啤酒样品处理方法的探讨

一引言在啤酒生产过程中,半成品及出厂成品的酒精含量、原麦汁浓度及发酵度等的测定是啤酒厂分析化验的重要内容,也是生产过程中进行质量控制和产品分等定级的重要依据。目前国内的啤酒生产厂家较为普遍地采用反复流注50次的方法进行样品预处理,以消除在测定过程中二氧化碳的影响。但从实际分析结果来看,采用反复流注的方法处理样品时,由于气温的波动,酒精会发生不同程度的挥发,酒精含量测定结果偏低,原麦汁浓度也随之偏低。特别是夏天气温较高时,测定误差更大。针对以上情况,我们对样品预处理方法进行了探讨,总结出了各种方法的优点与存在的问题,提出了受温度影响较小且简便易行的样品预处理方法供同行们参考。

QuEChERS结合GC-MS/MS法测定24批次桔梗中34种农药残留

建立基于QuEChERS法结合气相色谱-串联质谱法(GC-MS/MS)对桔梗中34种农药残留量的快速检测方法,并应用于24批桔梗样品筛查。采用QuEChERS法对样品进行前处理,在气相色谱-串联质谱多反应监测(MRM)模式下进行测定,考察其线性关系、定量限、回收率和精密度。以所建立的方法对24批桔梗样品中34种农药残留进行测定分析。34种农药在一定质量浓度范围内线性关系良好,相关系数r均>0.998,其LOQ在0.0003~0.6000 mg/kg之间;回收率均在60%~130%范围内,RSD均<15%。有18批次桔梗样品检出农药残留,检出率为75%;检出农药对硫磷、甲基异柳磷、治螟磷、三氯杀螨醇、氟虫腈,其含量均在0.001~0.015 mg/kg之间,低于药典规定的0.02 mg/kg的限度,所检样品合格率为100%;其余农药未检出。所建立的QuEChERS法结合气相色谱-串联质谱法可用于桔梗中34种农药残留物的定性定量分析,可为桔梗的质量管控提供技术支撑。

土壤中无机砷测定的三种前处理方法比较

对土壤无机砷分析的样品前处理技术——微波辅助提取、超声波提取、水浴提取进行了对比研究。结合氢化物发生-原子荧光光谱(HG-AFS)测定技术比较了3种方法对国家土壤标准物质中无机砷的提取效果,并对溶剂类型、提取时间和提取剂用量等影响因素进行了考察。与超声波提取法和水浴提取法相比,微波辅助提取法具有快速、高效的优势。

基于《中华人民共和国药典》优化丹参中33种禁用农药残留物检测的前处理方法

目的以丹参为研究对象,比较2020年版《中华人民共和国药典》中3类前处理方法对33种禁用农药残留物回收率的影响,进一步优化快速样品处理法(quick,easy,cheap,effective,rugged and safe,QuEChERS)。方法分别从基质效应和回收率方面比较《中华人民共和国药典》3类前处理方法,并对QuEChERS法进行研究与优化,样品加水后由1%醋酸-乙腈提取,依次加入QuEChERS盐包与QuEChERS净化管盐析净化,提取液经浓缩后分别加入水和内标磷酸三苯酯,结合液相色谱-串联质谱法和气相色谱-串联质谱法以添加水平为定量限浓度水平测定样品的回收率和RSD。结果采用《中华人民共和国药典》前处理方法时,丹参中33种禁用农药(54个单体)在添加水平为定量限浓度水平时,部分农药回收率较低;优化QuEChERS法后,丹参中33种禁用农药(54个单体)在一定浓度下,线性关系良好,r均大于0.990,其回收率为64.43%~127.35%时,RSD均<15%;199批饮片和60批药材中共检出2种农药,甲拌磷检出率为3.86%,克百威检出率为1.93%,但残留量均未超过2020年版《中华人民共和国药典》规定限度。结论优化后的QuEChERS法快速简便,有针对性地对丹参中33种禁用农药残留进行准确检测,对于丹参的生产种植与日常监控具有一定的参考意义。

