Non-targeted metabolite profiling by liquid chromatography-mass spectrometry (LC-MS) was used to determine the metabolite responses of Arabidopsis roots to auxin or ethylene. Crosstalk between these hormones regulates many important physiological processes in plants, including the initiation of lateral root formation and the response to gravity. These occur in part through alterations in the levels of flavonoids, specialized plant metabolites that have been shown to act as negative regulators of auxin transport. However, much remains to be learned about auxin and ethylene responses at the level of the metabolome. LC-MS analysis showed that a number of ions changed in response to both hormones in seedling roots. Although classes of specialized metabolites such as flavonols and glucosinolates change in abundance in response to both auxin and ethylene, there was little overlap with regard to the specific metabolites affected. These data will be integrated with information from transcriptomic and proteomic experiments to develop framework models that connect phytohormones and specialized metabolism with specific physiological processes. Previous studies by imaging techniques have shown that flavonols increase in response to both auxin and ethylene in the root elongation zone, but LC-MS showed that flavonols decreased in abundance in response to these hormones. Therefore a method was developed for targeted metabolite profiling of flavonols in individual root tips by flow injection electrospray mass spectrometry. This method uncovered spatial differences in metabolic profiles that were masked in analyses of whole roots or seedlings, and verified that flavonols increase in response to these hormones in root tips. / Master of Science

Inspired by the need to study injectant flow patterns near the test surface, a supersonic free-jet facility was designed and constructed. This facility provides a Mach 1.95 flow over a test section area of 6.35 cm by 5.08 cm. The facility was thoroughly tested and proved that it is durable, versatile, and capable of providing repeatable test conditions. When compared to the main supersonic tunnel at VPI & SU, the free-jet facility has many advantages, including greater optical and spatial access, longer available test durations, and less time needed between tests for the storage tanks to be refilled. As a part of the project, several diagnostic techniques were evaluated in the facility. Normal, sonic injection of helium through a circular injector was studied as a way to evaluate nanoshadowgraph photography, oil flow photography, and infrared imaging as qualitative flow visualization methods. Quantitative measurements of the local helium concentration within the boundary layer were taken to evaluate the effectiveness of an existing hot-film concentration probe. The tests showed that oil flow visualization is a very effective technique in the free-jet facility, producing clear photographs that could be directly scaled. Nanoshadowgraph photography also produced clear photographs of the flow field, although this method was more difficult to implement in the free-jet facility than in the main supersonic tunnel. Finally, infrared imaging, which was not possible in the main supersonic tunnel without major hardware reconfigurations, showed great promise as a method for studying normal injection. Although the tests revealed no conclusive information about injectant flow patterns in the boundary layer, a heat transfer analysis showed that it may be possible in future studies to use this technique as a way to quantitatively measure local helium concentration at the surface. Helium concentration was measured for test cases with both air and helium injection. The measurements were taken at two axial locations with the probe positioned at a distance of 0.1 injector diameters above the test surface. The air injection tests showed helium concentration levels up to 30 percent mole fraction, which is erroneous since no helium was present in the flow. Based on these results it was concluded that the existing probe was ineffective in the free-jet facility, with an uncertainty level of no less than 25 percent mole fraction helium. The cause of the high uncertainty and overall ineffectiveness was most likely the probe calibration and data reduction methods. / Master of Science

