An automated system for liquid-liquid extraction in monosegmented flow analysis

An automated system to perform liquid-liquid extraction in monosegmented flow analysis is described. The system is controlled by a microcomputer that can track the localization of the aqueous monosegmented sample in the manifold. Optical switches are employed to sense the gas-liquid interface of the air bubbles that define the monosegment. The logical level changes, generated by the switches, are flagged by the computer through a home-made interface that also contains the analogue-to-digital converter for signal acquisition. The sequence of operations, necessary for a single extraction or for concentration of the analyte in the organic phase, is triggered by these logical transitions. The system was evaluated for extraction of Cd(II), Cu(II) and Zn(II) and concentration of Cd(II) from aqueous solutions at pH 9.9 (NH3/NH4Cl buffer) into chloroform containing PAN (1-(2-pyridylazo)-2-naphthol) . The results show a mean repeatability of 3% (rsd) for a 2.0 mg l-1 Cd(II) solution and a linear increase of the concentration factor for a 0.5mg l-1 Cd(II) solution observed for up to nine extraction cycles

Automatic determination of mercury in samples of environmental interest

An automatic flow injection (FI) system for the determination of mercury was developed using a commercial Gold vapour atomic absorption spectrophotometer (CVAAS). Control and data acquisition in the FI system was done with an IBM-PC 286 XI compatible microcomputer and a home-made interface, using software written in QuickBasic 4.5. Mercury content was determined by: sampling using a combination of four electromechanical three-way poly(tetrafluoroethylene) valves; separation of the dissolved reduced mercury in a gas/liquid separation cell using nitrogen as carrier, followed by amalgamation of the stripped metal on a gold wire column; after stripping the metal, cleaning the separation cell using vacuum, which was controlled by a three-way electromechanical valve; heating the gold wire column automatically to release the amalgamated mercury using an external nichrome wire coil; storing the output signals automatically to calculate the final mercury concentration, using commercially available software. The optimized system presents a detection limit of 5.3 ng l(-1) of mercury (30 pg absolute) using 5.7 ml (three injections of 1900 mu l of the sample) with an analytical frequency of six samples per hour and reproducibility of 5%. The procedure was used to determine mercury in fish, hair and natural water samples.18619319

Automation of a plane grating spectrograph

A Zeiss model PGS-2 plane grating spectrograph was automated by replacing its photograph film detection system with an EGG-Reticon 1024S photodiode array (PDA) and by controlling the main instrument functions through the use of a home-made interface connected to a microcomputer. The array was cooled by four Peltier elements to allow integration of the emitted light for up to 40 s. The interface performs data acquisition from the sensor array, controls the grating position and the excitation source. A QuickBasic 4.5 program manages the interface, for data storage and treatment, and allows a graphical display and user-friendly interaction. Results show an absolute standard deviation for the wavelength localization of +/- 0.036 nm, and a spectral resolution of 0.05 nm at 443 nm when a 651 grooves/mm grating is employed. In each scan, the sensor array can collect data in a 18.7 nm wide window. Sensitivity was inferred from experimental data that showed an accurate localization of emission lines for Sn and Cu present in metal alloys at 0.006 and 0.03%, respectively. Quantitative results obtained for determination of Mn in steel samples and Ph in aqueous solution are also presented.18171

Automatic determination of mercury samples of environmental interest in

An automatic flow injection (FI) system for the determination of mercury was developed using a commercial cold vapour atomic absorption spectrophotometer (CVAAS). Control Pre-concentration procedures have a high level of reliability and applicability due to the lower detection limi

A versatile set up for implementing different flow analysis approaches Spectrophotometric determination of nickel in steel alloys

Abstract An arrangement capable of implementing the four principal types of flow analysis processes, monosegmented flow analysis (MSFA), flow injection analysis with multicommutation and binary sampling (FIA-MBS), flow injection analysis with sandwich sampling (FIA-SS) and sequential injection analysis (SIA) is described. The core of the flow manifold is a six-way solenoid valve that is assembled together with three three-way solenoid valves in order to provide a versatile flow network. Software was written in VisualBasic 3.0 to give a friendly working structure allowing the user to easily choose the flow variables and the kind of flow system. The reliability of the flow set up for implementation of the four flow analysis systems was evaluated by means of the spectrophotometric determination of nickel in steel alloys, based on the formation of a colored complex with dimethylglyoxime (DMG). The performances of the four different flow methodologies were compared. The reagent consumptions per determination were 4.0 mg of triethanolamine, 6.0 mg of potassium persulfate and 0.6 mg of DMG. When the flow set up was instructed through the software to implement MSFA, FIA-MBS, and FIA-SS approaches, a sampling frequency of 40 samples/h was obtained, while 30 samples could be processed per hour in the SIA mode. The precisions, evaluated as the relative standard deviation of ten determinations were 0.7%, 1.6%, 1.8% and 3.1% for the MFSA, FIA-MBS, FIA-SS and SIA systems, respectively. The results for determination of nickel in steel alloys presented good agreement with the reference method (ICP OES), showing no significant difference at a confidence level of 95%.

