Analysis of occurrence state of moisture in different tobacco materials by low-field nuclear magnetic resonance

In order to find out the occurrence state of moisture in tobacco materials, the inversion spectra of spin-spin relaxation time (T₂) of cut strips, cut stems, cut reconstituted tobacco were analyzed by low-field nuclear magnetic resonance (LF-NMR). The effects of moisture content and microstructure of the tobacco materials on the relaxation time and peak area of relaxation signal of water molecules in T₂ inversion spectra were investigated as well. The results showed that:1) Within the moisture content range of 10%-35%, there typically existed 2-4 proton signal peaks in T₂ inversion spectra of tobacco materials, of which the T₂₁ peak having the relaxation time of 0.01-10 ms reflected the relaxation signal intensity of hydrogen proton of moisture. 2) With the increase of moisture content in tobacco materials, the relaxation time of peaks T₂₁ for cut strips, cut stems and cut reconstituted tobacco gradually increased from 0.183 to 1.430, from 0.166 to 1.560 and from 0.166 to 1.650 ms, respectively. It reflected that the augmentation of the proportion of active migration moisture. 3) A significant linear correlation existed between the T₂₁ relaxation peak area and the moisture content in tobacco material, it suggested that the T₂ inversion signal could be used in the quantitative analysis of moisture content in tobacco materials. 4) Once the pores larger than 30 μm in natural tobacco material were damaged, the relaxation time of moisture reduced significantly, it indicated that the occurrence state of moisture in natural tobacco material was obviously affected by its microporous structure.