Presentation on theme: "FTIR ● Quite often EDS analysis will give only C and O peaks meaning that the material is organic. ● FTIR is sensitive to vibrations between bonds in materials."— Presentation transcript:
FTIR ● Quite often EDS analysis will give only C and O peaks meaning that the material is organic. ● FTIR is sensitive to vibrations between bonds in materials and gives a characteristic spectrum for each compound. ● Analysis of unknowns and comparison to stored spectra allows easy and accurate identification. ● Characteristic FTIR spectrum of 1-Hexene.
FTIR Functional Group Assignment ● Certain functional groups vibrate within a given frequency\wavelength range giving peaks in specific areas. ● Different functional groups and bond types can then be identified. ● The region below 1500cm -1 is known as the fingerprint region and contains very specific structure for each compound. ● Structural isomers can be distinguished, e.g trans-C-H bonds give a peak at cm -1, whilst cis-C-H bonds give a broad peak at ~700 cm -1.
FTIR Structural Information ● Certain bond types give peaks at specific positions, allowing elucidation of structure and bonding. ● Compare the spectra of a) Chlorobenzene and b) Toluene. ● Only structural difference is a Cl or CH 3 group on an aromatic ring – many differences in spectra. ● Triplet at ~3000 cm -1 for Toluene is not present in Chlorobenzene, also there is a difference in peak structure at ~1000 cm -1.
GC-MS – G as C hromotography – M ass S pectrometry ● GC - A mixture of compounds is injected into the GC unit. These liquids are vapourised then passed through a GC column which separates the compounds – the higher the molecular the weight the longer it takes to pass through the column. Once through the column the gas goes to the mass spectrometer. ● MS - A mass spectrometer creates charged particles (ions) from molecules. It then analyzes those ions to provide information about the molecular weight of the compound and its chemical structure. ● Simplistically, a chemical is broken down into smaller parts (ions) by a high energy electron beam. These ions then travel along an ion analyser which separates ions of different sizes prior to detection. ● These ion fragments can then be used to work out what ions\chemicals were present in the initial sample. A typical GC-MS unit GC-MS trace for Methanol Ions in the Spectrum
GC-MS – Example Traces Cholesterol Toluene
GC-MS – Interpretation\Patterns The MS of a typical hydrocarbon, n-decane is shown above. The molecular ion is seen as a small peak at m/z = 142. Notice fragments that differ by 14 mass units, formed by the cleave of bonds at successive -CH2- units
ICP-MS ● Inductively Coupled Plasma – Mass Spectrometry. ● Trace analysis technique with better (or equal) detection limits than Graphite Furnace Atomic Absorption (~ppm to ppb levels). ● Can handle simple and complex sample matrices. ● Better detection limits than ICP-OES (~ppm to ppb levels). ● Samples are loaded as liquids then vapourised by being sprayed into the plasma by a nebuliser. ● The vapourised particles are then analysed by the mass spectrometer in the same way as in GC-MS. ● Generally used for metals analysis. ● Stable and reproducible results.
What can it Measure?
Quick Overview ● Samples are decomposed to neutral elements in a high temperature plasma and analysed based on their mass to charge ratios. ● Can be thought of as 4 main processes:- 1 - Sample Introduction and aerosol generation. 2 - Ionisation by an argon plasma source. 3 - Mass discrimination. 4 - Detection system.
Sample introduction\ionisation ● Peristaltic pump takes sample and feeds it into the nebuliser (a) ● Sample is mixed with argon gas which forces the liquid out of the nebuliser producing a fine spray. ● The spray is then ionised in the Plasma (b) and the ions pass into the Mass Spectrometer for detection. ● Laser ablation can be used to ionise solid samples for analysis. a) b)
● There are a number of types of mass filter, but the most common it the ‘Quadrupole’ mass filter. ● It is made up of four rods aligned in a parallel diamond pattern. ● A combined AC and DC electrical potential is applied to these rods with opposite rods having a net negative or positive potential. When the AC and DC potentials are adjusted only ions with a specific mass/charge ration will travel along the quadrupole. ● Other ions are forced out of the path and not detected. A range of DC and AC settings are Scanned through allowing selection of all ion species, which are then passed to the detector. Mass Discrimination Three fragments enter the quadrupole. Only the pink fragment passes through and into the detector. The blue and green are unstable at this voltage and so never reach the detector.
Detection ● These electrons then strike additional active surfaces generating more electrons each time. ● This process is repeated to amplify the signal to a level that can be measured as an electrical pulse. ● By counting the pulses generated by the detector the system counts the individual ions that hit the first active surface (dynode). ● The collected data can then be translated in software to give useful information. ● Ions exit the Quadrupole and strike the surface of the detector generating an electronic signal. ● When an ion strikes the active surface (the dynode), extra electrons are released. Schematic of a detector
Equipment\Techniques ● Three SEM machines:- TESCAN MIRA – FE SEM, SEI, BEI, EDS and Variable Pressure and tensile testing stage ZEISS SUPRA VP 35 - SEI, BEI, EDS and Variable Pressure ZEISS ULTRA + - High Resolution SEI, BEI, EDS, WDS, STEM ● One TEM machine:- JEOL 2100 – LaB 6 High Resolution TEM, with CCD image capture, computer assisted operation and multiple sample (5) holder ● Surface analysis:- OMNISCAN - White Light Interferometer – non contact surface analysis to examine surface roughness etc ● Wet Chemical Analysis:- Standard wet chemical analysis, GC-MS, ICP-MS, BET (surface area analysis) etc ● Spectrometry Analysis:- UV-VIS, FTIR, ATR FTIR, Microscope FTIR