Towards an autonomous microfluidic sensor for dissolved carbon dioxide determination

An optoelectronic flow-through detectors for active ingredients determination in the pharmaceutical formulations

An optoelectronic flow-through detector for active ingredients determination in pharmaceutical formulations is explained. Two consecutive compact photodetector's devices operating according to light-emitting diodes-solar cells concept where the LEDs acting as a light source and solar cells for measuring the attenuated light of the incident light at 180˚ have been developed. The turbidimetric detector, fabricated of ten light-emitting diodes and five solar cells only, integrated with a glass flow cell has been easily adapted in flow injection analysis manifold system. For active ingredients determination, the developed detector was successfully utilized for the development and validation of an analytical method for warfarin determination in pure and pharmaceutical preparations. The developed method is based on the forming of a white, turbid product as a result of a reaction between the warfarin and semicarbazide which was used as an oxidizing agent. The developed flow-through detector system is semi mechanized, economic in materials consumption, easy to operate and characterized by excellent analytical results. Both developed analytical devices used in two channels flow injection system allow for turbidimetric measurements of warfarin in 0.9-154 μg ml^-1 and 123-1600 μg ml^-1 ranges of concentration, with limits of detections 0.73 μg ml^-1 and 24.66 μg ml^-1 for photodetectors 1& 2 respectively. The turbidity measurement procedure for the current flow system offers to conduct 60 tests per hour of the warfarin which is the most needs of quality control analysis in industrial applications. To ensure the analytical usefulness of the flow system, the warfarin has been analyzed in the real samples with a fully acceptable agreement and a correlation between the results offered by the developed flow system and the official method.

Dissolved Carbon Dioxide Sensing Platform for Freshwater and Saline Water Applications: Characterization and Validation in Aquaculture Environments

A sensing configuration for the real-time monitoring, detection, and quantification of dissolved carbon dioxide (dCO₂) was developed for aquaculture and other applications in freshwater and saline water. A chemical sensing membrane, based on a colorimetric indicator, is combined with multimode optical fiber and a dual wavelength light-emitting diode (LED) to measure the dCO₂-induced absorbance changes in a self-referenced ratiometric scheme. The detection and processing were achieved with an embeded solution having a mini spectrometer and microcontroller. For optrode calibration, chemical standard solutions using sodium carbonate in acid media were used. Preliminary results in a laboratory environment showed sensitivity for small added amounts of CO₂ (0.25 mg·L⁻¹). Accuracy and response time were not affected by the type of solution, while precision was affected by salinity. Calibration in freshwater showed a limit of detection (LOD) and a limit of quantification (LOQ) of 1.23 and 1.87 mg·L⁻¹, respectively. Results in saline water (2.5%) showed a LOD and LOQ of 1.05 and 1.16 mg·L⁻¹, respectively. Generally, performance was improved when moving from fresh to saline water. Studies on the dynamics of dissolved CO₂ in a recirculating shallow raceway system (SRS+RAS) prototype showed higher precision than the tested commercial sensor. The new sensor is a compact and robust device, and unlike other sensors used in aquaculture, stirring is not required for correct and fast detection. Tests performed showed that this new sensor has a fast accurate detection as well as a strong potential for assessing dCO₂ dynamics in aquaculture applications.