目的 从水分活度（water activity，A_w）和水分子流动性2个角度，考察中药饮片全蝎的水分吸附特性和热力学性质，为其干燥和储存提供指导。方法 通过静态称重法测定全蝎饮片在25、35、45 ℃下的吸附等温线，采用6种常用的水分吸附数学模型（GAB、Peleg、BET、Smith、Henderson和Halsey）拟合试验数据，确定最佳模型，研究其吸附热力学性质，并结合低场核磁共振（low-field nuclear magnetic resonance，LF-NMR）技术对吸湿平衡状态下全蝎饮片中各状态的水分进行表征，阐明其吸湿特性。结果GAB模型为全蝎饮片吸附的最佳拟合模型，在25、35、45 ℃条件下其相对安全含水量分别为22.72%、22.35%和23.06%，绝对安全含水量分别为13.21%、12.27%和11.71%。全蝎饮片的净等量吸附热（net equivalent adsorption，q_st）和微分熵（differential entropy，S_d）都随着含水量的升高而降低。吉布斯自由能（Gibbs free energy，ΔG）为负，说明吸湿过程是自发的放热反应。样品在不同温度吸湿平衡时，T₂₁、T₂₂、T₂₃、T₂₄均代表样品水分子中质子的峰，其中T₂₁、T₂₂和T₂₃还包含了饮片中醛类、酯类等亲脂性成分中质子的信号。T₂₁随着A_w的升高不断右移转化为T₂₂、T₂₃、T₂₄，说明饮片中水分子流动性逐渐增大，存在结合水向自由水转化。当A_w＜0.6时结合水（A₂₁＋A₂₂）增加趋势并不明显，但当A_w＞0.6时结合水（A₂₁＋A₂₂）大幅度增加。结论 结合吸附等温线、吸附热力学性质和LF-NMR技术，建议以12%作为全蝎饮片的干燥终点含水量，研究结果可为其他中药饮片安全储藏含水量的确定提供参考。

Objective The water adsorption characteristics and thermodynamic properties of Scorpio were investigated from the perspectives of water activity (A_w) and water molecular fluidity, which provided guidance for their drying and storage. Methods The adsorption isotherms of Scorpio at 25, 35, and 45 ℃ were determined by static weighing method. Six commonly used moisture adsorption models (GAB, Peleg, BET, Smith, Henderson and Halsey) were used to fit the experimental data to determine the best model. The thermodynamic properties of the adsorption were studied. Combined with low-field nuclear magnetic resonance (LF-NMR), the moisture of each state in the Scorpio under the moisture absorption equilibrium state was characterized to clarify its moisture absorption characteristics. Results The GAB model was the best fitting model for Scorpio adsorption. At 25, 35, and 45 ℃, the relative safe water content was 22.72%, 22.35%, and 23.06%, and the absolute safe water content was 13.21%, 12.27%, and 11.71%, respectively. The net isosteric heat of sorption (q_st) and differential entropy (S_d) of Scorpio decreased with the increase of water content. The Gibbs free energy (ΔG) is negative, indicating that the moisture absorption process is a spontaneous exothermic reaction. When the samples were in moisture absorption equilibrium at different temperatures, T₂₁, T₂₂, T₂₃ and T₂₄ all represented the peaks of hydrogen protons in the water molecules of the samples, among which T₂₁, T₂₂ and T₂₃ also contained the signals of hydrogen protons in lipophilic components such as aldehydes and esters in the decoction pieces. With the increase of A_w, T₂₁ continuously shifted to the right and transformed into T₂₂, T₂₃ and T₂₄, indicating that the fluidity of water molecules in the decoction pieces gradually increased, and there was a conversion from bound water to free water. When A_w < 0.6, bound water (A₂₁ + A₂₂) did not increase significantly, but When A_w > 0.6, bound water (A₂₁ + A₂₂) increased significantly. Conclusion Combined with adsorption isotherms, adsorption thermodynamic properties and LF-NMR technology, it is recommended to use 12% as the drying end point water content of Scorpio. The research results can provide reference for the determination of safe storage water content of other traditional Chinese medicine decoction pieces.

R283.6

国家自然科学基金项目（81960715）；国家自然科学基金项目（82060715）；江西省重点研发计划项目（20223BBG71001）