quantitative range of 1.56–25.00 ng/mL. The recovery from water samples containing varying concentrations of MC-LR ranged from 90% to 112%. After samples of tap water and pool water were assayed, it was concluded that tap water did not contain a measurable amount of the analyte, whereas pool water contained 2.39 ng/mL. Compared to other methods of analysis, SPR immunoassay has the advantage of being label-free, rapid, and cost-effective and can easily detect levels of MC-LR within the World Health Organization (WHO) drinking water guidelines. The SPR FIA system with reusable biosensor is compact and convenient for instant in situ determination of MC-LR levels in environmental water.     

Inductively Coupled Plasma Optical Emission Spectrometric Determination of Gadolinium in Urine Using Flow Injection On‐Line Sorption Preconcentration in a Knotted Reactor

Abstract

An on‐line gadolinium preconcentration and determination system, implemented with ultrasonic nebulization coupled to inductively coupled plasma optical emission spectrometry (ICP‐OES), associated with flow injection (FI) was studied. Gadolinium was retained as Gd‐2‐(5‐bromo‐2‐pyridilazo)‐5‐diethylaminophenol complex (Gd‐5‐Br‐PADAP) at pH 9.0, on the inner walls of the knotted reactor (KR). The collected analyte complexes were quantitatively eluted from the 200 cm KR with 30% (v/v) nitric acid. An enhancement factor of 255‐fold was obtained (17 for KR and 15 for USN). The detection limit (DL) value for the preconcentration of 15 mL of sample was 4.0 ng L^?1. The relative standard deviation (RSD) was 3.5%, calculated from the peak heights obtained. The calibration graph using the preconcentration system for gadolinium was linear, with a correlation coefficient of 0.9996 at levels near the detection limit up to at least 200 µg L^?1. The method was successfully applied to the determination of gadolinium in urine samples.     

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%.     

Highly Sensitive Determination of Iron Ions in Water With Bromopyrogallol Red by Light Absorption Ratio Variation Spectrophotometry

Abstract

The complexation between Fe ions (II, III) and bromopyrogallol red (BPR) is sensitive at pH 6.23 with the composition ratio at 1:2 of Fe to BPR, and it is selective in the presence of F^? and thiocarbamide. Using this reaction, the light absorption ratio variation approach was applied to the direct determination of Fe ions. The limit of detection is only 4.5 µg/L Fe. The Fe ions content existing in the Yangtze River, Taihu Lake, tap water and Huangpu River in Shanghai was determined with the recovery rate between 95.5 and 106%.     

Development of Sulfide‐Selective Optode Membranes Based on Immobilization of Methylene Blue on Optically Transparent Triacetylcellulose Film

Abstract

The development of reversible sulfide‐selective optode membranes, based on immobilization of methylene blue (MB) on optically transparent triacetylcellulose film, is described. The sensing scheme of the sulfide‐selective optode membranes is based on the decreasing absorbance of the membrane at 654 nm in the presence of sulfide, which can be related to the sulfide concentration in solution. The dynamic working range, detection limit, sensitivity, selectivity, and effect of pH are discussed in detail.

Under optimum experimental conditions, the membrane system shows a calibration response range from 3.1×10^?5 to 6.1×10^?4 M in a phosphate buffer of pH 7.5. Typical response times in the samples are 15–20 min. The lifetime of the system was about 30 days, with a relative standard deviation of <2%. The sensing membrane showed a good selectivity to sulfide over other anions. The optode membrane was applied to the determination of sulfide in real samples.     

1‐Pyrenemethanol,a Useful Fluorometric Reagent for the Detection and Determination of Carboxylic Acids in Atmospheric Samples

Abstract

A rapid fluorometric procedure for the selective and sensitive determination of carboxylic acids, based on pre‐column derivatization using 1‐pyrenemethanol, was optimized and applied to atmospheric sampling. The optimum conditions for derivatization were determined to be: reaction solvent–dichloromethane, temperature ?44°C, reaction time ?30 min, and reagent/total acid ratio ?15. Separation of the derivatives of acids up to twenty carbons by reversed‐phase (C₈) chromatography was achieved in 25 min using a water/acetonitrile gradient with a limit of detection for the derivatives of 20 pg for a 20 µL injection. A scanning detector with good spectral resolution allows qualitative identification of the components in complex samples. When used in atmospheric analysis, the recoveries of carboxylic acids from spiked samples were >80% with repeatabilities below 10% RSD. Low molecular weight acids were encountered predominantly in the vapor phase (0.20 to 92 ng/m³), whereas higher molecular weight acids were found mostly in particulate form (0.15–129 ng/m³).     