Thesis (MSc)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: Iron is an essential micronutrient for all phytoplankton and is found in seawater at picomolar-level concentrations. For the first time in South Africa, a technique that utilizes a flow injection analyser (FIA) coupled with a chemiluminescence reaction has been developed for the analysis of Fe in seawater samples. The developed method is an improvement on similar available methods and uses commercially available resin (IDA) as opposed to the one that requires synthesis in the laboratory. Furthermore, the method requires reduced reagent concentrations thereby providing better results in a cost-efficient and easy manner. The improvements resulted in better precision while eliminating the loss of resin through bleeding, a common problem when using 8-HQ resin as per prior methods. Method validation was performed using internationally calibrated reference material provided by GEOTRACES and the values obtained were within the error limits of certified range. An inter-laboratory calibration was also conducted as part of the verification of the system. Surface samples from the SANAE 51 cruise were analysed for dFe and TdFe. Subsequently, the method was implemented on the SANAE 53 voyage on board the SA Agulhas II, to assess trace metal sampling protocol for any contamination issues, as well as for the analyses of collected samples. Current results suggest some contamination during collection stages, but this is still to be verified by complementary data on macronutrients and chlorophyll. The method was successfully developed and implemented in a land based clean laboratory, as well as on board a vessel. / AFRIKAANSE OPSOMMING: Yster is „n noodsaaklike mikrovoedsel vir fitoplankton en word in seewater in pikomolêre konsentrasies gevind. Hierdie lae konsentrasies en potensiële besoedeling gedurende monsteropname vanaf „n skip se platform maak akkurate Fe-analise moeilik. Vir die eerste keer in Suid-Afrika is „n tegniek ontwikkel wat gebruik maak van „n vloei- inspuitinganaliseerder (VIA), met „n geassosieerde chemiluminessensiereaksie, om die analise van Fe in seewatermonsters uit te voer. In teenstelling met soortgelyke bestaande metodes wat labratorium-gesintetiseerde hars vereis, is die nuut-ontwikkelde metode „n verbetering wat gebruik maak van „n kommersieel-beskikbare hars (IDA). Verder vereis die metode verminderde reagenskonsentrasies wat sodoende beter resultate lewer op 'n koste-effektiewe en eenvoudiger wyse. Die verbeteringe het gelei tot verhoogde akkuraatheid en uitskakeling van die verlies van hars deur dreinering – „n algemene probleem wat ondervind is met die gebruik van 8-HQ hars in vorige metodes. Geldigheidsbepaling van die metode is met internasionaal-gekalibreerde verwysingsmateriaal, verskaf deur GEOTRACES, uitgevoer. Die waardes wat verkry is, was binne die foutgrense van die gesertifiseerde skaal. „n Interlaboratorium-kalibrasie is ook uitgevoer as deel van die verifikasie van die stelsel. Daarna is die metode geïmplementeer gedurende die SANAE 53 reis op die SA Agulhas II, om die spoormetaal-monsternemingprotokol vir enige besoedelingskwessies te evalueer, asook vir die ontleding van versamelde monsters. Huidige resultate dui op „n mate van besoedeling tydens die versamelingstadiums, maar dit moet nog geverifieer word deur aanvullende data van die totale oplosbare Fe, makrovoedingstowwe en chlorofil.

Flow injection systems have great potential for sample handling and analysis in process analytical chemistry. The flexibility and versatility of flow injection manifolds can he utilized in specific applications of sample conditioning and analysis. An overview of various flow injection methods, including flow reversals, double injection, and sequential injection is given, as well as different clean-up methods, such as gas diffusion, solid phase extraction, dialysis, and solvent extraction. Calibration techniques, such as single standard and multivariate calibration are also discussed. In addition, different aspects of process analytical chemistry, in particular sampling and sample handling, are discussed. The papers in this thesis describe a number of flow systems, where gradient-, gas diffusion-, and solid phase extraction- methodologies are applied, all of which have potential use in process analytical chemistry. Paper I is focused on multicomponent analysis of mixtures of organic acids by mathematically extracting information from complex spectra. The selectivity is improved by generating pH-gradients in the flow system. In paper II, the methodology of sensor injection is described and electrochemical and spectroscopic sensors are implemented in a sequential injection system. The method is illustrated by using pH sensors and a glucose electrode. Ammonia and ammonium ions are determined on-line to a bioprocess by gas diffusion in paper III. The benefit of frequent re-calibrations and in-line cleaning sequences are demonstrated. Finally a method for on-line determination of o-diphenols in the kraft process has been developed (paper IV). The o-diphenols are isolated from black liquor samples by solid phase extraction and thereafter transferred to a high performance liquid chromatography system for separation and quantification. / <p>Diss. (sammanfattning) Umeå : Umeå universitet, 1996, Härtill 4 uppsatser</p> / digitalisering@umu

