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.
Sample preparation and determination steps were performed in microplates using infrared thermography for the residual KOH determination (heat of neutralization).
In
this work, the in-tip thermal infrared enthalpimetry (in-tip
TIE) method is proposed for fast enthalpimetric analysis. In this
method, the reactions inside the tips of a multichannel pipette were
combined with temperature monitoring by an infrared camera. The filter
paper was used inside the tips to retain reagents as solutions (wetted
paper mode) or as solids (dried paper mode) to perform neutralization,
redox, or precipitation reactions. The dried reagents inside the tips
were obtained by oven drying a solution retained in the filter paper.
The determination of the total acidity of the vinegar, ascorbic acid
in vitamin C tablets, and chloride in soy sauces and saline inhalation
solutions was performed as examples of the application of the proposed
method. The agreement with reference methods ranged from 98 to 107%.
The use of reagents dried inside the tip was feasible, leading to
a simple aspiration of sample solution within the 12 tips of the pipette
to perform a rapid analysis (1 min). Therefore, up to 720 measurements
in 1 h were feasible for in-tip TIE over up to 12 measurements for
the reference methods. Moreover, miniaturization reduced reagent consumption
and residue generation. For example, for in-tip TIE, only 3.6 mL of
residues was generated (n = 12) over 60–240
mL in reference methods (n = 3). Contrarily to other
TIE methods, no microplates or stirring was required, opening possibilities
for field analysis since the multichannel pipette and the infrared
camera are both operated with batteries.
RESUMO -Este trabalho aborda a obtenção de um co-produto de abacaxi por meio do estudo da secagem da casca do fruto para obtenção de matéria prima para produção de chá. Os objetivos foram avaliar os efeitos da temperatura e velocidade do ar na secagem da casca de abacaxi em secador de leito fluidizado e na aceitação sensorial do chá. O processo de secagem seguiu um planejamento experimental 2² com três repetições no ponto central, cujas variáveis independentes foram temperatura (70 a 90 ºC) e velocidade do ar (8 a 10 m/s). O chá foi preparado por infusão a 100 ºC, sendo avaliado por teste de aceitação por 63 consumidores quanto à impressão global, cor, aroma e sabor, utilizando a escala hedônica estruturada de nove pontos. A temperatura do ar apresentou efeito negativo significativo sobre a umidade final do produto seco, ao nível de 95% de confiança, que atingiu teores entre 3% e 10% após 90 minutos de secagem. Nenhum dos atributos sensoriais avaliados sofreu efeito significativo pelas variáveis independentes, a 95% de confiança. Contudo, os resultados da aceitação sensorial indicaram que todas as formulações de chá elaboradas foram bem apreciadas pelos consumidores, apresentando médias hedônicas próximas a "gostei moderadamente" para impressão global, cor e aroma e acima de "gostei ligeiramente" para o sabor.
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