气相色谱讲义Gas Chromatography_105页.ppt

单击此处编辑母版标题样式,单击此处编辑母版文本样式,第二级,第三级,第四级,第五级,*,Chapter 2 Gas Chromatography(GC),2-1,Summary,Chromatographic separation technique(,色谱分离）,:A separation technique based on partition of 2 or more substances in a mixture in two phases(,色谱法、色层法、层析法,chromatographer,）,Chromatographic analysis,（,色谱分析）,:,Chromatographic separation applied on analytical chemistry,Advantages:,High separation efficiency,high detection efficiency,fast analytical,velocity,GC,Mobile phase&Stationary phase,（,流动相与固定相,):,Chromatographic separation involving partition of different species in a mixture in two phases,among which one phase(solid or liquid)does not move(,stationary phase,),the other phase(gas or liquid)takes the sample mixture to pass through the stationary phase packed in the column(,mobile phase,),Separations are affected due to the differences of substances affinities for a mobile phase and a stationary phase(,分离原理,）,.,GC,Gas supply,Flow controller,Oven,Column,To waste,Detector,Flow meter,(In one of these positions),Injection,system,Amplifier,Integrator,Recorder,GC,皂膜流量计,转字流量计,调整仪，标准仪,Setup of Gas Chromatograph,GC,inert gases,wothout,interaction with,analytes,or stationary phase,管状的,Thermal conductivity detector,Electron capture detector,IR,FPD,Flame photometric detector,Hydrogen flame ionization detector,Chromatogram of,xylene,isomers on a polar column,GC,Y,GC,0,12,4,Peak width at a half height,Peak width at peak base,Adjusted retention time,Rotention,time,Dead,time,Air peak,0.607h,1/2,h,2,s,Y,1/2,Y,t,R,t,R,t,M,Injection,t,Response signal,Chromatogram,Time(arbitrary units),Nomenclature of Chromatographic separation,Chromatographic Curve&Chromatogram,The chart of output detector response(concentration)versus time,The,protuberance in the curve is called,chromatographic peak,如果进样量很小，浓度很低，在吸附等温线（气固吸附色谱）或分配等温线（气液分配色谱）的线性范围内，则色谱峰是对称的。,Baseline(,基线,),Chromatographic curve under the experimental operation conditions,no components of materials flow out after the column(,在实验操作条件下，色谱柱后没有样品组分流出时的流出曲线称为基线，反映检测器系统噪声（,Noise),随时间的变化情况。稳定的基线应该是一条水平直线。,),Nomenclature of Chromatographic separation,Baseline drift(,基线漂移）,refer to,基线随时间定向的缓慢变化,Peak height,refer to,V,ertical,distance from the vertex of chromatographic peak to baseline,色谱峰顶点与基线之间的垂直距离，以（,h,）,表示。,Nomenclature of Chromatographic separation,Chromatogram and chromatographic peak,Baseline（a）,Peak height（h）,信号,进样,空气峰,色谱峰,h,a,色谱流出曲线,Retention value,表示试样中各组分在色谱柱中滞留时间的数值。通常用时间或用将组分带出色谱柱所需载气的体积来表示。,Rely on component partition on two phases(or absorption),Thermodynamic controlled(Properties of stationary phase&operation conditions),Qualitative Base,Nomenclature of Chromatographic separation,Dead Time,t,M,不被固定相吸附或溶解的物质,(,如空气，甲烷等）进入色谱柱时，从进样到出现峰极大值（浓度）所需的时间称为死时间，它正比于色谱柱的空隙体积。,见图,Rotention,time,t,R,The time at which the maximum of the peak appears after sample injection,见图,Nomenclature of Chromatographic separation,因为这种物质不被固定相吸附或溶解，故其流动速度将与流动相流动速度相近。