Sistemas de análises em fluxo com minibombas solenoide foram desenvolvidos para a determinação de glicerol livre e total em biodiesel e manganês em águas. Em um primeiro trabalho, glicerol livre foi determinado por espectrofotometria após oxidação com periodato, levando à formação de formaldeído, que reagiu com acetilacetona, formando o composto 3,5-diacetil-1,4-dihidrolutidina (DDL). O analito foi extraído com água, em substituição à extração utilizando solventes orgânicos. Resposta linear foi observada de 5 a 50 mg L-1, com limite de detecção estimado em 1 mg L-1 (99,7% de confiança), equivalente a 0,0004% em massa de biodiesel, valor 50 vezes menor que o limite estabelecido pelas legislações Brasileira, Norte americana e Europeia. O coeficiente de variação foi inferior a 1,5% (n = 10) e a frequência de amostragem foi estimada em 34 amostras h-1, com consumo de 340 &#181;g de KIO4 e 15 mg de acetilacetona por determinação. A mesma reação foi explorada para detecção fluorimétrica de glicerol livre e total em biodiesel, sendo essa espécie quantificada após reação de saponificação dos mono-, di- e triglicerídeos remanescentes no biodiesel. Para a determinação de glicerol livre, resposta linear foi observada no intervalo de 5 - 70 mg L-1, com limite de detecção estimado em 0,5 mg L-1, equivalente a 0,0002% (m/m) de biodiesel, com coeficiente de variação menor que 1,0 % (n = 20). Na determinação de glicerol total, faixa linear foi observada no intervalo de 25 - 300 mg L-1, com limite de detecção de 1,5 mg L-1 e coeficiente de variação de 1,4% (n = 10). As frequências de amostragem foram de 35 e 30 amostras h-1, para glicerol livre e total, respectivamente, consumindo 190 &#181;g de KIO4 e 13 mg de acetilacetona por determinação. Os resultados obtidos para as análises de biodiesel foram concordantes com os procedimentos de referência. A formação do complexo Mn(III)/EDTA foi explorada para a determinação de manganês em amostras de águas. Mn(II) foi oxidado em linha em um reator contendo dióxido de chumbo imobilizado em um poliéster. Espectrofotometria com longo caminho óptico foi empregada para aumento de sensibilidade, visando atender o limite máximo tolerado deste metal, estabelecido pelas legislações ambientais vigentes. Resposta linear foi observada no intervalo de 25 a 1500 &#181;g L-1, com limite de detecção estimado em 6 &#181;g L-1 (99,7% de confiança). Frequência de amostragem e coeficiente de variação foram estimados em 36 amostras h-1 e 2,6 % (n = 10), respectivamente, consumindo 500¨&#181;g de EDTA por determinação. A quantidade de chumbo no resíduo corresponde a 250 &#181;g por determinação e, com o reator empregado, é possível realizar até 1600 determinações. Interferências causadas por matéria orgânica nas amostras foram observadas e carvão ativo foi usado para remoção destes interferentes. Os resultados obtidos pelo procedimento proposto e por GF AAS foram concordantes (99,7 % de confiança). / Flow injection procedures based on solenoid micro pump were developed for free and total glycerol determination in biodiesel samples and manganese in fresh water. In a first work, free glycerol was determined by spectrophotometry, after glycerol oxidation by periodate, yielding formaldehyde, followed by formation of the colored product 3,5-diacetil-1,4-dihidrolutidine (DDL) upon reaction with acetylacetone. The analyte was extracted with water in replacement of organic solvents. A linear response was observed from 5 to 50 mg L-1, and detection limit was estimated as 1 mg L-1 (99.7% confidence level) equivalent to 0.0004% (w/w), 50 times lower than the threshold value established by Brazilian, European and American regulations. The coefficient of variation was lower than 1.5% (n=10) and sampling rate was estimated at 34 samples h-1, consuming 340 &#181;g of KIO4 and 15 mg of acetylacetone per determination. The same reaction was exploited for fluorimetric detection of free and total glycerol in biodiesel, and glycerol total was quantified after saponification of mono-, di- and triglycerides remaining in biodiesel. To free glycerol determination a linear response was observed from 5 to 70 mg L-1, with a detection limit of 0.5 mg L-1, which corresponds to 0.0002% (w/w) in biodiesel, and coefficient of variation was lower than 1.0% (n=10). To total glycerol determination, a linear response was observed from 25 to 300 mg L-1, with a detection limit of 1.5 mg L-1, and coefficient of variation of 1.4% (n=10). The sampling rate was estimated at 35 and 30 samples h-1, to free and total glycerol, respectively. The results obtained to biodiesel samples agreed at the 95% confidence level with reference procedures. The formation of the Mn(III)/EDTA complex was exploited for manganese determination in water. Mn(II) was oxidized in a reactor containing lead dioxide immobilized on polyester. Long pathlength spectrometry was exploited to increase sensitivity, aiming to reach the threshold limit established by environmental legislation. A linear response was observed from 25 to 1500 &#181;g L-1, with a detection limit of 6 &#181;g L-1(99.7% confidence level). Sample throughput and coefficient of variation were 36 samples h-1 and 2.6% (n=10), respectively, consuming 500 &#181;g of EDTA. The amount of lead in the residue corresponds to 250 &#181;g per determination, and it is possible to perform up to 1600 measurements. Interferences by organic matter were observed and active charcoal was employed to remove the interfering species. Results were in agreement with those attained by GF AAS at the 95% confidence level.

