Este trabalho teve como principal objetivo o estudo sistemático da obtenção da fase beta-BaB204 (beta-BBO) a partir de uma fase vítrea do sistema BaO-B2O3-TiO2. Foram estudadas amostras contendo entre 4 e 16% de TiO2. A avaliação das propriedades térmicas, estruturais e microestruturais das amostras foi realizada empregando as técnicas de Analise Térmica Diferencial (DTA), Difração de Raios-X (DRX), Microscopia óptica (MO), Microscopia Eletrônica de Varredura (MEV), Espectroscopia Raman, Absorção e Transmissão óptica no Infravermelho, Espectroscopia de Absorção de Raios-X (XAS) e Ressonância Magnética Nuclear (RMN). O coeficiente de Geração de Segundo Harmônico (GSH) foi obtido através das medidas do loci de casamento de fase e da Franja de Maker. O estudo do processo de cristalização revelou que em todas as amostras prevaleceu o mecanismo de cristalização superficial. Nas amostras contendo 4 e 8% de TiO2 foi observada a cristalização da fase beta-BBO enquanto que nas amostras contendo 15 e 16% de TiO2, foi observado que o processo de cristalização se inicia pela fase BaTi(BO3)2 e que somente após longos tempos de tratamento, a fase beta-BBO se toma a fase predominante. A identificação da fase BaTi(BO3) somente foi possível com a utilização da técnica de Espectroscopia Raman. O estudo da estrutura local através das técnicas de XAS e RMN mostrou que a estrutura local ao redor dos átomos de titânio, bário e boro nas amostras cristalizadas é pouco afetada quando a quantidade de TiO2 passa de 4 para 16%. A análise dos resultados da medida de geração de segundo harmônico mostrou que nas amostras contendo uma camada da superfície cristalizada, o valor do coeficiente de geração de segundo harmônico (deff) é equivalente ao do quartzo monocristalino e na amostra contendo 16% de TiO2, corresponde a 70% do valor observado na fase beta-BBO em sua forma monocristalina / This work consists of a systematic study of the beta-BaB2O4 (beta-BBO) crystalline phase obtained from the BaO-B2O3-TiO2 glass system containing amounts of titanium varying from 4 to 16 mol%. The thermal, structural and microstructural properties of the samples were evaluated by the following techniques: Differential Thermal Analysis (DTA), X-Ray Diffraction (XRD), Optical Microscopy (OM), Scanning Electron Microscopy (SEM), Raman Spectroscopy, Infrared Optical Absorption Spectroscopy, X-Ray Absorption Spectroscopy (XAS) and Nuclear Magnetic Resonance (NMR). The Second Harmonic Generation (SHG) coefficient (def) was obtained from the phase matching Loci and Maker fringe curves. A study of the crystallization process revealed that the surface crystallization mechanism predominated in each of the samples. Only the beta-BBO phase was observed in the samples containing 4 and 8 mol% of TiO2. However, in the samples containing 15 and 16 mol% of TiO2, crystallization of the BaTi(BO3)2 occurred first and was followed by crystallization of the P-BBO phase, which subsequently became the main phase as the period of heat treatment increased. The identification of the BaTi(BO3)2 phase in the early stage of the crystallization process was only possible by using the Raman spectroscopy technique. Based on the results obtained from the XAS and NMR techniques, it was found that the increasing the titanium concentration does not affect significantly the short-range order around Ti, Ba and B atoms. An analysis of the SHG data obtained from the crystallized surface of the glassy samples indicated that the SHG coefficient, def, was comparable to that of the z-quartz monocrystalline sample and, in the sample containing 16 mol% of TiO2, it corresponded to 70% of the value observed for the monocrystalline beta-BBO sample

