Hybrid magnetic amphiphilic composites based on carbon nanotube/nanofibers and layered silicates fragments as efficient adsorbent for ethynilestradiol

In this work, hybrid magnetic amphiphilic composites were prepared by the catalytic growth of carbon nanotubes (CNTs) and nanofibers CNF on layered silicates fragments. SEM, TEM, Raman, XRD, Mössbauer, TG/DTA showed that CVD with CH₄ at 800 °C produced CNF and magnetic Fe cores fixed on the surface of microfragments of silicates layers. Due to the amphiphilic character, the composites can be easily dispersed in water and efficiently adsorb hydrophobic contaminant molecules. For example, the composites showed remarkable adsorption capacities for the hormone ethinylestradiol, e.g. 2–4 mg m^?2, compared to ca. 0.1 mg m^?2 obtained for high surface area activated carbon and multiwall CNT. These results are discussed in terms of a high hydrophobic exposed surface area of the CNT and CNF fixed on the layered silicates fragments surface. Moreover, the composites can be easily removed from water by a simple magnetic separation process.     

Generation and mid-IR measurement of a gas-phase to predict security parameters of aviation jet fuel

The worldwide use of kerosene as aviation jet fuel makes its safety considerations of most importance not only for aircraft security but for the workers’ health (chronic and/or acute exposure). As most kerosene risks come from its vapours, this work focuses on predicting seven characteristics (flash point, freezing point, % of aromatics and four distillation points) which assess its potential hazards. Two experimental devices were implemented in order to, first, generate a kerosene vapour phase and, then, to measure its mid-IR spectrum. All the working conditions required to generate the gas phase were optimised either in a univariate or a multivariate (SIMPLEX) approach. Next, multivariate prediction models were deployed using partial least squares regression and it was found that both the average prediction errors and precision parameters were satisfactory, almost always well below the reference figures.     

Prediction of FCC gasoline octane numbers using FT-MIR and PLS

A method for predicting octane numbers (RON and MON) in fluid catalytic cracking (FCC) gasolines is proposed. Using FT-MIR and PLS, improvements have been obtained in sample throughput, reduced delay times, accuracy (repeatability and reproducibility), amounts of samples and reagents and environmental working conditions when compared with current standard methods. A total number of 140 daily production samples were taken; and from there, a learning group was prepared (44 samples); a validation set (96 samples) was prepared, as well. Sample spectra were recorded from 4000 to 600 cm^-1 at 4 cm^-1 intervals (traditional sealed NaCl cells). The PLS technique was used in its two variants (1 and 2-block). Both provided similar results. Their predictive characteristics are very good: SEP_RON=0.38; SEP_MON=0.40; repeatability <0.1 O.N.; reproducibility <0.3 O.N. (SEP=Standard Error of Prediction).     

Development of analytical method for determination of Sb(V), Sb(III) and TMSb(V) in occupationally exposed human urine samples by HPLC-HG-AFS

In the present paper, we develop a methodology for antimony speciation in occupationally exposed human urine samples by high-performance liquid chromatography with hydride generation atomic fluorescence spectrometry (HPLC-HG-AFS). The methodology was applied to the determination of Sb(V), Sb(III) and (CH₃)₃SbCl₂ (TMSb(V)). Retention time of Sb(V), Sb(III) and TMSb(V) species were 0.88, 2.00 and 3.61 and the detection limits were 0.18, 0.19 and 0.12 μg L^− 1, for 100 μL loop injection respectively which is considered useful for elevated/occupationally exposed urine samples. Studies on the stability of antimony species in urine samples on the function of the elapsed time of preservation (4 °C) and storage (− 70 °C) were performed. Results revealed that antimony species are highly unstable at − 70 °C, probably due to co-precipitation reaction. In this kind of matrix transformation during preservation time may occur, such as oxidation of Sb(III) to Sb(V) and transformation into species that do not elute from the column. EDTA shows that it is able to stabilize Sb(III) for more than one week of preservation time at 4 °C avoiding co-precipitation during storage at − 70 °C. Finally the methodology was applied to occupationally exposed human urine samples. 25% of specimens present antimony levels (Sb(V)) of more than 5 μg L^− 1.     

Speciation analysis of antimony in marine biota by HPLC-(UV)-HG-AFS: Extraction procedures and stability of antimony species

Speciation analysis of antimony in marine biota is not well documented, and no specific extraction procedure of antimony species from algae and mollusk samples can be found in the literature. This work presents a suitable methodology for the speciation of antimony in marine biota (algae and mollusk samples). The extraction efficiency of total antimony and the stability of Sb(III), Sb(V) and trimethylantimony(V) in different extraction media (water at 25 and 90 °C, methanol, EDTA and citric acid) were evaluated by analyzing the algae Macrosystis integrifolia (0.55 ± 0.04 μg Sb g⁻¹) and the mollusk Mytilus edulis (0.23 ± 0.01 μg Sb g⁻¹). The speciation analysis was performed by anion exchange liquid chromatography (post-column photo-oxidation) and hydride generation atomic fluorescence spectrometry as detection system (HPLC-(UV)-HG-AFS). Results demonstrated that, based on the extraction yield and the stability, EDTA proved to be the best extracting solution for the speciation analysis of antimony in these matrices. The selected procedure was applied to antimony speciation in different algae samples collected from the Chilean coast. Only the inorganic Sb(V) and Sb(III) species were detected in the extracts. In all analyzed algae the sum of total antimony extracted (determined in the extracts after digestion) and the antimony present in the residue was in good agreement with the total antimony concentration determined by HG-AFS. However, in some extracts the sum of antimony species detected was lower than the total extracted, revealing the presence of unknown antimony species, possibly retained on the column or not detected by HPLC-(UV)-HG-AFS. Further work must be carried out to elucidate the identity of these unknown species of antimony.     