Neste trabalho, apresentamos uma nova versão do injetor comutador, baseada na geometria retangular, mantendo a configuração de três peças, sendo a central móvel e as laterais fixas. Nesta condição, os parafusos de ajuste não funcionam como guia, tal como ocorre nos injetores da primeira geração. Este design facilita o deslocamento da parte móvel, contribuindo para a redução do atrito, o que permite o emprego de um pequeno motor de corrente contínua (12 V; 0,4 A), o qual foi usado para fazer o deslocamento da barra central da posição de amostragem para a de injeção e vice-versa. O funcionamento do injetor foi controlado pelo computador, usando apenas 2 bits de controle. A interface de controle projetada para esse fim, inclui a condição de reversão da direção de rotação do motor e lógica anti-duplicidade, então se os dois bits forem ativados ao mesmo tempo, a rotação do motor é mantida no sentido horário. Para testar a viabilidade deste injetor, o mesmo foi empregado para desenvolver um procedimento para determinação de etanol em bebidas destiladas. O procedimento fotométrico foi baseado na reação de etanol com dicromato de potássio. A detecção fotométrica foi realizada empregando um fotômetro de LED com máximo de emissão em 590 nm. O módulo de análise constituído pelo injetor e um conjunto de válvulas solenoide foi projetado para implementar o processo de reamostragem, adição intermitente de reagentes e transporte da zona de amostra com fluxo de ar. Após a definição das variáveis de controle, o sistema apresentou bom desempenho analítico, aliando vantagens tais como, boa velocidade, simplicidade de operação, versatilidade, proporcionando também um menor consumo de amostra e reagentes. Com relação às características analíticas, o sistema proposto apresentou faixa de resposta linear (r = 0,9972) para concentração etanol entre 10 - 50 % (v/v), limite de detecção de 2,0 % (v/v) etanol, desvio padrão relativo de 2,0 % (n =10) para uma amostra de etanol com concentração 40 % (v/v), um consumo de dicromato de 0,012 g por determinação e uma frequência analítica de 34 determinações por hora. / We present a new version of the commutator injector, based on the rectangular geometry, maintaining the three parts configuration with the central mobile and fixed side. In this condition, the adjusting screws do not functi as a guide, as occurs in the injector of first generation. This design facilitates the displacement of the movable part and contributes in reducing the friction, thus allowing the use of a small direct current motor (12 V, 0.4 A), which was used to perform the displacement of the central bar from the sampling position to the injection and vice-versa. The injector operation was controlled by a computer, which was done using only two control bits. The control interface designed for this purpose includes the condition for reversing the direction of the motor rotation and anti-duplication logic, so that both bits were activated at the same time, the motor rotation was maintained at clockwise direction. To test the feasibility of the injector, it was used to develop a procedure for determination of ethanol in spirit beverage. The procedure was based on the photometric reaction of ethanol with potassium dichromate. The photometric detection was performed using a LED based photometer with maximum of emission at 590 nm. The analytical module comprising the injector and a set of solenoid valves, was designed to implement the zone sampling process and Intermittent addition of reagents and sample zone displacement using an air stream. After definition of control variables, the system shown good analytical performance, combining advantages such as speed, simplicity of operation, versatility and also providing lower consumption of sample and reagents. With respect to analytical characteristics, the proposed system presented linear response range (r = 0.9972) between ethanol concentration to 10 - 50% (v/v), a detection limit of 2.0% (v/v) ethanol, relative standard deviation of 2.0% (n = 10) for a sample with an ethanol concentration of 40% (w/v), a dichromate consumption of 0.012 g by determination and a sampling rate of 34 determination per hour.