Entre os vários tipos de eletrodos de carbono, carbono polimérico vítreo obtido a partir de resina fenólica é particularmente atraente como material de eletrodo, devido à sua estabilidade térmica, robustez, resistência mecânica, condutividade elétrica e grande variedade potencial. Neste contexto, as propriedades eletroquímicas poliméricas de monolitos de carbono vítreo foram investigados em função de diferentes temperaturas de síntese (750 ° C, 950 ° C, 1100 ° C, 1300 ° C e 1650 ° C). Os sólidos foram obtidos utilizando resina fenólica previamente sintetizada, e depois da etapa de reticulação inicial a 60ºC foram submetidos a um aquecimento de até 1650 ºC em atmosfera de nitrogênio. Posteriormente foram confeccionados eletrodos utilizando para isto um molde de teflon e para o contato elétrico feltro de carbono. A influência do tratamento térmico (750, 950, 1100, 1300 e 1650 ºC) na estrutura do carbono polimérico vítreo foi investigada e correlacionada com os parâmetros eletroquímicos obtidos pela técnica de voltametria cíclica. Além disso, foi investigado como os grupos de superfície afetam os parâmetros cinéticos, tais como os coeficientes de massa e de transferência eletrônica, como também o coeficiente de difusão. De um ponto de vista geral, defeitos são removidos com o aumento da temperatura, como é verificado pela microscopia de força atômica, bem como a condutividade elétrica aumenta com o tratamento térmico. Em adição a isto, o comportamento eletroquímico usando tanto o sistema FeCN63-/4- quanto o Ferroceno é bastante similar ao eletrodo comercial de carbono vítreo. Para aplicações voltamétricas, amostras de carbono vítreo tratadas termicamente a 1300 e 1650ºC são os mais apropriados, pois as correntes de fundo dos eletrólitos são os mais baixos em toda a faixa potencial. Num conjunto de experiências exploratórias, é descrita a síntese e as propriedades magnéticas de um novo compósito óxido de ferro / carbono vítreo polimérico formado por meio de um aquecimento cuidadoso de uma matriz de resina polimérica de fenol-formaldeído pré-moldada com íon ferro disperso em resina - ácido cítrico - polietileno-glicol em atmosfera de nitrogênio. / Among several kinds of carbon electrodes, phenolic resin based polymeric glassy carbon is particularly attractive as electrode material due to its thermal stability, robustness, mechanical strength, electrical conductivity and large potential range. In this context, electrochemical properties of polymeric glassy carbon monoliths were investigated in function of different synthesis temperatures (750 °C, 950 °C, 1100 °C, 1300 °C, and 1650 °C). The solids were obtained using phenolic resin previously synthesized and, after initial curing step at 60 oC, the samples were thermally treated up to 1650 oC in nitrogen atmosphere. Afterwards, homemade electrodes were confectioned with Teflon mold, and felt carbon was used for electric contact. The influence of high temperature treatment (750 oC, 950 oC, 1100 oC, 1300 oC, and 1650 oC) on polymeric glassy carbon structure was investigated and correlated to electrochemical parameters obtained from cyclic voltammetry technique. Besides, it was investigated how the surface organic groups affect the kinetic parameters such as both electronic and mass transfer coefficients as well as diffusion coefficient. From a general point of view, defects are removed with temperature increase as verified by atomic force microscopy, as well as the electrical conductivity rises with thermal treatment. In addition to that, the electrochemical behavior by using both FeCN63-/4- and ferrocene systems is quite similar to commercial glassy carbon. For voltammetric application, glassy carbon samples heat-treated to 1300 oC and 1650 oC are the most appropriate due to the electrolyte background currents are lower over potential range. In a set of exploratory experiments, it is described the synthesis and magnetic properties of a new iron oxide/polymeric glassy carbon composite formed by means of a carefully heating of a premodelled polymeric phenol-formaldehyde resin matrix with iron ion dispersed in a citric acid-polyethylene glycol resin in a nitrogen atmosphere.