饮料酒中挥发性酚类物质分析方法研究进展

挥发性酚类化合物是饮料酒的香味组成部分,对于酒的闻香、口味及稳定性等方面均具有重要的作用。有研究者认为,4-乙基苯酚(4-EP)和4-乙基愈创木酚(4-EG)这2种挥发性酚,其在酒中的总浓度小于400μg/L时,为酒的风味贡献了辛香、烟香韵和革香韵;当其总浓度了大于620μg/L时,会使酒中产生腥异味,掩盖酒的香味。因此对酒中挥发性酚类物质的分析测定一直是研究的课题。目前饮料酒中挥发性酚的测定,主要采用各种样品前处理过程结合气相色谱或液相色谱的方法。随着先进仪器和设备的使用,样品前处理过程不断简化,饮料酒中挥发性酚的分析和测定正逐步向着简单、快速、准确度高的方向发展。文中综述了饮料洒中挥发性酚类物质分析方法的研究进展。

基于气相色谱-静电场轨道阱高分辨质谱法快速筛查和确证农产品中222种农药残留

该文在QuEChERS方法的基础上采用固相分散萃取样品处理一体机(Sio-dSPE)对样品进行前处理,结合气相色谱-静电场轨道阱高分辨质谱法(GC-Orbitrap MS)对农产品中多农药残留进行筛查和确证。对Sio-dSPE前处理方法中盐析剂和除水剂的种类、净化剂的种类与用量、基质效应等进行考察。在最优条件下,采用GC-Orbitrap MS对农产品中222种农药残留进行检测,线性范围为1~200μg/L,在莴苣、大米和茶叶中的定量下限分别为0.5~5μg/kg、1~10μg/kg、2.5~25μg/kg。在上述3种基质中分别进行10、20、50μg/kg浓度水平的加标回收实验,测得回收率分别为70.5%~121%、70.2%~119%、65.2%~125%,相对标准偏差(RSD)分别不大于11%、10%、12%。该方法具有样品处理简单、分析时间短、净化效果好等优点,适用于农产品中多农药残留的快速筛查与定量。

Optimization of Sample Pretreatment for Determination of Polycyclic Aromatic Hydrocarbons in Estuarine Sediments by Gas Chromatography

This study examined levels of polycyclic aromatic hydrocarbons (PAHs) in estuarine sediments in Licun (Qingdao, China) by gas chromatography under optimized conditions for sample pretreatment via ultrasonic extraction, column chromatography, and thin layer chromatography. Methanol and dichloromethane (DCM)/methanol (2:1, v/v) were used in ultrasonic extraction, and DCM was used as eluate for column chromatography. The developing system consisted of n-hexane and DCM at a ratio of 9:1 (v/v), with DCM as the extraction solvent for PAHs-containing silica gel scraped off the plate. When the spiking level is 100 ng, total recoveries of spiked matrices for four target PAHs (phenanthrene, anthracene, pyrene and chrysene) were 83.7%, 76.4%, 85.8%, and 88.7%, respectively, with relative standard deviation (RSD) between 5.0% and 6.5% (n = 4). When the spiking level is 1000 ng, associated total recoveries were 78.6%, 72.7%, 82.7% and 85.3%, respectively, with RSD between 4.4% and 5.3% (n = 4). The opti-mized method was advantageous for determination of PAHs in complex matrix due to its effective sample purification.

