Multicommutation in flow analysis. Part 1. Binary sampling: concepts, instrumentation and spectrophotometric determination of iron in plant digests

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Um procedimento empregando detecção quiluminescente para determinação de carbaril em águas naturais utilizando acetilcolinesterase e colina oxidase é descrito. O módulo de análise projetado para implementar o processo de multicomutação controlado por microcomputador foi constituído por cinco válvulas solenóides, duas colunas com enzimas imobilizadas em esferas de vidro e cela de fluxo para detecção de quimiluminescência. Nas melhores condições experimentais foi obtida faixa linear entre 25 a 700 μg L -1 de carbaril. Amostras de água foram fortificadas com carbaril e as recuperações variaram entre 95 e 101%. Limite de detecção e coeficiente de variação foram estimados em 11 μg L -1 (99,7% nível de confiança) e 1,3% (n = 20), respectivamente. Outras características analíticas tais como freqüência de amostragem de 72 determinações por hora, consumo de reagente de 2,1 mg de hexacianoferrato de potássio(III) e 0,069 mg de luminol por determinação, também, foram obtidas.A chemiluminescence procedure for the determination of carbaryl in natural waters using acetylcholinesterase and choline oxidase is described. The flow system designed to implement multicommutation approach controlled by microcomputer comprised five solenoid valves, two columns with immobilized enzymes on controlled pore glass beads and chemiluminometric flow cell. In the best experimental conditions a linear response ranging from 25 to 700 μg L -1 carbaryl was obtained. Water samples were spiked with carbaryl in order to access the accuracy and recoveries between 95 and 101% were obtained for a concentration level ranging from 25 to 100 μg L -1 carbaryl. Detection limit and variation coefficient were estimated as 11 μg L -1 (99.7% confidence level) and 1.3% (n = 20), respectively. Other profitable features such as a sample throughput of 72 determinations per hour, a reagent consumption of 2.1 mg potassium hexacyano ferrate(III) and 0.069 mg luminol per determination were also achieved.

Section: Apparatusmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

A chemiluminescence flow-based procedure for determination of carbaryl in natural waters exploiting multicommutation and enzymatic reaction

Pires¹,

Morales‐Rubio²,

Guárdia³

et al. 2007

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“…The set up was comprised of an IPC8 Ismatec peristaltic pump furnished with Tygon pumping tubes, six port and three-way solenoid valves (NResearch), a home made power supply interface 28 to match the electric current intensity and voltage required to drive the solenoid valves, a home-made Ag 2 S tubular electrode constructed as previously described, 29 a MicropH 2002 Crison potentiometer equipped with an Ag/AgCl reference electrode and a Pentium microcomputer equipped with a PCL-711S (Advantech) electronic interface card. The software to control the system was written in VisualBasic 3.0.…”

Section: Apparatus and Flow Set Upmentioning

confidence: 99%

Monosegemented flow potentiometric titration for the determination of chloride in milk and wine

Vieira¹,

Raimundo²,

Reis³

et al. 2003

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Este trabalho descreve um procedimento automático em fluxo monossegmentado para titulação potenciométrica aplicado à determinação de cloreto em leite e vinho. O sistema de fluxo foi desenvolvido com base em uma válvula solenóide de 6 vias, controlada por um microcomputador através de um programa escrito em VisualBasic 3.0. Um eletrodo indicador tubular de Ag 2 S seletivo a Cl -e um eletrodo de referência convencional de Ag/AgCl foram empregados. Um algoritmo baseado na diferença de potencial entre duas adições subsequentes de titulante foi desenvolvido, possibilitando a determinação do ponto final da titulação em, no máximo, 10 tentativas, com uma precisão melhor que 1,0%. O sistema proposto foi avaliado pela determinação de cloreto em leite e vinho, usando uma solução padrão de AgNO 3 como titulante. A exatidão foi avaliada comparando-se os resultados com aqueles obtidos pelo método da AOAC, não sendo encontradas diferenças significativas ao nível de confiança de 95%.An automated flow potentiometric titration procedure for the determination of chloride in milk and wine exploiting the monosegmented flow approach is described. The flow network was designed based on a six-way solenoid valve, controlled by a microcomputer running software written in VisualBasic 3.0, allowing selection of the titration conditions. An Ag 2 S tubular electrode selective for Cl -and a conventional Ag/AgCl electrode were employed as indicator and reference, respectively. An algorithm based on the potential difference between two subsequent titrant additions was developed, allowing to reach the end point in less than 10 attempts, with a precision better than 1.0%. The proposed system was evaluated by determining chloride in milk and wine, using a standard AgNO 3 solution as titrant. Accuracy was ascertained by comparing the results with those obtained using the AOAC procedure. No significant difference at a 95% confidence level was observed.Keywords: potentiometric titration, monossegmented flow, multicommutation, ion selective electrode, chloride in milk, chloride in wine IntroductionThe mechanisation of the potentiometric titration procedure was first described in 1914 1 and the introduction of flow injection analysis in 1975 2 improved this mechanisation, including for potentiometric and spectrophotometric titrations. [3][4][5] Flow injection titration usually employs a calibration step, in which the peak width (instead of height) is taken as the analytical parameter. The simplest approach, which was first proposed by Ruzicka et al. 6 in 1977, employs a single line manifold and is still being employed nowadays. 7,8 Different alternatives have been proposed to determine the stoichiometric point in a flow titration procedure. Continuous flow systems based on the ratio of sample and titrant flow rates have been exploited to achieve the end point. 9,10 In order to vary the flow rates of the solutions independently, two peristaltic pumps are necessary, which 260 Vieira et al. J. Braz. Chem. Soc. represents the main drawback of these...

