Development and Determination of Reference Material for Glycerol Trioleate/Glycerol Tristearate Solid Fat Content
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摘要: 固体脂肪含量是描述可可脂、人造黄油等油脂的重要质量指标。低场核磁共振法由于具有简单、快速、无需化学试剂等优点,已逐渐成为测量固体脂肪含量的主流手段。低场核磁共振直接法是一种相对测量方法,需要使用三油酸甘油酯/三硬脂酸甘油酯混合物对仪器进行校准、溯源。本文介绍了低场核磁共振及测量固体脂肪含量的原理,研究了三油酸甘油酯/三硬脂酸甘油酯混合物的固体脂肪含量的定值溯源路径,研究了其在不同温度下的稳定性,分析了混合油管在不同温度条件下测量不准确的原因,并最终确定了标准物质的定值方法与温度。Abstract: Solid fat content (SFC) is an important quality indicator for describing fats and oils, such as cocoa butter and margarine. Low-field nuclear magnetic resonance (NMR) has become the mainstream method for measuring SFC due to its simplicity, speed, and lack of chemical reagents. The low-field NMR direct method is a relative measurement method that requires calibration and traceability of the instrument using a mixture of glycerol trioleate and glycerol tristearate. This paper introduces the principles of low-field NMR and SFC measurement, studies the traceability path of SFC for the glycerol trioleate/glycerol tristearate mixture, investigates its stability at different temperatures, analyzes the reasons for inaccurate measurement of mixed oil tubes at different temperature conditions, and finally determines the calibration method and temperature of the reference materials.
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表 1 塑料/油管的均匀性
Table 1. The homogeneity of the plastic-in-oil tube
管1 管2 管3 管4 平均SFC 28.0% 43.3% 56.0% 72.0% 标准偏差 0.2% 0.2% 0.2% 0.1% 表 2 不同温度下低场核磁共振间接法的SFC测量结果
Table 2. Measurement results of SFC at different temperature by LFNMR direct method
温度/℃ SFC/% SFC/% SFC/% SFC/% SFC/% SFC/% 配制值 0.0 20.5 35.0 51.2 70.6 86.8 10 0.2 23 37.9 56.8 75.1 89.7 20 0.3 22.2 37.1 55.4 73.7 89.4 32 0 21.4 36.1 54.1 72.3 88.7 表 3 标准物质候选物定值结果
Table 3. Certification result of the reference material candidates
重复次数 B管SFC C管SFC 重复次数 B管SFC C管SFC M1 33.56% 69.98% N1 33.63% 69.88% M2 33.79% 70.00% N2 33.77% 69.94% M3 33.55% 69.87% N3 33.80% 69.88% M4 33.76% 69.94% N4 33.66% 69.90% M5 33.67% 70.01% N5 33.80% 70.07% M6 33.65% 69.91% N6 33.65% 70.00% 平均值 33.66% 69.95% 平均值 33.72% 69.95% 标准偏差 0.10% 0.05% 标准偏差 0.08% 0.07% 表 4 固体脂肪含量标准物质不确定度及其来源
Table 4. The uncertainty and its source of the SFC reference materials
固体脂
肪含量重复性引入的
不确定度($u_{\rm{r}} $)测量过程引入的
不确定度($u_{S F C}$)均匀性引入的
不确定度($u_{\rm{h} }$)稳定性引入的不
确定度($u_{\rm s_1}$)短期稳定性引入
的不确定度($u_{\rm s_2}$)合成不确
定度($u_{\rm{c}} $)B管 33.69% 0.17% 0.82% 0.35% 0.13% 0.16% 0.93% C管 69.95% 0.16% 0.77% 0.14% 0.20% 0.15% 0.84% 表 5 校正因子
$f $ 值统计Table 5. The statistics of the correction factor
$f $ 管1 管2 管3 管4 校正因子f 1.51 1.51 1.44 1.35 -
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