Effect of flow on the apparent transverse relaxation time in a microfluidic nuclear magnetic resonance chip

The detection of samples in a microfluidic nuclear magnetic resonance chip is generally performed under flow condition. To study the effect of sample flow on the apparent transverse relaxation time in a microfluidic nuclear magnetic resonance chip, theoretical calculations were performed on three microfluidic samples (including deionized water, absolute ethanol, and copper sulfate pentahydrate) for flow velocities in the range 1.7–25?mm/s. A microfluidic nuclear magnetic resonance device with a low cost microfluidic solenoid coil was fabricated to verify the theoretical calculations by experiments. The results show that the apparent transverse relaxation time of the sample is a monoexponential decay with respect to flow velocity. In addition, it was found that the experimental values and the theoretical values of the apparent transverse relaxation time are identical when the samples are prepolarized completely; but for the samples that are not prepolarized completely, all the experimental values are smaller than the theoretical values and their difference increases with the flow velocity of the sample. After further study, it was discovered that the relative error between the experimental values and the theoretical values is a monoexponential decay to the level of the sample to be prepolarized. This discovery is very useful, because it can be used to modify the theoretical calculation model of the apparent transverse relaxation time for the samples that are prepolarized incompletely, as well as improve the application of microfluidics on nuclear magnetic resonance.