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 mu m 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. (C) 2008 Elsevier B.V. All rights reserved.