Experimental Investigation of Pressure Drop Hysteresis in a Cocurrent Gas-Liquid Upflow Packed Bed

Extensive experimental work on hysteresis in a c℃urrent gas-liquid upflow packed bed was carried out with three kinds of packings and the air-water system. However, only when packed with small glass beads ((1.4 mm) was the bed pressure drop hysteresis observed. Two more liquids with different liquid properties were employed to further examine the influence of parameters on pressure drop hysteresis. The similarity of pressure drop hysteresis in packed beds was concluded in combination of experimental evidence reported in literature.

双填料固相萃取-高效液相色谱/质谱法同时检测腌菜中9种N-亚硝胺

亚硝胺是三大强致癌食品污染物之一,普遍存在于腌制和热加工食品中。本研究建立了一种基于液质联用技术结合多级反应监测模式扫描(MRM)检测N-亚硝胺的新型固相萃取-液相色谱方法,可以快速直接检测腌菜中9种N-亚硝胺。实验优化了液相色谱分离与检测条件,同时考察了4种固相萃取单柱(碱性氧化铝Al2O3、C18、硅胶、硅藻土)和2种双填料的混合固相萃取柱(Al2O3-C18,Al2O3-硅胶)吸附解析的净化效果。结果表明,采用Al2O3-C18混合柱纯化,液相色谱检测,外标法定量,对9种亚硝胺的回收率达75.7%～116.0%,检出限为0.20～0.49 mg/L。采用本方法检测不同产地的6类腌菜产品中亚硝胺含量,二甲基亚硝胺和二乙基亚硝胺的检出率相对较高,分别为37.5%和25.0%,其中二乙基亚硝胺在雪里蕻腌菜中最高含量达59.1 mg/L,亚硝基吗啉在所有样品中未检出。

人参寡糖的固相甲基化研究及定量分析

以CH_3I为甲基化试剂、NaOH为填料的填充柱对麦芽三糖进行固相甲基化,利用液相色谱-质谱(LC-MS)检测甲基化产物并优化甲基化条件。最优条件为4.6 mm×150 mm的不锈钢填充柱,流速40μL/min和柱温25℃,在此条件下分别对麦芽糖、蔗糖、蔗果四糖及人参寡糖提取物进行固相甲基化,并以蔗果四糖为例进行方法学考察。蔗果四糖的线性范围为10.8~5400 ng/mL,r^2=0.9974,平均加标回收率为122.5%。