Ihwg-μnir: A Miniaturised Near-infrared Gas Sensor Based On Substrate-integrated Hollow Waveguides Coupled To A Micro-nir-spectrophotometer.

A miniaturised gas analyser is described and evaluated based on the use of a substrate-integrated hollow waveguide (iHWG) coupled to a microsized near-infrared spectrophotometer comprising a linear variable filter and an array of InGaAs detectors. This gas sensing system was applied to analyse surrogate samples of natural fuel gas containing methane, ethane, propane and butane, quantified by using multivariate regression models based on partial least square (PLS) algorithms and Savitzky-Golay 1(st) derivative data preprocessing. The external validation of the obtained models reveals root mean square errors of prediction of 0.37, 0.36, 0.67 and 0.37% (v/v), for methane, ethane, propane and butane, respectively. The developed sensing system provides particularly rapid response times upon composition changes of the gaseous sample (approximately 2 s) due the minute volume of the iHWG-based measurement cell. The sensing system developed in this study is fully portable with a hand-held sized analyser footprint, and thus ideally suited for field analysis. Last but not least, the obtained results corroborate the potential of NIR-iHWG analysers for monitoring the quality of natural gas and petrochemical gaseous products.

Determinação espectrofotométrica de hexametilenotetramina (HMT) em medicamentos, utilizando ácido cromotrópico e forno de micro-ondas

This paper proposes a methodology for spectrophotometric determination of hexamethylenetetramine (HMT) by using chromotropic acid in a phosphoric acid media employing a domestic microwave oven as a source of heating. The reddish-purple soluble product is quantitatively formed after 30 s of irradiation and obeys the Beer´s law in the range between 0.1-1.2 mg L-1 HMT (r = 0.99925). The method was applied successfully in commercial pharmaceutical preparations containing dyes in their composition. The results showed that the method proposed is feasible for simplicity, speed, low cost, precision and accuracy when compared with United States Pharmacopeia official method.