Spectrophotometric flow-injection determination of sulphite in white wines involving gas diffusion through a concentric tubular membrane

Abstract

Um sistema de análises por injeção em fluxo é proposto para a determinação espectrofotométrica de sulfito em vinhos brancos. O método envolve conversão do analito a SO 2 , difusão gasosa através de uma membrana semi-permeável de Teflon ® , coleta em um fluxo alcalino (pH 8), reação com verde de Malaquita (VM) e monitorização a 620 nm. O projeto do sistema foi simplificado empregandose uma membrana tubular concêntrica. Foram investigados: concentrações dos reagentes, pH dos fluxos doador e receptor, intensidade iônica, temperatura, temporização, adição de agentes tensoativos e presença de interferentes em potencial presentes na matriz vinho. A sensibilidade analítica melhorou (ca. 100%) adicionando-se cloreto de cetil piridinio (CPC). O sistema proposto é robusto e deriva em linha base não é observada durante períodos de até 4 horas de operação. São requeridos apenas 400 µL de amostra e 0.32 mg VM por determinação. O sistema processa 30 amostras por hora, fornecendo resultados precisos (d.p.r. < 0.015 para 1.0 -20.0 mg L -1 SO 2 ) e concordantes com os obtidos por um procedimento alternativo.A flow-injection system is proposed for the spectrophotometric determination of sulphite in white wines. The method involves analyte conversion to SO 2 , gas diffusion through a Teflon ® semipermeable membrane, collection into an alkaline stream (pH 8), reaction with Malachite green (MG) and monitoring at 620 nm. With a concentric tubular membrane, the system design was simplified. Influence of reagent concentrations, pH of donor and acceptor streams, temperature, timing, surfactant addition and presence of potential interfering species of the wine matrix were investigated. A pronounced (ca. 100%) enhancement in sensitivity was noted by adding cetylpyridinium chloride (CPC). The proposed system is robust and baseline drift is not observed during 4 h operating periods. Only 400 µL of sample and 0.32 mg MG are required per determination. The system handles 30 samples per hour, yielding precise results (r.s.d. < 0.015 for 1.0 -20.0 mg L -1 SO 2 ) in agreement with those obtained by an alternative procedure.Keywords: concentric tubular membrane, sulfite, spectrophotometric flow analysis, micellar medium, gas diffusion IntroductionGas diffusion is a very effective means to enhance selectivity in analytical chemistry, and was implemented in a flow-injection system in the pioneer work dealing with the development of an improved procedure for determination of total CO 2 in plasma. 1 Since then, the strategy has been often exploited, as it is efficiently accomplished in flow systems. 2,3 Generally, a gaspermeable membrane is placed between two liquid streams, one of them -the donor stream -containing the sample under processing. The analyte is converted to a volatile chemical species that is removed from the sample matrix and collected by other stream -the acceptor stream.Sulphite is an important preservative in the food and beverage industry, especially with regard to wine production 4-8 and its content should be strictly controlle...

Spectrophotometric determination of sulphite and thiamin hydrochloride using proton transfer reaction-application to water sample and pharmaceutical formation

“…Scheme 2: Alizarine structure Several spectrophotometric methods are used for determination of sulphite such as quantification of sulphite ions in environmental samples [8], wine samples [9], other method based on a discoloring reaction between sulphite and flower anthocyanins in alkaline medium [10], another spectrophotometric methods used phosphate buffer at pH 7 with malachite green [11], or based on the bleaching of brilliant green dye by sulphite [12]. A flow injection analysis used for determination of sulphite in food and beverages [13], also a flow-injection determination of sulphite in white wines involving gas diffusion through a concentric tubular membrane [14]. B 1 can be determined with spectrophotometric methods in pharmaceutical preperation based on reaction of B 1 with 7-chloro-4-nitrobenzoxadiazole to produce brown color complex measured at 434 nm [15], another used 1,2-naphthoquine-4-sulphonate measured at 487 nm [16], others spectrophotometric methods using coupling reaction with diazotized sulfanilic acid [17], or diazotization reaction of B 1 with procaine hydrochloride which reacted with sodium nitrate and hydrochloric acid to form a red water-soluble azo dye in basic medium [18], or using prussian blue reaction [19], also a flow injection method used for determination of B 1 with diazotized metoclopramide [20], and a fluorimetric method can be used for the determination of B 1 [21].…”

Spectrophotometric Determination of Sulphite in Various Water Samples Via Chromium-1,5-Diphenylcarbazide Complex

“…In order to choose the optimum amount of sulphuric acid on the reaction of sulphite ions with chromate, and the formation of a stable coloured complex between chromate and DPC, different amounts (0-5.0) ml of 2N sulphuric acid were tested. The results are shown in Table 1 indicate that 2.5 ml of 2N H 2 SO 4 is considered optimum, as it gives the more stable coloured complex [11], therefore it was recommended for subsequent experiments.…”

“…The 5,5′-dithiobis(2nitrobenzoic acid) and para-rosanilineformaldehyde methods were rapid for the determination of sulfite since it only needed one main reagent and the methods were robust and easy to operate (8), other method determination sulphite at nanogram level in alcoholic and nonalcoholic beverage samples based on diffuse reflectance fourier transform infrared spectroscopic analysis on KBr matrix(9),or bleaching colour of malachite green by sulphite (10). A flow-injection is used for the determination of sulphite in white wines involving gas diffusion through a concentric tubular membrane (11). Other spectrophotometricmethod has been used for determination of sulphide, sulphite and ethanol involving gas diffusion (12), or quantification of sulphite ions in environmental samples (13).…”

Development of a Gas Diffusion Multicommuted Flow Injection System for the Determination of Sulfur Dioxide in Wines, Comparing Malachite Green and Pararosaniline Chemistries

“…Among the spectrophotometric methodologies described for free and/or total SO 2 in wines, reactions of sulfite with malachite green − and with pararosaniline , , , − have been often used due to their high sensitivity. The first method relies on the instantaneous decolorization of malachite green in the presence of neutral sulfite solutions.…”