B. Baumgartner, S. Freitag, C. Gasser, B. Lendl:
"A pocket-sized 3D-printed attenuated total reflection-infrared filtometer combined with functionalized silica films for nitrate sensing in water";
Sensors and Actuators B: Chemical, 310 (2020), S. 127847.

Kurzfassung englisch:
Strong anion-exchange materials carry a positive charge that allows them to trap and concentrate anions while
releasing other anions. Here, we introduced a quaternary ammonium anion exchange group into mesoporous
silica films coated on attenuated total reflection (ATR) crystals to enrich nitrate from aqueous phase in the
volume probed by the evanescent field. The ion-exchange and enrichment capabilities of the films were characterized
using FTIR spectroscopy. Thereby fast analyte enrichment and full sensor recovery were observed. In
addition, high enrichment factors of up to 1600 were achieved. After characterization, these coated ATR crystals
were used in a dedicated ATR-IR filtometer comprising a Fabry-Pérot filter detector unit and a miniaturized
thermal emitter with a overall dimensions of only 80mm×120mm×70 mm. The filter covered the spectral
region between 1250-1800 cm−1 allowing for recording IR spectra of nitrate enriched into the mesoporous silica
film. The sensor was calibrated using the Langmuir adsorption model as calibration function. From this a limit of
detection of 1.2 mg L−1 was derived for the ATR-IR filtometer. This emphasizes the high potential of functionalized
mesoporous silica films combined with low-cost filtometers for portable water sensors.

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