Chemometrics is a subfield of chemistry that emerged from advances in analytical instrumentation and computing. When seeking to solve chemical problems that depend on many concomitants experimental variables, chemometrics can be employed in order to extract as much information as possible in the least possible number of experiments. In addition, it is possible to evaluate the important effects and interactions among the variables to understand the processes being monitored in each system. In this sense, this article aimed to develop a didactic experiment of caffeine extraction using an espresso machine, applying the 25-1 fractional factorial design. The variables studied were temperature (75 and 78 °C), pressure (2 and 15 bar), granulation (bean and ground), type of coffee (special and traditional) and period of the day (morning and afternoon) to obtain maximum extraction of caffeine. The coffee extracts obtained were analyzed using UV-Vis molecular absorption spectrophotometry. The developed experiment showed the potential to spread the application of chemometrics in the academic environment and to facilitate the teaching of fractional factorial design.

Volatile Organic Compounds (VOCs) are air pollutants emitted from different sources, mainly by industries and motor vehicles. The evaluation of the emission of these compounds into the atmosphere should be done systematically and with a varied class of compounds. The large number of data generated during the monitoring of these VOCs requires the use of multivariate data tools to interpret the results. In this sense, this work aimed to monitor 10 aromatic VOCs present in the atmosphere of the largest cities in the Norte Fluminense (Campos dos Goytacazes) and Noroeste Fluminense (Itaperuna) regions. The VOCs were actively sampled and analyzed by gas chromatography with mass spectrometry detection after thermal desorption. After treatment of analytical results, it was observed that in both cities there is influence of vehicular emissions. In the city of Itaperuna, due to the relief and lower dispersion of contaminants, there is a higher occurrence of photochemical reactions. The exploratory analysis of the data allowed identifying the variables that were more significant and correlating these variables with the main sources of emission of the compounds. This is the first study of VOCs evaluation in Campos dos Goytacazes and Itaperuna, demonstrating the relevance of this research for understanding the behavior of VOCs in these cities, which have different reliefs and high traffic of cars and trucks in the studied sites.

Some of the main concerns when attempting to preserve artwork regard environmental factors, such as luminosity, temperature and, recently, even atmospheric pollution. From this perspective, volatile organic compounds (VOC) stand out due to the wide availability of contaminating sources in internal museum environments. Amongst artistic objects susceptible to VOC interference, paintings are more likely to undergo it because their stability is closely related to each component. Thus, it is crucial to comprehend the interaction between VOC and paintings, specifically those with inorganic and adhesive pigments, and evaluate changes in chromatic parameters and the formation of metallic carboxylates. Mock-ups of paintings were prepared with cadmium yellow, chromium oxide, ultramarine blue, linseed oil, and lead white or gypsum primer. Exposure was arranged within an airtight container containing a VOC-saturated atmosphere: formaldehyde, acetic acid, hexanal and 2-butanone oxime. Color alteration occurred for ultramarine blue (greenish coloration) and cadmium yellow (lost luminosity). Infrared analysis showed the formation of lead carboxylates (acetate, formate and hexanoate) in all pigments. Micrographs of ultramarine models, verified via scanning electron microscopy, showed that an otherwise flat and homogenous appearance replaced the granular aspect of the paint; the flat regions being indicative of carboxylate formation.

Triazine herbicides are widely used both in Brazil and internationally and are frequently detected in natural environments and drinking water. This study assesses atrazine degradation through solar radiation under tropical conditions and determines the toxicity of the intermediates. Atrazine degradation is tested through ultrapure water, humic acid solution and natural water experiments, with exposure to sunlight to simulate a natural environment. A yeast estrogen screen (YES) assay and Artemia salina test are carried out during the abiotic degradation. The atrazine degradation depends on the radiation intensity, since the experiments conducted in the summer reached 50% after ca. 17 days. No significant variations in this herbicide concentration are observed after 90 days of exposure in the fall. Atrazine degradation is observed only in humic acid and is responsible for indirect photolysis. Intermediates, namely, desethylatrazine (DEA) and deisopropylatrazine (DIA), are identified and quantified at the μg L-1 level. Thus, with the degradation of atrazine in water, the medium toxicity may decrease, since DEA and DIA have mean effective concentrations that kill 50% of Artemia salina (EC50) similars to atrazine (13 mg L-1). No estrogenic activity in the YES is detected for atrazine and its metabolites. These findings evidence that radiation intensity and organic substances in tropical countries influence the half-life of pesticides in aquatic environments.