测定流动相平均线速,时，可用柱长,L,与,t,M,的比值计算，即,=L/,t,M,Nomenclature of Chromatographic separation,Adjustedrotention,time,(t,R,),The difference between the,rotention,time and dead time,某组分的保留时间扣除死时间后，称为该组分的调整保留时间，即,t,R,=,t,R,t,M,More time the component spends due to dissolution in(or adsorption on)the stationary phase than inert components without interaction.,保留时间是色谱法定性的基本依据，但同一组分的保留时间常受到流动相流速的影响，因此色谱工作者有时用,保留体积,来表示保留值。,Dead Volume,V,M,指色谱柱在填充后，柱管内固定相颗粒间所剩留的空间、色谱仪中管路和连接头间的空间以及检测器的空间的总和。当后两相很小可忽略不计时，死体积可由死时间与色谱柱出口的载气流速,F,0,（,cm,3,min,-1,）,计算。,V,M,=t,M,F,0,式中,F,0,为扣除饱和水蒸气压并经温度校正的流速。,仅适用于气相色谱，不适用于液相色谱,Nomenclature of Chromatographic separation,Rotention,volume,V,R,指从进样开始到被测组分在柱后出现浓度极大点时所通过的流动相的体积。保留时间与保留体积关系：,V,R,=,t,R,F,0,=,t,M,F,0,Nomenclature of Chromatographic separation,V,R，,V,R,do not depend on velocity of the carrier gas.,Adjusted,rotention,volume,V,R,某组分的保留体积扣除死体积后，称为该组分的调整保留体积。,V,R,=V,R,V,M,=,t,R,F,0,The ratio of adjusted,rotention,value of the second component to that of the first component,r,21,=t,R(2),/t,R(1),=V,R(2),/V,R(1),t,R(2),/t,R(1),V,R(2),/V,R(1),由于相对保留值只与柱温及固定相性质有关，而与柱径、柱长、填充情况及流动相流速无关，因此，它在色谱法中，特别是在气相色谱法中，广泛用作定性的依据。,Nomenclature of Chromatographic separation,The higher r,21,the bigger difference between the adjusted,rotention,values of adjacent components,the better the separation.When r,21,=1,the two components can not separate at all.,Relative,rotention,value,r,21,在定性分析中，通常固定一个色谱峰作为标准（,s,），,然后再求其它峰（,i,）,对这个峰的相对保留值，此时可用符号,表示，即,=,t,R,(i),/,t,R,(s),式中,t,R,(i),为后出峰的调整保留时间，所以,总是大于,1,的。相对保留值往往可作为衡量固定相选择性的指标，又称,选择因子,。,Nomenclature of Chromatographic separation,Peak width,(,区域宽度,),色谱峰的区域宽度是色谱流出曲线的重要参数之一，用于衡量柱效率及反映色谱操作条件的动力学因素。表示色谱峰区域宽度通常有三种方法。,Standard deviation,Half width of chromatographic peak at 0.607 times peak height(0.607,倍峰高处色谱峰宽的一半,),Nomenclature of Chromatographic separation,Due to easiness to measure,Y,1/2,is always used to denote peak width.,Peak width at half-height,(,半峰宽度、,半峰宽、区域宽度）,Y,1/2,即峰高一半处对应的峰宽。它与标准偏差的关系为,Y,1/2,=2,s,SQR(2ln2)=2.354,Peak width at peak base,(,峰底宽度,),Y,即色谱峰两侧拐点上的切线在基线上的截距。它与标准偏差,的关系是,Y,=4,从色谱流出曲线中，可以得到许多重要信息：,Nomenclature of Chromatographic separation,Judge the number of the components included a mixture based on the number of peaks,Qualitative analysis based on the,rotention,value of chromatographic peak,Quantitative analysis based on areas or heights of chromatographic peaks,Rotention,value and peak width of chromatographic peaks is the basic to evaluate separation efficiency of chromatographic column,色谱峰两峰间的距离，是评价固定相（或流动相）选择是否合适的依据。,2.2,Theoretical foundation of,gas chromatographic analysis,2.2.1Gas solid or Gas liquid chromatography,Capillary column,（,毛细管柱）,:,The column has internal diameter of less than one mm,and inner wall of the column is usually coated with a film of s,tationary liquid,Chromatographic column,Packed column(,填充柱）,:,Packed stationary usually made from metal materials(copper or stainless steel)or glass,with a height of 0.5-10m and inside diameter of 2-6mm.U-shape or screwy(,螺旋形）,Stationary phase,Gas-solid chromatography,（气,-,固色谱）,:,porous solid materials or