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急速-蜗牛铁虫 (小有名气)
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[求助]
求助关于LC/APCI-MS 已有1人参与
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1、请问在LC/APCI-MS中，中性分子在APCI离子源中是不是只被离子化，不发生裂解？离子被碎片化是在APCI中还是在质谱中被碎片化的（离子是在哪里被碎片化的？）？ 2、APCI（大气压化学电离源）的负离子模式的工作基理是什么？是怎么由中性分子转变为负离子的？ |
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急速-蜗牛
3楼2015-12-28 13:24:06
thecoldest
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https://en.wikipedia.org/wiki/At ... chemical_ionization Ionization[edit]The analyte in solution is directly introduced into a pneumatic nebulizer via a direct inlet probe or through a connection to a standard high-performance liquid chromatography (HPLC) with an eluent flow rate between 0.2 and 2 mL/min. Once in the nebulizer, the analyte in solution is converted into a thin fog through the use of a high-speed nitrogen beam, and the droplets are then displaced by the gas flow through a heated quartz tube called a desolvation/vaporization chamber. [4] The mobile phase and the sample in the gas flow are then vaporized by the heat transferred to the spray droplets in the desolvation chamber and leave the tube as a mixture of the compounds of interest and hot gas (120oC).[4] They are subsequently carried along a corona discharge electrode where ionization occurs. The ionization can either be carried out in positive or negative ionization mode. In the positive mode, the relative proton affinities of the reactant ions and the gaseous analyte molecules allow either proton transfer or adduction of reactant gas ions to produce the ions of the molecular species. [4] In the negative mode, however, the ions are produced by either proton abstraction or adduct formation. In most cases, the evaporated mobile phase acts as the ionization gas and reactant ions are formed because of the effect of the corona discharge on the nebulized solvent. Generally, the primary ions formed by the corona discharge are ions such as a positively charged nitrogen or oxygen radical which can then form secondary reactant gas ions though collision with vaporized solvent molecules.[5] In a major distinction from chemical ionization, the electrons needed for the primary ionization are not produced by a heated filament, as a heated filament cannot be used under atmospheric pressure conditions. Instead, the ionization must occur using either corona discharges or β- particle emitters, which are both electron sources capable of handling the presence of corrosive or oxidizing gases. |
2楼2015-12-28 13:03:44
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4楼2015-12-29 20:49:39