A combinação sinérgica da análise por injeção em fluxo com eletroforese capilar, FIA-CE, é um novo campo em rápida expansão, que se estende da simples justaposição de equipamentos (FIA-CE at-line) ao verdadeiro interfaceamento ou hifenação (FIA-CE in-line ou on-line). Tipicamente, circuitos FIA construídos nos laboratórios são interfaceados com equipamentos comerciais de eletroforese capilar providos com detecção espectrofotométrica UV-Vis, e operam sob injeção (ou melhor, transferência) eletrocinética de amostra do circuito FIA para o capilar, vez que esta é mais simples para implementar que a transferência hidrodinâmica. Um novo sistema FIA-CE que combina a detecção condutométrica sem contato elétrico, DCSC, com transferência hidrodinâmica ou eletrocinética de amostra foi projetado e construído no laboratório utilizando-se material de baixo custo, além de uma fonte de alta tensão, uma bomba peristáltica e um microcomputador. No circuito FIA, utilizou-se um único solenóide na construção de injetor multicanal com válvulas de estrangulamento de dimensões reduzidas. O DCSC foi anteriormente desenvolvido por outros componentes do grupo. A interface FIA-CE consiste de uma agulha hipodérmica de aço inoxidável conectada à saída do circuito FIA, atuando como eletrodo aterrado, traspassada pelo capilar. Quatro diferentes eletrólitos podem ser chaveados por intermédio do microcomputador para alimentar o circuito FIA. Na CE, três níveis de pressão podem ser aplicados ao reservatório contendo o eletrodo ao qual se aplica a alta tensão, correspondente ao extremo do capilar mais próximo do detetor: a) potente aspiração, durante o procedimento de limpeza rápida; b) pequena pressão sub-ambiente (ajustada com um pressiostato simples) para a transferência sincronizada de amostra da interface; e c) pressão ambiente, durante a aquisição de dados do eletroferograma. O sistema opera sob controle de um flexível software de código aberto, aceitando procedimentos FIA usuais. As avaliações mostraram, afora a comodidade de uso do sistema, freqüência analítica maior, limites de detecção similares e melhor repetibilidade da área e posição dos picos em comparação a CE operada manualmente. / The synergistic combination of flow injection analysis with capillary electrophoresis, FIA-CE, is a new and rapidly evolving field, comprising juxtaposition of equipments (at-line FIA-CE) and true interfacing or hyphenation (in-line or on-line FIA-CE). Typically, FIA circuits assembled in the laboratory are interfaced to commercial electrophoresis equipments provided with UV-Vis detection and operated under electrokinetic sample injection (or better, transfer from the FIA circuit), that is simpler to implement than hydrodynamic transfer. A new FIA-CE system that combines contactless conductivity detection, CCD, with hydrodynamic and electrokinetic sample transfer was designed and constructed in the laboratory from low cost parts, besides a high voltage supply, a peristaltic pump and a PC. In the FIA circuit, a solenoid actuated multi-channel pinch-valve injector was downsized from a previous prototype. The oscillometric CCD was formerly developed by other components of the group. The interface consists of a hypodermic needle, connected to the FIA circuit and serving as grounded electrode, trespassed by the capillary. Four different electrolytes can be switched by the PC and three levels of pressure can be applied to the vial with the HV electrode and the tip of the capillary near the detector (opposite to the FIA-CE interface): a) strong aspiration, during fast cleansing procedure; b) slightly sub-ambient pressure (adjusted with a simple pressurestat) for synchronized sample transfer at the interface; and c) ambient pressure, during data acquisition of the electropherogram. The system runs under control of flexible, open-code software, accepting usual FIA procedures. Evaluations showed, besides convenience of use, higher analytical frequency, similar detection limits and better repeatability of peak positions and areas in comparison with manually operated CE.