adsorptive particles with higher surface area,Mechanism:,Adsorption&Elution(,desorption,),Gas-liquid chromatography,（气,-,液色谱）,:,Chemical inert solid particles,(,担体,support),coated with a film of organic chemical of high-,boiling point,（,Stationary liquid,固定液）,Mechanism:,Dissolution&volatilization,2.2,Theoretical foundation of,gas chromatographic analysis,Partition Coefficient(,K,):,Concentration ratio of the component in stationary phase and mobile phase,when the partition process arrives at equilibrium under given temperature.,K=,Concentration of the component in stationary phase,Concentration of the component in mobile phase,=,c,S,/c,M,Gas chromatographic analysis based on the difference of the partition coefficients of different substances,Partition Process:,Adsorption,elution,and dissolution,volatilization process of the substances between stationary phase and mobile phase.,2.2,Theoretical foundation of,gas chromatographic analysis,Partition ratio(capacity factor,capacity ratio,k,):,Mass ratio of the component in two phases when partition process arrives at equilibrium under given temperature and pressure,k=,m,S,/,m,M,m,S,refers to mass of the component distributed in stationary phase,m,S,mass of the component distributed in mobile phase,Relationship between k and K,K=,c,S,/c,M,=(,m,S,/V,S,)/(,m,M,/V,M,)=k V,M,/V,S,=k,b,V,M,refers to mobile phase volume in column,that is,柱内固定相颗粒间的空隙,(lacuna,）,体积,。,V,S,Stationary phase volume in column(,在气,-,液色谱中为固定液体积，气,-,固色谱中为吸附剂的表面容量。,Phase ratio(,相比，,b,),:,V,M,/V,S,反映各种色谱柱柱型及其结构特征,Packing column:6-35,Capillary column:50-1500,Stationary liquid,Capillary wall,Stationary phase,Relationship of,K,and,k,K refers to concentration ratio and k mass ratio,K and k depends on thermodynamic properties of the components and stationary phase,Tc,(,柱温），,Pc(,柱压）,K,only,relys,on properties of the component and double phases,but not phase ratio.But,k,relys,on not only properties of the component and double phases,but also phase ratio(amount of stationary phase),With a given chromatographic system,separation of the components is determined by relative amount of the components in both phases,but not relative concentration.,The bigger,k,value,the longer,rotention,time,the easier separation.,k,=0 corresponds to dead time,t,M,.,Ratio of the,velocity,of carrier gas and the component in column:,R,s,=,u,S,/u,=w=,m,M,/(,m,S,+,m,M,)=1/(1+m,S,/,m,M,),=1/(1+k),Where,u,refers to,velocity,of carrier gas in column in unit of cm.s,-1,u,velocity,of the component in column,w,mass fraction.,Retardation factor(,滞留因子,Rs,）：,Defining L as column length,following formula are vivid:,t,R,=L/,u,S,t,R,=L/,u,S,=,t,M,u,/,u,S,=,t,M,u/,u,S,=t,M,(1+k),k=(,t,R,-t,M,)/,t,M,=t,R,/,t,M,t,M,=L/u,Above equation can be employed to evaluate,k,value.,2.2.1Basic theory of chromatographic separation,Partition of different components in double phases,Depending on partition coefficient,molecular structure and properties of the components,stationary phase,mobile phase.Characterized