Climatologia da pluviosidade na bacia hidrográfica do Rio Paranaíba

The main aim of this research was to study pluviosity in the Paranaíba Riverbasin, especially concerning the variability frame and trends. For this end, we used data from 22 pluviometric stations of the Agência Nacional da Águas- ANA(National Water Agency)spatially distributed throughout the basin area. The data comprised the years 1979-2013, which is a historical series of 35 years, and was downloaded through the ANA website and tabulated using the Hydro 1.2 software (2015) and Excel. After tabulation process were applied based methodologies for statistical analysis of annual variability, monthly, daily and seasonal rainfall in the basin beyond the trend analysis. Results of this research showed that the annual rainfall averageis 1491 mm. Seasonality is a hallmark and rainfall variability occurs spatially and temporally. Rains are accumulated in the rainy season accumulating 85% of the annual volume in the basin. In daily analysis it was found that the daily rainfall above 30 mm occur in only 3% of the time. Dry season comprises 15% of the rainfall. Trend analysis using linear regression pointed to a downward trend in rainfall in 46% of jobs, stability in 18% of posts and increased rainfall by 36%. As for the analysis using the sign test indicated that 32% of the analyzed rainfall stations showed an increasing trend of rainfall over the time series and 68% of stations showed downward trend. This research is important because shows how rainfall worksin the area of the Paranaiba basin, and may be used to develop better management of natural resources and the area through public policies for this purpose.

Avaliação das condições de precipitação do azul da Prússia sobre pó de grafite visando o desenvolvimento de eletrodos de pasta de carbono para a quantificação de nitrito

An amperometric FIA method for nitrite quantification based on nitrite electroreduction and employing a carbon paste electrode (CPE) chemically modified with iron hexacyanoferrate (HCF) as an amperometric detector was developed. The influence of experimental conditions on the preparation of the electrode materials was evaluated and the materials obtained in each study were used for the development of modified electrodes. The electrochemical sensors were prepared by a fast, simple, and inexpensive procedure, and the long-term performance of the electrodes were quite satisfactory as the stability was maintained over one year. HCF was an effective redox mediator for nitrite electroreduction in acidic media, allowing nitrite detection at +0.2 V vs. Ag/AgClsat, which is a potential free of possible interfering species that are normally present in food and water samples. The electrochemical cell used in the FIA system was similar to a batch injection analysis cell, enabling recirculation of the carrier solution. This is an attractive feature because it allows the use of a high flow rate (6 mL min-1) leading to high sensitivity and analysis speed, while keeping reagent consumption low. The proposed method had a detection limit of 9 μmol L-1 and was successfully employed for nitrite quantification in spiked water and sausage samples. The obtained results were in good agreement with those provided by the spectrophotometric official method. At a 95 % confidence level it was not observed statistical differences neither in nitrite content nor in the precision provided by both methods. The experimental conditions for the synthesis of HCF were optimized and the best electrode material was prepared by mixing FeCl3, K4[Fe(CN)6] and carbon powder subjected to an acid and thermal treatment (400 ºC), followed by ultrasonic agitation at 4 °C. This material was used to construct an electrode with improved analytical performance to reduce nitrite, which presented greater stability compared to HCF film electrodeposited on the EPC, showing that the preparation procedure of the electrode material is an effective strategy for the development of HCF modified electrodes.