Made available in DSpace on 2016-08-19T12:56:46Z (GMT). No. of bitstreams: 1 Dissertacao Helmara.pdf: 1239564 bytes, checksum: f5a4e670235603269ce13bb3db2a2938 (MD5) Previous issue date: 2013-06-06 / Conselho Nacional de Desenvolvimento Científico e Tecnológico / Due to the implementation of more restricted environmental regulation laws, the control of pollution agent such as sulfur compounds has provides the development of new analytic methodologies for its quantification on different matrices, including biodiesel fuel. Thus, this work aims to compare three different sensors - film bismuth and mercury film on the surface of a glassy carbon electrode and solid silver amalgam (dental) - for the determination of sulfur in biodiesel, by means of stripping voltammetric cathodic square wave mode (VRC/SW) as supporting electrolyte with a solution of sodium acetate (1,4 mol.Lˉ¹) and acetic acid (0.33 mol.Lˉ¹) in metanol/2-propanol. In general, the mercury film electrode (MFE) has presented the best electrochemical behavior to the definition of peak reduction, being then selected as standard electrode to the measurements. The sulfur quantization on biodiesel samples was performed by adding 70 μL of soybean biodiesel and tallow fatty with TMAH, adding later, aliquots of standard sulfur. The method showed good linearity (0.998), suggesting an average sulfur concentration of 6,870x10ˉ7 (± 6,857x10ˉ⁸) mol.Lˉ¹, within a confidence interval of 95%, to a limit of detection 3,294x10ˉ¹º mol.Lˉ¹ and quantification limit of 1,098x10ˉ9 mol.Lˉ¹. Besides, for the untreated sample, the experimental has provided a LD of 6,54 x 10ˉ9 mol.Lˉ¹. Finally the proposed method has been compared with the results of a collaborative study (ANP 01/2012) of the same sample using the Teste-t de Student, verifying that the proposed method and official methods (EN ISO 20846, EN ISO 20884) are statistically equivalent to a confidence level of 95%, thereby demonstrating the feasibility of the method. / O controle da poluição ambiental tem exigido, cada vez mais, a determinação de enxofre em uma variedade de matrizes. Diferentes métodos analíticos têm sido desenvolvidos para determinação deste analito em biodiesel, empregando várias técnicas, que vão desde a análise cromatográfica aos métodos espectroanalíticos. No presente trabalho são apresentados os resultados da avaliação de diferentes sensores eletroquímicos para determinação de enxofre em Biodiesel, utilizando a técnica voltamétrica de redissolução catódica no modo onda quadrada (VRC/SW) tendo como eletrólito suporte uma solução de acetato de sódio (1,4 mol.Lˉ¹) e ácido acético (0,33 mol.Lˉ¹), em metanol/2-propanol. Foram avaliados três sensores (filme de bismuto e filme de mercúrio na superfície de carbono vítreo, e eletrodo sólido de amálgama de prata dentária) na determinação de enxofre, sendo observado que o eletrodo de filme de mercúrio (EFM) apresentou os melhores resultados relacionados ao comportamento eletroquímico na definição do pico de redução. Portanto, o EFM foi o sensor escolhido para aplicação na amostra de biodiesel. A determinação do analito em Biodiesel foi realizada adicionando-se 70 μL de Biodiesel de Soja e Sebo (01/2012, interlaboratorial) tratado com TMAH, adicionando, posteriormente, alíquotas de padrão de enxofre. O método apresentou uma boa linearidade (0,998), determinando-se assim uma concentração média de enxofre de 3,687 x 10ˉ7± 6,857 x 10ˉ⁸ mol.Lˉ¹, a um intervalo de confiança de 95%, para um limite de detecção de 3,294 x 10-10 mol.Lˉ¹ e limite de quantificação de 1,098 x 10ˉ9 mol.Lˉ¹, o que demonstra uma boa sensibilidade da técnica. Além disso, avaliou-se o estudo sem tratamento da amostra, na qual obteve-se LD de 6,54 x 10ˉ9 mol.L-1. O presente método foi comparado com os resultados de um estudo interlaboratorial (ANP 01/2012) da mesma amostra, utilizando o Teste-t de Student, verificando que o método proposto e os métodos oficiais (EN ISO 20846; EN ISO 20884) são estatisticamente equivalentes a um nível de confiança de 95%, demonstrando assim a viabilidade do método.

