Thesis (M. Phil.)--University of Hong Kong, 1993.

Orientador: Devaney Ribeiro do Carmo / Banca: Newton Luiz Dias Filho / Banca: Marcelo Firmino de Oliveira / Resumo: O presente trabalho apresenta a preparação e caracterização de uma sílica micelar template modificada com Ti(IV), e posterior reação em H3PO4. O produto formado, chamado de SMT-2, foi caracterizado por espectroscopia na região do infravermelho (FTIR), difração de Raios X (DRX), análise de área superficial e porosidade. Este material não adsorveu metais e sim compostos fenotiazínicos. Uma caracterização dos compostos fenotiazínicos nas cavidades da SMT-2 foi realizada empregando técnicas de FTIR, termogravimetria e voltametrica cíclica. O voltamograma cíclico do eletrodo de pasta de grafite modificado apresentou dois pares redox com potencial padrão (E0'), onde E0' = (Epa+Epc)/2, 0,09 V para o pico I e 0,42 V para o pico II (v=50 mV s-1; solução tampão Britton-robinson; pH 2) versus Ag/AgCl que foi atribuído ao monômero e dímero do azul de orto toluidina nas cavidades da SMT-2, estes resultados foram análogos ao azul de metileno e azure A. Em uma segunda etapa, preparou-se óxido de titânio seguindo uma nova metodologia de síntese. Por analogia a SMT-2, o material preparado foi modificado com H3PO4, que foi descrito como TiP, e contrariamente ao SMT-2, o material apresentou capacidade de adsorver íons metálicos (Co2+, Cu2+, Ni2+). Após a caracterização do TiP pelas técnicas supracitadas, efetuaram-se os estudos de adsorção de íons de Co2+, Cu2+ e Ni2+ em meio aquoso, etanol/água (42%) e etanol (99%) onde se determinou para estes metais os respectivos tempos de equilíbrio de sorção. Após a determinação do tempo de equilíbrio para a adsorção dos íons metálicos em cada sistema, determinou-se a capacidade específica de sorção (NfMax) através de isotermas de sorção. Para o Co2+, os valores de Nf foram: em meio aquoso (4,95 x 10-4 mol g-1), etanol/água 42% (6,09 x 10-4 mol g-1) e... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: This work presents the preparation of a micellar template silica modified with Ti (IV), and subsequent reaction with H3PO4. The product formed, called SMT-2, was characterized by spectroscopy in infrared region (FTIR), X-ray diffraction (XRD), surface area analysis and porosity. This material did not adsorbed metals but adsorbed phenothiazine compounds. A characterization of phenothiazine compounds in the wells of SMT-2 was performed using techniques of FTIR, thermogravimetric analysis and cyclic voltammetry. The cyclic voltammogram of modified graphite paste electrode showed two redox couples with standard potential (E0'), where E0' = (Epa + Epc) / 2, 0.09 to peak I and 0.42 to peak II ( v = 50 mV s-1 BR solution, pH 2) vs. Ag / AgCl which was assigned to the monomer and dimer of ortho toluidine blue into the wells of SMT-2, these results were similar to methylene blue and azure A. In a second step, prepared titanium oxide following a new methodology for synthesis. By analogy of SMT-2, the prepared material was modified with H3PO4, which was abbreviated as TiP, contrary to the SMT-2, the material shows the ability to adsorb metal ions (Co2+, Cu2+, Ni2+). After characterizing the TiP by the techniques described above, were conducted studies of ion adsorption of Co2+, Cu2+ and Ni2+ in water, ethanol/water (42%) and ethanol (99%) which was determined for these metals their equilibrium times sorption. After determining the equilibrium time for adsorption of metal ions in each system, we determined the specific sorption capacity (NfMax) through sorption isotherms. For the Co2+, the values of Nf were in water (4.95 x 10-4 mol g-1), ethanol/water 42% (6.09 x 10-4 mol g-1) and ethanol 99% (3.00 x 10-4 mol g-1), with concentrations of Co2 + ions ranging from 9.03 to 18.63 x 10-4 mol L-1. As for the Cu2 + these values were: in water... (Summary complete electronic access click below) / Mestre