On‐Line Preconcentration System for Cobalt Determination in Bee Honey Using Flow Injection‐Flame AAS

Abstract

A methodology for the on‐line preconcentration and determination of cobalt by flame atomic absorption spectrometry (FAAS) coupled with flow injection (FI) in bee honey samples is proposed. For the retention of cobalt, 2‐(5‐bromo‐2‐pyridylazo)‐5‐diethylaminophenol (5‐Br‐PADAP) complexing reagent, and Amberlite XAD‐7 resin were used, at pH 9.5. The Co‐(5‐Br‐PADAP) complexes were completely removed from the column with ethanol. An enrichment factor (EF) of 50‐fold for a sample volume of 50 mL was obtained. The detection limit (DL) for the preconcentration of 50 mL of aqueous solution was 0.18 µg L^?1. The precision for 10 replicate determinations at the 10 µg L^?1 cobalt levels was 3.6% relative standard deviation (RSD), calculated with peak heights obtained. The calibration graph using the preconcentration system for cobalt was linear with a correlation coefficient of 0.9997 at levels near the DL, up to at least 300 µg L^?1. The method was successfully applied to determination of total cobalt in honey samples.     

DETERMINATION OF COPPER(II) IN NATURAL WATERS BY EXTRACTION USING N-O-VANILLIDINE-2-AMINO-P-CRESOL AND FLAME ATOMIC ABSORPTION SPECTROMETRY

A simple and accurate solvent extraction method was developed for the separation and preconcentration of trace levels of copper(II) in water using N-o-vanillidine-2-amino-p-cresol prior to its determination using flame atomic absorption spectrometry. Analytical parameters such as the pH of the aqueous phase, extraction time, concentration of the reagent, concentration of the nitric acid back extraction agent, volumes of aqueous phase and back extraction agent, and concomitant ions on the extraction yield of the copper(II) were investigated and optimized. Under the optimal conditions, the detection limit (3σ) was 0.61 µ g L^?1 for a 25 mL blank solution, yielding a preconcentration factor of 12.5. The method was succesfully applied to the determination of copper(II) in tap water, river water, and seawater. The accuracy of the method was verified by analyzing two certified reference materials and spiked water samples. The results obtained were in agreement with the certified values and the recoveries for spiked water samples were between 98 and 112%.     

Determination of benzimidazoles in pharmaceuticals and human serum by high-performance liquid chromatography

A liquid chromatographic method is described for the quantification of prednisolone, benzimidazoles, and preservatives using a C₁₈ analytical column as stationary phase. The mobile phase was 30:70 methanol:pH 2.5 phosphate buffer at a flow rate of 1.0 mL min^?1 with absorbance detection at 235 nm. The method was linear for concentrations ranged from 40–10,000 ng mL^?1. Low values of coefficient of variance were obtained when samples were analyzed as replicates. Excellent recovery values were recorded in commercial products and fortified samples. International Conference of Harmonization protocols were employed to perform comprehensive method validation. The reported method has applications for pharmaceutical and serum samples.     

Determination of methyl gallate in Bauhinia retusa extract by high-performance liquid and thin-layer chromatography

Two stability-indicating chromatographic methods are reported for the determination of methyl gallate in crude extracts of Bauhinia retusa. Separation by high performance thin layer chromatography was conducted on silica gel aluminum sheets using 9.5:0.5:0.2 (v/v/v) chloroform:methanol:acetic acid at 280 nm. The results from the 2–40 µg/band were used to prepare a linear calibration graph. The limits of detection and quantitation were 0.5 and 1.5 µg/band, respectively. The reverse phase high performance liquid chromatographic isolation of methyl gallate was performed at ambient temperature with an injection volume of 10 μL. The mobile phase consisted of 40:60 (v/v) methanol:0.1% ortho-phosphoric acid. The separation was performed at 1 mL/min using a detection wavelength of 280 nm. The calibration graph for methyl gallate was rectilinear from 0.02–40 µg/mL with limits of detection and quantitation of 0.004 and 0.010 µg/mL, respectively. For both methods, intra-day and inter-day precision were evaluated and the relative standard deviation was less than 2%, indicating good precision. The robustness was evaluated by making small and deliberate changes to appropriate parameters and the calculated relative standard deviation was less than 2%.The chromatographic methods were employed to determine methyl gallate in crude Bauhinia retusa extracts.     