An extensive study has been made of the factors affecting sample dispersion in flow injection analysis. This has included the effect of different manifold parameters on peak height and shape, and the use of various flow models to describe the physical processes involved. The factors investigated included sample flow-rate, tube length and diameter, sample volume, and the diffusion coefficient of the solute. The role of the detector has also been investigated, and was found to exert a strong influence on the observed dispersion behaviour of a flow injection manifold. In the light of this, a low volume flow cell was constructed which minimised the contribution of the detector to dispersion. Different modes of sample injection ("time" and "slug" injection) have been studied, and an automatic valve constructed in connection with the work. Both new and existing flow models have been evaluated in terms of their ease-of-use and ability to predict peak shape. Conditions for which the different models were valid were derived both experimentally and from consideration of the assumptions of the models. The applications of such models to the characterisation and design of flow manifolds has also been considered, and this approach compared to the purely theoretical and empirical approaches that have been described in the literature. The models examined in this thesis are the convection, diffusion, tanks-in-series, well-stirred tank, two-tanks in- parallel and two-tanks-in-series models. Finally, the practical implications of this work for the design of flow injection manifolds and the derivation of so-called "rules for dispersion" have been discussed, and suggestions made for further areas of research.

O presente trabalho teve por objetivo o desenvolvimento e aplicação de diferentes procedimentos para quantificação do fármaco furosemida, explorando suas reações e características físicas. Os métodos apresentados podem ser divididos em estáticos e em fluxo. Dentre os procedimentos estáticos utilizou-se a titrimetria de óxido-redução, a qual explorou as reações de hidrólise e oxidação do fármaco; a determinação espectrofotométrica em batelada, que explorou a reação de complexação com íons Fe3+, e a determinação empregando métodos eletroanalíticos, como voltametria cíclica, de pulso diferencial e de onda quadrada, nos quais o comportamento eletroquímico do analito foi explorado. Todos os procedimentos estáticos serviram de base para o desenvolvimento de procedimentos dinâmicos, em fluxo, visando minimizar a manipulação de padrões e amostras, bem como reduzir o consumo de reagentes e soluções, a geração de resíduos e aumentar a freqüência analítica. Com relação aos procedimentos dinâmicos foram realizados experimentos empregando detectores espectrofotométricos com base em reações de óxido-redução e complexação, fluorimétricos, com base na emissão pelo analito quando excitado e no seu aumento em ambientes micelares, e eletroanalíticos, com base na hidrólise e oxidação do fármaco em meios adequados. Observou-se, como previsto, perda de sensibilidade nos métodos dinâmicos quando comparados aos procedimentos estáticos, porém com aumento na freqüência analítica, redução de custos operacionais, minimização na manipulação das soluções. Os resíduos gerados foram reaproveitados na maioria dos casos. Todos os procedimentos descritos foram aplicados a amostras comerciais e/ou material biológico sintético, com resultados satisfatórios quando comparados estatisticamente aos obtidos para mesma amostra por meio de método de comparação oficial. Ensaios de adição e recuperação demonstraram, também, a aplicabilidade das estratégias apresentadas; não foram observadas interferências dos demais constituintes das formulações farmacêuticas. / The development and application of different procedures for the quantification of the drug furosemide, exploiting its reactions and physical properties are described. The presented methods were based in static and flow injection procedures. Among the static redox procedures titrimetry was applied, which exploited the hydrolysis and oxidation reactions of this drug; batch spectrophotometric determination was carried out applying the complexation between furosemide and ferric ions and, electroanalytical determinations, by cyclic, differential pulse and square wave voltammetry, were developed exploiting the electrochemical behavior of the analyte. All the static procedures were used as base to the development of flow injection methods, aiming to minimize the manipulation of standards and samples, as well as to reduce the reagent and solutions consumes and the waste generation, and to improve the analytical frequency. Based on the flow injection procedures some experiments were developed using spectrophotometric detectors, applying redox and complexation reactions; fluorimetric detectors, based on the fluorescence emission generated by the analyte when excited and exploiting its improvement by micellar media; and electrochemical detectors, based on the hydrolysis and oxidation under suitable conditions. Lost of sensitivity could be observed in the flow injection procedures, on the other hand, improvement on analytical frequency, reduction on operational costs and minimization on solutions handling could also be noted. The waste generated was reused in the majority of the cases. All the procedures described were applied to commercial samples and/or synthetic biological material, with satisfactory results when statistically compared to those obtained by a reference method to the same samples. Recovery tests also demonstrated the applicability of the developed strategies. Interference from the constituents of the pharmaceutical formulations was not observed.