Orientador: Devaney Ribeiro do Carmo / Banca: Newton Luiz Dias Filho / Banca: Regina Massako Takeuchi / Resumo: O presente trabalho apresenta a preparação de um silsesquioxano nanoestruturado, o cloropropilsilsesquioxano (S) que foi organofuncionalizado com os seguintes agentes modificadores: 4-amino-3-hidrazinico-5-mercapto-1,2,4-triazol (Purpald®) e o 4-amino-5-4(piridil)-4H-1,2,4-triazol-3-tiol (APTT), os materiais obtidos dessa funcionalização foram descritos como SP e SA, respectivamente. Os materiais SP e SA foram caracterizados por diversas técnicas espectroscópicas: Espectroscopia na região do infravermelho (FT-IR), Ressonância magnética nuclear 29Si e 13C no estado sólido (RMN), Difração de Raios- X (DRX), Espectroscopia de Energia Dispersiva de Raios X (EDX), Termogravimetria e Análise Térmica Diferencial (TG - DTA). Após a devida caracterização, realizaram-se estudos de adsorção de íons metálicos (Cu2+, Cd2+ e Ni2+) nos sítios ativos do SA, porém, curiosamente não se observou a mesma capacidade de sorção pelo SP. Diferentes meios foram estudados no processo de adsorção dos íons metálicos supracitados: aquoso, etanólico 99% e etanólico 42%, determinando-se o tempo de equilíbrio de adsorção, que para ambos os meios e metais esse tempo máximo foi em média 35 min. Determinado o tempo de equilíbrio de adsorção dos íons metálicos em cada sistema, determinou-se a capacidade específica de sorção (Nfmax) através de isotermas de adsorção. Para o Cu2+, os valores de Nf foram: meio aquoso (3,09 × 10-4 mol g-1), etanólico 42% (1,03 × 10-4 mol g-1) e etanólico 99% (1,86 × 10-4 mol g-1), com concentrações de íons Cu2+ variando de 1,74 a 29,64 mol L-1. Os valores encontrados para o Ni2+ foram: em meio aquoso (2,11 × 10-4 mol g-1), etanólico 42% (0,97 × 10-4 mol g-1) e etanólico 99% (1,05 × 10-4 mol g-1), com concentrações de íons Ni2+ variando de 2,25 a 33,18 mol L-1. Para os íons cádmio não foram... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: This work presents the preparation of a nanostructured silsesquioxane, the cloropropilsilsesquioxano (S) that was organofunctionalised with the following modifying agents: 4-amino-3-hydrazino 5 - mercapto 1,2,4 triazole (Purpald ®) and 4- amino-5-4 (pyridyl)-4H-1,2,4-triazole-3-thiol (APTT), the materials obtained of the functionalization were described as SP and SA, respectively. The materials SA and SP were characterized by various spectroscopic techniques such as spectroscopy in the region of infrared (FTIR), nuclear magnetic resonance 29Si and 13C solid-state (NMR), X-ray diffraction (XRD), Energy Dispersive Spectroscopy Rays (EDS), Thermogravimetry and Differential Thermal Analysis (TG - DTA). After proper characterization, were carried studies on adsorption of metallic ions such as Cu2+, Ni2+ and Cd2+ in the active sites of SA, but curiously did not observe the same sorption capacity of the SP. Different methods were studied in the adsorption of metal ions above: aqueous, 99% ethanolic and 42% ethanolic, determining the adsorption equilibrium time, which for both means and metals the maximum time averaged 35 min. After determining the adsorption equilibrium time of metal ions in each system, we determined the specific sorption capacity (Nfmax) through adsorption isotherms. For Cu2+, the values of Nf were: aqueous solution (3.09 × 10-4 mol g-1), 42% ethanolic (1.03 × 10-4 mol g-1) and 99% ethanolic (1.86 × 10-4 mol g-1), with Cu2 + ion concentrations ranging from 1.74 to 29.64 mol L-1. The values obtained for the Ni2+ were: aqueous solution (2.11 × 10-4 mol g-1), 42% ethanolic (0.97 × 10-4 mol g-1) and 99% ethanolic (1.05 × 10-4 mol g-1), with Ni2 + ion concentrations ranging from 2.25 to 33.18 mol L-1. For the cadmium ions were not observed saturation of adsorption sites in the concentration range studied, not getting the maximum... (Summary complete electronic access click below) / Mestre

