In this paper, a simple, sensitive and precise electroanalytical method was developed using a chemically-reduced graphene-oxide (CRGO)-modified glassy carbon electrode and square wave voltammetry (SWV) for determination of ciprofloxacin in pharmaceutical formulations (tablets) and milk samples. Advantages of this sensor include a potential displacement of 100 mV and a 5-fold current increase for the electrochemical oxidation of ciprofloxacin, which resulted in a highly sensitive sensor, when compared to unmodified electrode. The improved properties of the modified electrode are likely due to the formation of a porous surface evidenced by the change in electrode kinetics (thin-layer diffusion process). The proposed sensor is free from interference of sample matrix (pharmaceutical formulations and low/high-fat milk) avoiding cumbersome processes such as previous separations, solvent extraction, or sample filtration (samples were only diluted in Britton-Robinson buffer solution). The results by SWV showed a limit of detection of 0.21 µmol L-1 (correspondent to 0.069 mg L-1), which is lower than the ones obtained using other carbon-based electrodes, relative standard deviations lower than 12%, and satisfactory recoveries in the range from 84 to 109%. The results obtained were statistically similar (95% confidence level) with those performed through high-performance liquid chromatography (HPLC).

RESUMO Foram avaliadas, no presente trabalho, as alterações na biomassa microbiana devido à aplicação de doses crescentes de dejetos lÃquidos de suÃnos (DLS) em diferentes sistemas de preparo de solo. O experimento foi conduzido em um Latossolo Vermelho eutrófico textura argilosa, em Palotina, PR; diferentes doses de dejetos lÃquidos de suÃnos (0, 30, 60 e 120 m3 ha-1 ano-1) foram aplicadas antes das estações de verão e inverno em sistema de preparo do solo convencional (PC) e sistema de plantio direto (PD), em três repetições. O experimento foi conduzido com a cultura de soja ou milho no verão e trigo ou aveia no inverno. As amostras de solo foram coletadas em março e outubro de 1998 e 1999 nas profundidades de 0-5, 5-10 e 10-20 cm. O preparo do solo e as diferentes doses de DLS influenciaram o teor de C, N e P da biomassa microbiana. A biomassa microbiana e sua atividade apresentaram boa sensibilidade para detectar alterações no solo, devido ao manejo. A biomassa microbiana e a relação Cmic/Corg foram aumentadas com a aplicação crescente de DLS. O quociente metabólico sob PC aumentou em profundidade ocorrendo o inverso sob PD. A biomassa microbiana foi enriquecida com N e P em virtude das doses crescentes de dejetos lÃquidos de suÃnos.

ABSTRACT The objective of this work was to evaluate the changes in microbial biomass C, N and P due to the application of pig slurry under different soil tillage systems. The experiment was established in a clayey Oxisol, Eutrophic Red Latossol in Palotina, PR. Different quantities of pig slurry (0, 30, 60 and 120 m3 ha-1 year-1) were applied to the soil prior to the summer and winter crop season under conventional tillage (CT) and no tillage (NT), in three replicates. The area was cultivated with soybean (Glycine max L.) or maize (Zea mays L.) in the summer and wheat (Triticum sativum Lam.) or oat (Avena sativa L.) in the winter. The soil samples were collected in March and October of 1998 and 1999 at depths of 0-5, 5-10 and 10-20 cm. The soil tillage and pig slurry application influenced the microbial biomass C, N and P. The microbial biomass and the microbial activity presented high sensibility to detect changes in the soil due to tillage and the application of pig slurry. The soil microbial biomass and Cmic/Corg relation increased as the quantity of applied pig slurry increased. The metabolic quotient under CT increased with depth while under NT it decreased. The soil microbial biomass was enriched in N and P under NT and as the quantity of applied pig slurry increased.