Beyond Karl Fischer titration: a monolithic quantum cascade sensor for monitoring residual water concentration in solvents

Beyond Karl Fischer titration: a monolithic quantum cascade sensor for monitoring residual water concentration in solvents

Článek WoS

Quality control of liquids is an important part of analytical chemistry. The gold standard for measuring residual water in organic solvents and pharmaceutical applications is Karl Fischer titration. It has a high sensitivity, selectivity and accuracy. The downsides are a time-consuming offline analysis, together with the need for toxic reagents producing waste, and it suffers from poor inter-laboratory reproducibility. In this work, we present a high-performance lab-on-a-chip sensor exploiting mid-IR spectroscopy for liquid sensing. It is operating at 6.1 mu m wavelength and is suitable for robust and flexible real-time in situ analysis of the residual water concentration in isopropyl alcohol. This is demonstrated in two experiments. A custom-made 60 mu L flow cell is employed to measure only minute amounts of analyte in an inline configuration. In a second approach, the whole sensor is immersed into the analyte to demonstrate sensitive and rapid in situ operation on the millisecond time scale. This is confirmed by the ability for time resolved single water-droplet monitoring, while they are mixed into the liquid sample. We obtain a limit of detection between 120 ppm and 150 ppm with a concentration coverage spanning three orders of magnitude from 1.2 x 10(-2)%(vol) to 25%(vol) for the flow cell and 1.5 x 10(-2)%(vol) to 19%(vol) in the in situ configuration, respectively.

Quality control of liquids is an important part of analytical chemistry. The gold standard for measuring residual water in organic solvents and pharmaceutical applications is Karl Fischer titration. It has a high sensitivity, selectivity and accuracy. The downsides are a time-consuming offline analysis, together with the need for toxic reagents producing waste, and it suffers from poor inter-laboratory reproducibility. In this work, we present a high-performance lab-on-a-chip sensor exploiting mid-IR spectroscopy for liquid sensing. It is operating at 6.1 mu m wavelength and is suitable for robust and flexible real-time in situ analysis of the residual water concentration in isopropyl alcohol. This is demonstrated in two experiments. A custom-made 60 mu L flow cell is employed to measure only minute amounts of analyte in an inline configuration. In a second approach, the whole sensor is immersed into the analyte to demonstrate sensitive and rapid in situ operation on the millisecond time scale. This is confirmed by the ability for time resolved single water-droplet monitoring, while they are mixed into the liquid sample. We obtain a limit of detection between 120 ppm and 150 ppm with a concentration coverage spanning three orders of magnitude from 1.2 x 10(-2)%(vol) to 25%(vol) for the flow cell and 1.5 x 10(-2)%(vol) to 19%(vol) in the in situ configuration, respectively.

FT-IR; ORGANIC-SOLVENTS; WAVE-GUIDES; IN-VITRO; SPECTROSCOPY; TEMPERATURE; LASER

FT-IR; ORGANIC-SOLVENTS; WAVE-GUIDES; IN-VITRO; SPECTROSCOPY; TEMPERATURE; LASER

PILAT, F.; SCHWARZ, B.; BAUMGARTNER, B.; RISTANIC, D.; DETZ, H.; ANDREWS, A.; LENDL, B.; STRASSER, G.; HINKOV, B.

2024

28.03.2023

Royal Society of Chemistry

CAMBRIDGE

1473-0189

Lab on a chip

23

7

Spojené království Velké Británie a Severního Irska

1816

1824

9

https://pubs.rsc.org/en/content/articlelanding/2023/LC/D2LC00724J

http://hdl.handle.net/11012/213677

d2lc00724j