Magister Scientiae - MSc / Various dermatological disorders, such as formation of black pigmented patches on the surface of the skin arise from the over-activity of tyrosinase enzyme's degenerative action. This enzyme is further implicated in the involvement of melanin in malignant melanoma, the most lifethreatening skin tumors. Although, synthetic products were found effective to combat this menace, nevertheless, overtime detrimental effect on human skin is a challenge. Investigation of natural tyrosinase inhibitors from methanol extracts of medicinal plants of Lamiaceae family using L-tyrosine as substrate on three different complementary assays (TLC bio-autography, spectrophotometry and cyclic voltammetry) was carried out accordingly. The result indicated Salvia chamelaeagnea, Salvia dolomitica, Plectranthus ecklonii, Plectranthus namaensis, and Plectranthus zuluensis, with significant zone of inhibition against tyrosinase on TLC bio-autography, spectrophotometry result showed that extracts of Plectranthus ecklonii (IC50 = 21.58 μg/mL), Plectranthus zuluensis (IC50 = 23.99 μg/mL), Plectranthus madagascariensis (IC50 = 23.99 μg/mL) and Salvia lanceolata (IC50 = 28.83) demonstrated good anti-tyrosinase activity when compared with kojic acid (IC50 = 3.607 μg/mL). On the other hand, cyclic voltammetry are in consonant with above results thereby supported the nomination of some of the extracts as strong anti-tyrosinase agents. Salvia chamelaeagnea showed strong activity in cyclic voltammetry and clear zone of inhibition on TLC bioautography, these reasons gave us justification for further chemical study to isolate the bioactive constituents. Phytochemical investigation of the bioactive extract of Salvia chamelaeagnea using different chromatographic methods including column chromatographic and semi preparative HPLC afforded six (6) known compounds viz carsonol (C1), carnosic acid (C2), 7- ethoxylrosmanol (C3), ursolic acid (C4), rosmanol (C5) and ladanein (C6). Their chemical structures were elucidated by analyses of spectroscopic (1H and 13C NMR) data as well as correlations with existing literature. The methanolic extract of S. chamelaeagnea (SC) showed moderate antityrosinase (IC50 = 267.4 μg/mL) activity, total antioxidant capacities measured as: Oxygen radicals absorbance capacity (ORAC; 14970 ± 5.16 μM TE/g), ferric-ion reducing antioxidant power (FRAP; 9869.43 ± 7.87 μM AAE/g) and trolox equivalent absorbance capacity (TEAC; 13706.5 ± 0.95 μM TE/g). Excellent total antioxidant capacities were demonstrated by C1 and C5 respectively as FRAP (9338.92 ± 1.72; 8622.73 ± 1.92) μM AAE/g; TEAC (16505 ± 0.86; 10641.5 ± 0.52) μM TE/g; ORAC (14550.5 ± 3.65; 14633.90 ± 3.84) μM TE/g and including the inhibition of Fe2+ -induced lipid peroxidation (IC50 = 32.5; 30.25) μg/mL. All the compounds except C4 are electro-active with well-defined oxidation-reduction peaks while C1 demonstrated the highest tyrosinase inhibitory activity by strongly decreased the inhibition current with time using cyclic voltammetry method. The isolated compounds especially C1, C2 and C5 are well known to combat with ageing problems and documented for their powerful activity against oxidative stress and alzheimer's diseases, which are ageing related symptoms. The isolation of such bioactive compounds indicated the synergetic effect of the results of the three methods used in this thesis. This is the first report on the evaluation of both anti-tyrosinase and total antioxidant capacities of the isolated compounds from S. chamelaeagnea. The findings therefore can be used as background information for exploitation of skin depigmentation and antioxidant agents from natural source.

