试比较电喷雾电离(ESI)与大气压化学电离(APCI)的特点和区别。

答案：(1)电喷雾(ESI)的特点。电喷雾电离是最软的电离技术，通常只产生分子离子峰，因此可直接测定混合物，并可测定热不稳定的极性化合物；它的易形成多电荷离子的特性可用于分析蛋白质和DNA等生物大分子；通过调节离子源电压控制离子的碎裂(源内CID)测定化合物结构。通常小分子经过ESI电离后得到[M+H]+，[M+Na]+或[M-H]-单电荷离子，生物大分子产生多电荷离子，由于质谱仪测定m/z，因此质量范围只有几千质量数的质谱仪可测定质量数十几万的生物大分子。

(2)大气压化学电离(APCI)特点。大气压化学电离也是软电离技术，只产生单电荷峰，适合测定相对分子质量小于2000的弱极性的小分子化合物；适应高流量的梯度洗脱/高低水溶液变化的流动相；通过调节离子源电压控制离子的碎裂。

(3)电喷雾与大气压化学电离的比较

①电离机理。ESI采用离子蒸发，而APCI电离是高压放电发生了质子转移而生成[M+H]+或[M-H]-离子。

②样品流速。APCI源可从02～2mL/min；而电喷雾源允许流量相对较小，一般为02～1mL/min。

③断裂程度。APCI源的探头处于高温，对热不稳定的化合物就足以使其分解。

④灵敏度。通常认为ESI有利于分析极性大的小分子和生物大分子以及其他分子量大的化合物，而APCI更适合于分析极性较小的化合物。

⑤多电荷。ESI易形成多电荷离子，而APCI源不能生成一系列多电荷离子。

和ESI 相比,相应的MALDI 对有较大分子量、更强疏水性和更低等电点的肽的检测能力更强对MS 检测器的最优选择基于何种应用离子化：个人觉得MALDI 更高,因为相对来说单位的样品可以得到的能量更为集中,且激光的能量更为可控,所以我个人的理解是其离子化的效率更高些ESI 在氮吹过程中应该存在大部分样品损失的情况传输效率：我觉得这个仍然是 MALDI 更为有优势大家知道,MS 的性能与其真空度是正相关的,MALDI 对真空度不存在直接的对应使用环境,即可以实现很好的真空度而 ESI 则不行MALDI 类型的质谱仪高灵敏度的实现我想有以上事实很大一部分的功劳两种离子源应该都是在其最优状态下进行工作,而且样品也是各自更为适用的类型这样的讨论才具有可行性MALDI 在离子化效率问题上是弱于ESI 的,在离子传输效率上是强于ESI 的 ESI:大分子且不易挥发要加附加电解质使中性大分子带电而被分离主要看分子离子峰（正离子分离：+ Na+,K+等；负离子分离：+ Cl-等） MALDI:一般有机分子到大分子都可以分子先被离子化,成碎片进入质谱分析仪能看到碎片离子峰能得到较多的化学信息

