Unilateral NMR Sensor to Monitor Dairy Products
- 1. Niumag Corporation, Suzhou, China
- 2. Shanghai University of Medicine and Health Science, Shanghai, China
- 3. Schlumberger-Doll Research, Cambridge, United States
Motivation: Unilateral NMR based sensor can be advantageous in monitoring product quality noninvasively without sample pre-treatment. This ability is highly desirable to detect milk product physical parameters fast and effectively in order to monitor the quality of packaged dairy products.
Methods: We will discuss the magnetic design in order to achieve the desired depth of investigation to meet the application requirement, the objectives of the RF field need and the design planar RF coil and probe for performing NMR under non-uniform magnetic field,. The design and build of the entire unilateral NMR system will be described.
Results：The NMR system is capable of high-power pulses (90špulse width of 2.5us), a short system dead time (10us), and the shortest echo time of 30 us. We have used the SGSE-CPMG (Static-Gradient-Spin-Echo-CPMG) pulse sequence to acquire signals from a 5-mm depth of investigation with a constant field gradient about 2.8T/m. This field gradient is also used to measure diffusion coefficients. Using this system and SGSE-CPMG sequence we have shown to rapidly detect common forms of milk adulteration and to monitor the freshness of yogurt sold in a box. We found an exponential relationship between the T2 relaxation time of milk water and adulteration mass concentration. We also observed a significant increase of T2 of yogurts after the expiration date thus NMR T2 can be an effective means to quantify the freshness of yogurt in the intact packaging.