>Magister Scientiae - MSc / Pollution of water sources, aquifers and wetland systems caused by industry, agriculture, and municipally treated wastewater is a worldwide problem that contributes to the scarcity of clean and potable water. Rivers, channels, lakes, oceans, and ground water are often contaminated by a variety of organic substances that can affect aquatic life and threaten human health. Organic compounds such as antibiotics that are not effectively removed by modern day water treatment technology are a growing threat to water quality and health. The emergence of antibiotics in the environment particularly aquatics have become a matter of concern as they may result in induction and spread of bacterial resistance which may be harmful to humans or animals. After administration, antibiotics for human use or their metabolites are excreted into the effluent and reach the sewage treatment plant (STP). Not all Antibiotics in sewage treatment plants are eliminated. Consequently they can pass through the sewage system and may end up in environmental and even potable water systems. Antibiotic residues have been reportedly found in places such as hospital wastewaters, wastewater treatment plants and surface waters all over the world with concentrations ranging from approximately 60-120000 ng/, 2-580 ng/L and 5-1300 ng/L respectively. The current methods that are used to detect antibiotics can be quite expensive and time consuming due to sample preparation (necessary for detection of very low concentrations of antibiotics in water) and technology used in the instruments. Electrochemical sensors and biosensors are simple systems, with high selectivity and sensitivity for individual measurements and cost effectiveness. The development of composites based on conductive phases dispersed in polymeric matrices has led to important advances in analytical electrochemistry. Polyamic acid and graphene oxide are both materials with well-defined electrochemistry and are easily processable in the design of various sensor formats. In this study we present a novel polyamic acid - graphene oxide (PAA/GO) electrode which was prepared for electrochemical screening of antibiotic residues in aqueous systems. Polyamic acid (PAA) and graphene oxide (GO) were successfully synthesized independently and characterized using SEM which was used to study the morphology of the PAA, FTIR spectroscopy to confirm chemical structures and functional groups as well as CV and SWV which were used to identify the unique electrochemical behavior of PAA and GO respectively. Polyamic acid-graphene oxide nanocomposite was prepared and characterized by CV, SWV, FTIR and SEM. The novel electrode (PAA/GO/SPCE) was prepared by electrochemically depositing PAA/GO (0.03 mg/mL) onto SPCE electrodes using 5 cycles between −1000 mV and 1000 mV at 50 mVs. The analytical performance of the electrochemical sensor towards detection of neomyxin and norlfoxacin was compared to standard Uv-vis spectroscopy method. The Uv-vis spectroscopy showed LOD of 1.61x10-5 M and 1.41x10-5 M for norfloxacin and neomycin respectively. The PAA/GO electrochemical sensor had a LOD of 3.37x10-7 M for norfloxacin and 1.066x10-6 M for neomycin. Sensitivity of the UV/vis method was comparable to electrochemical sensor sensitivity for neomycin and norfloxacin.

>Magister Scientiae - MSc / The main aim of this study is to investigate theelectrochemical determination of two beneficial (selenium and zinc) and two toxic (chromium and vanadium) metals in the potable water within the City of Cape Town's distribution area. The Water Laboratory of the City's Scientific Services Branch analyses for these metals in their elemental state, using the Inductively Coupled Plasma Optical Emission Spectrometer (ICP-OES). This is a standard method used for the detection of trace metals. The most sensitive voltammetric method for determining these metals is by adsorptive stripping voltammetry, using a thin mercury film electrode with a glassy carbon support. This voltammetric method is used for quantitative determination of specific ionic species. Because of mercury's toxicity it is not really favoured for trace metals anymore. Many other possibilities are under investigation, e.g. bismuth-film, modified glassy carbon and antimony electrodes. The boron-doped diamond (BDD) electrode has distinct advantages when used to determine metal concentrations. Advantages of BDD electrodes include lower detection limit, speciation and wider potential window. In this study cyclic voltammetry (CV) was used to determine the copper, cadmium and lead concentrations in potable water by means of square wave voltammetry (SWV) and a bare glassy carbon electrode (GCE). Furthermore, a boron-doped diamond electrode (BDDE) was used to investigate the possibilities of determining selenium, chromium and vanadium by SWV. Real samples (potable water samples) were analysed electrochemically to qualify and quantify these metals and determine whether they comply with the SANS 241:2006 drinking water guidelines.The copper, cadmium, lead and selenium peaks appear very close to the theoretical values, which indicate that these metals can be detected by SWV method, but further analysis with more samples is advised. Even though responses were observed for vanadium and chromium, it was not reliable and requires further investigation. Further studies into the analyses of zinc are also advised.

