Daniele de Freitas Ferreira

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.

Miniaturized, high-throughput and green determination of the saponification value of edible oils using thermal infrared enthalpimetry

Saponification value (SV) is one of the parameters used to evaluate the quality of edible oils, and it is determined by titration after heating the oil with KOH solution. This method is time-consuming, and requires a high amount of reagents and energy to perform the analysis. In the present study, the determination of SV is proposed using thermal infrared enthalpimetry (TIE) in a high-throughput and green way. Sample preparation and determination steps were performed in the same vessel (polypropylene microplate), which was adapted for the simultaneous preparation of 24 samples and determination of the remaining KOH by TIE. Optimization of parameters such as sample mass, heating time, stirring speed and dispensing rate was performed and the best conditions found were 120 mg, 5 h, 250 rpm and 0.57 mL s−1, respectively. Subsequently, the SVs of canola, corn, olive, rice, soy and sunflower oils were determined by TIE and the results were compared with those obtained by AOAC 920.160; no statistical differences were found (Students t-test, p > 0.05). A decrease in the sample mass and reagent consumption of up to 41 times was observed. Additionally, TIE allowed a sample throughput of at least two orders of magnitude higher than the conventional method, showing its feasibility for routine analysis. In addition, a reduction in energy consumption of 625 times was observed. Therefore, the proposed TIE method allowed the determination of the SVs of edible oils in a simple and high-throughput way in accordance with the principles of green analytical chemistry.