by,rotention,value(,rotention,time or,rotention,volume),thermodynamic controlled.,Movement of different components in column,Depending on mass transfer(,传质,)resistance of different components in stationary phase and mobile phase.,Characterized by peak width at half-height,kinetic controlled,Theories,Two approaches can be taken to explain the separation process,Plate theory,proposed in 1941 by Martin and,Synge,.Based on an analogy with distillation and counter current extraction,Rate theory,accounts for the dynamics of a separation 1956,J.J.Van,Deemter,.,Each has advantages and limitations.,Plate theory(,塔板理论,),借用传统的蒸馏过程处理色谱过程,将色谱柱比作一个分馏塔，色谱柱由许多假想的塔板组成（即将色谱柱分成许多各小段），在每一个塔板内，一部分空间被涂在担体上的液相占据，另一部分空间则充满气相（载气），载气占据空间称为板体积,D,V.,当欲分离的组分随载气进入色谱柱后，就在两相间进行分配。由于流动相在不停地移动，组分就在这些塔板间隔的气液两相间不断地达到分配平衡。,Plate theory assumes:,在一小段间隔（塔板）内，气相平均组成与液相平均组成能很快达到分配平衡。达到分配平衡的一小段柱长称为理论塔板高度,H,（,Height equivalent to theoretical plate),载气进入色谱柱，不是连续的，而是脉动式的，每次进气为一个板体积,试样开始时都加在第,0,号塔板上，且试样沿色谱柱方向的扩散（纵向扩散）可忽略不计,分配系数在各塔板上是常数,Assuming the column consists of 5 plates,n=5(number of theoretical plates),r is defined as number of plate,r=0,1,2,n-1.With,m,=1,k,=1,w,=1/2,when carrier gas of one more plate volume enters the column,pulsantly,partition in each plate is shown as follows:,Mass in mobile phase,Mass in stationary phase,原塔板,1,固定相中组分的质量（,0.125+0.125=0.25),与随载气带入的原塔板,0,流动相中组分质量,(0.125),重新分配,:(0.25+0.125)/2=0.188,Partition table of the component in any plate in a column with,n,=5,k,=1 and,w,=1/2,Total amount of the solute in a plate,Chromatogram of the component in a column with n=5,N is number of plate volume of carrier gas,Peak asymmetry since n is too small,Concentration maximum at N=8-9,Peak symmetry near normal distribution when n 50,n=10,3,10,6,for gas chromatography,When number of theoretical plates is big enough,chromatogram approaches normal distribution curve,following relationship between concentration,C,and time,t,is obtained:,Where C,0,is injection concentration(,进样浓度）,C,concentration at outlet,（,出口）,of the column at time,t,流出曲线方程式,Relationship of n to peak width:,Where,L,is length of chromatographic column,t,R,Y,1/2,Y,in the same units,n,theoretical plate number,H,theoretical plate height.,为了扣除死时间或死体积的影响，实际工作中常用有效塔板数（,Effective plate number),和有效塔板高度（,Effective plate height),作为柱效能指标：,n,=,1+k,k,2,n,有效,色谱柱的柱效能还与物质的性质有关，同一色谱柱的柱性能对不同物质是不同的。,色谱柱的理论塔板数越大，表示组分在色谱柱中达到分配平 衡的次数越多，固定相的作用越显著，因而对分离越有利。但不 能预言并确定各组分是否有被分离的可能，因为分离的可能性决定于试样混合物在固定相中分配系数的差别，而不决定于分配 次数的多少。,n,有效,不能作为有无实现分离可能的依据，而只是在一定条件下柱分离能力发挥程度的标志。,塔板理论没有考虑动力学因素的影响，因而不能解决塔板高度受什么因素影响以及流速对理论塔板数的影响等问题。,（扩散）,Rate theory of chromatography,It is based on a Gaussian distribution similar to that of plate theory,He was attempting to account for the dynamics of the separation process.,2,3,H=A+Cu,B,u,0.01k,2,d,p,2,(1+k),2,D,g,u,+,（填充的不均匀性）,（弯曲因子）,（组分在载气流中的分子扩散系数）,（固定相的液膜厚度）,(,涡流扩散项,）,（,分子扩散项,）,（,液相传质过程,）,0.01k,2,d,p,2,(1+k),2,D,g,u,Gas term(,气相传质过程,）,(,涡流扩散项,）,（,分子扩散项,）,（,传质项,）,涡流扩散项（,vortex diffusion term),由于填充物颗粒的阻碍作用，当气体通过时，会不 断改变流动方向，使样品组分在气相中形成类似“涡流”的流动，引起色谱峰的扩张。