Magister Scientiae - MSc (Biotechnology) / It has been estimated that the world population will reach about 10 billion by the year 2050 and in order to accommodate the increased demand of food, the world agricultural production needs to rise by 70 % in the year 2030. However, the realisation of the goal in food production is hindered by limited arable land caused by urbanisation, salinisation, desertification and environmental degradation. Furthermore, abiotic and biotic stresses affect plant growth and development, which lead to major crop losses. The long term goal of this study is to improve food security by producing genetically engineered agricultural crops that will be tolerant to diverse stresses. This research aims at developing stress tolerant crops through the determination of important signalling molecules and second messengers, such as nitric oxide (NO), carbon monoxide (CO) and calcium ion (Ca2+), which can bind to plant proteins such as AtNOGC1 in order to induce stress tolerance in plants.

A duloxetina (DLX) é um duplo inibidor seletivo balanceado da recaptação de serotonina e norepinefrina empregado para o tratamento do transtorno depressivo maior e para o manejo da dor neuropática diabética periférica. O objetivo deste estudo foi desenvolver e validar métodos analíticos para determinação de DLX em cápsulas e realizar estudos da estabilidade do fármaco. A substância usada como padrão de referência nas análises foi caracterizada por espectroscopia no infravermelho, ressonância magnética nuclear (RMN), calorimetria diferencial de varredura e espectrometria de massas. As análises qualitativas foram realizadas por cromatografia em camada delgada (CCD), espectrofotometria na região do ultravioleta (UV) e cromatografia líquida de alta eficiência (CLAE) permitindo a identificação do fármaco no produto farmacêutico. A espectrofotometria UV, CLAE e voltametria de redissolução catódica (CSV) foram validadas para determinação quantitativa de DLX em cápsulas. Estes métodos propostos foram específicos, robustos, lineares, precisos e exatos para determinação de DLX em microgrânulos de revestimento entérico. Estudos preliminares da estabilidade da DLX durante o desenvolvimento do método indicativo de estabilidade por CLAE demonstraram que o fármaco foi rapidamente degradado em meio ácido, na presença de peróxido de hidrogênio e de radiação a luz UVC, enquanto que este foi mais estável em meio alcalino. A cinética de degradação descreveu as mudanças na concentração da DLX em condição ácida e sob fotodegradação. A degradação ácida da DLX, em solução de HCl 0,1 M, mostrou cinética aparente de zero ordem e a fotodegradação demonstrou uma cinética aparente de primeira ordem. O produto de degradação principal observado na hidrólise ácida (PDA-14) foi analisado e isolado por CCD preparativa. Espectros de RMN-1H, RMN-13C e COSY foram avaliados e a estrutura do PDA-14 foi confirmada como 1-naftol. Esta substância produz efeitos citotóxicos e consequentemente o produto farmacêutico é uma cápsula de gelatina contendo microgrânulos com revestimento entérico para evitar a degradação ácida da DLX no estômago. / The duloxetine (DLX) is a double balanced selective serotonin and norepinephrinereuptake inhibitor employed for the treatment of major depressive disorder and for the management of diabetic peripheral neuropathic pain. The aim of this study was to develop and validate analytical methods to the determination of DLX in capsules and accomplish studies of this drug stability. The substance used as reference standard in the analysis was characterized by infrared spectroscopy, nuclear magnetic resonance (NMR), differential scanning calorimetry, and mass spectrometry. The qualitative analyses were performed by thin layer chromatography (TLC), ultraviolet spectrophotometry (UV), and high performance liquid chromatography (HPLC) allowing the identification of the drug in pharmaceutical dosage form. The UV spectrophotometry, HPLC, and cathodic stripping voltammetry (CSV) were validated for quantitative determination of the DLX in capsules. These proposed methods were specific, robust, linear, precise, and accurate to the determination of DLX in entericcoated pellets. Preliminary studies of DLX stability during the development of stability-indicating HPLC method demonstrated that the drug was rapidly degraded in acid medium, in the presence of hydrogen peroxide and light UVC radiation, while it was more stable in alkali medium. The kinetics of degradation described the concentration changes of DLX in acid condition and on photodegradation. The acid degradation of DLX in 0.1M HCl solution showed apparent zero-order kinetics and the photodegradation demonstrated apparent first-order kinetics. The main degradation product observed in acid hydrolysis (DP-14) was analyzed and isolated by TLC preparative. 1H NMR, 13C NMR and COSY spectra were evaluated and the structure of DP-14 was confirmed as 1-naphthol. This substance produces cytotoxic effects and consequently the finished pharmaceutical dosage form is a gelatin capsule containing enteric-coated pellets to avoid the acid degradation of DLX in the stomach.