Effect of sample treatment on determination of arsenic （Ⅲ） and arsenic （Ⅴ） in aqueous and tissue samples by hydride generation atomic absorption spectrometry

The purpose of this procedure was to optimize and improve a method that used for the determination of arsenic （Ⅲ） and arsenic （Ⅴ） in biological and environmental samples. The method is based on hydride generation and atomic absorption spectrometry. For both As （Ⅲ） and As （Ⅴ） the parameters such as NaBH4, HCI concentration, and pH were optimized. Absorption signal of As （Ⅴ） was approximately 17% of As （Ⅲ） signal. Therefore, for estimation of As （Ⅲ） and As （Ⅴ） concentrations in various samples the difference between the absorbance obtained for arsenic, without and with previous treatment of samples with potassium iodide （KI）, can be applied. The calibration graphs were linear （r〉0.99）, and the detection limits of the method based on three times the standard deviation of the blank were 0.14 and 0.64 μL^-1 for As （Ⅲ） and As （Ⅴ）, respectively. The relative standard deviation （R.S.D.） of measurements was less than 10%. As a means of checking performance method, water samples were spiked with known concentrations of both As （Ⅲ） and As （Ⅴ）, and recovery above 94% was obtained. The proposed method was applied successfully to determine inorganic As （Ⅲ） and As （Ⅴ） in various environmental and total As in biological samples.

Diethylstilbestrol in Fish Tissue Determined Through Subcritical Fluid Extraction and with GC-MS

As the key point in sex hormone analysis, sample pre-treatment technology has attracted scientists' attention all over the world, and the development trend of sample preparation forwarded to faster and more efficient technologies. Taking economic and environmental concerns into account, subcritical fluid extraction as a faster and more efficient method has stood out as a sample pre-treatment technology. This new extraction technology can overcome the shortcomings of supercritical fluid and achieve higher extraction efficiency at relatively low pressures and temperatures. In this experiment, a simple, sensitive and efficient method has been developed for the determination of diethylstilbestrol(DES) in fish tissue using subcritical 1,1,1,2-tetrafluoroethane(R134a) extraction in combination with gas chromatography-mass spectrometry(GC-MS). After extraction, freezing-lipid filtration was utilized to remove fatty co-extract. Further purification steps were performed with C_(18) and NH_2 solid phase extraction(SPE). Finally, the analyte was derived by heptafluorobutyric anhydride(HFBA), followed by GC-MS analysis. Response surface methodology(RSM) was employed to optimizing the extraction condition, and the optimized was as follows: extraction pressure, 4.3 MPa; extraction temperature, 26℃; amount of co-solvent volume, 4.7 m L. Under this condition, at a spiked level of 1, 5, 10 μg kg^(-1), the mean recovery of DES was more than 90% with relative standard deviations(RSDs) less than 10%. Finally, the developed method has been successfully used to analyzing the real samples.

Local Data Analysis for Eliminating End Restraint of Triaxial Specimen

A data processing method was proposed for eliminating the end restraint in triaxial tests of soil. A digital image processing method was used to calculate the local deformations and local stresses for any region on the surface of triaxial soil specimens. The principle and implementation of this digital image processing method were introduced as well as the calculation method for local mechanical properties of soil specimens. Comparisons were made between the test results calculated by the data from both the entire specimen and local regions, and it was found that the deformations were more uniform in the middle region compared with the entire specimen. In order to quantify the nonuniform characteristic of deformation, the non-uniformity coefficients of strain were defined and calculated. Traditional and end-lubricated triaxial tests were conducted under the same condition to investigate the effects of using local region data for deformation calculation on eliminating the end restraint of specimens. After the statistical analysis of all test results, it was concluded that for the tested soil specimen with the size of 39.1 mm × 80 ram, the utilization of the middle 35 mm region of traditional specimens in data processing had a better effect on eliminating end restraint compared with end lubrication. Furthermore, the local data analysis in this paper was validated through the comparisons with the test results from other researchers.

AN ELIMINATION ALGORITHM OF EXTREME VALUES FOR INTEGRATED TRISPECTRUM

In this paper, an algorithm for eliminating extreme values and reducing the estimation variance of an integrated trispectrum under low signal-to-noise ratio and short data sample conditions is presented. An analysis of the results of simulations using this algorithm and comparison with the conventional power spectrum and integrated trispectrum methods are presented.

