Evaluation of the Analytical Method Applied to Geochemical Biomarkers in a Paleoenvironmental Study of Coastal Barrier Associated to Conceição Lagoon (Florianópolis / SC)

Abstract

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...