CAS OpenIR
低场核磁共振在线控温分析系统的研制和应用
陈芳宇
Thesis Advisor李秀男, 李东侠
2020-07-01
Degree Grantor中国科学院大学
Degree Name博士
Degree Discipline化学工程
Keyword在线温控系统,横向弛豫时间,相转变,运动性,熔化温度
Abstract

低场核磁共振技术(LF-NMR)主要是以氢质子为探针研究分子间的迁移运动,在低场核磁共振检测分析中,常用横向驰豫时间T2反映分子的运动过程。通过测定样品中分子横向弛豫时间表征样品中的孔结构变化、溶胀和相转变等,实现无损、快速、动态实时的原位检测。由于低场核磁共振技术具有原位、快速、准确等优势,使其在生物材料、制药行业、食品安全以及高分子材料等多个领域具有广阔的应用前景。但是在实际应用中往往需要测定样品在不同温度下的状态,目前已有的LF-NMR无法实现对样品的在线控温,不能保证测定时样品温度的稳定性,而分子的结构和运动性会受到温度变化的影响。因此需要一种设备实现对样品精确控温的同时进行低场核磁的检测,以确保对样品检测的准确性。为准确测定温度变化对样品产生的影响,针对现有低场核磁共振系统无法对样品进行控温检测的问题,本文设计并研制了LF-NMR在线控温分析系统。该分析系统增加了样品控温装置,为保证控温系统的稳定性和控温精度,选用了具有抗干扰性的氟化液和光线材质的温度探头,并利用超级恒温循环水浴对样品槽进行控温。该控温分析系统可使样品检测过程中的检测精度达到±0.1℃,并且对样品的控温速率可以达到不低于1.2℃/min,同时保证了控温系统的稳定性,实现了LF-NMR在线控温分析系统对样品的在线控温。首先利用LF-NMR在线控温分析系统对不同品种的巧克力熔化过程进行了测定,研究了可可含量对脂肪运动性的影响,分析了可可、粗脂肪等含量对巧克力熔化温度的影响。在样品程序升温过程中,持续测定了巧克力中液体油分子运动的横向弛豫时间(T2),并对四个不同品牌巧克力的熔化过程进行了评价。最终得到的结果表明,四种不同品牌的黑巧克力样品的弛豫时间T2对液体油分子的运动都具有高敏感性,不同品种黑巧克力在熔化过程中,弛豫时间T2值随温度升高显著增加,且脂肪的运动性也增加,为巧克力熔化温度的测定提供了理论基础。同时,通过峰面积变化准确检测到巧克力的熔化温度,进而得出不同品牌巧克力的熔化温度随着可可含量以及粗脂肪含量的增加逐渐升高。构建了一种LF-NMR在线控温分析系统准确表征巧克力熔化温度的新方法,这对巧克力及其他软质食品的生产、加工、质量控制和保藏运输具有重要参考意义。利用LF-NMR在线控温分析系统进一步对温敏性壳聚糖水凝胶材料的胶凝化过程和胶凝温度进行了在线实时检测。首次采用LF-NMR在线控温分析系统原位表征温敏性壳聚糖水凝胶胶凝过程中水分子T2值的变化,从水分子运动的角度分析水凝胶的相转变机制。并结合另两种传统测量方法包括热重法差示扫描量热法(TG/DSC)、流变学方法对壳聚糖/b-甘油磷酸钠(CS/GP)温敏性水凝胶材料相转变过程和胶凝化温度进行了分析讨论。结果显示凝胶网络中不同水分所对应的T2对水凝胶的相转变过程非常敏感,凝胶的孔径会随着继续加热不断减小,同时水凝胶网络收缩使胶内水逐渐被挤出至胶外,且随着GP浓度的增加胶凝化温度点逐渐降低。此外,由于水分子的流动在溶胶-凝胶过程中的变化很大,与传统的测量方法DSC(RSD:1.2%–3.7%,n=5)和流变学(RSD:1.1%–2.3%,n=5)相比,LF-NMR测量更敏感、更准确(RSD≤ 0.1%, n=5)。综上所述,本文设计并研制了LF-NMR在线控温分析系统,并该系统分别对巧克力的熔化过程以及温敏性壳聚糖水凝胶的凝胶化过程进行了表征,从分子运动的角度对熔化过程和相转变行为机制进行了研究。并利用LF-NMR在线控温分析系统对巧克力熔化温度以及水凝胶相转变温度进行了测定,其非侵入性和非破坏性使测定结果具有更高的准确性和更好的重复性。由此可见,LF-NMR在线控温分析系统不仅为分子的结构变化以及相转变行为的表征提供一种有力的工具,而且从分子运动性变化的角度为巧克力的熔化温度和水凝胶的胶凝化温度的研究开拓了新的思路。LF-NMR在线控温分析实现了对样品精确控温的同时进行核磁共振检测,促进低场核磁共振技术更广泛的应用。;Low-field nuclear magnetic resonance technology (LF-NMR) mainly uses hydrogen protons as probes to study the mobility of molecules. In the analysis of low-field nuclear magnetic resonance,, the transverse relaxation time T2 is often used to reflect the movement of molecules. By measuring the relaxation time of the molecules to characterize the pore structure changes, swelling and phase transition in the sample, the LF-NMR enables non-destructive, fast, dynamic, real-time detection. Due to the advantages of the low-field NMR, it has broad application prospects in many fields such as biomaterials, pharmaceutical industry, food safety and polymer materials. In practical applications, it is often necessary to measure the state of the sample at different temperatures. The existing LF-NMR cannot achieve the online temperature control of the sample, it cannot guarantee the stability of the sample temperature during the measurement, and the structure and mobility of the molecule are affected by temperature changes. Therefore, there is a need for a device to perform accurate temperature control of the sample while detecting, which greatly improves the accuracy of the sample detection.In order to accurately meaure the effect of temperature changes on the sample, in view of the problem that the existing low-field nuclear magnetic resonance system cannot control the temperature of the sample, the LF-NMR online temperature control analysis system is designed and developed in this paper. The analysis system adds a sample temperature control device to ensure the stability and accuracy of the temperature control system. The anti-interference fluorinated liquid and temperature probe are selected, and the temperature of the sample tank is controlled by the super constant temperature circulating water bath. The temperature control analysis system can make the detection accuracy of the sample detection process reach ± 0.1 °C, and the temperature control rate of the sample can reach no less than 1.2 °C/min, while ensuring the stability of the temperature control system. The LF-NMR on-line temperature control analysis system was implemented to control the temperature of sample.Firstly, the LF-NMR online temperature control analysis system was used to measure the melting process of different