High signal to noise ratio in low field NMR on chip, simulations and experimental results

A μfluidic chip with integrated microcoil was developed for nuclear magnetic resonance (NMR) spectroscopy on limited volume samples (nanoliters range). This chip will be used for the online monitoring of micro chemical reactions. Design rules for the microcoil to achieve the best signal to noise ratio (SNR) were obtained by finite element simulation. For pure water in a low field NMR magnet (60 MHz., i.e. 1.4 Tesla) a SNR of 550 was achieved which is to our knowledge higher than any other μfluidic chip with integrated detection coil. It is also shown that a spectral resolution of 0.025 ppm is obtained when a microchannel with an arbitrary cross section is placed parallel to the magnetic field. A high SNR at low magnetic field for small volume samples is essential for the development of portable NMR systems where mini permanent magnets of 1 Tesla are used.