Application of programmed-temperature split/splitless injection to the trace analysis of aliphatic hydrocarbons by gas chromatography.

The dependence of the programmed-temperature solvent split sampling technique using a PSS (programmed-split/splitless) injection mode on different variables affecting the introduction of large sample volumes for a mixture of alkanes in capillary GC was evaluated. Apart from the studies found in the literature on different factors such as speed of injection. presence of adsorbent in the liner, internal diameter of the liner, initial and final injector temperature, split flow-rate and initial split time, affecting the chromatographic signal of different compounds, others were studied whose influence has not been considered until now. They include length of the microsyringe needle, adsorbent distribution in the liner, injection volume on analyte discrimination, speed of injector heating, time which the column stays at the initial temperature and time that the injector stays at the final temperature. Once finalised, the study of the PSS injection mode was compared with the conventional mode of gas chromatography splitless injection, and found that the proposed method increases sensitivity in GC trace analysis. Finally, the application of both injection modes in the determination of aliphatic hydrocarbons was tested in an atmospheric particulate sample.     

Synthesis and pharmacological evaluation of 4-halo progesterone derivatives as antiandrogen.

The pharmacological activity of eight pregnane derivatives 17-alpha acetoxyprogesterone 9, 17-alpha acetoxy-4, 5-epoxypregnan-3, 20-dione 10, 17-alpha acetoxy-4-chloro-4-pregnene-3, 20-dione 11, 17-alpha acetoxy-4-bromo-4-pregnene-3, 20-dione 12, 17-alpha hydroxy-4-bromo-4-pregnene-3, 20-dione 13, 4-chloro-17-alpha hydroxy-4-pregnene-3, 20-dione 14, 17-alpha benzoyloxy-4-bromo-4-pregnene-3, 20-dione 15 and 17-alpha benzoyloxy-4-chloro-4-pregnene-3, 20-dione 16 was determined. These compounds were evaluated as antiandrogens on gonadectomized hamster seminal vesicles. The pharmacological data in this study indicate that compounds 15 and 16 having a C-17 benzoyloxy moiety showed the highest antiandrogenic activity as measured by the reduction of the weight of the seminal vesicles, followed by the steroids 11 and 12 (17-alpha acetoxy group). The free alcohols 13 and 14 exhibited a lower antiandrogenic activity. Apparently, the ester moiety at C-17 is a necessary requirement for the presence of high antiandrogenic activity. Shows the inhibitory effect on the conversion of testosterone (T) to DHT, of the above described steroids as measured by the amount of produced DHT 2 expressed as pmoles of DHT/g of protein/h. Steroids 11, 12 and 16 showed a much higher inhibitory activity on the conversion of testosterone (T) to dihydrotestosterone (DHT) than presently used finasteride 3.     

A review of the main factors influencing the FT-IR-PLS abilities exemplified with petrochemical qualimetric applications

Quality control usually involves monitoring several variables directly related with industrial necessities using univariate tests. One powerful alternative is to link multivariate analytical techniques and multivariate chemometrics. In this way, Fourier Transform Infrared spectroscopy and Partial Least Squares regression are used to discuss and review several advantages and drawbacks encountered in using such combination in industrial facilities. Typical drawbacks are selection of data pretreatment, errors in reference methods, selection of calibration and validation sets and model-aging. This review is exemplified with petrochemical applications although other fields are also considered (mainly when dealing with data pretreatment).     

Microwave-assisted extraction and ultrasonic slurry sampling procedures for cobalt determination in geological samples by electrothermal atomic absorption spectroscopy

Slurry sampling is compared to microwave-assisted acid digestion for cobalt determination in soil/sediment samples by electrothermal atomic absorption spectrometry (ETAAS). Furnace temperature programs and appropriate amounts of three chemical modifiers were optimised in order to get the highest signals and good separations between the atomic and background signals. Using nitric acid (0.5% (v/v)) as liquid medium, no chemical modifier was needed. The detection limit, based on integrated absorbance, was 0.04 μg g⁻¹ for digests and slurries. Within-batch precision and analytical recoveries were satisfactory for both procedures. Accuracy was tested by analysing a reference soil and a sediment from IRMM. The methods were further compared employing a set of roadside soils and estuarine sediments. As no significant differences (95% confidence) were found, practical analytical properties were suggested in order to select one of them.     

A review of the main factors influencing the FT-IR-PLS abilities exemplified with petrochemical qualimetric applications

Quality control usually involves monitoring several variables directly related with industrial necessities using univariate tests. One powerful alternative is to link multivariate analytical techniques and multivariate chemometrics. In this way, Fourier Transform Infrared spectroscopy and Partial Least Squares regression are used to discuss and review several advantages and drawbacks encountered in using such combination in industrial facilities. Typical drawbacks are selection of data pretreatment, errors in reference methods, selection of calibration and validation sets and model-aging. This review is exemplified with petrochemical applications although other fields are also considered (mainly when dealing with data pretreatment).