Chapter 8 – Mass Spetrometry8章–质谱.pptVIP

* * Chapter 8 – Mass Spectrometry A Mass Spectrometer = separates a mixture of atoms according to their different masses(by mass to charge ratio) First: sample must be vaporized and accelerated using a voltage Second: Gaseous sample must be ionized Third: Gaseous Ions are deflected by a magnetic field Fourth: By varying the magnetic field, you can deflect different masses to the detector ? ? ? Box diagram Inlet: System is under vacuum, the inlet acts as a conduit between Laboratory at atmospheric conditions to mass specIon Source: Method to place sample into the gas phase and ionize (Examine Figure 7.1, p. 302) Various methods to ionize: EI, CI, MALDI, ESIOnce ionized, the sample can be accelerated using charged Plates into the …Mass Analyzer: Separate masses by electric or magnetic fieldsDetector: Measures ion currents and amplifies signalsVacuum System: To prevent contamination of samples, need to Keep system at low pressure, ~10-9 torr. Simple vacuum pumps (rotary vane) in lab only reach 10-2 – 10-3 torr. System MS History Historical Context Thomson J.J. On the Masses of the Ions in Gases at Low Pressures Philosophical Magazine, 1899, 48:295, p.547-567J.J. Thomson discovered that neon consisted of a mixture of two different isotopes (masses 20 and 22) rather than only a single isotope. This observation of the existence of stable isotopes is perhaps the greatest achievement that can be claimed by mass spectroscopy. Later studies showed that there are three stable isotopes of neon. At first there were very few who believed in the existence of these bodies smaller than atoms. I was even told long afterwards by a distinguished physicist who had been present at my [1897] lecture at the Royal Institution that he thought I had been pulling their legs.“ J.J. Thomson (1936). Recollections and Reflections. G. Bell and Sons: London. p. 341 Aston F.W. Isotopes and Atomic WeightsNature, 1920, 105, p.617 Won Nobel Prize in Chemistry 1922for his discovery,