Polycyclic aromatic hydrocarbons (PAH) are products of incomplete combustion of biomass and fossil fuels, that are produced on a larger scale by anthropogenic sources. Burning sugarcane plantations can be a source of atmospheric PAH in regions where this culture predominates. Campos dos Goytacazes, Brazil, is surrounded by sugarcane crops that still use fire as a facilitating method for the harvesting process. This study aims to evaluate the presence of outdoor and indoor PAH in 10 µm particulate matter (PM10) at one university in Campos dos Goytacazes. PM10 samples were collected from January to November 2018. Samples were extracted using an ultrasonic probe and analyzed by gas chromatography coupled to mass spectrometry (GC-MS). The ideal extraction conditions (3 min; 150 W; 50 mL) were defined by 23 full factorial design. The analysis showed a significant PM10 level increase (23.19 to 34.50 µg m-3 in outdoor, and 15.15 to 31.66 µg m-3 in indoor samples) and higher total PAH concentration in the harvesting season (outdoor: 0.73 ng m-3; indoor 0.52 ng m-3) than in non-harvesting season (outdoor: 0.49 ng m-3; indoor: 0.28 ng m-3), however, average PAH values found in outdoor samples in harvesting season did not show significant difference from non-harvesting season.

Como alternativa aos relativamente complexos e dispendiosos métodos espectroscópicos, as propriedades redox dos ácidos húmicos, determinadas por titulação potenciométrica, vêm sendo usadas na avaliação da estabilidade do C do solo. O objetivo deste estudo foi estabelecer um índice redox de estabilidade do C (RICS) e correlacioná-lo com alguns atributos de diferentes solos modais brasileiros (distintos estádios de intemperismo ou manejo), a fim de mais facilmente comparar sistemas. O RICS foi eficiente para comparação de solos e variou similarmente com os métodos químicos e espectroscópicos usados na caracterização dos ácidos húmicos. Os valores de pH, ponto de efeito salino nulo zero, soma de bases, teor de cálcio trocável, índice de intemperismo, bem como de razão entre oxigênio e carbono, teores de quinonas e de radicais livres semiquinonas, carbono aromático e intensidade de fluorescência dos ácidos húmicos, mostraram estreitas relações com o RICS. Os solos menos intemperizados, com argilas mais ativas e mais alta fertilidade apresentaram maior RICS. Os solos sob longo tempo de manejo com cana-de-açúcar mostraram RICS seguindo a ordem decrescente: cana crua, cana queimada com vinhaça, cana queimada sem vinhaça.

As an alternative to the relatively complex and expensive spectroscopic methods, the redox properties of humic acids, determined by potentiometric titrations, have been used to evaluate the stability of soil organic C. The objective of the present study was to establish a Redox Index of C Stability (RICS) and to correlate it with some properties of the humic acids extracted from different modal soils in Brazil (distinct weathering stages or management) to facilitate system comparison. The RICS was efficient for soil comparison and variations were comparable to those of the chemical and spectroscopic methods used for humic acid characterization. The values of soil pH, point of zero salt effect, sum of bases, exchangeable Ca content, weathering index, as well as the humic acid O/C ratio, quinone and semiquinone free radical contents, aromatic C and fluorescence intensity were closely related with the RICS. The RICS was higher in less weathered soils, with more active clays and higher fertility. The RICS values of soils under long-term sugarcane management were ranked in decreasing order: unburned, burned with vinasse, burned without vinasse.

Previous studies indicated that free radicals control organic matter redox activities. In the present study, organic matter of an ultra-filtrated material collected from seven samples taken seasonally from the Paraiba do Sul River for two years were titrated with an oxidizer (I2) in an inert atmosphere. Standard formal potential values for the electrode MO Ox, MO Red ranged from 0.754 to 0.786 V at a 25 ºC temperature. Organic matter oxidation capacity (COx) per carbon mass varied according to pH values, and changes in COx were related to rainfall and river flow intensities.

This article describes an experiment designed to teach quantitative determination in gas chromatography (GC) in Organic and Analytical Chemistry practical classes. The experiment consisted of extracting and analyzing eugenol from clove seeds to perform a quantitative approach aimed at comparing results obtained by external and internal calibration procedures. Therefore, this experiment proved to be very effective tool to enhance students awareness on the need to understand different types of calibration in GC and on how to avoid common experimental errors, and to find the best ways to eliminate their interference during the quantitative analysis phase.

