Melamine detection by mid- and near-infrared (MIR/NIR) spectroscopy: a quick and sensitive method for dairy products analysis including liquid milk, infant formula, and milk powder

Melamine (2,4,6-triamino-1,3,5-triazine) is a nitrogen-rich chemical implicated in the pet and human food recalls and in the global food safety scares involving milk products. Due to the serious health concerns associated with melamine consumption and the extensive scope of affected products, rapid and sensitive methods to detect melamine's presence are essential. We propose the use of spectroscopy data-produced by near-infrared (near-IR/NIR) and mid-infrared (mid-IR/MIR) spectroscopies, in particular—for melamine detection in complex dairy matrixes. None of the up-to-date reported IR-based methods for melamine detection has unambiguously shown its wide applicability to different dairy products as well as limit of detection (LOD) below 1 ppm on independent sample set. It was found that infrared spectroscopy is an effective tool to detect melamine in dairy products, such as infant formula, milk powder, or liquid milk. ALOD below 1 ppm (0.76 ± 0.11 ppm) can be reached if a correct spectrum preprocessing (pretreatment) technique and a correct multivariate (MDA) algorithm—partial least squares regression (PLS), polynomial PLS (Poly-PLS), artificial neural network (ANN), support vector regression (SVR), or least squares support vector machine (LS-SVM)—are used for spectrum analysis. The relationship between MIR/NIR spectrum of milk products and melamine content is nonlinear. Thus, nonlinear regression methods are needed to correctly predict the triazine-derivative content of milk products. It can be concluded that mid- and near-infrared spectroscopy can be regarded as a quick, sensitive, robust, and low-cost method for liquid milk, infant formula, and milk powder analysis.     

快速准确书写糖基材料中基元结构的规律

在生命活动中发挥重要作用的糖类物质,因其结构相对稳定而广泛存在于自然界。随着对重要糖类化合物结构的认识,糖基材料越来越受到化学、生物医学、材料学领域的关注,相关研究不断深入。但在许多出版物中,其结构的书写、表达方式时常出现不当甚至错误,容易引起混乱。本文从分析环己烷的构型构象式出发,依次推导常见单糖、低聚糖、多糖结构单元的书写方法,如：葡萄糖、纤维二糖、麦芽糖、蔗糖、纤维素、淀粉、甲壳素、壳聚糖等。并总结相关规律,以便读者能够识别、分辨现行刊物中相关结构的正确性与准确度,并在撰稿时能够正确、准确、快速地书写相关糖类物质的结构式。     

液相色谱-串联质谱法测定育肥猪配合饲料中的阿奇霉素

通过对提取溶剂、净化方法及色谱-质谱条件的优化,建立了配合饲料中阿奇霉素（AZM）的液相色谱-串联质谱测定方法。样品经乙腈超声波提取,MCX固相萃取柱净化,BDSHypersilC18（2.4μm,100mm×2.1mm）色谱柱分离,以甲醇-0.05mol/L乙酸铵水溶液为流动相梯度洗脱,正离子模式电离,多反应监测模式检测,同位素内标法定量。在优化条件下,AZM在1~250μg/L范围内线性关系良好,相关系数（r2）为0.9991,检出限（S/N≥3）为2.8μg/kg,定量下限（S/N≥10）为8.4μg/kg;在0.5,1,5,10mg/kg加标水平下,回收率为87.0%~106.6%,批内相对标准偏差为0.58%~5.4%,批间相对标准偏差为3.1%~5.4%。该方法准确、灵敏,选择性强,基质干扰小,可用于配合饲料中AZM的测定。     

理想完全互溶双液系相图的数学解析

理想完全互溶双液系是两个组分都严格遵守Raoult定律的体系,从数学角度看,其平面相图有着确定的函数关系。本文以Clausius-Clapeyron方程为基础,推导了该类理想体系的p-x、T-x及p-T相图的函数解析式。     

正相液相色谱法测定婴幼儿配方乳粉中1,3-二油酸-2-棕榈酸甘油三酯

建立并比较了正相色谱与反相色谱测定婴幼儿配方乳粉中1,3-二油酸-2-棕榈酸甘油三酯的方法。利用乙醚和石油醚提取婴幼儿配方乳粉中的油脂,经旋转蒸发浓缩后,分别采用银离子色谱柱和C18色谱柱,配合蒸发光散射检测器检测。其中采用银离子色谱柱以二氯甲烷-丙酮为流动相梯度洗脱的正相色谱法完全分离了1,3-二油酸-2-棕榈酸甘油三酯(OPO)和1,2-二油酸-3-棕榈酸甘油三酯(OOP)两种同分异构体,方法的重复性和线性关系良好,回收率为93.0%~101.5%,精密度(RSD)为2.89%~4.56%,检出限为20 mg/kg。该方法可准确测定婴幼儿配方乳粉中OPO的含量。     

基于液相色谱-四极杆/飞行时间质谱和化学计量学的婴幼儿配方乳粉化学指纹图研究

在反相色谱条件下,采用液相色谱-飞行时间串联质谱技术检测了18种婴幼儿配方乳粉,并应用主成分分析技术对大量的实验数据进行统计分析处理,研究了不同数据提取参数对分析结果的影响,通过T值检验筛选出3种罐标显示添加水解蛋白的婴幼儿配方乳粉的特征组分,提出了其中G号样品的16个特征组分的化学信息,并构建了相关的化学指纹图。     

基于拆分思想的酸碱滴定误差公式简便推导

提出了一种酸碱滴定误差公式推导的新方法。该方法利用拆分思想即可方便地导出酸碱滴定误差公式,避免了现行教材中利用物料平衡方程(MBE)和电荷平衡方程(CBE)联立推导该公式的繁琐,便于学生理解和掌握。