Eustáquio V.R. Castro

Fingerprinting of sildenafil citrate and tadalafil tablets in pharmaceutical formulations via X-ray fluorescence (XRF) spectrometry.

The production of counterfeited drugs is a criminal problem that carries serious risks to public health in the worldwide. In Brazil, Viagra and Cialis are the most counterfeit medicines, being used to inhibit the phosphodiesterase type 5 (PDE-5), treating thus, problems related to erectile dysfunction. X-ray fluorescence (XRF) is a suitable technique to control the quality of new pharmaceutical formulations and distinguish between authentic and counterfeit tablets. XRF has advantageous features like multielemental capability, good detectivity, high precision, short analysis times, and is nondestructive, which makes it suitable to be extended to a great variety of samples. In this work, the inorganic fingerprinting chemical of forty-one commercial samples (Viagra, Cialis, Lazar, Libiden, Maxfil, Plenovit, Potent 75, Rigix, V-50, Vimax and Pramil) and fifty-six counterfeit samples (Viagra and Cialis) were obtained from XRF data. XRF presented an excellent analytical methodology for semi-quantitative determination of active ingredient (in case of sildenafil citrate that presents S in its structure) and excipients such as calcium phosphate, titanium oxide and iron oxide (P, Ca, Ti and Fe). The matrix data were allied to chemometric methods (Principal Component Analysis and Hierarchical Cluster Analysis) to classify the tablets investigated between authentic and counterfeit, grouping the samples into of seven groups: A, B, C, D and E (counterfeit group) and F and G (authentic group).

Studies on crude oil‐water biphasic mixtures by low‐field NMR

Low‐field 1H NMR was used in this work for the analysis of mixtures involving crude oils and water. CPMG experiments were performed to determine the transverse relaxation time (T2) distribution curves, which were computed by the inverse Laplace transform of the echo decay data. The instruments ability of quantifying water and petroleum in biphasic mixtures following different methodologies was tested. For mixtures between deionized water and petroleum, one achieved excellent results, with root mean squared error of cross‐validation (RMSECV) of 0.8% for a regression between the water content (wt %) and the relative area of the water peak in the T2 distribution curve, or a standard deviation of 0.9% for the relationship between the water content and the relative water peak area, corrected by the relative hydrogen index of the crude. In the case of biphasic mixtures of Mn2+‐doped water and crude oils, the best result of RMSECV = 1.6% was achieved by using the raw magnetization decay data for a partial least squares regression. Copyright

Direct determination of phosphorus in biodiesel samples by graphite furnace atomic absorption spectrometry using a solid sampling accessory

A procedure for the direct determination of P in biodiesel samples by graphite furnace atomic absorption spectrometry (GF AAS) using an automatic solid sampling accessory without any sample pre-treatment or dilution is proposed. Studies showed that it is necessary to use a chemical modifier and a Pd in Triton X-100 solution showed the best results. The pyrolysis and atomization temperatures (1300 °C and 2700 °C, respectively), as well as the Pd mass (30 µg) were determined by multivariate optimization. The other parameters of the temperature programs were defined by univariate optimization. The limit of detection at the optimized conditions was 7.2 ng (1.2 µg g−1) using 20 µL of chemical modifier solution as blank for typical sample masses between of 2.00 and 6.00 mg. Aqueous calibration solutions were used and the calibration curves showed correlation coefficients better than R2 = 0.99. The characteristic mass was 9.1 ng. The method’s accuracy was confirmed both by the analysis of reference materials and by comparison with an independent procedure (EN 14107). No statistically significant difference was observed between obtained and expected values.

LSD and 9,10-dihydro-LSD Analyses in Street Drug Blotter Samples via Easy Ambient Sonic-Spray Ionization MassSpectrometry (EASI-MS)

Normally, the identification of the LSD drug is performed by forensic laboratories, using the Ehrlich spot test. However, this is a nonspecific analysis. Additionally, the Brazilian Federal Police has identified the presence of a new compound in seized blotters: 9,10‐dihydro‐LSD, an uncontrolled substance. In this work, easy ambient sonic‐spray ionization mass spectrometry in the positive ion mode, EASI(+)‐MS, was used to characterize LSD and 9,10‐dihydro‐LSD compositions directly from the surface of blotters. The presence of LSD in the seized blotter samples were also confirmed via high‐performance liquid chromatography with ultraviolet detector. In a set of 41 blotters analyzed by EASI(+)‐MS, 28 showed positive results for LSD, seven for 9,10‐dihydro‐LSD, and another six samples showed negative results for both LSD and 9,10‐dihydro‐LSD. The combination of thin layer chromatography with EASI‐MS also demonstrated to be a relatively simple and powerful screening tool for forensic analysis of street drugs.

