Degradation of alachlor herbicide by gamma radiation from cobalt-60 in aqueous and alcohol solution

Alachlor has been widely used in agriculture all over the world. It is suggested that it may be a carcinogen and an environmental estrogen. The aim of this work was to verify the degradation the alachlor by gamma radiation. Gamma radiation from ⁶⁰Co was used to degrade the alachlor herbicide in water and methanol solution. The alachlor in water and alcohol solution in the concentration of 100 mgL⁻¹ was irradiated with doses of 0.25–50 kGy, at dose rate 5–6 and 2.7 kGyh⁻¹. High performance liquid chromatography was used as an analytical technique to determine the degradation rate of herbicide studied.     

A simplified version of the total kjeldahl nitrogen method using an ammonia extraction ultrasound-assisted purge-and-trap system and ion chromatography for analyses of geological samples

The total Kjeldahl nitrogen (TKN) method was simplified by using a manifold connected to a purge-and-trap system immersed into an ultrasonic (US) bath for simultaneous ammonia (NH₃) extraction from many previously digested samples. Then, ammonia was collected in an acidic solution, converted to ammonium (NH₄⁺), and finally determined by ion chromatography method. Some variables were optimized, such as ultrasonic irradiation power and frequency, ultrasound-assisted NH₃ extraction time, NH₄⁺ mass and sulfuric acid concentration added to the NH₃ collector flask. Recovery tests revealed no changes in the pH values and no conversion of NH₄⁺ into other nitrogen species during the irradiation of NH₄Cl solutions with 25 or 40 kHz ultrasonic waves for up to 20 min. Sediment and oil free sandstone samples and soil certified reference materials (NCS DC 73319, NCS DC 73321 and NCS DC 73326) with different total nitrogen concentrations were analysed. The proposed method is faster, simpler and more sensitive than the classical Kjeldahl steam distillation method. The time for NH₃ extraction by the US-assisted purge-and-trap system (20 min) was half of that by the Kjeldahl steam distillation (40 min) for 10 previously digested samples. The detection limit was 9 μg g⁻¹ N, while for the Kjeldahl classical/indophenol method was 58 μg g⁻¹ N. Precision was always better than 13%. In the proposed method, carcinogenic reagents are not used, contrarily to the indophenol method. Furthermore, the proposed method can be adapted for fixed-NH₄⁺ determination.     

Exploratory analysis and inductively coupled plasma optical emission spectrometry (ICP OES) applied in the determination of metals in soft drinks

A 2³ factorial design and a CCD (Central Composite Design) were employed to optimize the operational conditions for determining Al, Ba, Ca, Cd, Cr, Cu, K, Mg, Na, Ni, Pb, Sn and Zn in soft drink samples by inductively coupled plasma optical emission spectrometry (ICP OES). Satisfactory parameters of merit were obtained (Plasma stability, linearity, SBR, BEC, LOD and LOQ). The accuracy was evaluated by means of a recovery study. Thirty five soft drink samples were analyzed. The results obtained were used in an exploratory analysis, in which principal component analysis and cluster analysis were applied in order to differentiate the several soft drink classes. Adequate LOQ values were obtained for all elements (0.34 μg L^− 1 for Ca to 88.7 μg L^− 1 for Mg) and the recovery study results ranged between 80 and 100%. Cluster analysis revealed four sample classes characterized by flavor and other characteristics, such as being light, diet, low calorie or regular beverages. A model with 4 PCs was obtained by means of a principal component analysis, which explained 99.8% of the total variance.     

Synthesis of pseudo-C-nucleosides from β-formyl-α,β-unsaturated ester bearing a β-furanosidic moiety

Abstract  

Pseudo-C-nucleosides have potential biological activity, and an efficient synthesis of new pseudo-C-nucleosides has been developed via the reaction of a β-formyl-α,β-unsaturated ester bearing a β-sugar moiety with hydrazines in neutral and acidic conditions. The preparation of the β-formyl-α,β-unsaturated ester was accomplished by oxidation of the secondary hydroxyl group of 3-O-benzyl-1,2-O-isopropylidene-α-d-glucofuranose, followed by elongation of its carbon chain with (ethoxycarbonylmethylene)triphenylphosphorane and oxidation of the hydroxymethyl group.     