Neste trabalho, propõe-se o desenvolvimento de procedimento analítico automático para determinação espectrofotométrica de microcistinas em águas empregando o processo de multicomutação em fluxo. O módulo de análise para implementar o procedimento analítico empregou um bomba de seringa para propulsão de fluído e válvulas solenóide para controlar a amostragem. A bomba de seringa foi construída no laboratório de Química Analítica, CENA/USP, onde foi empregado um motor de passo para fazer o deslocamento do êmbolo da seringa. Como detectores foram empregados, um fotômetro da Oriel Instrument e um fotômetro desenvolvido no laboratório de Química Analítica, CENA/USP, baseado em um fotodiodo da BURR-BRAWN e projetado para este procedimento. Uma cela de fluxo com caminho óptico de 40 mm e volume interno de 32 \'mü\'L, foi construída sob medida para permitir fácil acoplamento da fonte de radiação (LED) e dos fotodetectores, formando uma unidade compacta. O controle do sistema de fluxo, incluindo o motor de passo, foi executado por um microcomputador usando um software escrito em linguagem Quick Basic 4.5. Os sinais gerados pelos fotômetros em diferença de potencial eram convertidos para digital por um multímetro e enviados para o computador através da interface serial 232. O sistema proposto foi empregado para determinação de microcistinas em águas de rios e lagoas. A exatidão foi averiguada comparando com os dados obtidos empregando um equipamento ELISA. A faixa de concentração situada entre (0,1 e 0,8 \'mü\'gL-1) de microcistina indica que o sistema proposto pode ser usado em serviços de tratamento de águas onde o requerimento da ANVISA (Portaria n°518, 2004) deve ser alcançado / In this work, it was proposed the development of an automated analytical procedure based on multicommutation for the photometric determination of microcystins water. The flow module to implement the analytical procedure employed a syringe pump for solution propelling and solenoid valves for sampling control. The syringe pump was constructed in the laboratory CENA/USP, employed a step-motor to carry out the displacement of the syringe piston. As photodetectors was employed an Oriel Instrument photometer and a photometer developed in the laboratory CENA/USP based on a BURR-BRAWN photodiode and designed to be used in this procedure. A flow cell with optical pathlength of 40 mm and inner volume of 32 \'mü\'L was tailored to allow easily coupling of radiation source (LED) and photodetector, forming a compact unit. The control of the flow system, including the step-motor was performed by a microcomputer using a software wrote in Quick BASIC 4.5. The signals generated by the photometers in difference of potential were converted to digital by a digital multimeter and sent to the microcomputer through the serial interface 232. The proposed system was employed for the photometric determination of microcystins in water. Accuracy was assessed comparing the results with those obtained using a ELISA instrument. The concentration response (0,1 e 0,8 \'mü\'gL-1 microcystins) and limit of detection lower than 0.01 \'mü\'gL-1 microcystins, indicated that the proposed system can be used in plants of water treatment where the ANVISA requirement must be maintained