液相色谱-串联质谱法测定蜂产品中吡虫啉及其3种代谢物

建立了蜂蜜和蜂花粉中吡虫啉及其代谢物吡虫啉烯烃、吡虫啉脲、6-氯烟酸的液相色谱-串联质谱(LC-MS/MS)检测方法.在QuEChERS方法基础上,针对目标物化学性质和样品杂质情况,对提取溶液的pH值、提取次数、净化材料等参数进行了优化.最终以5％甲酸-乙腈溶液提取两次,无水MgSO4、NaCl盐析分层,提取液经增强型脂类去除材料(EMR)净化,以LC-MS/MS进行测定,基质外标法进行定量分析.结果表明,蜂蜜和蜂花粉中吡虫啉、吡虫啉烯烃、吡虫啉脲、6-氯烟酸的平均加标回收率为86.0％～111.5％, 相对标准偏差在1.7％～9.6％之间, 检出限分别为0.20, 3.50, 0.40和14.00 μg/kg,定量限分别为0.60, 11.64, 1.20和45.00 μg/kg.本方法分析速度快、灵敏度高、重现性好,适用于蜂蜜和蜂花粉中吡虫啉及其3种代谢物的快速测定.     

Na或Cu掺杂对Si/NiO异质结的光电性能影响

利用磁控溅射方法制备了引入Na或Cu元素前后Si/NiO异质结。实验结果表明,Na元素引入后的Si/NiO：Na异质结的整流特性最佳。此时,Si/NiO：Na异质结光学透过率可以达到70%,这可能是由于Si/NiO：Na异质结的结晶质量较优、薄膜内缺陷少所致。Si/NiO：Na异质结I-V曲线的拟合结果显示界面态状态也会影响其整流特性。而Si/NiO和Si/NiO：Cu异质结都没能获得较好的整流特性,可能是薄膜内缺陷增多所致。这一结论得到了XRD、SEM、AFM和UV结果的支持。     

Uphill anomalous transport in a deterministic system with speed-dependent friction coefficient

We investigate the transport of a deterministic Brownian particle theoretically, which moves in simple onedimensional, symmetric periodic potentials under the influence of both a time periodic and a static biasing force. The physical system employed contains a friction coefficient that is speed-dependent. Within the tailored parameter regime, the absolute negative mobility, in which a particle can travel in the direction opposite to a constant applied force, is observed.This behavior is robust and can be maximized at two regimes upon variation of the characteristic factor of friction coefficient. Further analysis reveals that this uphill motion is subdiffusion in terms of localization(diffusion coefficient with the form D(t) ~t~(-1) at long times). We also have observed the non-trivially anomalous subdiffusion which is significantly deviated from the localization; whereas most of the downhill motion evolves chaotically, with the normal diffusion.     

磁性“一步法”-液相色谱-串联质谱法测定水产品中28种有机磷农药残留

基于磁性纳米材料建立了磁性“一步法”前处理技术,结合液相色谱-串联质谱(LC-MS/MS)方法,实现了水产品中28种有机磷农药残留的精准定量分析。针对水产品富含蛋白质、脂肪和脂肪酸的特点,选择磁性聚合物(聚二乙烯基苯-吡咯烷酮,Fe₃O₄-PLS)为净化剂,通过疏水作用、氢键和π-π键等相互协同作用高效吸附基质干扰组分,净化样品。优化了萃取溶剂类型及用量、盐析与除水剂、Fe₃O₄-PLS和C18用量等实验条件。在最佳样品前处理条件下,28种有机磷农药的方法检出限(MLOD)为0.03～0.85μg/kg,方法定量限(MLOQ)为0.50～2.00μg/kg;不同添加浓度水平下目标物的平均回收率为60.1%～119.0%,相对标准偏差(RSDs)为0.8%～19.0%,方法的灵敏度和准确度高。与QuEChERS方法对比,本方法在萃取溶剂、盐析与除水剂和净化剂用量以及分析效率等方面均展现出明显的优势。采用本方法检测不同种类水产品中有机磷农药残留,结果表明,本方法具有良好的实用性,可为水产品中有机磷农药残...     

