Investigation of different chemical modifiers based on the Pd/Mg mixture for the determination of sulfur in shale oil by high-resolution continuum source graphite furnace molecular absorption spectrometry.

This study investigated different combinations of Pd/Mg, as chemical modifier, for sulfur determination, via CS molecule, in shale oil samples by high-resolution continuum source graphite furnace molecular absorption spectrometry (HR-CS GF MAS). It was evaluated the mixture Pd/Mg in aqueous solution, Pd/Mg in propan-1-ol and the Pd/Mg in propan-1-ol plus Ru as a permanent modifier. The best sensitivity was achieved with Pd/Mg mixture in propan-1-ol. The high solubility of the samples in propan-1-ol promotes a better interaction with the modifier and, consequently, a more efficient thermal stability of the CS molecules. Due to the high sulfur content in the samples, the analytical line at 258.288 nm was used. Only a minimum sample preparation was required, i.e., a dilution in propan-1-ol by a factor of 1:10 (w/w). Temperatures of 800 °C and 2200 °C were the optimized conditions for pyrolysis and vaporization, respectively. The calibration curve was constructed with l-cysteine aqueous standard solutions. The characteristic mass was 27 ng; detection and quantification limits were 0.012% (w/w) and 0.039% (w/w), respectively. The accuracy of the proposed method was confirmed by the statistical agreement (Student's and Welch's t-test at 95% confidence level) using the certified reference material CRM NIST 1084a and an OTE oil sample whose sulfur content was previously determined by the standard method ASTM D4294. The method was successfully applied in three shale oil samples. The sulfur content in the investigated samples ranged from 1.0% (w/w) to 1.3% (w/w).

Chitosan: a new solution for removal of smear layer after root canal instrumentation.

AIM: To evaluate, by scanning electron microscopy (SEM), the efficacy of smear layer removal using chitosan compared with different chelating agents, and to quantify, by atomic absorption spectrophotometry with flame (AASF), the concentration of calcium ions in these solutions after irrigation. METHODOLOGY: The root canals of twenty-five canines were prepared using a crown-down technique and irrigated with 1% sodium hypochlorite. The teeth were randomly divided into groups (n = 5), according to the type of final irrigation: 15% EDTA, 0.2% chitosan, 10% citric acid, 1% acetic acid and control (without final irrigation). The total volume of each chelating solution was collected from the canals and analysed by AASF for quantification of calcium ions in the solutions. Then, the roots were split longitudinally and examined by SEM for evaluation of smear layer removal in the middle and apical thirds. Cleaning scores were attributed and analysed statistically using the Kruskal-Wallis and Dunn tests. The AASF data were analysed by one-way anova and Tukey-Kramer test. A significant level of α = 0.05 was adopted. RESULTS: 15% EDTA, 0.2% chitosan and 10% citric acid had similar smear layer removal capacity with a significant difference (P < 0.05) from 1% acetic acid and the control group. There was no significant difference (P > 0.05) between the smear layer remaining in the middle and apical thirds. The highest calcium ion concentration was observed with 15% EDTA (121.80 ± 5.13) and 0.2% chitosan (104.13 ± 19.23), with no significant difference. The lowest calcium ion concentration was obtained with 1% acetic acid (25.62 ± 7.68), whilst 10% citric acid (70.38 ± 11.15) had intermediate results, differing significantly from the other solutions (P < 0.01). CONCLUSIONS: 15% EDTA, 0.2% chitosan and 10% citric acid effectively removed smear layer from the middle and apical thirds of the root canal. 15% EDTA and 0.2% chitosan were associated with the greatest effect on root dentine demineralization, followed by 10% citric acid and 1% acetic acid.