電噴霧四級(jí)桿飛行時(shí)間qtof理論(編輯修改稿)
2025-01-31 21:03 本頁(yè)面
【文章內(nèi)容簡(jiǎn)介】 l z m The aim of an electrostatic reflector, also called reflectron is to improve mass resolution. It creates a retarding field that acts as an ion mirror by deflecting the ions and sending them back through the flight tube. The reflector corrects the energy dispersion of ions with the same m/z ratio. Indeed, ions with more kiic energy will perate the reflectron more deeply and will spend more time in the reflectron. Thus they reach the detector at the same time as slower ions of the same m/z. Ions receive kiic energy from electric field. E = 1/2mv2 Resolution of Ions – TOF Assembly m1 = m2, but E1 E2 Orthogonal Detector accelerator Think of the TOF operation as a drag race between vehicles of different sizes, but all having identical engines: ? “Start line” = orthogonal accelerator。 “Finish line” = TOF detector ? Just as all vehicles have the same engine (., horsepower), all ions are pulsed up the flight tube with the same kiic energy. ? Since m = 2E/v2, the smaller vehicles/ions will reach the finish line/detector before the larger ones. START FINISH Principle of the TOF Mass Analyzer A detector converts an ion signal into an electrical signal. Here, the detector is a microchannel plate detector. It has millions of small pores which are coated inside with a semiconductive layer. Each of these channels work as an independent electron multiplier. Microchannel plates are effective for the detection of signals over a large dynamic range without saturation. In addition, the time response of this detection system is very rapid, therefore avoiding deterioration of peak resolution. Multiplication process in a channel Microchannel Plate Detector Q Separation CID Dry Gas Heater Dual Ion Funnel Analytical Quadrupole Collision Cell Orthogonal Accelerator Detector Reflectron Flight Tube Glass Capillary Collision Gas Supply API Spray Chamber Sprayer Hexapole micrOTOFQ MS2 Possibilities TOFMS In Source CID 3質(zhì)譜基本術(shù)語(yǔ)： 分辨率 Mass Resolution 同位素分布模式 Isotope Patterns 單同位素質(zhì)量 Monoisotopic Mass ………………. It is a measure of a mass spectrometer’s ability to distinguish two pounds of nearly equal mass. 600 800 1000 1200 1400 1600 1800 2023 2200 2400 m/z 100 200 300 400 500 600 700 800 900 1000 1100 . 1618 1623 1628 m/z 301 273 “ easy‖ “ not so easy‖ Resolution What is meant by ?Resolution‘? The narrower the FWHM, the higher the resolution. With the same FWHM, higher masses will have higher resolution than lower masses. Resolution = (m/z) / FWHM FWHM Full Width at Half Maximum 1 5 2 1 . 9 7 4 31 5 2 2 . 9 7 7 2+ M S , 0 . 6 0 . 9 m i n ( 4 0 5 7 )0100200300400I n t e n s .1520 1521 1522 1523 1524 1525 m / zm/z How do we measure mass resolution? Isotopic Distribution Patterns 13 12 100 90 80 70 60 50 40 30 20 10 0 C1 122 121 120 100 90 80 70 60 50 40 30 20 10 0 C10 1,206 1,204 1,202 1,200 100 90 80 70 60 50 40 30 20 10 0 C100 12,030 12,020 12,010 12,000 100 90 80 70 60 50 40 30 20 10 0 C1000 Isotopes are atoms with the same number of protons in the nuclei, but with different numbers of neutrons. Only 21 elements have only one stable isotope. All other elements are mixtures of at least 2 stable isotopes, and the proportions of these isotopes can vary greatly depending on the element. Carbon has 2 stable isotopes, C12 and C13, with natural abundance of % and % respectively. As the number of carbons increase in a molecule, the isotopic distribution pattern will reflect the mass contribution of the isotopes with their extra neutrons. pQLYENKPRRPYIL MW Res. 1,000 1,682 1,680 1,678 1,676 1,674 1,672 100 90 80 70 60 50 40 30 20
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