(The top one percent most highly cited articles published in Engineering/ Computer Science/ Economics & Business during 2003-2015) (53 papers)： Huchang Liao,Zeshui Xu, Xiaojun Zeng, José M Merigó Lindahl, Qualitative decision making with correlation coefficients of hesitant fuzzy linguistic term setsKnowledge-Based Systems, 2015, 76: 127-138 Na Chen, Zeshui Xu Hesitant fuzzy ELECTRE II approach: A new way to handle multi-criteria decision making problems Information Sciences, 2015, 292: 175-197 Zeshui Xu, Huchang Liao Intuitionistic fuzzy analytic hierarchy processIEEE Transactions on Fuzzy Systems, 2014, 22(4): 749-761 Huchang Liao,Zeshui Xu, Xiaojun Zeng Distance and similarity measures for hesitant fuzzy linguistic term sets and their application in multi-criteria decision making Information Sciences, 2014, 271(1): 125-142 Huchang Liao,Zeshui Xu Multi-criteria decision making with intuitionistic fuzzy PROMETHEE Journal of Intelligent and Fuzzy Systems, 2014, 27: 1703-1717 Huchang Liao,Zeshui Xu Priorities of intuitionistic fuzzy preference relation based on multiplicative consistency IEEE Transactions on Fuzzy Systems, 2014, 22(6): 1669-1681 Xiaolu Zhang,Zeshui Xu The TODIM analysis approach based on novel measured functions under hesitant fuzzy environment Knowledge-Based Systems, 2014, 61: 48-58 Rosa Ma Rodríguez, Luis Martínez, Vicenç Torra,Zeshui Xu, Francisco Herrera Hesitant fuzzy sets: State of the art and future directionsInternational Journal of Intelligent Systems, 2014, 29(6): 495-524 Huchang Liao,Zeshui Xu Subtraction and division operations over hesitant fuzzy setsJournal of Intelligent and Fuzzy Systems, 2014, 27: 65-72 Huchang Liao,Zeshui Xu Some new hybrid weighted aggregation operators under hesitant fuzzy multi-criteria decision making environmentJournal of Intelligent and Fuzzy Systems, 2014, 26: 1601-1617 Huchang Liao,Zeshui Xu, Meimei Xia Multiplicative consistency of hesitant fuzzy preference relation and the application on group decision makingInternational Journal of Information Technology and Decision Making, 2014, 13(1):47-76 (ESI热点论文) Bin Zhu,Zeshui Xu Consistency measures for hesitant fuzzy linguistic preference relationsIEEE Transactions on Fuzzy Systems, 2014, 22(1): 35-45 Huchang Liao,Zeshui Xu A VIKOR-based method for hesitate fuzzy multi-criteria decision makingFuzzy Optimization and Decision Making, 2013, 12(4): 373-392 (ESI热点论文) Zeshui Xu, Xiaolu Zhang Hesitant fuzzy multi-attribute decision making based on TOPSIS with incomplete weight informationKnowledge-Based Systems, 2013, 52: 53-64 (ESI热点论文) Meimei Xia,Zeshui Xu, Na Chen Some hesitant fuzzy aggregation operators with their application in group decision makingGroup Decision and Negotiation, 2013, (22): 259-279 Na Chen,Zeshui Xu, Meimei Xia Correlation coefficients of hesitant fuzzy sets and their applications to clustering analysisApplied Mathematical Modelling 2013, (37): 2197-2211 Meimei Xia,Zeshui Xu, Huchang Liao Preference relations based on intuitionistic multiplicative informationIEEE transactions on Fuzzy Systems 2013, (21): 113-133 Yuan Jiang,Zeshui Xu, Xiaohan Yu Compatibility measures and consensus models for group decision making with intuitionistic multiplicative preference relationsApplied Soft Computing, 2013, 13(4): 2075-2086 Xiaohan Yu,Zeshui Xu Prioritized intuitionistic fuzzy aggregation operatorsInformation Fusion, 2013, 14(1): 108-116 Na Chen,ZeshuiXu, Meimei Xia Interval-valued hesitant preference relations and their applications to group decision makingKnowledge-BasedSystems, 2013, 37: 528-540 Meimei Xia,Zeshui Xu, Bin Zhu Some issues on intuitionistic fuzzy aggregation operators based on Archimedean t-conorm and t-normKnowledge-Based Systems, 2012, 31(1): 78-88 Bin Zhu,Zeshui Xu, Meimei Xia Hesitant fuzzy geometric Bonferroni meansInformation Sciences, 2012, 205(1): 72-85 (ESI热点论文) Bin Zhu,Zeshui Xu, Meimei, Xia Dual Hesitant Fuzzy Sets Journal of Applied Mathematics, Volume 2012 (2012), ArticleI 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2006, 35(4): 417-433 Zeshui Xu An overview of methods for determining OWA weightsInternational Journal of Intelligent Systems, 2005, 20(8): 843-865 Zeshui Xu A method based on linguistic aggregation operators for group decision making with linguistic preference relationsInformation Sciences, 2004, 166(1-4): 19-30 Zeshui Xu Uncertain linguistic aggregation operators based approach to multiple attribute group decision making under uncertain linguistic environmentInformation Sciences, 2004, 168/(1-4): 171-184 Zeshui Xu, Qingli Da An over view of operators for aggregating informationInternational Journal of Intelligent Systems, 2003, 18(9): 953-969

ESI: 大分子且不易挥发。要加附加电解质使中性大分子带电而被分离。主要看分子离子峰（正离子分离：+ Na+, K+等；负离子分离：+ Cl-等）

MALDI: 一般有机分子到大分子都可以。分子先被离子化，成碎片进入质谱分析仪。能看到碎片离子峰。能得到较多的化学信息。

不会。

从理论上来讲，ESI在正模式下只会出现加合离子（M＋H、M＋Na等），APCI和APPI可能出现M＋离子，但在实际工作中（LC－MS），可能会遇到M＋离子，如果化合物是没有问题的，而M＋则是在质谱过程中产生的。

在FAB离子化过程中，可同时生成正负两种离子，这两种离子都可以进行质谱分析。样品分子如带有强电子捕获结构，特别是带有卤素原子，则可以产生大量的负离子。

溶剂喷口跟counter electrode （也就是右边有小孔的黑条）通过雾化后的带点液滴以及离子形成了一个回路。所以阴离子是以电子的形式在回路中流动的。喷口与counter electrode之间形成了一个电场用来加速带正电的离子。只有一小部分离子能通过小孔，大部分离子碰撞到counter electrode形成回路。逃离的这部分正电荷使得原来的回路整体会带上少量的负电荷，这个我估计是通过接地的办法解决的。

带正电荷的离子通过小孔之后进入质量分析器。质量分析器有多种类型,比如扇形磁场、四极杆、飞行时间等等，涉及的原理不同。总之就是想办法把不同质荷比的离子给区分开来。经过质量分析器分离的离子达到检测器，记录下不同质荷比的离子的丰度，就可以形成常见的质谱图啦。

具有特定质荷比的离子能够以合适的半径通过质量分析器达到离子捕集器，形成电信号；而其他质荷比的离子由于偏转半径跟质量分析器管道半径不同，就打到了管壁上，不能到达捕集器。通过改变磁场强度，可以依次让不同质荷比的离子通过质量分析器，从而扫描整个区间内的所有不同质荷比的离子，最后经过处理，形成质谱。带一个Na+的分子，其质量增大了23，电荷为+1，形成 M+23离子，通过质量分析器被感应器（离子捕集器）探测到。打到感应器之后其所带电荷或者通过回路或者通过接地被中和。至于整个分子在感应器上变成了什么，这不是质谱所感兴趣的。