varieties of chocolate. The effects of cocoa content on fat motility were studied, and the effects of cocoa and crude fat content on chocolate melting temperature were analyzed. During the sample program temperature increase, therelaxation time (T2) of the movement of liquid oil molecules in chocolate was continuously measured, and the melting processes of four different brands of chocolate were evaluated. The results show that the T2 of four different brands of dark chocolates were highly sensitive to the movement of liquid oil molecules. During the melting process of different varieties of chocolate, the T2 increases significantly with increasing temperature, which was consistent with the increase in fat motility, providing a theoretical basis for the determination of the melting temperature. At the same time, the melting temperature of chocolate was accurately detected through the change in peak area, and it was concluded that the melting temperature of different brands of chocolate gradually increased with the increase of cocoa content and crude fat content. A new method of LF-NMR on-line temperature control analysis system was constructed to accurately characterize the melting temperature of chocolate, which has important reference significance for the production, processing, quality control, storage and transportation of chocolate and other soft foods.The LF-NMR online temperature control analysis system was further detected the gelation process and gelation temperature of the temperature-sensitive chitosan hydrogel material in real time. The analysis system characterized the change of the T2 of water molecules during the gelation process of the temperature-sensitive chitosan hydrogel, and analyzed the phase transition mechanism of the hydrogel from the perspective of water molecule movement. Combined with two other traditional measurement methods including thermogravimetric differential scanning calorimetry (TG/DSC) and rheological methods to analyze the phase transition process and gelation temperature of the chitosan/β-glycerophosphate (CS/GP) temperature-sensitive hydrogel materials. The results show that T2 was very sensitive to the phase transition of the hydrogel, and the pore size of the gel will continue to decrease with continued heating. At the same time, the water inside the hydrogel network will gradually squeeze out of the gel, and the gelation temperature will gradually decrease as the GP concentration increases. Moreover, as the mobility of water molecules varies greatly during the sol-gel phase transition, the LF-NMR measurement was more sensitive and accurate (RSD ≤ 0.1%,n = 5) compared with DSC (RSD: 1.2%–3.7%,n = 5) and rheology (RSD: 1.1%–2.3%,n = 5).In summary, this paper designed and developed an LF-NMR online temperature control analysis system, and the system was used to characterize the melting process of chocolate and the gelation process of temperature-sensitive chitosan hydrogel respectively. From the perspective of molecular motion, the melting process and the behavior mechanism of phase transition were studied. The system measured the melting temperature of chocolate and the phase transition temperature of hydrogel. Its non-invasive and non-destructive properties make the measurement result more accurate and repeatable. It can be seen that the LF-NMR online temperature control analysis system not only provides a powerful tool for the structural change of molecules and the characterization of phase transition behavior, but also the new research ideas have been opened for the research on the melting temperature of chocolate and the gelation temperature of hydrogels. LF-NMR on-line temperature control analysis realizes accurate temperature control of samples while performing nuclear magnetic resonance detection, which will promote the application of low-field nuclear magnetic resonance technology. 

Language中文
Document Type学位论文
Identifierhttp://ir.ipe.ac.cn/handle/122111/49738
Collection中国科学院过程工程研究所
Recommended Citation
GB/T 7714
陈芳宇. 低场核磁共振在线控温分析系统的研制和应用[D]. 中国科学院大学,2020.
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