MassSpectrometery质谱法.doc

Mass SpectrometeryMass spectrometry gives information on the molecular or atomic weight of compound or atom. Mass spectrometry is used on molecules as well as elements. In molecules, information about the molecular formula and structure can also be derived based on fragmentation patterns that may occur. In elements, the information can be used to calculate the average atomic mass and relative abundance(s) of each isotope of an element.The Mass Spectrometer has FOUR major stages:1. Ionization: 2. Acceleration:3. Deflection:4. Detection:Example: The overall mass spectrum for chlorine looks like this:What are the isotopes of chlorine? Cl-35 and Cl-37Are there peaks corresponding to these two values? _What are the ratios of two isotopes in nature? _What about the 3 lines at the end of the spectrum? _Various isotopes exist for different elements:M+ + 1 can be found for elements: carbon, hydrogen and nitrogenM+ + 2 can be found for elements: oxygen, sulfur, bromine and chlorineOther recognizable features of some elements are:For bromine the M+ + 2 peak is as large as the M+ peakFor chlorine the M+ + 2 peak is one-third as large as the M+ peakFor iodine there is a large gap between a cluster of fragments and an M+ peak at 127For nitrogen the M+ peak will have an odd number valueUltraviolet-Visible SpectroscopyBased on electronic transitions of conjugated systems (systems that have unsaturation(s) and their electrons are delocalized). Since pi-bond electrons are more easily excited than sigma bond electrons, the energies required for the transitions are in the ultraviolet region but often extend into the visible region. Thus it has known as UV-VIS spectroscopy.Compounds that contain unsaturated groups that absorb in the UV-VIS region are called _. For example, _ is a chromophore due the six delocalized electrons. However, the amount of energy needed to excite these pi-bond electrons is also affected by the substitutents attached to the chromophores. These substituents are called _.Most organic compounds absorb in the UV range however molecules with an extensive number of pi-electrons will absorb in the visible region. Example include: Beta-carotene, chlorophyll and phenolphthalein in a basic medium.The rule: the higher the number of conjugated double bonds the longer the wavelength (toward visible) of which the compound absorbs light.Beta-caroteneHow does a UV-VIS spectrometer work? The spectrometer compares the amount of light transmitted through the sample (sample beam) with the amount of light transmitted in a reference beam. The information is then recorded as %transmittance (A) to the wavelength.This concept can be extended to UV-VIS Spectrophotometry as well. The information from this technique can be used to determine the concentration of a solution.The absorbance (A) of a sample at a particular wavelength is governed by Beers Law:Where,Ir:Is:c:l:e:Since, the path length is fixed, and the molar absorptivity coefficient (e) is constant, this means that absorbance is directly proportional to the concentration. At low concentrations a linear relationship exists between concentration and absorbance. The amount of light absorbed is related to the concentration.By preparing solutions of varying concentrations, at a certain wavelength the absorbance data can be generated for each dilution. This can be plotted to create a standard curve or a calibration curve. This standard curve can be used to determine the concentration of an unknown solution.ChromatographyPurpose: To separate mixtures into components. All chromatography techniques operate on the principle of partition or adsorption.Stationary phaseA solid or liquid on a solid surface.Particle do NOT move.Mobile phaseA liquid or gas that flows through the stationary phase and carries components with itPartitionTwo liquids that do not mix or are _. Sometimes applied to a gas/liquid separation (GLC).Separating types of molecules based on how a compound distributes itself between two immiscible phases. Based on solubility of substance.AdsorptionA substance forming some sort of a _ to the surface of another one.mobile phaseAnd remember: polar molecules are miscible in a polar solvent, while non-polar molecules are miscible in non-polar solvents.Example 1:Stationary phase: polarMobile phase: non-polar solvent.Component to be separated is a mixture of a polar molecule (A) and a non-polar molecule (B).Which molecule will travel the furthest? _Why?Example 2:Stationary phase: polarMobile phase: polar solvent.Component to be separated is a mixture of a polar molecule (C) and a non-polar molecule (D).Which molecule will travel the furthest? _Why?Types of ChromatographyTypeStationary PhaseMobile PhaseApplicationsTypeStationary PhaseMobile PhaseApplicationsThe difference between paper chromatography and TLC? Sample can be isolated for further analysis.TypeStationary PhaseMobile PhaseApplicationsUsed for separation on a larger scaleEluent: solution that passes through the column.Elution: process of washing solution through column.Another type of column chromatography is Ion-Exchange Chromatography: this has beads of ion-exchange resin for the stationary column. A ion-exchange resin is a polymer with ions bonded to it. The process of separating the ions is based on desirable ions from sample displace ions already bonded to the resin.TypeStationary PhaseMobile PhaseAp