Oxidized carbon nanotubes as sorbent for miniaturized solid-phase extraction of progestins from environmental water samples prior to their determination by HPLC-UV.

A solid-phase extraction method is presented for micro-extraction of three progestins (levonorgestrel, 19-norethisterone acetate and medroxyprogesterone acetate) from water samples. A mini-column was packed with 60 mg of oxidized multiwalled carbon nanotubes and coupled to a flow injection assembly. The extraction parameters, such as washing solution, eluent type, eluent volume, flow rate and sample volume, were optimized. Separation and determination were performed by HPLC with UV detection. The method has a good linear range (0.90-9.0 µg L-1), acceptable limits of detection (0.05-0.14 µg L-1) and low RSDs (0.8-4.6%). Attractive features of the method include low consumption of organic solvents and preconcentration factors of up to 100. The method was applied to analyze stream, underground and effluent water samples, and recoveries between 74 and 121% were obtained. Graphical abstractSchematic representation of the flow injection assembly couples to an ox-MWCNTs extraction column used to perform the solid phase extraction procedure of progestins in environmental water samples.

Analysis of metals and phosphorus in biodiesel B100 from different feedstock using a Flow Blurring® multinebulizer in inductively coupled plasma-optical emission spectrometry.

A simple and fast method for determining the content of Na, K, Ca, Mg, P, and 20 heavy metals in biodiesel samples with inductively coupled plasma optical emission spectrometry (ICP OES) using a two-nozzle Flow Blurring(®) multinebulizer prototype and on-line internal standard calibration, are proposed. The biodiesel samples were produced from different feedstock such as sunflower, corn, soybean and grape seed oils, via a base catalyst transesterification. The analysis was carried out without any sample pretreatment. The standards and samples were introduced through one of the multinebulizer nozzles, while the aqueous solution containing yttrium as an internal standard was introduced through the second nozzle. Thus, the spectral interferences were compensated and the formation of carbon deposits on the ICP torch was prevented. The determination coefficients (R(2)) were greater than 0.99 for the studied analytes, in the range 0.21-14.75 mg kg(-1). Short-term and long-term precisions were estimated as relative standard deviation. These were acceptable, their values being lower than 10%. The LOQ for major components such as Ca, K, Mg, Na, and P, were within a range between 4.9 ng g(-1) for Mg (279.553 nm) and 531.1 ng g(-1) for Na (588.995 nm), and for the other 20 minor components they were within a range between 1.1 ng g(-1) for Ba (455.403 nm) and 2913.9 ng g(-1) for Pb (220.353 nm). Recovery values ranged between 95% and 106%.

An ultrasonic-accelerated oxidation method for determining the oxidative stability of biodiesel.

Biodiesel is considered an alternative energy because it is produced from fats and vegetable oils by means of transesterification. Furthermore, it consists of fatty acid alkyl esters (FAAS) which have a great influence on biodiesel fuel properties and in the storage lifetime of biodiesel itself. The biodiesel storage stability is directly related to the oxidative stability parameter (Induction Time - IT) which is determined by means of the Rancimat® method. This method uses condutimetric monitoring and induces the degradation of FAAS by heating the sample at a constant temperature. The European Committee for Standardization established a standard (EN 14214) to determine the oxidative stability of biodiesel, which requires it to reach a minimum induction period of 6h as tested by Rancimat® method at 110°C. In this research, we aimed at developing a fast and simple alternative method to determine the induction time (IT) based on the FAAS ultrasonic-accelerated oxidation. The sonodegradation of biodiesel samples was induced by means of an ultrasonic homogenizer fitted with an immersible horn at 480Watts of power and 20 duty cycles. The UV-Vis spectrometry was used to monitor the FAAS sonodegradation by measuring the absorbance at 270nm every 2. Biodiesel samples from different feedstock were studied in this work. In all cases, IT was established as the inflection point of the absorbance versus time curve. The induction time values of all biodiesel samples determined using the proposed method was in accordance with those measured through the Rancimat® reference method by showing a R(2)=0.998.