The chemical speciation of trace metals controls their potential bioavailability and therefore toxicity to exposed organisms. Despite previous studies demonstrating the ameliorative effects of dissolved organic carbon (DOC) on metal toxicity, the effectiveness of ligands from varying sources and of potentially variable composition in controlling speciation has not been studied in detail in estuarine waters. In addition, the effect of DOC on radionuclide contaminants in combination with trace metals has not been investigated in any waters. This is of particular interest in the estuarine environment, where both anthropogenic and natural ligands, and contaminants that pose a potential threat to ecosystem health, can be present. Competitive ligand exchange adsorptive cathodic stripping voltammetry (CLE-AdCSV) with complexation capacity titrations was employed to determine the speciation of dissolved Cu and Zn, two metals that possess revised environmental quality standards (EQS) which now account for potential metal bioavailability. Dissolved metal concentrations in the < 0.4 and < 0.2 μm filter fractions of samples from the Tamar Estuary were determined during seasonal transects made over a calendar year. Samples were taken over a full salinity range (0-35) and from locations thought to contain DOC from a variety of sources (e.g. terrigenous, biogenic, sewage). No seasonal trends in metal speciation were identified, but a semi-quantitative assessment of DOC type using 3-D fluorimetry showed domination of humic and fulvic type ligands in the upper estuary, and biogenic-type ligands in the lower estuary, the former appearing the most important in controlling Cu and Zn complexation. Filter size fraction differences showed a major portion of the dissolved metal is associated with the 0.2 ≥ 0.4 μm fraction, indicating an importance of larger molecule ligands in controlling potentially bioavailable metal. Sample ligand concentrations ([L_x]) ranged from 1-372 nM (Cu) and 3-412 nM (Zn), and metal-ligand conditional stability constants (log K_(ML_x )) from 10.5-13.5 (Cu) and 7.5-10 (Zn), which are similar to reported literature. Calculated free metal ion concentrations ([M2+]) of 0.3 – 109 nM (Zn) and 1.4 x 10-13 – 7.3 x 10-11 M (Cu) compared well (92% showed no significant differences (P = 0.02)) with direct measurements of [Zn2+] made for the first time in estuarine waters using “Absence of Gradients and Nernst Equilibrium Stripping” (AGNES) after optimisation for estuarine waters. AGNES fully complements CLE-AdCSV in terms of analytical capability and shows that methods are now available that are capable of directly determining [Zn2+] in estuarine waters for use in environmental monitoring studies. Calculations made using the chemical equilibrium speciation programme Visual MINTEQ (VM) showed [Cu2+] and [Zn2+] could be predicted to within one order of magnitude of measured values when log K_(ML_x ) and [L_x] are determined and input into the model. This was in contrast to poor agreement between measured and predicted [M2+] when VM was used with the NICA-Donnan complexing model, which assumes a set portion of the total DOC concentration input is fulvic acid that actively complexes metals. These results corroborate a lack of identification of a relationship between metal speciation in the Tamar samples and DOC concentration, highlighting that knowledge of DOC type, log K_(ML_x )and L_x are important when assessing environmental risk, setting EQSs and for accurate modeling of [Cu2+]. Finally, a combined chemical and biological study investigating the effects of mixtures of DOC, Zn and the radionuclide tritium (3H) on the marine mussel presents the first evidence of a protective effect of Zn on DNA damage caused by 3H. The association of 3H with DOC remains elusive and an assessment of DOC type is recommended for future research, but the study emphasises the importance of investigating mixture effects in order to avoid inaccurate risk assessment and potentially costly site remediation.

