Sequential injection analysis implementing multiple standard additions for As speciation by liquid chromatography and atomic fluorescence spectrometry (SIA-HPLC-AFS)

An analytical procedure for multiple standard additions of arsenic species using sequential injection analysis (SIA) is proposed for their quantification in seafood extracts. SIA presented flexibility for generating multiple specie standards at the ng mL(-1) concentration level by adding different volumes of As(III), As(V), monomethylarsonic (MMA) and dimethylarsinic (DMA) to the sample. The mixed sample plus standard solutions were delivered from SIA to fill the HPLC injection loop. Subsequently, As species were separated by HPLC and analyzed by atomic fluorescence spectrometry (AFS). The proposed system comprised two independently controlled modules, with the HPLC loop acting as the intermediary device. The analytical frequency was enhanced by combining the actions of both modules. While the added sample was flowing through the chromatographic column towards the detection system, the SIA program started performing the standard additions to another sample. The proposed method was applied to spoiled seafood extracts. Detection limits based on 3 sigma for As(III), As(V), MMA and DMA were 0.023, 0.39, 0.45 and 1.0 ng mL(-1), respectively. (C) 2011 Elsevier B.V. All rights reserved.

Effectiveness of the standard evaluation method for hydraulic nozzles employed in stored grain protection trials

In stored grains, smaller depositions and great variation with respect to theoretical insecticide doses are frequently found. The objective of this work was to study the effectiveness of the standard method (ISO 5682/1-1996) employed to evaluate hydraulic nozzles used in stored corn and wheat grain protection experiments. The transversal volumetric distribution and droplet spectrum of a model TJ-60 8002EVS nozzle were determined in order to calibrate a spraying system for an application rate of 5 L/t and to obtain theoretical concentrations of 10 and 0.5 mg/kg of fenitrothion and esfenvalerate, respectively. After treatment, the corn and wheat grains were processed and deposition was analyzed by gas chromatography. The type of grain did not have any influence on insecticide deposition and was dependent upon insecticide only. The insecticide deposits on the grains only reached 42.1 and 38.2% of the intended theoretical values for fenitrothion and esfenvalerate concentrations, respectively. These results demonstrate the ineffectiveness of the standard evaluation method for hydraulic nozzles employed in stored grain protection experiments.

A new IRT-based standard setting method : Application to eCat-Listening

Resumen tomado de la publicaci??n

A New Indirect Electroanalytical Method to Monitor the Contamination of Natural Waters with 4-Nitrophenol Using Multiwall Carbon Nanotubes

The electrochemical detection of the hazardous pollutant 4-nitrophenol (4-NP) at low potentials, in order to avoid matrix interferences, is an important research challenge. This study describes the development, electrochemical characterization and utilization of a multiwall carbon nanotube (MWCNT) film electrode for the quantitative determination of 4-NP in natural water. Electrochemical impedence spectroscopy measurements showed that the modified surface exhibits a decrease of ca. 13 times in the charge transfer resistance when compared with a bare glassy carbon (GC) surface. Voltammetric experiments showed the possibility to oxidize a hydroxylamine layer (produced by the electrochemical reduction of 4-NP on the GC/MWNCT surface) in a potential region which is approximately 700 mV less positive than that needed to oxidize 4-NP, thus minimizing the interference of matrix components. The limit of detection for 4-NP obtained using square-wave voltammetry (0.12 mu mol L(-1)) was lower than the value advised by EPA. A natural water sample from a dam located in Sao Carlos (Brazil) was spiked with 4-NP and analyzed by the standard addition method using thee GC/MWCNT electrode, without any further purification step. the recovery procedure yielded a value of 96.5% for such sample, thus confirming the suitability of the developed method to determine 4-NP in natural water samples. The electrochemical determination was compared with that obtained by HPLC with UV-vis detection.

Experimento didático sobre cromatografia gasosa: uma abordagem analítica e ambiental

This paper describes an experiment to teach the principles of gas chromatography exploring the boiling points and polarities to explain the elution order of a series of alcohols, benzene and n-propanone, as well as to teach the response factor concept and the internal standard addition method. Retention times and response factors are used for qualitative identification and quantitative analysis of a hypothetical contamination source in a simulated water sample. The internal standard n-propanol is further used for quantification of benzene and n-butanol in the water sample. This experiment has been taught in the instrumental analysis course offered to chemistry and oceanography students.

Tyrosinase-based phenol remediation

Dissertation for the obtention of the Master Degree in Biotechnology

Contaminação por crômio de águas de rios proveniente de curtumes em Minas Gerais

In order to evaluate the chromium contamination from tannery discharges into rivers in the State of Minas Gerais, samples of water and suspended material were collected and submitted to chemical analysis. The total content of chromium in the samples was measured by flame atomic absorption spectrophotometry. Water samples were analysed by standard addition method, while chromium concentration in suspended materials was determined by calibration curves. Localities investigated were Ipatinga, Matias Barbosa, Dores de Campo, Ressaquinha, Ubá and Juiz de Fora. Samples from a not-industrialized area were also analysed to obtain regional background values. Metal inputs were related to effluent discharges into the rivers. Suspended material transported Cr downriver. Chromium concentration in river water exceeded 656 times the value of the Brazilian Environmental Standards, while its concentration in suspended material ranged from 15 to 11066 µg g-1.