Prediction of the distillation temperatures of crude oils using 1H NMR and support vector regression with estimated confidence intervals

This paper aims to estimate the temperature equivalent to 10% (T10%), 50% (T50%) and 90% (T90%) of distilled volume in crude oils using (1)H NMR and support vector regression (SVR). Confidence intervals for the predicted values were calculated using a boosting-type ensemble method in a procedure called ensemble support vector regression (eSVR). The estimated confidence intervals obtained by eSVR were compared with previously accepted calculations from partial least squares (PLS) models and a boosting-type ensemble applied in the PLS method (ePLS). By using the proposed boosting strategy, it was possible to identify outliers in the T10% property dataset. The eSVR procedure improved the accuracy of the distillation temperature predictions in relation to standard PLS, ePLS and SVR. For T10%, a root mean square error of prediction (RMSEP) of 11.6°C was obtained in comparison with 15.6°C for PLS, 15.1°C for ePLS and 28.4°C for SVR. The RMSEPs for T50% were 24.2°C, 23.4°C, 22.8°C and 14.4°C for PLS, ePLS, SVR and eSVR, respectively. For T90%, the values of RMSEP were 39.0°C, 39.9°C and 39.9°C for PLS, ePLS, SVR and eSVR, respectively. The confidence intervals calculated by the proposed boosting methodology presented acceptable values for the three properties analyzed; however, they were lower than those calculated by the standard methodology for PLS.

Salinidade em petróleo bruto: otimização de metodologia e proposta de um novo método para extração de sais em petróleo

The quantity of salts in the crude oils depends on the origin and of the wells production and these salts cause several problems during the transport and the process of refine as corrosions, incrustations and deactivation of the employed catalysts in the refineries. In this study were implemented changes for improvements in the execution of ASTM D 6470 method and has also developed a new methodology of extraction system of salts using process of mechanical agitation without heating. The results of the optimization produce larger efficiency and safety to the process compared to the traditional ASTM method.

NMR property calculations and experimental study of the 1,6-epoxycarvone and α-epoxypinene: a comparison of models

This work aims at using theoretical calculations of shielding tensors (σ) through different methods [gauge‐independent atomic orbital (GIAO), continuous set of gauge transformations (CSGT) and individual gauges for atoms in molecules (IGAIM)] and spin‐spin coupling constants J using GIAO method to compare these methods and to corroborate the data obtained with the assignment of all of 1H and 13C NMR signals and the relative stereochemistry of the 1,6‐epoxycarvone and the α‐epoxypinene. All the 1H and 13C NMR signals were assigned unequivocally. The stereochemistry for the epoxides is trans and the B3LYP theory level with CSGT and IGAIM methods is the best choice to evaluate theoretical chemical shifts for compounds studied. Copyright

Stereochemistry of cyclopentane derivatives from (2,3)J(CH) dependence on dihedral angle (theta H--C--C--X).

The 2, 3JCH dependence on dihedral angle (θ HCCX) for cyclopentane derivatives was investigated. We observed that the combined use of experimentally obtained 2, 3JCH values and the theoretically determined dihedral angles between the corresponding nuclei can be used to infer the relative stereochemistry of the ring substituents in cyclopentane derivatives. There is a good correlation between the magnitude of 3JCH and the dihedral angle between the hydrogen and the coupled carbon (R2 = 0.88). Copyright

1H and 13C NMR spectral data of bioactive cage-like polycyclic compounds

Bioactive cage‐like polycyclic compounds have attracted the attention of several research groups because of their unique appearance and their biological activities. Their structures were established on the basis of 1H NMR and 13C NMR spectroscopic data. The 1H and 13C signal assignments and most homonuclear hydrogen coupling constants were assigned by use of techniques such as 1D 1H and 13C NMR and 2D gCOSY, non‐edited gHSQC and gHMBC. The gNOESY experiments proved the endo‐stereochemistry. Copyright

Determination of Ca, Mg, Sr and Ba in crude oil samples by atomic absorption spectrometry

The presence of Ca, Mg, Sr and Ba in crude oil samples should be controlled, since they can lead to incrustations on steel pipes, valves, pumps and other equipment used in crude oil drilling. This paper proposes procedures for the determination of these metals in crude oil by atomic absorption spectrometry, using the formation of O/W emulsions for sample preparation. Emulsions were prepared in 0.2% v/v HNO3 using Triton X-100 as a surfactant and showed good stability for the four studied analytes of at least 5 days after preparation. Flame atomic absorption spectrometry (FAAS) was used for the determination of Ca, Mg and Sr and graphite furnace atomic absorption spectrometry (GFAAS) was used for the determination of Ba. External calibration could be performed for the determination of Ca, Mg and Sr with inorganic standard solutions in the form of emulsions; for Ba, calibration was possible in aqueous medium. The limits of detection obtained were 0.54, 0.09, 0.10 and 0.04 μg g−1 for Ca, Mg, Sr and Ba respectively in the crude oil samples. Recoveries ranging from 96 to 104% and the good agreement among the found and certified values in the analysis of a certified reference material (NIST 1085b) warranted the accuracy of the procedures.