As especificações do biodiesel são garantidas por um rigoroso controle de qualidade; entre outros parâmetros, a quantificação de antioxidantes é fundamental para assegurar um produto satisfatório para comercialização. No presente estudo, foram desenvolvidas técnicas voltamétricas e cromatográficas para análise direta de BHA, TBHQ, BHT e PG em biodiesel. Medidas por voltametria de pulso diferencial (DPV) em mistura biodiesel:etanol 1:1 (v/v), contendo perclorato de tetra-hexilamônio como eletrólito suporte e empregando ultramicroeletrodo (ume) de Pt, mostraram picos da corrente diferencial de oxidação bem definidos para TBHQ e PG, sendo obtidos gráficos de calibração lineares na faixa de concentrações de 10-3 mol L-1. Analogamente, empregando um ume de Au em microemulsão de biodiesel livre de surfactante (SFME) contendo tetrafluoroborato de tetra-n-butilamônio, medidas por DPV apresentaram picos da corrente diferencial bem definidos para TBHQ e BHT. Para esses compostos, foram obtidos gráficos de calibração lineares na faixa de concentrações de 10-4 mol L-1. Em ambos os casos, devido à sobreposição dos voltamogramas, os teores de antioxidantes foram calculados por um procedimento matemático de deconvolução empregando o software Origin 8.0®. A quantificação de BHA, BHT e TBHQ por cromatografia GC/qMS em biodiesel diluído em metanol apresentou linearidade entre 5 e 25 mg L-1, para cada um dos antioxidantes. Medidas por HPLC em fase reversa com coluna fenílica apresentaram boa separação dos picos cromatográficos na análise simultânea de BHA, BHT, TBHQ e PG assim como curvas de calibração com linearidade entre 10 e 80 mg L-1, para cada um dos antioxidantes. A identificação dos ésteres metílicos de ácidos graxos (FAMEs) no biodiesel foi realizada por UHPLC-ESI-Orbitrap/MS; os teores de FAMEs e antioxidantes permaneceram estáveis nas amostras fortificadas mesmo após 8 semanas de exposição à luz solar, porém diminuíram significativamente em amostras não-fortificadas. As metodologias propostas são de fácil preparo e baixo consumo de amostra, podendo vir a ser do interesse da indústria para o monitoramento de antioxidantes em biodiesel, na linha de produção. A principal vantagem é não ser necessário nenhum tipo de pré-tratamento da amostra: a simples diluição em metanol ou etanol ou a preparação do biodiesel na forma de SFME conferem rapidez e simplicidade à determinação dos antioxidantes investigados. / Biodiesel features are assured by strict quality control procedures; among those, antioxidants quantification is essential to guarantee a good and satisfactory final product for commercialization. In the present study, voltammetric and chromatographic methodologies were developed for direct analyses techniques of BHA, TBHQ, BHT and PG in biodiesel. Differential pulse voltammetry (DPV) in biodiesel:ethanol 1:1 (v/v), with tetrahexylammonium perchlorate as supporting electrolyte at a Pt ultramicroelectrode (ume), presented well-defined oxidation peaks for TBHQ and PG, with corresponding linear calibration graphs in the range of 10-3 mol L-1. Likewise, DPV at an Au ume in biodiesel surfactant-free microemulsion (SFME), with tetra-n-butylammonium tetrafluoroborate, presented well-defined oxidation peaks for TBHQ and BHT. For these compounds, linear calibration graphs were obtained in the range of 10-4 mol L-1. In both techniques, due to significant voltammograms overlapping, amounts of antioxidants were calculated through mathematical deconvolution process using software Origin 8.0®. BHA, BHT and TBHQ quantification by GC/qMS in biodiesel diluted in methanol presented linearity between 5 and 25 mg L-1 for each antioxidant. Reversed-phase liquid chromatography by HPLC using phenyl column showed good peak separation in simultaneous analysis of BHA, BHT, TBHQ and PG and calibration curves with linearity between 10 and 80 mg L-1. Biodiesel fatty acid methyl esters (FAMEs) identification was carried out by UHPLC-ESI-Orbitrap/MS; both FAMEs and antioxidants contents remained stable in spiked samples even after 8 weeks under sunlight exposure; in non-spiked samples, FAMEs content was significantly reduced. All proposed methodologies are easy to perform and present low sample consumption, which are interesting features for industry to monitor the aforementioned and other antioxidants in biodiesel. Their main advantage lies in the absence of any sample pre-treatment: the simple dilution in methanol or ethanol or biodiesel preparation as SFME deliver speed and simplicity for determination of target antioxidants.