Il est bien établi que les propriétés mécaniques et rhéologiques d'une large classe de matériaux vitreux amorphes met en jeu – contrairement aux dislocations dans les cristaux – des rearrangements structuraux localisés formant par un processus de cascade des bandes de cisaillements. Cette localisation de la déformation est observée dans divers systèmes vitreux ainsi que dans des simulations numériques. Cette réponse mécanique complexe reste mal comprise à une échelle microscopique et il n'est pas clair si l'écoulement plastique peut être associé à une origine structurale locale ou à des processus purement dynamiques.Dans cette thèse nous envisageons ces problématiques à l'aide de simulations atomiques athermales sur un système Lennard-Jones modèle. Nous calculons le tenseur élastique moyenné localement sur une échelle nanométrique. A cette échelle, le verre est assimilable à un matériau composite comprenant un échafaudage rigide et des zones fragiles. L'étude détaillée de la déformation plastique à différents taux de cisaillement met en évidence divers régimes d'écoulement. En dessous d'un taux de cisaillement critique dépendant de la taille du système, la réponse mécanique atteind une limite quasistatique (effets de taille fini, cascades d'événements plastiques, contrainte seuil) alors que pour des taux de cisaillement plus importants les propriétés rhéologiques sont fixées par le taux de cisaillement imposé. Dans ce régime nous mettons en évidence la croissance d'une longueur de coopérativité dynamique et discutons de sa dépendance avec le taux de cisaillements. / It is commonly acknowledged that the mechanical properties and the rheology of a wide class of amorphous glassy materials involves – in contrast to dislocations in crystals – localized structural rearrangements that can form through a cascade mechanism shear bands. The phenomenon of strain localization has been observed experimentally in alloys, metallic and covalent glasses, polymers, complex fluids, granular media, foams, as well as in numerous simulations. This complex mechanical response remains poorly understood at a microscopical level and the origin of the plastic flow in driven glasses cannot be unambiguously attributed to either a local origin or to purely dynamic processes independently of any structural origin. In this thesis we approach these problems by the use of athermal atomistic simulations on a model Lennard-Jones glass. We compute the locally averaged elasticity tensor of the glass at a nanometric level. At this scale, the glass appears as a composite material composed of a rigid scaffolding and of soft zones. Moreover we use this local elastic order parameter to relate structure and dynamics in the sheared glass. The detailed analysis of the plastic deformation at different shear-rates shows that the glass follows different flow regimes. Below a system size dependent critical shear-rate the mechanical response reaches a quasistatic limit (finite size effects, cascades of plastic rearrangements, yield stress) while at higher shear rates the rheological properties are determined by the externally applied shear-rate. In the later regime we report on the growth of a cooperativity length scale and discuss the scaling of this length with shear-rate.

Ce travail propose une étude expérimentale visant à caractériser les processus dynamiques se produisant au sein de matériaux vitreux mous. La première partie présente des mesures de diffusion de traceurs nanométriques dans la Laponite (une suspension colloïdale) obtenues par une méthode de recouvrement de fluorescence (FRAP). Cette étude montre que la diffusion varie avec la concentration de Laponite et la taille du traceur. Un modèle hydrodynamique de diffusion confinée permet de décrire quantitativement les données expérimentales. Une deuxième partie concerne l’étude expérimentale du vieillissement de matériaux vitreux. Nous testons en pratique le concept théorique de température effective. Celle-ci est obtenue grâce à la technique de FRAP par la mesure simultanée de la diffusion et la convection de sondes fluorescentes dans la Laponite en cours de prise. Contrairement à certaines mesures de la littérature, le système est bien gouverné par la température ambiante. Nous présentons ensuite une étude visant à caractériser le comportement de la Laponite cisaillée. Nous avons pour cela mis au point un dispositif permettant d’appliquer un champ électrique au système, et ainsi créer des déformations locales. L’effet obtenu s’est révélé trop faible, avec d’assez grandes incertitudes (probablement liées à la complexité du système), pour être considéré comme significatif. Enfin, nous avons étudié les propriétés du Carbopol, un fluide à seuil, en mesurant sa dynamique d’ascension par capillarité. La rugosité de surface des capillaires influe énormément sur la montée du fluide. Nous montrons aussi que l’ascension est pilotée par la rhéologie du système, notamment par le seuil d’écoulement. / This work is based on an experimental analysis of the dynamical processes which occur within soft glassy materials. The first part provides measurement results of nanotracers diffusion in Laponite (a colloidal suspension) obtained by a method of fluorescence recovery (FRAP). This study shows that the diffusion is affected by the concentration of Laponite as well as the size of the tracer. A hydrodynamic model with confined diffusion allows a quantitative description of the experimental data. In a second part, an experimental study is carried out, dealing with the aging processes of glassy materials. The theoretical concept of effective temperature is probed experimentally. The effective temperature is determined using the technique of FRAP, by simultaneously measuring diffusion and convection of fluorescent probes within the aging Laponite. Contrary to some measurements found in literature, results show that the system is controlled by the bath temperature. The following study then aims at characterizing the behavior of the sheared Laponite : an experimental device is developed in this perspective, by applying an electric field to the system and thus creating local deformations. However, the observed effect appears to be too low, with relatively large uncertainties (probably linked to the complexity of the system), which impede on the significance of our results. Finally, the properties of Carbopol, a yield stress fluid, are analyzed by measuring the dynamics of capillary rise. It is shown that the surface roughness of capillary strongly affects the rise of the fluid and that the latter is controlled by the rheology of the system, and more specifically by the yield stress value.

