Infrared thermal imaging combined with paper microzone plates and natural reagent extracts for simple, fast, and green enthalpimetric analysis

Combining In-Tip Reaction and Infrared Thermal Imaging for Fast and Portable Enthalpimetric Analysis

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.

Open source, low-cost device for thermometric titration with non-contact temperature measurement

This work proposes a simple device for thermometric titration using a contactless sensor. A low-cost infrared sensor (around $5) was adapted in a disposable, polystyrene vessel for monitoring the temperature to determine the endpoint of neutralization, redox, and complexation titrations, using a homemade syringe pump to titration control. Open-source software was developed to control the device using the Raspberry Pi platform and to perform automatic endpoint determination. The influence of sample volume, the flow rate of titrant, and sensor distance from the solution were evaluated to lower the variation among measurements. The parameters chosen in this regard were 10 mL of sample, 0.8 mL min^-1 of titrant solution flow rate, and 3 cm of distance from the sensor to the solution. Results for the determination of the acidity of sauces and the ascorbic acid and calcium content of pharmaceutical products were compared with those from official compendia. The performance of the sensor also was compared with an infrared camera. The proposed method agreed with conventional ones to an extent ranging from 93% to 106%. The robust analytical performance and low cost of the system are essential features that could broaden the use of enthalpimetric analysis in several laboratories.