三七药材禁用农药残留的检测研究

目的:建立中药材三七中33种禁用农药残留的检测方法。方法:以乙腈为溶剂,高速匀浆提取。检测方法:气相色谱-串联质谱(GC-MS/MS)法,采用DB17MS弹性石英毛细管柱(30 m×0.25 mm×0.25μm),电子轰击离子源(EI);超高效液相色谱-串联质谱(UPLC-MS/MS)法,采用十八烷基硅烷键合硅胶柱Hypersil GOLD aQC18(150 mm×2.1 mm,3μm),以0.1%甲酸水溶液(含5 mmol·L^(-1)甲酸铵)和0.1%甲酸乙腈溶液(含5 mmol·L^(-1)甲酸铵)(95∶5)为流动相,梯度洗脱,电喷雾离子源(ESI),正离子模式下多反应监测(MRM)。结果:GC-MS/MS法检测的禁用农药质量浓度在20~600 ng·mL^(-1)范围内线性关系良好,相关系数在0.9903以上,回收率在85.0%~127.6%,精密度RSD(n=6)在1.3%~25.0%;UPLC-MS/MS法检测的禁用农药质量浓度在20~600 ng·mL^(-1)范围内线性关系良好,相关系数在0.9911以上,回收率在76.2%~123.7%,精密度RSD(n=6)在1.0%~13.0%。基于GC-MS/MS和UPLC-MS/MS分析方法,60批样品中共检出12种农药,其中特丁硫磷检出率最高为10.8%;农药残留超出限量范围的有特丁硫磷、苯线磷、氯唑磷、地虫硫磷、杀虫脒,其中杀虫脒超出限量值的3倍。结论:本方法能快速有效地检测中药材三七中的农药多残留,为其他药用植物中的农残检测提供借鉴,为三七规范化种植提供依据。

Pretreatment of Soil Samples Rich in Short-Range-Order Minerals Before Particle-Size Analysis by the Pipette Method

The possibilities of combining the dissolution of short-range-order minerals （SROMs） like allophane and imogolite, by ammonium oxalate and a particle size distribution analysis performed by the pipette method were investigated by tests on a soil sample from Reunion, a volcanic island located in the Indian Ocean, having a large SROMs content. The need to work with moist soil samples was again emphasized because the microaggregates formed during air-drying are resistant to the reagent. The SROM content increased, but irregularly, with the number of dissolutions by ammonium oxalate： 334 and 470 mg g-1 of SROMs were dissolved after one and three dissolutions respectively. Six successive dissolutions with ammonium oxalate on the same soil sample showed that 89% of the sum of oxides extracted by the 6 dissolutions were extracted by the first dissolution （mean 304 mg g-l）. A compromise needs to be found between the total removal of SROMs by large quantities of ammonium oxalate and the preservation of clay minerals, which were unexpectedly dissolved by this reagent. These tests enabled a description of the clay assemblage of the soil （gibbsite, smectite, and traces of kaolinite） in an area where such information was lacking due to the difficulties encountered in recuperation of the clay fraction.

Recent developments in the detection of melamine

In recent years,there were two reported outbreaks of food borne illness associated with melamine.The presence of melamine and its related compounds in milk,feed,and other foods has resulted in the need for reliable methods for the detection and accurate quantification of this class of contaminants.The sample pretreatment for melamine in a complex matrix usually involves a liquid extraction by a polar solvent,followed by a further clean-up with solid phase extraction.Analyses of melamine and related compounds are commonly carried out by liquid or gas chromatographic methods conjugated with mass spectrometry.Other innovative screening methods,which use antibodies,molecularly imprinted polymers,capillary electrophoresis,and gold nanoparticles,are also used to develop assays and biosensors to melamine.However,many of these methods have been hindered by matrix effects,the solubility of melamine-cyanuric acid complex,and background contamination.This article reviews recent developments for detecting melamine and discusses future directions.