Suppose we make a new compound containing of C,H, and N
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Suppose we make a new compound containing of C,H, and N - PowerPoint PPT Presentation

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Suppose we make a new compound containing of C,H, and N We probably know what it was we were trying to make That doesn’t mean we succeeded We must have evidence that the compound we made is what we wanted.

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The PE 2400 is a conventional elemental analyzer. It operates by flash combustion of the specimen encapsulated in tin cups or disks whereby the specimen is completely combusted at a temperature of 1760 °C. The resulting gases are chemically scrubbed of the halogens (and of sulfur in the CHN mode) and are separated in a GC column. Detection is conducted by a thermal conductivity detector (TCD). Total C, H, and N are calculated with a precision of 0.1µg. Element ratios are more significant since they minimize instrument error. Molar element ratios may be reliably reported for up to three decimal places.

  • Measuring Principle

  • The sample under test is weighed in using a tin capsule. The required amount is 2 to 3 mg of organic material and can hardly exceed 10 mg, if inorganic matter with little carbon content is investigated. After folding the capsule (looking rather like wrapped tin foil) the sample is placed in the autosampler.

  • The tin capsule enclosing the sample falls into the reactor chamber where excess oxygen is introduced before. At about 990 °C the material is "mineralized". Formation of carbonmonoxide is probable at this temperature even under these conditions of excess oxygen.

  • The complete oxidation is reached at a tungsten trioxide catalyst which is passed by the gaseous reaction products. The resulting mixture should thus consist of CO2, H2O und NOx. But also some excess O2 passes the catalyst.

  • The product gas mixture flows through a silica tube packed with copper granules. In this zone held at about 500 °C remaining oxygen is bound and nitric/nitrous oxides are reduced. The leaving gas stream includes the analytically important species CO2, H2O und N2. Eventually included SO2 or hydrohalogenides are absorbed at appropiate traps.

  • High purity helium (Quality 5.0) is used as carrier gas. Finally the gas mixture is brought to a defined pressure/volume state and is passed to a gas chromatographic system. Separation of the species is done by so called zone chromatography. In this technique a staircase type signal is registrated. Step height is proportinal to the substance amount in the mixture.

  • Blank values are taken from empty tin capsules

  • Calibration is done by elemental analysis of standard substances supplied by the instrument's manufacturer for this purpose.

  • Mass Spectrometry = analysis to find out the mass of your compound

    • Organic molecules: structural information by looking at fragments

    • Metal complexes: most interested in showing that the metal is bound to the ligand

    • Looking for the Molecular Peak or Cation Peak

  • How does a Mass Spectrometer Work?

    • The sample is heated to vaporize under vacuum, and then ionized

    • Electron Impact: high energy beam of electrons knocks out electrons from the molecule

    • Electrospray: High voltage applied as a liquid is pushed through a capillary results in highly charged droplets. Evaporation of the solvent results in ionized solute molecules.

    • Charged plates accelerate the ion into the mass analyzer

    • Magnetic fields cause the path of the ion to curve based on mass

    • The detector is tuned to one mass at a time to generate the spectrum

Average Atomic Masses and Isotope Splitting

  • Why isn’t the mass of Carbon listed at exactly 12 on the periodic table?

  • Natural carbon: 12C(98.89%), 13C(1.11%), and 14C (negligible)

    • Avg. Mass = (0.9889)(12 amu) + (0.0111)(13.0034 amu) = 12.01 amu

    • No individual atoms have this mass

    • On average, all natural carbon atoms have this mass

    • 12.01 amu is the correct value to use for calculations involving carbon

  • What is avg. mass of Cu?

  • 69.09% 63Cu (62.93 amu) and 30.91% 65Cu (64.93 amu)

  • Copper complexes will never show up as simple peaks, but complex ones