液相色谱-串联质谱法测定葡萄中链霉素和双氢链霉素

研究系统地优化了样品前处理过程及仪器分析中影响链霉素和双氢链霉素残留分析准确度与响应灵敏度的各主要因素,建立了葡萄中链霉素和双氢链霉素残留的快速精准定量分析方法。葡萄样品经磷酸溶液(pH=2)超声提取、Oasis HLB单固相萃取柱富集净化后,采用Waters HSS T3色谱柱(100 mm×2.1 mm, 1.8 μm)分离,柱温35 ℃,进样量2 μL,以0.1%甲酸水溶液-甲醇溶液(60∶40, v/v)为流动相进行等度洗脱,在正离子、电喷雾电离源多反应监测模式下测定,外标法定量。链霉素和双氢链霉素在2~400 μg/L质量浓度范围内线性关系良好,相关系数(R²)分别为0.9991和0.9997;在5、10、20和40 μg/kg 4个添加水平下的平均回收率为76.8%~91.9%,相对标准偏差为0.4%~10.2%;链霉素和双氢链霉素的检出限(LOD)为1 μg/L,定量限(LOQ)为5 μg/kg。为验证该方法的适用性,将方法适用于无籽红提、新郁葡萄、夏黑葡萄等实际样品中进行添加回收实验,链霉素和双氢链霉素的平均回收率分别为77.2%~83.9%和70.8%~78.9%, RSD为3.0%~15.6%。该法的准确度和精密度均符合葡萄中链霉素和双氢链霉素分析要求,且操作简便、准确,灵敏度高,适用于葡萄中链霉素和双氢链霉素残留量的检测分析。     

Competition between two kinds of information among random-walking individuals

A model is proposed to describe the competition between two kinds of information among N random-walking individuals in an L × L square, starting from a half-and-half mixture of two kinds of information. Individuals remain or change their information according to their neighbors’ information. When the moving speed of individuals v is zero, the two kinds of information typically coexist, and the ratio between them increases with L and decreases with N. In the dynamic case (v>0), only one information eventually remains, and the time required for one information being left scales as Td～vαLβNγ.     

超高效液相色谱-四极杆-飞行时间质谱测定果蔬中维生素C

利用超高效液相色谱-四极杆-飞行时间质谱（UPLC-Q-TOF/MS）快速与高分辨的分析优势,通过系统地考察样品制备、仪器分析中影响维生素C响应灵敏度和稳定性的各主要因素,建立了果蔬中维生素C的定量分析方法。果蔬样品在干冰保护下高速匀浆获得均匀的匀浆液,用0.1%（v/v）甲酸溶液提取后,采用Waters Acquity-UPLC T3色谱柱（100 mm×2.1 mm,1.8 μm）分析,柱温为30℃,进样量为5 μL,流动相为0.05%（v/v）甲酸-甲醇溶液（8：2,v/v）,流速为0.25 mL/min。提取的定量离子为[M-H]^-（m/z 175.0238）,定性离子为[M-C₃H₄O₃]^-（m/z 87.0077）,质量允许误差为5×10^-6（5 ppm）。结果表明：维生素C在0.02~5.0 mg/L范围内峰面积与质量浓度呈线性,线性相关系数（R²）为0.9992;检出限及定量限分别为0.008 mg/L（S/N=3）和0.02 mg/L（S/N=10）;在不同添加水平下,维生素C的平均回收率为89.3%~113%,相对标准偏差小于5.40%。在优化的条件下,对32批次的国产和新西兰猕猴桃样品进行检测,国产猕猴桃中维生素C的含量范围为498~1625 mg/kg,新西兰进口猕猴桃中维生素C的含量范围为247~449 mg/kg。该方法操作简便,重复性良好,可用于果蔬中维生素C含量的准确测定。     

一对姊妹不等式的联想

受文[1]和文[2]启发，本文将给出与不等式①类似的一个不等式．文末提出三个与②，③，④三式类似的不等式猜想．     

大数据条件下概率统计教学的两点思考

本文借助"概率元"工具讨论了高维、分量类型不一致的随机变量的分布描述方法,借助"随机模拟"技术和贝叶斯方法讨论了过程数据的处理方法,希望借此给当下统计教学一些补充,突出统计学在大数据时代的地位.     

Variations in epidemic distribution with some characteristic parameters

Considering the spread of an epidemic among a population of mobile agents that can get infected and maintain the infection for a period, we investigate the variation in the homogeneity of the distribution of the epidemic with the remaining time of infection τ, the velocity modulus of the agent v, and the infection rate α. We find that the distribution of the infected cluster size is always exponential. By analyzing the variation of the characteristic infected cluster size coefficient, we show that the inhomogeneity of epidemic distribution increases with an increase in τ for very low v, while it decreases with an increase in τ for moderate v. The epidemic distribution also tends to a homogeneous state as both v and α increase.