Compact Design for a Square Wave Excitation Contactless Conductivity Detector: Determination of Metal Cations in Environmental Water Samples

Abstract

A compact and inexpensive contactless conductivity detection (CCD) based on a square wave excitation voltage, was implemented by integrating the function generator, detective cell, and detective circuit on a printed circuit board with a size of 100 mm length and 50 mm width, and it exhibited excellent sensitivity at the optimal frequency of 198 kHz. The separation for 13 metal ions was demonstrated by optimizing some most significant concentration factors, such as the concentration of 2‐(N‐morpholino) ethanesulfonic acid/DL‐histidine (MES/His), cetyltrimethylammonium bromide (CTAB), and α‐hydroxyisobutyric acid (HIBA). Under the optimized condition of 15 mM MES/His, 0.02 mM CTAB, and 0.5 mM HIBA, the detection limits were in the range of 0.9～5 µM for K⁺, Ba²⁺, Ca²⁺, Na⁺, Mg²⁺, Mn²⁺, and Li⁺; 7～25 µM for Pb²⁺, Cd²⁺, Zn²⁺, Co²⁺, Cu²⁺, and Ni²⁺. This CCD was further used to determine the metal cations in the real samples, such as tap water and low pH galvanic bath rinse water, and the results demonstrated that this CCD system was feasible for analysis of ions in an environmental sample.     

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.     

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

Abstract

The construction and general performance of a novel potentiometric membrane sensor for determination of atropine has been developed. It is based on the formation of the ion association complex of the atropinium cation with phosphotungstate counter anion as electroactive material dispersed in a PVC matrix, β‐Cyclodextrin and o‐nitrophenyl octyl ether serve as a plasticizer. The sensor shows a fast, stable, near Nernstian response for 1×10^?2 M to 1×10^?6 M atropine at 25°C over the pH range of 3–8 with a cationic slope of 51±0.5 mV/decade. The lower detection limit is 8×10^?7 M and the response time is 20–45 sec. Selectivity coefficients of atropine, relative to a number of interfering substances, were investigated. There are negligible interferences caused by most of the studied cations, anions, and pharmaceutical excipients. The direct determination of atropine shows an average recovery of 98.6% and a mean relative standard deviation (RSD) of 1.6% at 100 µg/mL. The results obtained by determination of atropine in some formulations (atropine injection and eye drops) are favorably comparable with those obtained by the British Pharmacopoeia method. The developed membrane electrode has been used as end point indicator electrode for some potentiometric titrations.     

Evaluation of Halogen‐Specific Detector (XSDTM) for Trace Analysis of Chlorinated Fatty Acids in Fish

Abstract

The applicability of a halogen‐specific detector (XSD?, manufactured by OI Analytical) was evaluated for GC analysis of chlorinated fatty acid methyl esters (FAMEs) that are present at trace levels in transesterified fish extract, a complex matrix consisting of similar but nonchlorinated compounds. A characteristic of the XSD working principle is that thermal electron emission, negative surface ionization and positive surface ionization are all operative in a concerted manner. While the XSD is not superior to other GC detectors in terms of signal‐to‐noise, its merit is in its high selectivity (10⁶) and low detection limit (2 pg Cl) for chlorinated fatty acids, and ease of operation and maintenance. Its reasonably wide linear range (up to 10 ng Cl) is desirable for trace analysis of chlorinated FAMEs. A major drawback of this detector is a certain degree of peak broadening and peak tailing of eluted compounds with concentrations larger than ～1 ng Cl/µL in the injected solution even though this value does not exceed the upper limit of the XSD linear range. Nevertheless, in trace analysis of chlorinated compounds, the concentrations of analytes are usually well below 1 ng Cl/µL. Parallel use of the XSD and a universal detector such as FID in gas chromatography is useful for optimizing operation conditions for trace analysis and simultaneously analyzing nonchlorinated major components.     

Determination of Ammonia in Seawater by Multichannel Flow Injection Analysis

An analytical method that uses multichannel flow injection is reported to determine ammonia in seawater. The sample throughput was twenty-eight samples per hour. The linear dynamic range for ammonia was from 20.0–1000.0 μg N · L^?1 with a limit of detection of 0.27 μg N · L^?1, and recovery values between 98.1% and 104.6%. The relative standard deviation values for nitrogen as ammonia were 2.15–3.33% (n = 6). Statistical t-test analysis indicated that analysis by the flow injection method provided results that were statistically the same as standard procedures. The reported method was suitable for the determination of ammonia in seawater.     

Fluorimetric Determination of Aluminium using Sequential Injection Analysis (SIA): State of Our Art and Future Developments

Abstract

This paper describes some of our recent advances and proposed future work in the area of fluorimetric determination of Al using sequential injection analysis (SIA). A rapid, automated system was developed with turnover times for sample analysis of <2 min, and attainable limits of detection of <1 ng/mL. The method is cost‐effective and highly competitive. It utilizes three different approaches: (i) molecular imprinted polymers (MIPs); (ii) micellar enhanced treatment; and (iii) renewable surface application. The merits and limitations of each approach are discussed, and the optimum conditions of analysis are presented. The overall sensitivity achieved was more than adequate for general analysis. Proposed new developments involve greater signal enhancement, and improved analytical strategy. The facility is capable of routine application, and is highly beneficial to developing countries in need of cost‐effective techniques for analysis of environmental samples, body fluids, and foodstuffs.