Determinação espectrofotométrica de alumínio em concentrados salinos utilizados em hemodiálise empregando pré-concentração em fluxo

An automatic flow injection procedure for spectrophotometric aluminium determination in purified water and solutions containing high salts concentrations used for hemodyalisis treatment was developed. The method was base on reaction of Al3+ with cianine eriochrome R (ECR) after preconcentration using the AG50W-X8 cationic-exchange resin. Elution was carried out using a 1 % (m/v) calcium chloride solution. The manifold comprised an automatic proporcional injector controlled by a computer equipped with an eletronic interface and software written in QuicBASIC 4.5 with facilities to control the injector and perform data acquisition. Samples with concentration ranging from 4.96 to 19.90 µg L-1 Al were analyzed and recoveries between 88 and 113% were obtained by using the standard addition method. Other profitable analytical characteristics such as a relative standard deviation 1.3 % (n = 10) for a typical sample 14.5 µg L-1 Al, a linear response ranging up to 60.0 µg L-1Al, and a sampling throughput of 10 determinations per hour were achieved. A detection limit of 4.2 µg L-1 Al was estimated as suggested by IUPAC.

Identificação e quantificação do cristal violeta em aguardentes de mandioca (tiquira)

Tiquira is a traditional homemade alcoholic distillate produced in the Maranhão State (Brazil), gotten from cassava (Manihot esculenta, Crantz.). It can be normally found on street markets. Due to the addition of tangerine leaves, the original tiquira has a bluish color. Samples of this beverage were acquired in the local trade and analyzed from the spectroanalytical point of view. The results indicated that these drinks had been adulterated by the addition of crystal violet, a potencialy hazardous compound. The identification and quantification of crystal violet in 10 spiked samples was accomplished by UV-Vis spectrophotometry through the standard addition method. In order to verify the efficiency of the proposed method, experiments on the quantification and recovery were carried out and the results indicated a content of crystal violet in the 10-6 to 10-7 mol L-1 range.

Determinação voltamétrica do herbicida glifosato em águas naturais utilizando eletrodo de cobre

The aim of this work was to investigate the copper electrode behavior in the voltammetric determination of glyphosate. The best conditions for this determination are phosphate buffer 0.05 mol L-1 and pH 7.3, and the peak potential is observed at 187 mV. LD and LQ values are 59 µg L-1 e 196 µg L-1, respectively. A water sample was analysed for glyphosate and identical results were obtained by using the analytical curve and the standard addition method. The comparison with a voltammetric method with Hg electrode, after a reaction with nitrite, showed quite concordant results for the analysis of the surface water sample. Therefore, the proposed method can be applied to direct determinations of the herbicide in waters, decreasing the time of analysis; besides, the method is in agreement with the "green chemistry" concept.

Experimento didático sobre cromatografia gasosa: uma abordagem analítica e ambiental

This paper describes an experiment to teach the principles of gas chromatography exploring the boiling points and polarities to explain the elution order of a series of alcohols, benzene and n-propanone, as well as to teach the response factor concept and the internal standard addition method. Retention times and response factors are used for qualitative identification and quantitative analysis of a hypothetical contamination source in a simulated water sample. The internal standard n-propanol is further used for quantification of benzene and n-butanol in the water sample. This experiment has been taught in the instrumental analysis course offered to chemistry and oceanography students.

RAPID AND SENSITIVE DETERMINATION OF PALLADIUM USING HOMOGENEOUS LIQUID-LIQUID MICROEXTRACTION VIA FLOTATION ASSISTANCE FOLLOWED BY GRAPHITE FURNACE ATOMIC ABSORPTION SPECTROMETRY

A method for the determination of trace amounts of palladium was developed using homogeneous liquid-liquid microextraction via flotation assistance (HLLME-FA) followed by graphite furnace atomic absorption spectrometry (GFAAS). Ammonium pyrrolidine dithiocarbamate (APDC) was used as a complexing agent. This was applied to determine palladium in three types of water samples. In this study, a special extraction cell was designed to facilitate collection of the low-density solvent extraction. No centrifugation was required in this procedure. The water sample solution was added to the extraction cell which contained an appropriate mixture of extraction and homogeneous solvents. By using air flotation, the organic solvent was collected at the conical part of the designed cell. Parameters affecting extraction efficiency were investigated and optimized. Under the optimum conditions, the calibration graph was linear in the range of 1.0-200 µg L-1 with a limit of detection of 0.3 µg L-1. The performance of the method was evaluated for the extraction and determination of palladium in water samples and satisfactory results were obtained. In order to verify the accuracy of the approach, the standard addition method was applied for the determination of palladium in spiked synthetic samples and satisfactory results were obtained.

