Single step determination of fragrances in Cucurbita flowers by coupling headspace solid-phase microextraction low-pressure gas chromatography-tandem mass spectrometry

Coupling headspace solid-phase microextraction (HS-SPME) and low-pressure gas chromatography-tandem mass spectrometry (LP-GC-MS-MS) has been used for determining 20 volatile compounds present in flowers. HS-SPME coupled with LP-GC-MS-MS acts in a synergic way allowing a fast extraction and analysis of the target compounds. The method has been optimised studying the influence of the adsorption temperature and adsorption time. The best results were obtained heating the SPME vials at 60 degrees C for 5 min using 65 microm poly(dimethylsiloxane-divinylbenzene) fibers. The validation of the method ensures the fitness for the purpose of the analytical method, achieving appropriate lower limits, recoveries and precision. The analytical method has been applied to the characterisation of zucchini flowers fragrances in air using passive sampling, in order to improve our knowledge on zucchini fragrances and to better pollination technique in future steps.     

Identification des configurations Z et E en série cyclopropylidénique. Stéréosélectivité de la migration exocyclique de la double liaison cyclopropénique en milieu basique

The identification of E- and Z-2-alkyl-3-ethylidenecyclopropane having a functional group (ketone, ester, alcohol) at C-1 of the ring, is realized by chemical means and by NMR induced shifts using Eu(dpm)₃. These structure assignments show that the cyclopropene ester, ketone, alcohol double bond migration in basic media leads preferentially to the E-configuration; the stereoselectivity may reach 90%. Moreover, the prototropy is regiospecific and stereospecific compared to the ring.     

Reduction of analysis time in gas chromatography. Application of low-pressure gas chromatography-tandem mass spectrometry to the determination of pesticide residues in vegetables

An alternative to conventional capillary gas chromatography (GC) is evaluated as a new approach to determine pesticide residues in vegetables. Low-pressure gas chromatography-tandem mass spectrometry (LP-GC-MS-MS) is proposed after a fast and simple extraction of the vegetable samples with dichloromethane and without clean up. The use of the above-mentioned GC technique reduced the total time required to determine 72 pesticides to less than half the present time (31 min), increasing the capability of a monitoring routine laboratory. The use of guard column and plug of carbofrit into the glass liner in combination with LP-GC was evaluated. The method was validated with limits of quantitation low enough to determine the pesticide residues at concentrations below the maximum residue levels stated by legislation. In order to assess its applicability to the analysis of real samples, 25 vegetable samples previously determined using conventional-capillary GC-MS-MS were analysed by LP-GC-MS-MS. The results obtained with the compared techniques showed differences lower than 0.01 mg kg(-1).     

Determination of imidacloprid and its metabolite 6-chloronicotinic acid in greenhouse air by high-performance liquid chromatography with diode-array detection

A method is described for analysing and sampling imidacloprid and its metabolite 6-chloronicotinic acid in greenhouse air by high-performance liquid chromatography (HPLC) with diode-array detection (DAD). The trapping efficiency of two solid sorbents, Amberlite XAD-2 and Amberlite XAD-4 and the use of different desorption procedures have been tested. To validate the methodology, standard atmospheres containing known concentrations of these pesticides and with different relative humidities were generated. No breakthrough was observed in the range of concentrations studied. Dissipation of analytes was investigated in a 24 h period after application by using personal samplers in a field experiment.     

Determination of phosphate in natural water employing a monosegmented flow system with simultaneous multiple injection

A monosegmented flow system was employed for the determination of low contents of phosphate in natural water. In this approach, sample and reagents are simultaneously injected to a PTFE reaction coil where the homogenization of the mixture occurs while the monosegment is pumped forwards the photometric detector. The proposed system was evaluated by determining phosphate ion, based on the reaction of association between molybdophosphate and malachite green. It was evaluated individually the best concentration of the reagent solution in relation to blank signal (absorbance of the blank) and the sensitivity of the method. A factorial design was proposed to explain the contribution of each component on the formation of the ion association complex, evaluating the individual contributions as well as the synergistic and antagonistic effects. With the established conditions, phosphorous is determined in the concentration range of 5.0-75 μg P PO₄³⁻ l⁻¹ (r=0.9992), with a detection limit of 0.70 μg P PO₄³⁻ l⁻¹ and a relative standard deviation of 2% (20 μg P PO₄³⁻ l⁻¹, n=8). The proposed method has a sampling frequency of 72 h⁻¹.     

