Bruna Tischer

Determination of toxic elements in tricyclic active pharmaceutical ingredients by ICP-MS: a critical study of digestion methods

The determination of As, Cd, Hg and Pb in tricyclic active pharmaceutical ingredients (APIs) was performed by ICP-MS after digestion by both combustion and wet digestion methods. Carbamazepine was digested using the dry ashing method recommended in United States Pharmacopeia 35th edition and significant losses of analytes were observed in recovery tests (38.0 ± 8.9, 99.5 ± 7.1, and 89.4 ± 6.3% of recovery for As, Cd and Pb, respectively). Mercury was completely lost by volatilization during digestion. The digestion of carbamazepine, amitriptyline hydrochloride and imipramine hydrochloride by microwave-assisted wet digestion in closed vessels (MW-AD) was not effective and a yellow-orange solid residue was observed for all substances. 1H NMR of the carbamazepine residue indicated the nitration of carbamazepine aromatic rings forming stable nitro compounds. High pressure asher digestion systems were also used and solid residues were observed for carbamazepine and amitriptyline hydrochloride even under drastic digestion conditions (280 °C, 120 min). A complete digestion of all substances was obtained only by the use of high temperature and long time of digestion and reduction of sample mass to 0.08 g (320 °C, 180 min). The microwave-induced combustion (MIC) method for digestion of tricyclic APIs allowed the digestion of 0.5 g of all substances with high efficiency (RCC lower than 1%) using diluted nitric acid as absorbing solution (7 mol l−1). The recoveries using this method were between 94 and 103% for the evaluated elements. The low RCC and acidity of digests obtained using MIC allowed the compatibility with ICP-MS and makes MIC a promising alternative as a sample preparation method for subsequent determination of toxic elements in APIs by ICP-MS.

Infrared Thermal Imaging: A Tool for Simple, Simultaneous, and High-Throughput Enthalpimetric Analysis

In this work, the feasibility of infrared thermal imaging (ITI) is demonstrated to show its potential application in analytical chemistry. A system of ITI was combined with disposable microplates to perform enthalpimetric analysis, which was selected as an example in order to show the reliability of this method. In this way, the novel thermal infrared enthalpimetry (TIE) method was evaluated in neutralization, precipitation, redox, and complexation reactions, with a multichannel pipet for adding the reagent and an infrared camera to monitor the temperature of multiple reactions (up to 24 simultaneous reactions) in a contactless way. Analytical signals were obtained in only 10 s, and the difference in temperature (ΔT) before and after the reaction was used for the construction of calibration curves by use of reference solutions. More than 10,000 values were considered for the temperature determination for each reaction. The proposed method was applied for determination of the total acidity of vinegar as well as the chloride, iron, and calcium content of pharmaceuticals. The results were compared with those from conventional techniques (titration), and agreement between 96% and 101% was obtained. Sample throughput could even reach thousands of samples analyzed in 1 h. These preliminary results demonstrate the important features of TIE and possible application for other matrices and analytical parameters. The proposed TIE could be spread to cover other enthalpimetric techniques, different reactors (e.g., microfluidic and paper analytical devices), and portable devices, thus reaching other fields of chemistry.

Rapid microplate, green method for high-throughput evaluation of vinegar acidity using thermal infrared enthalpimetry

Infrared thermal imaging was combined with disposable microplates to perform enthalpimetric analysis using an infrared camera to monitor temperature without contact. The proposed thermal infrared enthalpimetry (TIE) method was used to determine the total, fixed and volatile acidities of vinegars. Sample preparation and analysis were performed in the same vessel, avoiding excessive sample handling and reducing energy expenditure by more than ten times. The results agreed with those of the conventional method for different kinds of vinegars, with values of 1.7%, and 2.3% for repeatability and intermediate precision, respectively. A linear calibration curve was obtained from 0.040 to 1.30molL(-1). The proposed method provided rapid results (within 10s) for four samples simultaneously, a sample throughput of up to 480 samples per hour. In addition, the method complies with at least eight of twelve recommendations for green analytical chemistry, making TIE a promising tool for routine vinegar analysis.

One-Shot, reagent-free determination of the alcoholic content of distilled beverages by thermal infrared enthalpimetry

A simple and fast method is proposed for determining the alcoholic content of distilled beverages by thermal infrared enthalpimetry (TIE), in which purified water is added directly and the temperature rise caused by the heat of dilution is monitored using an infrared camera. A calibration curve was constructed with hydroalcoholic reference solutions to determine the alcoholic content of vodka, whisky, and cachaça. The influence of the total volume of solutions in the reactor, the stirring speed, the dispensing rate, and the ratio between hydroalcoholic samples and water were evaluated to reach an optimum mixture and provide low variation among measurements. Optimized conditions for those respective parameters were 2.4mL, 200rpm, 0.57mLs-1, and 1:1. To evaluate the accuracy, alcoholic content was also determined by a conventional method (AOAC method 942.06, pycnometry), with agreement ranging from 99.4% to 100.9%. No sample preparation (e.g., dilution or distillation) was required with the proposed method, decreasing the time required for analysis by at least one order of magnitude. The proposed method required less energy consumption by a factor of about three thousand in comparison with the conventional method. The proposed TIE method was robust, able to determine the alcoholic content of diverse distilled beverages. Due to these features and the high sample throughput (up to 480 samples per hour), the proposed method could be considered suitable for routine analysis and agrees with the principles of green analytical chemistry.

Green and fast determination of the alcoholic content of wines using thermal infrared enthalpimetry

An innovative use of thermal infrared enthalpimetry (TIE) is proposed for the determination of alcoholic content of red and white wines. Notwithstanding the presence of ethanol in beverages, absolute ethanol was added directly to wines, and the temperature rise caused by the heat of dilution was monitored using an infrared camera. Analytical signals were obtained in only 10 s for four samples simultaneously, and a calibration curve was constructed with hydroalcoholic reference solutions. A linear calibration curve was obtained from 3.0 to 18.0% (v/v) ethanol (R2 = 0.9987). The results showed agreement ranging from 98.2 to 104.0% with 942.06 and 969.12 methods of AOAC. Organic compounds (e.g., sugar) did not interfere in the determinations. The proposed method provided fast results, with a throughput of 480 samples per hour and negligible energy consumption (0.001 kWh). In addition, the consumption of reagents was reduced when compared with conventional method fulfilling green analytical chemistry requirements.