Simultaneous quantitation of water and residual solvents in pharmaceuticals by rapid headspace gas chromatography with thermal conductivity detection (GC-TCD)

Diphenyl imidazole-based fluorescent chemosensor for Al3+ and its Al3+ complex toward water detection in food products

A sophisticated fluorescent chemosensor, 2-(4-nitrophenyl)-4,5-diphenyl-1H-imidazole (NPDI), was designed and synthesized through a one-step condensation reaction. NPDI exhibited a fluorescence enhancement response toward Al3+, accompanied by significant emission color change without interference from other tested metal ions. The binding stoichiometry and mechanism was corroborated using various techniques. The limit of detection (LOD) for Al3+ could reach 7.25 × 10-8 mol/L and the binding constant was found to be 1.47 × 105 L/mol. Furthermore, the in-situ formed NPDI·Al complex functioned a secondary chemosensor for water by quenching effect. The fluorescence quenching mechanism could be attributed to hydrogen bonding interaction of nitro substituent with water. The LOD was calculated to be 0.012 %, indicating NPDI·Al heightened sensitivity to water. Additionally, NPDI·Al complex was employed for the moisture detection in the surroundings. Finally, the practical application of NPDI·Al complex had been successfully used in the determination of water content in food products.

Microcantilever-Based In Situ Temperature-Programmed Desorption (TPD) Technique

Temperature-programmed desorption (TPD) is an essential technique for characterizing the fundamental properties of advanced catalysts like catalytic activity and kinetics. However, the available TPD instruments are bulky and use ex situ detectors to measure the probe molecules in the elution gas flow. Herein, we demonstrate an in situ TPD technique by developing a silicon microcantilever that integrates functional elements for mass measuring and programmable sample heating. An only nanogram-level sample is required to load on the microcantilever free end, where the integrated microheater provides programmed temperatures and the desorption-induced mass change can be measured in situ. In situ TPD can continuously measure the number of desorbed molecules from the catalyst during programmed heating, without the need for ex situ detectors. With a single-time in situ TPD measurement, the desorption activation energy can be directly calculated. The proposed in situ TPD method outperforms the existing TPD techniques and is expected to enable next-generation TPD applications.

Full evaporation headspace gas chromatography with thermal conductivity detection for the direct determination of water in solid pharmaceutical bulk products

Headspace gas chromatography (HS-GC) has the potential to be used for water determination in pharmaceutical products. In this article, its use for the determination of water in solid samples is explored without the need of dissolution by means of the full evaporation technique (FET). This way, water is thermally removed from a small amount of sample which is directly weighed in the vial. This simplifies considerably the method since no diluent has to be searched and HS saturation is avoided. Blank corrections were performed to compensate for atmospheric moisture variation. Moreover, the performance of mass spectrometry (MS) and thermal conductivity detection (TCD) was compared. The method showed excellent figures of merit when working with TCD, such as R²> 0.99 and RSD< 5% for each level of the calibration curve. Eight samples were carefully studied at different equilibration temperatures to find the optimal working conditions for each case and the results were compared to the ones obtained by Karl Fischer titration (KFT). Both methods showed restrictions and proper case by case optimization/validation turned out to be mandatory. Hyphenation with a flame ionization detector (FID) in series with the TCD showed the benefit to be useful for testing residual solvents (RS) simultaneously.

Highly Sensitive Water Detection Through Reversible Fluorescence Changes in a syn-Bimane Based Boronic Acid Derivative

Reported herein is a fluorometric and colorimetric sensor for the presence of trace amounts of water in organic solvents, using syn-bimane based boronate ester 1. This sensor responds to the presence of water with a highly sensitive turn-off fluorescence response, with detection limits as low as 0.018% water (v/v). Moreover, analogously high performance was observed when compound 1 was adsorbed on filter paper, with the paper-based sensor responding both to the presence of liquid water and to humid atmospheres. Reusability of the paper-based sensor up to 11 cycles was demonstrated, albeit with progressive decreases in the performance, and 1H NMR and mass spectrometry analyses were used to explain the observed, hydrolysis-based sensor response.

Ethanol Biofuel Cells: Hybrid Catalytic Cascades as a Tool for Biosensor Devices

Biofuel cells use chemical reactions and biological catalysts (enzymes or microorganisms) to produce electrical energy, providing clean and renewable energy. Enzymatic biofuel cells (EBFCs) have promising characteristics and potential applications as an alternative energy source for low-power electronic devices. Over the last decade, researchers have focused on enhancing the electrocatalytic activity of biosystems and on increasing energy generation and electronic conductivity. Self-powered biosensors can use EBFCs while eliminating the need for an external power source. This review details improvements in EBFC and catalyst arrangements that will help to achieve complete substrate oxidation and to increase the number of collected electrons. It also describes how analytical techniques can be employed to follow the intermediates between the enzymes within the enzymatic cascade. We aim to demonstrate how a high-performance self-powered sensor design based on EBFCs developed for ethanol detection can be adapted and implemented in power devices for biosensing applications.