Determination of polybrominated diphenyl ethers in water and soil samples by cloud point extraction-ultrasound-assisted back-extraction-gas chromatography–mass spectrometry

A novel and efficient analytical methodology is proposed for extracting and preconcentrating polybrominated diphenyl ethers (PBDEs) from samples of environmental interest prior gas chromatography–mass spectrometry (GC–MS) analysis. It is based on the induction of micellar organized medium by using a non-ionic surfactant (Triton X-114) to extract the target PBDEs. To enable coupling the efficient extracting technique with GC analysis, ultrasound-assisted back-extraction (UABE) into an organic solvent was required. Several factors, including surfactant type and concentration, equilibration temperature and time, ionic strength, pH and buffers nature and concentration were studied and optimized over the extraction efficiency of the proposed technique. Under optimal experimental conditions, the target analytes were quantitatively extracted achieving an enrichment factor of 250 when 10 mL aliquot of ultrapure water spiked with PBDE-standard mixture (10 pg mL⁻¹ each PBDE) was extracted. Method detection limits (MDLs) calculated with aqueous PBDEs solutions as three times the signal-to-noise ratio (S/N), ranged from 1 to 2 pg mL⁻¹ with RSDs values ≤8.5% (n = 5). The coefficients of estimation of the calibration curves obtained following the proposed methodology were ≥0.9987 and linear range of all PBDEs was 4–150 pg mL⁻¹. The proposed methodology was validated by carrying out a recovery study by spiking the samples at two different concentration levels of PBDEs (10 and 50 pg mL⁻¹ for waters samples). Recoveries values in the range of 96–106% for water samples were obtained showing satisfactory robustness of the method for analyzing PBDEs in water samples. The proposed methodology was applied for the analysis of PBDEs: 2,2′,4,4′-tetraBDE (BDE-47), 2,2′,4,4,5-pentaBDE (BDE-99), 2,2′,4,4,6-pentaBDE (BDE-100) and 2,2,4,4′,5,5′-hexaBDE (BDE-153) in water samples, including drinking, lake, river water and soil samples. Significant quantities of PBDEs were not found in the analyzed samples.     

LC Method for Studies on the Stability of Sibutramine in Soft Gelatin Capsules

A sensitive and rapid liquid chromatographic method was successfully developed and validated for the determination of sibutramine hydrochloride in bulk and capsules. Sibutramine in the presence of its degradation products was analyzed using UV detection at 225 nm. Chromatography was performed on a reversed-phase C₈ (150 × 4.0 mm I.D., 5 μm) analytical column under isocratic conditions. The mobile phase was composed of acetonitrile:water (aqueous phase containing 0.3% triethylamine and pH adjusted to 7.0) (75:25, v/v) at a flow-rate of 1.1 mL min⁻¹. No chromatographic interference was found during the analysis. Light was the stress condition which most contributed to sibutramine degradation. The method showed a linear response (r > 0.999) from 30 to 90 μg mL⁻¹. The mean recovery for capsules was 101.2%. Inter-day assays showed relative standard deviations of 0.42 and 1.62% for bulk and capsules, respectively. The developed method is able to separate sibutramine from its major degradation products and it may be used in the quality control of this active pharmaceutical ingredient in both bulk and capsules.

     

Structural studies of cyclic ureas: 3. Enthalpy of formation of barbital

A thermochemical and thermophysical study has been carried out for crystalline barbital [5,5′-diethylbarbituric acid]. The thermochemical study was made by static bomb combustion calorimetry, from which the standard () molar enthalpy of formation of the crystalline barbital, at T = 298.15 K, was derived as −(753.0 ± 1.8) kJ · mol⁻¹. The thermophysical study was made by differential scanning calorimetry over the temperature interval (265 to 470) K. A solid–solid phase transition was found at T = 413.3 K. The vapour pressures of the crystalline barbital were measured at several temperatures between T = (355 and 377) K, by the Knudsen mass-loss effusion technique, from which the standard molar enthalpy of sublimation, at T = 298.15 K was derived as (117.3 ± 0.6) kJ · mol⁻¹. The combination of the experimental results yielded the standard molar enthalpy of formation of barbital in the gaseous phase, at T = 298.15 K, as −(635.8 ± 1.9) kJ · mol⁻¹. This value is compared and discussed with our theoretical calculations by several methods (Gaussian-n theories G2 and G3, complete basis set CBS-QB3, density functional B3P86 and B3LYP) by means of atomization and isodesmic reaction schemes.     

Digital image-based flame emission spectrometry

A digital image-based flame emission spectrometric (DIB-FES) method for the quantitative chemical analysis is proposed here for the first time. The DIB-FES method employs a webcam to capture the digital images which are associated to a radiation emitted by the analyte into an air-butane flame. Since the detection by webcam is based on the RGB (red-green-blue) colour system, a novel mathematical model was developed in order to build DIB-FES analytical curves and estimate figures of merit for the proposed method. In this approach, each image is retrieved in the three R, G and B individual components and their values were used to define a position vector in RGB three-dimensional space. The norm of this vector is then adopted as the RGB-based value (analytical response) and it has revealed to be linearly related to the analyte concentration. The feasibility of the DIB-FES method is illustrated in three applications involving the determination of lithium, sodium and calcium in anti-depressive drug, physiological serum and water, respectively. In comparison with the traditional flame emission spectrometry (trad-FES), no statistic difference has been observed between the results by applying the paired t-test at the 95% confidence level. However, the DIB-FES method has offered the largest sensitivities and precision, as well as the smallest limits of detection and quantification for the three analytes. These advantageous characteristics are attributed to the trivariate nature of the detection by webcam.