涡流扩散项的大小与填充物的平均颗粒直径,d,p,(,单位未,cm),大小及填充的不均匀性有关，而与载气性质，线速度和组分无关。,空心毛细管柱，涡流扩散项,A,为零。,使用细粒度和粒度分布均匀的颗粒作为担体，且填充均匀，可以减少涡流扩散，提高柱效能。,返回,分子扩散项,B/u(,纵向扩散项,),(Longitudinal diffusion term),试样组分被载气带入色谱柱后，以“塞子”的形式存在于柱内很小一端空间中，在“塞子”的前后（纵向）存在着浓差而形成浓度梯度，使运动着的分子产生纵向扩散。纵向扩散项的大小,B,为：,B=2,g,D,g,g,为弯曲因子，表示因载体填充在柱内而引起气体扩散路径弯曲的因素。,D,g,为组分在气相中的扩散系数（,cm,2,.s,-1,),B,的影响因素：,g,与填充物有关：由于固定相颗粒的存在，使分子不能自由扩散，从而使扩散程度降低。,空心毛细管柱：没有填充物的阻碍，扩散程度最大，,g,=1,填充柱：由于填充物的阻碍，扩散路径弯曲，扩散程度降低，,g,10,时，对,R,的增加不明显，也会显著增加分析时间,k,的最佳范围：,1 10,与柱选择性的关系,a,越大，柱选择性越好，分离效果越好。如果两个相邻峰的选择因子足够大，则即使色谱柱的理论塔板数较小，也可以实现分离。,分离度、柱效、柱选择性的关系,通过上式可以计算相关指标的值,L=,16R,2,H,有效,a,a,-1,2,=n,有效,H,有效,例：,设有一对物质，其,a,=1.15,要求在某填充柱上得到完全分离，试计算至少需要多长的色谱柱？,解：要实现完全分离，,R,1.5,故所需有效理论塔板数为：,使用普通色谱柱，一般有效理论塔板高度为,0.1cm,故所需柱长应为：,Selection of separation conditions,(,分离操作条件的选择,),Selection of carrier gas and its flow rate,Selection of column temperature(,自学）,Properties and amount of mixed liquid,（,自学）,Properties and size of supports,（,自学）,Injection time and injection amount,（,自学）,Selection of carrier gas and its flow rate,According to Van,Deemter,equation:,Following equation can be obtained by differentiating above equation:,实际工作中，为了缩短分析时间，常使流速稍高与最佳流速。,and,Combining above equation and Van,Deemter,当流速较小时，,H,B,/,u,分子扩散项,(B,项,),就成为色谱峰扩张的主要因素，此时应采用分子量较大的载气,(N,2,、,Ar,),，,使组分在载气中有较小的扩散系数。而当流速较大队,HC,u,传质项,(C,项,),为控制因素，宜采用低分子量的载气,(H,2,、,He),，,此 时组分在载气中有较大的扩散系数，可减小气相传质阻力，提高柱 效。选择载气时还应考虑对不同检测器的适应性。,对于填充柱，,N,2,的最佳实用线速为,1012cm,s,H,2,为,15 20cm,s,通常载气的流速习惯上用柱前的体积流速,(,mL,min),来表示，也可通过皂膜流量计在柱后进行测定。若色谱柱内径 为,3mm,，,N,2,的流通一般为,40,60mL,min,，,H,2,的流速为,6090,mL,min,。,Selection of column temperature(,自学）,Understand how to select column temperature,Properties and amount of stationary liquid,（,自学）,What influence does stationary liquid have,How to select?,Requirement for mixed liquids,separation characterization,Properties and size of supports,（,自学）,Definition of support,requirement for support,how to select it?,Injection time and injection amount,（,自学）,How do they affect peak shape?How to select them?,2-5 Detectors of GC,(,Concentration sensitive detector&mass flow rate sensitive detector,),Thermal conductivity detector(,热导池检测器，,TCD),Self-study&Exam:,热导池的构造，工作原理及影响检测灵敏度的因素。,Hydrogen flame ionization detector(,氢火焰离子化检测器,FID),氢火焰电离化检测器，简称氢焰检测器。,对大多数有机化合物有很高的灵敏度，一般比热导池检测器的灵敏度高几个数量 级，能检测至,ppb,级,(10,-12,g.s,-1,),的痕量物质，故适宜于痕量有机物的分析。,结构简单，灵敏度高，响应快，稳定性好，线形范围宽（,10,-6,）,.,Selfstudy&Exam:,结构、作用原理、操作条件,Electron capture detector(,电子俘获检测器，,ECD),ECD,Flame photometric detector(,火焰光度检测器，,FPD),FPD is highly sensitive and highly selective to the compounds containing,sulphur,phosphor,etc.,检测器,检测器的性能指标,Self-study&Exam,检测器的灵敏度、检出限，最小检出量、响应时间、线形范围等的概念，物理意义，计算公式等。,2-6,Qualitative analytical methods for GC,Qualitative analysis based on chromatographic,rotention,value,直接根据色谱保留值进行定性,各种物质在一定的色谱条件下（固定相、操作条件）均有确定的保留值，可以作为定性指标。,适合于已知混合物及已确定存在范围或类型的化合物的鉴定,对于完全未知的化合物鉴定，可靠性较差。,方法的可靠性与色谱柱的分离效率（柱效）有密切关系,常采用仅与柱温有关，而与操作条件（柱长、固定液含量、载气流速等）无关，重现性较好的相对保留值,r,21,作为定性指标。,与文献值比较,与标准样对照,混合进样,:,将标准样与未