“…However it reacts also with iron ions forming a compound which absorbs at the same wavelength range observed for the nickel compound, thus causing strong interference 4 . To overcome this drawback, a triethanolamine solution was used as masking reagent, added to the sample bulk during the sampling step, by employing the binary sampling approach 17 . Under this condition, the reaction coil (B1) is loaded with a string comprising slugs of sample in tandem with slugs of triethanolamine.…”

Section: Flow Diagrams and Flow Proceduresmentioning

confidence: 99%

The use of ion exchange resin for reagent immobilization and concentration in flow systems: determination of nickel in steel alloys and iron speciation in waters

Martelli¹,

Reis²,

Korn³

et al. 1997

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Neste trabalho, foi investigado o emprego de persulfato de potássio imobilizado em resina aniônica AG1-X8, como agente oxidante, na determinação espectrofotométrica de níquel em ligas metálicas, e na especiação de Fe (III)/Fe (II) em águas de rio, utilizando-se sistema de análise em fluxo. O diagrama de fluxo foi desenvolvido para que a oxidação da espécie de interesse e o recondicionamento da resina pudessem ser efetuados em linha. A determinação de níquel baseou-se no método da dimetilglioxima, apresentando uma freqüência analítica de 80 determinações por hora. Com este sistema, obteve-se um baixo consumo de reagentes, 10 mg (200 µL) de persulfato de potássio e 8,0 µg (133 µL) de dimetilglioxima por determinação. Para uma solução de amostra contendo 21,5% (m/m) de Ni, encontrou-se um desvio padrão relativo de 1% (n = 10). Aplicando-se o teste-t pareado, obteve-se uma concordância com 95% de confiança entre os resultados do sistema proposto e os obtidos com espectrofotometria de absorção atômica com chama. Na determinação de Fe (III), utilizou-se tiocianato de potássio como reagente cromogênico, alcançando-se uma frequência analítica de 60 determinações por hora. O método apresentou um consumo de reagentes de 3,5 mg (70 µL) persulfato de potássio e de 5,4 mg (270 µL) de tiocianato de potássio por determinação. O desvio padrão relativo calculado para uma solução de amostra contendo 3,17 mg L -1 de Fe (III) foi de 1,5% (n = 10). Os resultados empregando-se o método proposto para Fe (II) foram comparados com aqueles obtidos com o método espectrofotométrico, baseado na reação com 1,10 -fenantrolina, apresentando uma concordância com nível de confiança de 95%.Flow injection systems employing potassium peroxydisulphate as oxidizing reagent, immobilized on the anionic exchange resin AG1-X8 are proposed for spectrophotometric determination of nickel in steel alloys and for the speciation of iron (III)/iron (II) in waters. The flow networks were designed to provide facilities to perform on line analyte oxidation and resin reconditioning steps. The feasibility was ascertained by determining nickel in acid solutions of steel alloys and performing speciation of iron (III)/iron (II) in waters, using as chromogenic reagents dimethylglyoxime for nickel and potassium thiocyanate for iron. Profitable features such as a throughput of 80 and 60 samples per hour, 1.0 and 1.5% (n = 10) as relative standard deviations for nickel (21.5% m/m) and iron (III) (3.17 mg L -1 ), low reagents consumption (10 and 3.5 mg of potassium peroxydisulphate, 8.0 µg dimethylglyoxime and 5.4 mg of potassium thiocyanate, for nickel and iron, respectively) were observed. The accuracy for both procedures were ascertained by applying paried t-test between results obtained with flame atomic absorption spectrophotometry (FAAS) for Ni and 1,10-phenantroline spectrophotometric method for Fe (II), and no significant difference at 95% confidence level were observed.