Argentimetric assay of ranitidine in bulk drug and in dosage forms

Two simple, rapid and cost-effective methods based on titrimetric and spectrophotometric techniques are described for the assay of RNH in bulk drug and in dosage forms using silver nitrate, mercury(II)thiocyanate and iron(III)nitrate as reagents. In titrimetry, an aqueous solution of RNH is treated with measured excess of silver nitrate in HNO3 medium, followed by determination of unreacted silver nitrate by Volhard method using iron(III) alum indicator. Spectrophotometric method involve the addition a known excess of mercury(II)thiocyanate and iron(III)nitrate to RNH, followed by the measurement of the absorbance of iron(III)thiocyante complex at 470 nm. Titrimetric method is applicable over 4-30 mg range and the reaction stoichiometry is found to be 1:1 (RNH: AgNO3). In the spectrophotometric method, the absorbance is found to increase linearly with concentration of RNH which is corroborated by the correlation coefficient of 0.9959. The system obey Beer's law for 5-70 µg mL-1. The calculated apparent molar absorptivity and sandell sensitivity values are found to be 3.27 ´ 10³ L mol-1 cm-1, 0.107 µg cm-2 respectively. The limits of detection and quantification are also reported for the spectrophotometric method. Intra-day and inter-day precision and accuracy of the methods were evaluated as per ICH guidelines. The methods were successfully applied to the assay of RNH in formulations and the results were compared with those of a reference method by applying Student's t and F-tests. No interference was observed from common pharmaceutical excipients. The accuracy of the methods was further ascertained by performing recovery tests by standard addition method.

Spectrophotometric determination of lansoprazole in pharmaceuticals using bromate-bromide mixture based on redox and complexation reactions

Two sensitive spectrophotometric methods are described for the determination of lansoprazole (LPZ) in bulk drug and in capsule formulation. The methods are based on the oxidation of lansoprazole by insitu generated bromine followed by determination of unreacted bromine by two different reaction schemes. In one procedure (method A), the residual bromine is treated with excess of iron (II), and the resulting iron (III) is complexed with thiocyanate and measured at 470 nm. The second approach (method B) involves treating the unreacted bromine with a measured excess of iron (II) and remaining iron (II) is complexed with orthophenanthroline at a raised pH, and measured at 510 nm. In both methods, the amount of bromine reacted corresponds to the amount of LPZ. The experimental conditions were optimized. In method A, the absorbance is found to decrease linearly with the concentration of LPZ (r = -0.9986) where as in the method B a linear increase in absorbance occurs (r = 0.9986) The systems obey Beer's law for 0.5-4.0 and 0.5-6.0 µg mL-1 for method A and method B, respectively. The calculated molar absorptivity values are 3.97µ10(4) and 3.07µ10(4) L mol-1cm-1 for method A and method B, respectively, and the corresponding Sandell sensitivity values are 0.0039 and 0.0013 µg cm-2. The limit of detection (LOD) and quantification (LOQ) are also reported for both methods. Intra-day and inter-day precision, and accuracy of the methods were established as per the current ICH guidelines. The methods were successfully applied to the determination of LPZ in capsules and the results tallied well with the label claim and the results were statistically compared with those of a reference method by applying the Student's t-test and F-test. No interference was observed from the concomitant substances normally added to capsules. The accuracy and validity of the methods were further ascertained by performing recovery experiments via standard-addition method.

Novel potentiometric sensors for the selective determination of domperidone

The fabrication and electrochemical response characteristics of two novel potentiometric sensors for the selective determination of domperidone (DOM) are described. The two fabricated sensors incorporate DOM–PTA (phosphotungstic acid) ion pair as the electroactive material. The sensors include a PVC membrane sensor and a carbon paste sensor. The sensors showed a linear, stable, and near Nernstian slope of 56.5 and 57.8 mV/decade for PVC membrane and carbon paste sensors, respectively over a relatively wide range of DOM concentration (1.0 9 10-1–1.0 9 10-5 and 1.0 9 10-1–3.55 9 10-6 M). The response time of DOM–PTA membrane sensor was less than 25 s and that in the case of carbon paste sensor was less than 20 s.Auseful pH range of 4–6 was obtained for both types of sensors. A detection limit of 7.36 9 10-5 M was obtained for PVC membrane sensor and 1.0 9 10-6 M was obtained for carbon paste sensor. The proposed sensors showed very good selectivity toDOMin the presence of a large number of other interfering ions. The analytical application of the developed sensors in the determination of the drug in pharmaceutical formulations such as tablets was investigated. The results obtained are in good agreement with the values obtained by the standard method. The sensors were also applied for the determination ofDOMin real samples such as urine by the standard addition method.