In this work we developed a promising analytical method combining Fourier transform near-infrared (FT-NIR) spectroscopic technique and first-order multivariate calibration using partial least-squares (PLS) model to simultaneously quantify the main greenhouse gases (GHG’s): methane (CH4), carbon dioxide (CO2), nitrous oxide (N2O) and water vapor (H2O). The models were built using 70 mixtures with different concentration of these gases, 0.25-32.0 ppm to CH4 and N2O, and 50-1100 ppm to CO2 and different values of relative humidity (52-85%, 20 ºC) in synthetic air. After preparing each of the mixtures, they were analyzed by using FT-NIR and a reference analytical technique based on gas chromatography with mass spectrometric detection (GC-MS). The FT-NIR spectrometer was coupled with a long optical path cell, with 105.6 meters of optical path. In sequence, the spectra of all mixtures and its concentration values for each gas were used to build the multivariate calibration models, using PLS regressions. For this, the mixtures were grouped with Kennard Stone algorithm, 50 samples to calibration set and 20 samples to prediction set. The values of RMSEP (root mean square error of prediction) obtained for each model are 0.66, 28.7 and 0.66 ppm, respectively, for CH4, CO2, and N2O. The limits of quantification (LOQ) for each PLS models are 0.26, 3.6, and 0.99 ppm, respectively, for CH4, CO2, and N2O. The results show the potentiality of application of this system to monitoring emission sources in which the concentration of these gases are relatively high, as urban centers, industrial areas, and landfills.

Electric field-assisted solid phase extraction using syringe type cartridges (E-SPE) is a recent approach with a high capacity to obtain differential selectivity and/or recovery in comparison with conventional solid phase extraction (SPE). In this work, E-SPE was employed for the extraction of the anionic dye sunset yellow. During the washing step the electric field was evaluated with the top electrode negatively (E-SPE(–/+)) or positively charged (E-SPE(+/–)) and the results were compared with conventional SPE to understand how the electrochromatographic parameters can influence the recovery of the dye. Using the E-SPE(–/+) the electric field can increase the elution of the dye from the cartridge by over 57-fold. This notable result can be attributed to the electrophoretic velocity of the dye in the direction of the flow rate of the eluent. These results demonstrated that E-SPE is an interesting approach to elute ionic compounds with reduced volumes of eluent or less amount of organic solvent.

Um novo sistema em fluxo é apresentado com a finalidade de pré-concentrar e determinar o mercúrio reativo em efluentes. O sistema é baseado na redução do mercúrio reativo presente em 500 mL de amostra com uma solução de Sn(II). O mercúrio reduzido é arrastado por uma corrente de argônio que passa por um tubo de vidro (comprimento de 60 cm, e diâmetro interno de 3 mm) inclinado a 15º. A superfície interna desse tubo é recoberta previamente com um filme líquido de uma solução oxidante contendo H2O2 (12%, m/v) e HNO3 (3,0 mol L-1) produzida após a introdução e passagem de um monossegmento líquido contendo esses reagentes. O Hg0 arrastado sofre um processo oxidativo e o Hg(II) formado é retido no filme. Após 10 minutos de arraste o fluxo de argônio é interrompido e um monossegmento (350 µL) contendo PAR [4-(2-piridilazo) resorcinol], 1,0 x 10-3 mol L-1 em tampão amônia / cloreto amônio (4,0 mol L-1; pH 9,0) é introduzido e passa através do tubo de vidro. Um complexo fortemente colorido é formado entre o PAR e o Hg(II) o qual é levado ao sistema de detecção constituído por um diodo emissor de luz (LED, lambdamáx = 525 nm) e um detector fotodiodo. O tempo de processamento de uma amostra é de 12 min. O sistema é lavado e uma nova camada de líquido é formada, preparando o sistema para uma nova determinação. Esse método concentra a amostra 148 vezes e permite a obtenção de um limite de detecção de 0,16 µg L-1.