A matéria orgânica do solo é o maior reservatório de C nos sistemas naturais. Em tais sistemas a qualidade e a estabilidade do C podem ser estimadas pelo aumento da concentração das frações humificadas que, dentre outros fatores, está condicionada ao balanço entre as perdas e os ganhos que envolvem as reações de oxidação e de redução da matéria orgânica do solo. O objetivo deste estudo foi avaliar a eletroquímica, usando titulações redox iodimétricas, de ácidos húmicos isolados de solos cultivados continuamente com cana-de-açúcar submetida ou não à queima da palha para a colheita ou à adição anual de vinhaça. Os ácidos húmicos apresentaram valores do potencial formal padrão do eletrodo entre 0,760 e 0,779 V a 25 ºC. A capacidade de oxidação dos ácidos húmicos variou de 1,01 a 3,44 mol c kg-1 a pH 5,0 e de 1,64 a 6,44 molc kg-1 a pH 7,0. Observou-se correlação positiva e significativa entre a capacidade de oxidação dos ácidos húmicos e suas concentrações de grupos funcionais fenólicos, quinonas e semiquinonas.

Soil organic matter is the largest carbon reservoir in natural systems. In such systems the carbon quality and stability can be estimated based on the increase of humified fractions which, among other factors, is related to the balance between losses and accumulations involving oxidation and reduction reactions of the soil organic matter. The objective of this study was to evaluate the electrochemistry of humic acids isolated from soils cultivated continually with sugar-cane, with or without pre-harvest burning and annual vinasse application using iodimetric redox titrations. The formal electrode potentials of the humic acids had a similar pattern, with values between 0.760 and 0.779 V, at 25 ºC. The oxidation capacity of humic acids varied from 1.01 to 3.44 mol c kg-1 at pH 5.0 and from 1.64 to 6.44 mol c kg-1 at pH 7.0. Positive and significant correlations were observed between the oxidation capacity and the humic acid contents of phenolic, quinone and semiquinone functional groups.

Dependendo das condições do sistema, os ácidos húmicos podem atuar como oxidantes ou redutores. Nos sistemas naturais, o fluxo de elétrons está diretamente associado à quantidade e à qualidade do húmus. O potencial do eletrodo e a capacidade de oxidação informam sobre os fatores intensidade e capacidade dos sistemas redox, respectivamente. Estudos prévios têm aventado a hipótese de que radicais livres nos ácidos húmicos participam dessas reações redox. No presente estudo, seis ácidos húmicos isolados de adubos orgânicos foram titulados com um oxidante (I2) em atmosfera inerte e condições especificadas. Os ácidos húmicos apresentaram valores do potencial formal-padrão do eletrodo semelhantes: entre 0,773 e 0,794 V a 25 ºC. A capacidade de oxidação dos ácidos húmicos variou de 3,88 a 4,39 mol c kg-1 a pH 5,0 e de 5,35 a 7,89 mol c kg-1 a pH 7,0. Foi observada correlação positiva e significativa entre a capacidade de oxidação dos ácidos húmicos e as suas concentrações de grupos funcionais fenólicos, quinonas e semiquinonas.

According to the system conditions, humic acids act as oxidants or as reductants. In natural systems the electron flow is directly associated with humus content and quality. Electrode potential and oxidation capacity inform about the intensity and capacity of the redox systems. In previous studies it has been assumed that free radicals participate in humic acid redox reactions. In our study six humic acids isolated from composed organic residues were titrated with an oxidant (I2) in inert atmosphere and specified conditions. Humic acids presented similar standard formal electrode potentials, with values between 0.773 and 0.794 V, at 25 ºC. The oxidation capacity of humic acids varied from 3.88 to 4.39 mol c kg-1 at pH 5.0 and from 5.35 to 7.89 mol c kg-1 at pH 7.0. Positive and significant correlations were observed between the oxidation capacity and the concentrations of the phenolic, quinone and semiquinone functional groups in the humic acids.