Multicomponent determination of pesticides in vegetables by gas chromatography with mass spectrometric detection and multivariate calibration

Three multivariate calibration methods, partial least squares (PLS-1 and PLS-2) and principal component regression (PCR), were applied for the first time to the simultaneous determination of a mixture of six pesticides in vegetables samples by gas chromatography with mass spectrometric detection (GC-MS). PLS-1 method showed better prediction ability than PLS-2 and PCR methods. The GC-MS chromatograms obtained of vegetable samples spiked with the target pesticides were used to build the calibration matrix. The PLS-1 models were evaluated by predicting the concentrations of independent test samples. Also, the proposed models were successfully applied for the determination of these pesticides in vegetable samples after an extraction step with dichloromethane. By using the first derivative signals in PLS-1 models, simultaneous determination of the compounds was not improved.     

Effect of cellulase-assisted refining on the properties of dried and never-dried eucalyptus pulp

The effect of two different cellulases on the hornification phenomenon,in which drainability (Schopper–Riegler method) and mechanical propertiesdiminish when pulps are dried, was studied. The enzyme applications testedincluded a commercial enzyme named ComC (Pergalase A40 from CIBA) and alaboratory enzyme from Paenibacillus sp. strain BP-23namedCelB. Industrial never-dried Eucalyptus globulus bleachedkraft pulp was split in two halves and one of them was dried at ambientcontrolled conditions. We compared enzyme effects on both pulps (wet pulp anddried pulp) before and after PFI mill refining. Enzyme applications increaseddrainability (Schopper–Riegler method) and water retention value (WRV) ofnever-dried bleached pulp, although this did not imply an enhancement of themechanical properties of paper. Cellulase treatment of dried pulps, bycontrast,gave rise to increased drainability and WRV and also to improved mechanicalproperties. The changes caused by drying became less significant after enzymeapplication. Handsheets from CelB-treated dried pulps showed an improvement oftensile and burst indexes while tear decreased. The effect produced by CelB canbe considered a biorefining step. In fact, by means of enzyme treatment withCelB the properties of paper manufactured from dried pulp equalled theproperties attained from wet fibres, with the exception of tear index. Changeswere also found in surface fibre morphology, such as flakes and peeling due tocellulase treatment. The surface modification of fibres with cellulases givesrise to better bonding properties and a closer structure of paper. The finalconclusion is that treatment with cellulases could compensate the hornificationeffect and lead to an important saving of refining energy. The novel enzyme,CelB, was the most effective in improving paper properties and counterbalancingthe hornification effect caused by drying.     

Joint Particle Filter and UKF Position Tracking in Severe Non-Line-of-Sight Situations

The performance of localization techniques in a wireless communication system is severely impaired by biases induced in the range and angle measures because of the non-line-of-sight (NLOS) situation, caused by obstacles in the transmitted signal path. However, the knowledge of the line-of-sight (LOS) or NLOS situation for each measure can improve the final accuracy. This paper studies the localization of mobile terminals (MT) based on a Bayesian model for the LOS-NLOS evolution. This Bayesian model does not require having a minimum number of LOS measures at each acquisition. A tracking strategy based on a particle filter (PF) and an unscented Kalman filter (UKF) is used both to estimate the LOS-NLOS situation and the MT kinetic variables (position and speed). The approach shows a remarkable reduction in positioning error and a high degree of scalability in terms of performance versus complexity.