A green method for determination of ethanol in homeopathic medicines using thermal infrared enthalpimetry.

In this work, a simple and fast method is proposed for the determination of ethanol in homeopathic medicines using thermal infrared enthalpimetry (TIE). Samples containing alcohol in a wide concentration range (from 5% to 95% v/v) were used. Purified water or absolute ethanol was added directly into homeopathic medicine and increase of temperature was monitored using an infrared camera. Total volume, stirring speed and dispensing rate of solutions were the most significant parameters studied for method optimization. A response surface methodology (RSM) was used for optimization of the experimental conditions. The method was validated in the following parameters: selectivity, linearity, linear range, precision (repeatability and intermediate precision), limit of detection and quantification, accuracy and robustness. Linear range was obtained from 4% to 55% (ethanol, v/v). The proposed method showed accuracy in agreement with the conventional one. The proposed method it was demonstrated a good alternative for determination of ethanol in homeopathic medicines, presenting low cost, fast analysis and agreement with the principles of green analytical chemistry.

Effect of simultaneous cooling on microwave-assisted wet digestion of biological samples with diluted nitric acid and O2 pressure.

The present work evaluates the influence of vessel cooling simultaneously to microwave-assisted digestion performed in a closed system with diluted HNO3 under O2 pressure. The effect of outside air flow-rates (60-190 m(3) h(-1)) used for cooling of digestion vessels was evaluated. An improvement in digestion efficiency caused by the reduction of HNO3 partial pressure was observed when using higher air flow-rate (190 m(3) h(-1)), decreasing the residual carbon content for whole milk powder from 21.7 to 9.3% (lowest and highest air flow-rate, respectively). The use of high air flow-rate outside the digestion vessel resulted in a higher temperature gradient between liquid and gas phases inside the digestion vessel and improved the efficiency of sample digestion. Since a more pronounced temperature gradient was obtained, it contributed for increasing the condensation rate and thus allowed a reduction in the HNO3 partial pressure of the digestion vessel, which improved the regeneration of HNO3. An air flow-rate of 190 m(3) h(-1) was selected for digestion of animal fat, bovine liver, ground soybean, non fat milk powder, oregano leaves, potato starch and whole milk powder samples, and a standard reference material of apple leaves (NIST 1515), bovine liver (NIST 1577) and whole milk powder (NIST 8435) for further metals determination by inductively coupled plasma atomic emission spectroscopy (ICP-OES). Results were in agreement with certified values and no interferences caused by matrix effects during the determination step were observed.