Neste trabalho foram aperfeiçoadas as etapas para determinação de hidrocarbonetos alifáticos e aromáticos em sedimentos. Durante as etapas de extração e concentração foram avaliados fatores determinantes como tempo, solvente extrator e sistema de resfriamento. Quanto ao cleanup, foram estudados diferentes volumes e misturas de solventes de eluição. Os resultados obtidos foram considerados aceitáveis (70-120%). A linearidade, limites de detecção e quantificação foram estudados construindo-se curvas analíticas (R > 0,99) com valores que demonstraram grande sensibilidade do método. A precisão e exatidão foram avaliadas com ensaios envolvendo material de referência certificado e adição e recuperação de analitos em sulfato de sódio. Nos testes de adição e recuperação os desvios ficaram abaixo de 20%, com recuperação dos alifáticos e aromáticos de 59-105% e 55-113%, respectivamente. Para os sedimentos de referência, os desvios obtidos foram inferiores aos valores certificados, com recuperações satisfatórias. O presente trabalho proporcionou a melhoria de um método já consolidado, possibilitando obter resultados com elevada confiabilidade analítica.The main steps involved in the determination of aliphatic and aromatic hydrocarbons in sediments were evaluated in this work. In the extraction, factors such as the cooling system, time and solvent were evaluated. During the extraction and concentration, steps aspects such as time, extraction solvent and cooling system were evaluated. In the cleanup different solvents and elution mixtures were studied. The results were considered satisfactory (70-120%). Linearity and limits of detection and quantification were studied by means of calibration curves (R > 0.90) and the results demonstrated high sensitivity of the method. Precision and accuracy were studied by recovery tests using a certified reference material and sodium sulfate. In recovery tests, the standard deviations were below 20%, with percent recoveries for aliphatic and aromatics ranging from 59 to 105% and 55 to 113%, respectively. For the reference sediment, the standard deviations were lower than the certified values, with satisfactory recovery values. The present work provided a way of improving an already established method with high analytical reliability.

Geochemical biomarkers play an important role in studies of palaeoenvironment reconstruction based on historical variation of sedimentary records. However, a great number of steps are usually involved for their analytical determination including extraction, clean up, derivatization (esterification and silanization) and individual calibration curves for accurate results. Thus, prior to the extraction an optimization procedure may be required to verify possible losses through the analytical method. In the present work distinct reaction times during the sterification step, NaCl concentration to separate the aqueous and organic phases and extracting solvents were assessed. The best working conditions achieved were reaction time of 8 hours, NaCl solution 20 % (m/v) and hexane. For the biomarkers analytical parameters sensitivity, linearity (R 2 ), LOD and LOQ were obtained with external calibration curves and checked against those obtained with spiked sediment. The results showed no significant differences for the analytical parameters. Due to the lack of certificate material, the precision and accuracy were studied by recovery tests. Solutions containing mix of aliphatic hydrocarbons, alcohols, carboxylic acids, sterols and ketones were added to sediment samples and submitted to all the steps of the process. This mix was left in contact with sediment samples for 1 hour, 24 hours and 7 days, in 3 concentration levels. The recovery were all within the acceptable range 70-120% and RSD < 10%. The analytical method was applied to samples taken from two single sediment cores (stations T3 and T4 with 525 cm and 364 cm depth, respectively) collected at the Mozambique-Barra da Lagoa (Florianópolis -Santa Catarina) beach. A preliminary assessment of the hydrocarbon distribution indicated a mixed source of organic matter through the T3 profile while the T4 core was dominated by terrestrial hydrocarbons with predominance of C3 plants.Keywords: Optimization; geochemical biomarkers; paleoenvironmental study; Conceição Lagoon. ResumoOs biomarcadores geoquímicos são de grande importância em estudos de reconstrução de paleoambientes. Devido ao grande número de etapas envolvidas na sua determinação, tais como extração com solvente, fracionamento, derivatização (esterificação e silanização) e quantificação, é preciso garantir que os resultados obtidos sejam confiáveis. Desta forma, antes das extrações dos biomarcadores nos perfis sedimentares deve-se fazer uma otimização de forma a identificar possíveis perdas envolvidas e avaliar o método analítico que será utilizado. No presente trabalho foram avaliadas a etapa de esterificação (tempos de reação e forma de extração). As melhores condições de trabalho foram com tempo de reação de 8 horas, solução de NaCl a 20% (m/v) e hexano. A sensibilidade analítica, linearidade (R 2 ), LOD e LOQ obtidos por meio de curvas de calibração externa para os biomarcadores não foram significativamente diferentes dos resultados obtidos por adição dos padrões em sedimento. A precisão e exatidão do...