Flow through FTIR sensor based on solid phase spectroscopy (SPS) on conventional octadecyl (C18) silica

The concept of a novel FTIR flow through sensor based on rigid silica C18 particles placed in a mid-IR flow cell is presented applied to the example of caffeine determination in soft drinks. The system is based on a standard flow cell equipped with two polyethylene spacers of different size that yield a gap inside the assembled flow cell. Particles of appropriate size (<25 μm diameter) suspended in methanol are pumped into the assembled flow cell where the particles are retained at the gap formed by the two spacers. Using an automated sequential injection system, pre-conditioning, sample–sensor interaction and sorbent regeneration can be performed in a highly reproducible way. The characterization and validation results clearly demonstrate the capability of the developed flow through FTIR sensor to determine non-polar molecules, such as caffeine, at the parts per million level, with a linear range from 1.8 to 115 mg L−1, a precision expressed as R.S.D. of 4.1% and a sample throughput of approximately 10 samples/h. Furthermore, the sensor has the potential to be easily adapted to the analysis of polar, non-polar, cationic and anionic molecules by changing the solid support, providing interesting possibilities for the development of new applications in the trace analysis of organic molecules.