Development of the Earth’s Field NMR Spectrometer for Liquid Screening

Earth’s field nuclear magnetic resonance (NMR) can be used for non-destructive in-bottle liquid screening by evaluating the spin–lattice relaxation times of protons in various liquids. An Earth’s field NMR apparatus has been developed and optimized to measure the spin–lattice relaxation times of various liquids contained in 500 ml PET bottles. Two methods to generate 90-degree readout pulses using transient oscillating signals generated in a resonator are reported. The lower detection limit of pure water was 1 ml. The minimum measurable spin–lattice relaxation time was 50 ms.