Le but de cette étude était de déterminer si le partage de petites molécules dans un système d'emballage/aliment change lorsque le polymère passe d’un état vitreux à caoutchoutique. La sorption par un polystyrène amorphe vitreux est un processus très lent. L’hystérésis observée entre les cycles de sorption et de désorption du n-hexane peut être due principalement à la variation de la vitesse à laquelle le système évolue au voisinage de la Tg et à une augmentation du volume libre dans le polymère. La sorption de vapeur de n-hexane ne modifie pas l’état physique du système, alors que celle du toluène induit un passage de l’état vitreux à caoutchoutique. Toutefois, le comportement du coefficient de partage du système toluène/PS reste inchangé lors de la transition vitreuse du système. L'effet de plastification provoquée par la sorption des composés volatils a été étudié. La sorption de certains composés volatils induit un abaissement significatif de la température de transition vitreuse du polystyrène. L'effet plastifiant du n-hexane lors de sa sorption par le PS était plus forte que celle des autres composés étudiés. Les valeurs de coefficients de partage du p-xylène et de l'éthylbenzène entre un film de polystyrène et l'éthylène glycol sont plus faibles que celles du n-hexane et du toluène à 25 °C. Finalement, malgré les modifications structurales induites par la sorption, l’énergie d’activation du coefficient de partage n’est pas significativement modifiée lors de la transition vitreuse. / The aim of this work was to find out whether the partitioning behavior of small molecules in a polymer food packaging system changes as the system traverses through its glass transition. Sorption in glassy amorphous polystyrene is a very slow process. The large hysteresis between sorption-desorption cycles of n-hexane/PS was hypothesized to be mainly due to varying rate at which the glass transition temperature was reduced and increase in system’s volume. The equilibrium sorption in glassy amorphous polystyrene at 25 °C, of n-hexane vapor did not modify the state of the system, whereas that of toluene vapor modified the system’s state significantly. The partitioning behavior of toluene/PS remained unchanged across the glass transition of the system. The plasticization effect caused by sorption was studied and revealed that it modifies the glass transition of a volatile/PS mixtures quite significantly. Such information is useful in knowing state modifications of the system as long as sorption/migration occurs, and thus assisting interpretation. The plasticizing effect of n-hexane in amorphous PS was stronger than that of three other volatiles studied. The estimated partition coefficient values of p-xylene and ethylbenzene between polystyrene film and ethylene glycol were several times lower than the experimental values of n-hexane and toluene at 25 °C. Finally, glass transition or change from glassy to rubbery states and vice-versa does not significantly modify the activation energy of sorption.

Magister Scientiae - MSc (Dept. of Chemistry) / This study reports the synthesis of graphene by oxidizing graphite to graphite oxide using H2SO4 and KMnO4 and reducing graphene oxide to graphene by using NaBH4. Graphene was then characterized using FT-IR, TEM, AFM, XRD, Raman spectroscopy and solid state NMR. Nafion-Graphene in combination with a mercury film electrode, bismuth film electrode and antimony film electrode was used as a sensing platform for trace metal analysis in 0.1 M acetate buffer (pH 4.6) at 120 s deposition time, using square-wave anodic stripping voltammetry (SWASV). Detection limits were calculated using 3σblank/slope. For practical applications recovery studies was done by spiking test samples with known concentrations of metal ions and comparing the results to inductively coupled plasma mass spectrometry (ICPMS). This was then followed by real sample analyses. / South Africa

Nous nous sommes intéressés à la description de la dynamique d'un liquide surfondu en étudiant un modèle qui repose sur un ingrédient simple. En partant d'un système de Lennard-Jones monodisperse dans le plan euclidien, nous avons ajouté de la frustration en courbant le plan de sorte à former une sphère de rayon arbitraire. A l'aide d'un algorithme de dynamique moléculaire sphérique, nous avons montré que ce système présentait bien une dynamique vitreuse d'équilibre, caractérisée par la fonction de diffusion intermédiaire incohérente $F_s(k,t)$, qui ralentit fortement et change de comportement à basse température, pour une faible variation de la statique. Le système se comporte comme un verre fort pour les courbures les plus grandes, mais sa fragilité augmente lorsque la courbure diminue. L'allure de $F_s(k,t)$ est également modifiée quand la courbure diminue, ce que nous avons essayé d'expliquer par l'étude de la théorie de couplages de modes (MCT) sur la sphère. Nous avons dérivé