Flow injection spectrofluorimetric determination of cystine and cysteine

Abstract

Um procedimento relativamente simples e sensível com detecção espectrofluorimétrica foi desenvolvido para a determinação de cistina e cisteína por sistema de injeção em fluxo com determinação seqüencial. Esse método é fundamentado na redução de Tl(III) com cisteína em meio ácido, produzindo o reagente fluorescente TlCl 3 2-(λ ex = 227 nm, λ em = 419 nm). Antes da injeção, a solução da amostra foi dividida em dois fluxos. O primeiro fluxo foi tratado com coluna de redução de Cd e então refluxado com a solução do carregador para reagir em pH 5,0 com Tl(III), passado através de uma cela de reação de 100 cm e posteriormente para a cela fluxo do espectrofluorímetro, onde a intensidade de fluorescência foi medida (λ ex = 227 nm, λ em = 419 nm). Esse sinal está relacionado às concentrações de cistina e cisteína. O segundo fluxo da solução de amostra foi injetado diretamente no fluxo carregador para reagir e, então, pela cela de reação e detector para medida da intensidade de fluorescência. O sinal nessa etapa é relacionado apenas à cisteína. Assim, o conteúdo de cistina foi determinado diretamente da diferença entre os dois sinais. Cistina e cisteína podem ser determinadas no intervalo de 0,10 a 5,50 μmol L -1 e 0,20 a 8,0 μmol L -1 , respectivamente, em uma razão de 20 amostras por hora. O limite de detecção (3s/k) foi 0,10 μmol L -1 para os dois analitos. Os desvios padrões relativos para a determinação de dez replicatas de 4,0 e 3,5 μmol L -1 de cistina ou cisteína foram 1,1% e 1,8%, respectivamente. A influência de substâncias interferentes foi estudada. O método proposto foi aplicado com sucesso na determinação seqüencial de ambos analitos em amostras farmacêuticas.A relatively simple and sensitive procedure with spectrofluorimetric detection was developed for the determination of cystine and cysteine by flow injection system with sequential determination. This method is based on the reduction of Tl(III) with cysteine in acidic media, producing a fluorescence reagent, TlCl 3 2-(λ ex = 227 nm, λ em = 419 nm). Before injection, the sample solution was divided into two streams. The first stream was treated with Cd reduction column and then joined with the carrier to react with Tl(III) at pH 5.0 and then passed through a 100 cm reaction coil to the flow cell of the spectrofluorimeter, where the fluorescence intensity was measured (λ ex = 227 nm, λ em = 419 nm). This signal is related to cystine and cysteine concentrations. The second stream of sample solution was injected directly into the carrier stream to react with the reagents and then passed through the reaction coil and detector for measuring the fluorescence intensity. The signal in this step is related only to cysteine. Thus, the cystine content was determined directly from difference of the two signals. Cystine and cysteine can be determined in the range of 0.10 to 5.50 μmol L -1 and 0.20 to 8.0 μmol L -1, respectively, at a rate of 20 samples per hour. The limit of detection (3s/k) was 0.10 μmol L -1 for both analytes. The relative standard deviations for te...

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Evaluation of a Graphite-Polyurethane Composite Electrode Modified with Copper Nanoparticles as an Amperometric Flow Detector in a Wall-Jet System for the Determination of Cysteine

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“…Due to this ability of thiols group of being rapidly oxidized, cysteine presents antioxidant properties. [1][2][3] Cys can undergo the ionization of its α-carboxyl group with pK a1 = 2.0 and α-ammonium group, with pK a2 = 8.2. 4 Cys structural formula is represented in Figure 1.…”

“…Thus, controlling the content of this amino acid in body fluids, pharmaceuticals and food supplements is of relevance and several analytical methods for Cys determination have been described. Literature describes such determination using spectrophotometric, [5][6][7] spectrofluorimetric, 3,8 chromatographic, 9,10 voltammetric, 2,11,12 capillary electrophoresis 13 and amperometric 1,14,15 procedures. Electrochemical methods present many advantages in comparison to other analytical methods, as simplicity,…”

Smart platform for the time since death determination from vitreous humor cystine

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