Gran method for end point anticipation in monosegmented flow titration

An automatic potentiometric monosegmented flow titration procedure based on Gran linearisation approach has been developed. The controlling program can estimate the end point of the titration after the addition of three or four aliquots of titrant. Alternatively, the end point can be determined by the second derivative procedure. In this case, additional volumes of titrant are added until the vicinity of the end point and three points before and after the stoichiometric point are used for end point calculation. The performance of the system was assessed by the determination of chloride in isotonic beverages and parenteral solutions. The system employs a tubular Ag2S/AgCl indicator electrode. A typical titration, performed according to the IUPAC definition, requires only 60 mL of sample and about the same volume of titrant (AgNO3) solution. A complete titration can be carried out in 1 - 5 min. The accuracy and precision (relative standard deviation of ten replicates) are 2% and 1% for the Gran and 1% and 0.5% for the Gran/derivative end point determination procedures, respectively. The proposed system reduces the time to perform a titration, ensuring low sample and reagent consumption, and full automatic sampling and titrant addition in a calibration-free titration protocol.Este trabalho descreve o uso do método de linearização de Gran em titulações em fluxo monossegmentado com detecção potenciométrica. O programa de controle pode estimar o ponto final após a adição de três ou quatro alíquotas de titulante. Alternativamente, o ponto final da titulação pode ser determinado pelo método da segunda derivada. Neste caso, alíquotas adicionais de titulante são adicionadas até a proximidade do ponto final e três pontos antes e após o ponto estequiométrico são usados para o cálculo de ponto final. O desempenho do sistema foi avaliado pela determinação de cloreto em soluções isotônicas e parenterais. O sistema emprega um eletrodo indicador tubular de Ag2S/AgCl. Uma titulação típica, realizada de acordo com a definição IUPAC, requer apenas 60 mL de amostra e aproximadamente o mesmo volume de titulante (AgNO3). Uma titulação completa pode ser realizada entre 1 e 5 min. Foram obtidas exatidão e precisão (desvio padrão relativo de 10 replicatas) de 2% e 1% para o método de Gran e 1% e 0,5% para o método de Gran associado ao método da segunda derivada, respectivamente. O sistema proposto reduz o tempo para realizar uma titulação, com baixo consumo de amostra e reagente, além de possibilitar uma amostragem automática completa e adição de titulante sem a necessidade de uma etapa de calibração.111115Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES

Design and development of a multichannel potentiometer for monitoring an electrode array and its application in flow analysis

A versatile potentiometer that works with electrode arrays in flow injection and/or monosegmented flow systems is described. The potentiometer is controlled by a microcomputer that allows individual, sequential multiplexed or random accesses to eight electrodes while employing only one reference electrode. The instrument was demonstrated by monitoring an array of seven flow-through ion-selective electrodes for Ag+ and for three electrodes for Cl-, Ca2+ and K+. The figures of merit of the individual and multiplexed (summed) readings of the electrode array were compared. The absolute standard deviation of the measurements made by summing the potential of two or more electrodes was maintained constant, thus improving the precision of the measurements. This result shows that an attempt to combine the signals of the electrodes to produce a more intense signal in the Hadamard strategy is feasible and accompanied by a proportional improvement in the precision of individual measurements. The preliminary tests suggest that the system can allow for 270 determinations per hour, with a linear range from 1.0 × 10-2 to 1.0 × 10-4 mol l-1 for the three di¡erent analytes. Detection limits were estimated as 3.1 × 10-5, 3.0 × 10-6 and 1.0 × 10-5 mol l-1 for Cl-, Ca2+ and K+, respectively

Electric field-assisted solid phase extraction: study of electrochromatographic parameters with an anionic model compound

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Electric field-assisted solid phase extraction using syringe type cartridges (E-SPE) is a recent approach with a high capacity to obtain differential selectivity and/or recovery in comparison with conventional solid phase extraction (SPE). In this work, E-SPE was employed for the extraction of the anionic dye sunset yellow. During the washing step the electric field was evaluated with the top electrode negatively (E-SPE(-/+)) or positively charged (E-SPE(+/-)) and the results were compared with conventional SPE to understand how the electrochromatographic parameters can influence the recovery of the dye. Using the E-SPE(-/+) the electric field can increase the elution of the dye from the cartridge by over 57-fold. This notable result can be attributed to the electrophoretic velocity of the dye in the direction of the flow rate of the eluent. These results demonstrated that E-SPE is an interesting approach to elute ionic compounds with reduced volumes of eluent or less amount of organic solvent.Electric field-assisted solid phase extraction using syringe type cartridges (E-SPE) is a recent approach with a high capacity to obtain differential selectivity and/or recovery in comparison with conventional solid phase extraction (SPE). In this work, E262310318Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)FAPESP [2007/07079-0, 2008/03064-1, 2008/57808-1]CNPq [Proc. 573894/2008-6