A new flow system to pre-concentrate and determine reactive mercury in effluents by photometry is presented. The system is based on the reduction of the reactive mercury present in a 500 mL sample with a Sn(II) solution. The reduced mercury is swept out by an argon stream and carried to a straight glass tube (60 cm long, 3 mm i.d.) inclined in an angle of 15º. The inner surface of this tube has been previously covered by a renewable liquid layer of an oxidant solution containing H2O2 (12%, m/v) and HNO3 (3.0 mol L-1) produced after introduction and passage of a liquid monosegment containing those reagents. The swept Hg0 undergoes an oxidative process and the Hg(II) formed is retained in the layer. After a 10 min sweep time interval the argon flow is stopped and a reagent monosegment (350 µL) containing PAR [4-(2-pyridylazo)resorcinol], 1.0 x 10-3 mol L-1, in an ammonia/ ammonium chloride buffer (4.0 mol L-1; pH 9.0) is introduced and passes through the glass tube. A strongly coloured complex between PAR and Hg(II) is formed and carried to the detection system composed of a light emitting diode (LED, lambdamax = 525 nm) and a photodiode detector. Sample processing time is about 12 min. The system is washed and a fresh liquid layer is formed, preparing the system for a new determination. This method concentrates the sample by a factor of 148 and achieves a detection limit of 0.16 µg L-1.

Este trabalho descreve o uso do método de linearização de Gran em titulações em fluxo monossegmentado com detecção potenciométrica. O programa de controle pode estimar o ponto final após a adição de três ou quatro alíquotas de titulante. Alternativamente, o ponto final da titulação pode ser determinado pelo método da segunda derivada. Neste caso, alíquotas adicionais de titulante são adicionadas até a proximidade do ponto final e três pontos antes e após o ponto estequiométrico são usados para o cálculo de ponto final. O desempenho do sistema foi avaliado pela determinação de cloreto em soluções isotônicas e parenterais. O sistema emprega um eletrodo indicador tubular de Ag2S/AgCl. Uma titulação típica, realizada de acordo com a definição IUPAC, requer apenas 60 mL de amostra e aproximadamente o mesmo volume de titulante (AgNO3). Uma titulação completa pode ser realizada entre 1 e 5 min. Foram obtidas exatidão e precisão (desvio padrão relativo de 10 replicatas) de 2% e 1% para o método de Gran e 1% e 0,5% para o método de Gran associado ao método da segunda derivada, respectivamente. O sistema proposto reduz o tempo para realizar uma titulação, com baixo consumo de amostra e reagente, além de possibilitar uma amostragem automática completa e adição de titulante sem a necessidade de uma etapa de calibração.

An automatic potentiometric monosegmented flow titration procedure based on Gran linearisation approach has been developed. The controlling program can estimate the end point of the titration after the addition of three or four aliquots of titrant. Alternatively, the end point can be determined by the second derivative procedure. In this case, additional volumes of titrant are added until the vicinity of the end point and three points before and after the stoichiometric point are used for end point calculation. The performance of the system was assessed by the determination of chloride in isotonic beverages and parenteral solutions. The system employs a tubular Ag2S/AgCl indicator electrode. A typical titration, performed according to the IUPAC definition, requires only 60 mL of sample and about the same volume of titrant (AgNO3) solution. A complete titration can be carried out in 1 - 5 min. The accuracy and precision (relative standard deviation of ten replicates) are 2% and 1% for the Gran and 1% and 0.5% for the Gran/derivative end point determination procedures, respectively. The proposed system reduces the time to perform a titration, ensuring low sample and reagent consumption, and full automatic sampling and titrant addition in a calibration-free titration protocol.

A flow injection spectrophotometric system was projected for monitoring hydrogen peroxide during photodegradation of organic contaminants in photo-Fenton processes (Fe2+/H2O2/UV). Sample is injected manually in a carrier stream and then receives by confluence a 0.1 mol L-1 NH4VO3 solution in 0.5 mol L-1 H2SO4 medium. The product formed shows absorption at 446 nm which is recorded as a peak with height proportional to H2O2 concentration. The performance of the proposed system was evaluated by monitoring the consumption of H2O2 during the photodegradation of dichloroacetic acid solution by foto-Fenton reaction.

This paper shows the assembly of an ozonization system to be used in laboratory scale, mainly to study effluent treatability. The system is simple, practical and provides easy acquisition of data when interfaced to a microcomputer. The performance of ozone generation and K La values are also described.