No abstract

A full experimental design at two levels is applied for the estimation of the significance of select factors that may influence the ion chromatography (IC) determination of F-, Cl-, Br-, NO(-)3, SO(-2)4, and PO(-3)4 in serum samples. The factors studied are various sample deproteinization procedures, eluent composition, and flow rates. Deproteinization using either acetonitrile-NaOH or ultrafiltration can be used in order to obtain a significant protein removal before IC analysis; however, the former is recommended because it is less time-consuming and cheaper. Better resolution is obtained when a sodium hydroxide solution is used as the eluent. There is no influence of the sample's deproteinization procedures on the chromatographic resolution.

Hydrogen sulphide coolers are jacketed shell-and-tube heat exchangers designed to cool down the gas from 416.15 K to 310.15 K, as well as to remove sulphur carryovers. It is difficult to accurately compute their performance by traditional methods, since thermal analysis is based on several simplifications and empirical correlations. To overcome this limitation, the aim of present research was to propose an artificial neural network model for prediction of coolers outputs, using the mean absolute percentage error, correlation coefficient and extrapolation capability as selection criteria. Structure optimization was carried out through a network growing strategy, using 120 experimental data points for networks training, validation and testing. Model generalization was verified by comparing responses against the predictions of a validated phenomenological model, based on the ε-NTU method, for one set of 20 unseen data points. Best performance was obtained with the 6-5-4-3 multilayer perceptron, using the Levenberg-Marquardt learning algorithm. 99.47 % overall correlation and 0.33 % mean absolute percentage error were achieved when computing the hydrogen sulphide and water streams outlet temperatures. Despite the high prediction performance, a few model responses were found deprived of physical sense.

Dimensional analysis was used on this study with the aim of stablishing a model for prediction of the monoethanolamine heat exchangers output. The passive experimentation method was applied to gather 14 400 data points, since the exchangers are installed in an online amine treating unit. After identification of those parameters having a relevant effect on heat transfer processes, the Buckingham Pi theorem and the method of repeating variables were implemented. Once the dimensionless groups were formulated, the explicit equation was found by means of a least-squares regression analysis. The simulation model was evaluated by comparing predicted results against measured rich amine exit temperatures. In this respect, 98.96 % correlation, 0.023 % mean absolute percentage error and 1.376 K maximum absolute error were achieved. Findings of this research may serve as a shortcut for quick and accurate anticipation of the equipment performance, since the plant is often operated outside design parameters. Despite the above, obtained explicit equation is only valid for the studied set of heat exchangers.

Total and organic mercury contents were determined from samples of surface soils (0-5 cm), sieved at Յ63 μm, collected from 10 different locations in the upper Manzanares River watershed, using cold vapor atomic absorption spectroscopy. Methylmercury was determined using a HPLC-UV detector. The mean total mercury concentration was 1.3 μg. g-1 , a value permitted by the Canadian environment quality guidelines for farming soils, but high for European standards. Using certifi ed reference materials, we verifi ed that a modifi cation of the method described by Qian et al. (2000) was effective for organic mercury extraction, with a recovery of 92.17% for DORM-2 and 92.11% for TORT-2. This modifi ed method was applied to soil samples, obtaining concentrations of 0.5-1.0 μg.g-1 of organic mercury. The parameters for determining methylmercury using HPLC-UV were optimized; the best results were obtained with a 4.6 mm × 25 cm Zorbax CN − column, with a mobile phase of 70/30 V/V of methanol: ammonium acetate 0.05 mol.l-1 , with a fl ow rate of 0.5 ml.min-1 ; the methylmercury was detected at 4.99 min retention time. Methylmercury was not found in the soil samples. Using the certifi ed reference material we proved that the method used produced reliable results. The analysis confi rmed the existence of mercury in this farming area.