Destruction of Padron® (dye and picloram) was evaluated using a photoreactor and a solar reactor. Photolysis was observed using only a germicide lamp (GL). Black light (BL) and H2O2 (172 mmol L-1) promoted a conversion of 49% and 6% of dye and picloram, respectively. Photocatalytic processes were more efficient using TiO2/GL (96%-dye; 60%-picloram) than TiO2/BL (44%-dye; 40%-picloram). Photolysis using sunlight was not observed during PadronÒ recirculation in the reactor constructed with four borosilicate tubes. Meanwhile, adding H2O2 resulted in 12% conversion of dissolved organic compounds. Finally, the most efficient mineralization (60%) was obtained using the Fenton reaction ( H2O2-176 mmol L-1; FeSO4x6H2O-90 mmol L-1) and sunlight.

Silica gel is widely used as adsorbent for isolating and purifying natural compounds. Intensive use and high cost make this process expensive and generate solid residues contaminated with many different organic compounds. In the present work a simple method for recycling silica was investigated, by using Advanced Oxidative Processes. Silica gel was treated with H2O2/solar light and compared with a sample treated by conventional methods (high temperature and oxidation with KMnO4). High temperature treatment changes the structure of the silica and, consequently, the separation efficiency. Oxidation by using KMnO4 requires multiple steps and produces residues, including manganese and oxalic acid. The method using H2O2/solar light to recuperate silica gel does not modify its separation efficiency and is less expensive than the traditional methods. Additionally, HPLC and GC-MS analysis indicate that H2O2/solar light eliminates all residues of the silica gel.

Vários aspectos da química aquática do mercúrio elementar (Hg0) são importantes para o entendimento do destino deste metal no ambiente, mas no entanto têm sido pouco estudados. Neste trabalho, observou-se que a dissolução reativa do mercúrio elementar é dependente da concentração do metal em solução, da velocidade de oxidação do metal, da concentração de material particulado, da natureza e concentração de outros íons e do pH. Quando 1 g L-1 de Hg0 foi usado em água destilada em um sistema aberto para a atmosfera, a concentração de mercúrio solúvel aumentou em função do tempo, obtendo-se 5,4 mg L-1 de Hg total no estado estacionário. Deste total, 3,2 mg L-1 foram devido às espécies Hg2+ formadas via oxidação. Em amostras de água de lago, os resultados mostraram uma inibição no processo de dissolução reativa e a concentração total do metal em água foi de 3,1 mg L-1 no estado estacionário. Este efeito inibitório foi atribuído ao material particulado. Em água do mar, a concentração total de Hg solúvel aumentou em função do tempo, atingindo um valor de 17,8 mg L-1 depois de 10 h. Em seguida, a concentração de Hg solúvel diminuiu, atingindo 4,8 mg L-1. Os experimentos realizados em diferentes valores de pH (4,0; 7,0 e 9,0), mostraram que a dissolução reativa do metal acontece em maior extensão em pH 4,0. Estudos de adsorção de ambas as espécies, íon mercúrico e mercúrio elementar, sobre o material particulado, mostraram uma dependência da área superficial, obtendo-se a seguinte ordem: 400 mesh > 200 mesh > sedimento in natura. As implicações destes resultados são discutidas, levando em consideração o cenário Amazônico.

Several aspects of the aquatic chemistry of elemental mercury (Hg0) are vital to the understanding of the fate of this metal in the environment, yet have scarcely been studied. Reactive dissolution of metallic mercury is shown to be dependent on the metal concentration in solution, the metal oxidation rate, particulate material concentration, nature and concentration of other ions, and pH. When using 1 g L-1 of Hg0 in distilled water open to the atmosphere, the concentration of soluble mercury increases as a function of time, reaching 5.4 mg L-1 of total Hg in the steady state. From this, 3.2 mg L-1 were due to Hg2+ formed via oxidation. In lake water, results showed an inhibition in the reactive dissolution process, and the total metal concentration in water was 3.1 mg L-1 in the steady state. This inhibitory effect was attributed to particulate material. In seawater, the total concentration of soluble Hg increases as a function of time, reaching a peak of 17.8 mg L-1 after 10 h. After this, the soluble concentration dropped, to 4.8 mg L-1. Experiments performed at different values of pH (4.0;7.0 and 9.0), showed that the dissolution of the metal occurred to a higher extent at pH 4.0. Adsorption studies of both mercuric ions and elemental mercury species onto particulate material showed a dependence on the surface area, following the sequence 400 mesh > 200 mesh > sediment in natura. The implications of such findings are discussed, taking into consideration the Amazonian scenario.