l'équation dynamique de MCT sphérique puis étudié la limite aux temps longs de sa solution. On obtient une transition dynamique qui est similaire à celle de la MCT euclidienne, ce qui ne permet pas d'expliquer l'effet de courbure sur $F_s(k,t)$, bien que celle-ci ait une influence sur la valeur de la température de transition. Enfin, nous nous sommes intéressés au rôle des "défauts", dont un nombre minimal de $12$ est imposé par la topologie. A basse température, les défauts tendent à se réunir en structures linéaires, ce qui est prévu théoriquement et observé dans certaines expériences. Les défauts ont une contribution importante à la relaxation, sans pour autant que l'influence des autres particules ne soit négligeable. / We are interested in the description of the dynamics of a supercooled liquid through the study of a model which relies on a simple geometrical ingredient. Starting from a monodisperse Lennard-Jones system on the euclidean plane, we add frustration by curving the space to form a sphere of arbitrary radius. Using a molecular dynamics algorithm, we showed that this system indeed behaves like a glassy liquid at equilibrium. The dynamics, caracterized by the self-intermediate scattering function $F_s(k,t)$, slows down strongly and changes shape at low temperature, for a small variation of the statics. The system behaves like a strong glass for high curvatures, but its fragility increases when the curvature decreases. The shape of $F_s(k,t)$ is also modified when the curvature decreases, which we tried to explain theoretically through the study of the mode coupling theory (MCT) on the sphere. We derived the dynamical equation of spherical MCT and studied the long time limit of its solution. We predict a dynamic transition similar to the one predicted by euclidean MCT, which does not allow us to explain the effect of curvature on $F_s(k,t)$, though the curvature has an influence on the value of the transition temperature. Finally, we studied the role of "defects", among which a minimal number of $12$ is imposed by topology. At low temperature, the defects tend to form linear structures, as predicted theoretically and observed in some experiments. The defects have a strong contribution in the relaxation; however, the role of other particles is not negligible.

Electrochemical oxidation of acyclovir at glassy-carbone electrode and boron-doped diamond electrode gives one pH-dependent oxidation signal; the corresponding electrode reaction is controlled by diffusion. It is followed by a second indistinctive signal in the pH range 2,0 - 9,0. Further, optimization of conditions was carried out for determination of acyclovir using DC and DP voltammetry. The calibration dependence on GC electrode in B−R buffer (pH = 6,0) is linear only in the concentration range from 2 to 10 μmol∙l−1 for DCV with limit of detection 0,38 μmol∙l−1; for DPV it is not linear. BDD electrode has to be activated to prevent its passivation. Anodic activation at +2,4 V for 15 s with simultaneous stirring of solution results in relative standard deviation of 0,9% for acyclovir concentration of 1∙10−4 mol∙l−1. Using DCV and DPV methods linear concentration dependences were obtained in 0,1 mol∙l-1 nitric acid and in pH 6,0 B−R buffer. The lowest limit of detection and limit of quantification (LOD = 0,47 μmol∙l−1 a LOQ = 1,55 μmol∙l−1) and linear range from 0,6 to 100 μmol∙l−1 was reached in pH 6,0 B−R buffer. Further, standard addition method was used to quantify acyclovir in Zovirax tablets. Satisfactory recoveries of 101,1 ± 2,3 % using DCV and 98,8 ± 2,2 % using DPV at BDD (compared with the...

The aim of this diploma thesis was to develop an electrochemical method for three phytosterols, namely stigmasterol β-sitosterol and ergosterol using voltammetry techniques on glassy carbon electrode and boron doped diamond electrode. The work builds on previous results, where it was shown that the electrochemical oxidation of phytosterols requires perchloric acid in acetonitrile. When this acid is used, a dehydration reaction occurs. Calibration dependences were measured here for all phytosterols in an environment with a water content of 0.43%. The stability of the signal with increasing distilled water content was further investigated. Then the calibration dependences in the increased water content were measured again. If we want to use HPLC-type separation techniques, we must first find out how the phytosterols will behave in this environment, and therefore the signal stability on the buffer content was investigated. The buffers used were phosphate and acetate buffer. Subsequently, the concentration dependence was measured in an environment with a higher content of phosphate buffer. Furthermore, the possibility of detecting two phytosterols at once was investigated. Key words: dehydration, glassy carbon electrode, boron doped diamond electrode, oxidation, phytosterols, voltammetry