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Nuclear magnetic resonance (NMR) as the method of express-determination of water and oil content in sunflower, soybean, cotton seeds, groundnut and rape seeds has several advantages in comparison with other techniques. NMR allows to minimize the total duration and cost of the analysis keeping exactness and reproducibility of the results without frequent recalibration. NMR also provides ecological purity of the analysis. NMR as method of seeds analysis is included in the following standards:
- GOST R 8.620-2006 (in Russia)
- ISO/CD 10565 (in Europe)
Mass portions of water and oil in seeds are evaluated based on determination of contribution of oil and water fractions in NMR signal.
Fig. 1. "FID - spin echo" pulse sequence
First 900 RF pulse excites all hydrogen nuclei of a sample. The amplitude of Free Induction Decay (AFID) immediately after the 900 RF pulse is proportional to the total oil plus water content. Second 1800 RF pulse excites the spin system again, but the amplitude of the spin echo signal (Aecho) after second pulse is proportional to the oil content only. Water content can be obtained by subtraction spin echo amplitude from initial FID amplitude. NMR arbitrary units allow calculation oil and water content in grams or in percents using precision calibration curves.
TD-NMR spectrometer Spin Track from Resonance Systems Ltd. fulfils requirements of ISO/CD 10565 and provides high precision and reproducibility of measurements.
Characteristics of measurements*:
|Oil content, %||5-60||0.5||0.2|
|Moisture content**, %||5-10||0.5||0.2|
*Sample volume - 45 ml, analysis duration not more than 2 min.
**Usage of additional hardware increases valuable moisture range up 30%.
The procedure of calibration can be performed using the set of original calibration samples developed by Resonance Systems Ltd.