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CIC Photonics

CIC Photonics. IRGAS Training. Schedule - Day 1. FTIR analysis IR spectrum Michelson interferometer Fast Fourier transform and corrections Interferogram, single beam spectrum, absorption spectrum and transmission spectrum Beer’s law Instrument resolution

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CIC Photonics

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  1. CIC Photonics IRGAS Training

  2. Schedule - Day 1 • FTIR analysis • IR spectrum • Michelson interferometer • Fast Fourier transform and corrections • Interferogram, single beam spectrum, absorption spectrum and transmission spectrum • Beer’s law • Instrument resolution • Quantification analysis-Classical Least Squares introduction • Hardware description • Bomem WorkIR • Instrument purge • Manual manifold • SPGAS software • IRGAS 100 • IRGAS configuration manager • Data retrieval

  3. Schedule - Day 2 • SPGAS software cont. • Qmax – quantification manager • IRGAS spectra reprocessing software • Hardware installation • System power • Pipe installation • Instrument purge • Software installation • IRGAS software • Bomem Ethernet drivers • System verification • System maintenance

  4. FTIR Analysis Tab 1

  5. Light Spectrum • Infrared is invisible light ranging from 1mm to 750nm in wavelength • Infrared light can be divided into three parts: • Far infrared -1mm to 10µm • Mid infrared - 10µm to 2.5µm • Near infrared - 2.5µm to 750 nm

  6. Infrared (IR) Spectrum • IRGAS System mid infrared range • 2.5µm – 25µm in wavelength • 4000 cm-1 – 400 cm-1 in wavenumbers • Wavelength (λ) • Wavelength = (1/wavenumber)*10,000 • Wavenumber (cm-1) • Wavenumber = (1/λ)*10,000

  7. IR Molecules • Not every molecule absorbs infrared light • Monoatomic • He, Ar, Ne, etc… • Homoatomic diatomic • N2, O2, H2, etc… • N N • Molecules that do absorb infrared light • Water is a good example O H H

  8. Michelson Interferometer 2 1 3 4 • Step 1: Beam leaves IR source and hits beamsplitter where it is sent straight through and at a 90° angle • Step 2: The 90° angle beam hits a fixed mirror and is sent back to the beamsplitter • Step 3: The beam that went straight through hits a movable mirror and is sent back to beamsplitter • Step 4: The two beams recombine, go through the gas cell and travel to the detector

  9. Michelson Interferometer AB AC • When AB=AC the phase of the frequencies look the same • When AB=AC+1/4λ, then the phase of the frequencies are opposite in regards to maximums and minimums

  10. Michelson Interferometer • When AB=AC and the two recombine you get stronger maximums and minimums • When AB=AC+1/4λ and the two recombine they cancel one another out and result in a flat line

  11. ABB Bomem Michelson Interferometer • It has two sets of mirrors that move by a pivoting motion • This design is called a wishbone configuration • This configuration is more robust • It can be placed in any orientation • This configuration only has to be smooth at one point vs. the traditional interferogram that has to be smooth along a rail

  12. ABB Bomem Michelson Interferometer

  13. ABB Bomem Michelson Interferometer Wishbone Beamsplitter IR Source Laser

  14. Fast Fourier Transform ZPD • The highest peak intensity is attained when AB=AC • The maximum of the highest intensity peak is called the zero path difference (ZPD) point • After the interferogram has been created by the instrument, the Fourier transform is applied to it, which then results in a single beam spectrum

  15. Single Beam Spectrum

  16. Single Beam Spectrum

  17. Single Beam Spectrum

  18. Single Beam Spectrum

  19. Transmission • The ratio between the sample and the background spectrum

  20. Transmittance Spectrum

  21. Chemometrics • Based on the transmission spectrum chemometrics can be applied • Chemometrics: The application of statistical and mathematical methods for the design or optimization of chemical experiments and for the efficient extraction of information from chemical data • Two types of chemometrics: • Qualitative (identification) • Quantitative (quantity)

  22. Absorbance

  23. Beer’s Law • Says that concentration is directly proportional to absorbance (linearity) • Beer’s law equation is A= abC • Where A = absorbance a = absorptivity of the molecule b = pathlength that the light travels C = concentration

  24. Instrument Resolution • The more points per peak the higher the resolution • The higher the resolution the more noise, but the better peak separation • Common resolution used for an ABB Bomem instrument is 2 cm-1 • Ranges between 1 cm-1 to 128 cm-1

  25. Why Do We Need a Gas Cell • Intensity of a peak is directly related to the # of moles in a sample • In the same area: • Solid will be very packed • Liquid will be less packed • Gas will be even less packed

  26. Long Path Gas Cell Objective mirrors ¼” VCR fittings Field mirror Window retainers

  27. 4Runner 6 Meter Gas Cell

  28. Gas Cell Mirrors Top view of field mirror

  29. IR Beam Path

  30. Classical Least Squares (CLS) • The base equation is As = Ac*K + e • Where As = sample absorption Ac = calibrated absorption K = concentration e = noise • Using the above equation find K that minimizes e • To minimize e we use the CLS method • In this situation there are more equations then variables

  31. Classical Least Squares (CLS) • To simplify matters we assume that e = 0 • The equation then becomes: As = Ac*K • Matrix form:

  32. Classical Least Squares (CLS) • In order to solve for K (Ac-1*As = K), Ac needs to be an inverse matrix • Therefore: AcT*As = (AcTAc)*K (1x1) = (1x1)*K

  33. Problems with Initial CLS Approach • Baseline becomes unstable throughout the day • It can shift, slope, or curve • These changes can be compensated for in the calibrated absorption matrix

  34. Classical Least Squares (CLS) • Accounting for these baselines changes the equation • The eqn. becomes: As = AcK1+ K2+ K3+ K4 • The calibrated absorption matrix can be increased to accommodate the number of species being tested

  35. Weighted Multi-band CLS • A more complex version of the standard CLS • The spectrum is separated into bands • Each band is then calculated • After all the bands are calculated they are added in a weighted averaged fashion • The ones with the highest error and lowest signal are counted for less then the ones with the lowest error and highest signal

  36. Hardware Description Tab 2, 3, & 4

  37. ABB Bomem WorkIR

  38. Manual Manifold Purge Gas In Process Gas In Check Valve Maintenance Valve Process Gas Out Permeation Box Purifier Gas Cell Nitrogen Outflow Check Valve Pressure/Flow Transfer Optics Gas Flow Optical Path Pressure/Flow Spectrometer Nitrogen Outflow

  39. Manifold Parameters • Flow Restrictor • A flow of 30 psi in will give a flow of 5 slpm to the instrument • Purifier • Gives dry N2 to below 2 ppb • Has a lifetime of more than a year if it is used 24/7

  40. Vibrations • There are a number of designs of suspension systems to counteract vibrations • These designs help to keep the data from being affected by a simple bump of the instrument bench

  41. Typical Gas Cells • Have a flow similar to turbulent flow and have a longer residence time

  42. Laminar Flow Gas Cells • The flow is like a waterfall • Therefore there will be less turbulence • Heated laminar flow gas cells • The gas is in contact with the walls letting it reach a temperature similar to the gas cell prior to entering the cell

  43. Gas Cell Flow Diagrams

  44. f/5 Beam Geometry • The higher the f / #, the smaller the objective mirrors, the more light that is lost, the smaller the throughput

  45. SPGAS Software Tab 6, 7, 8, 9, & 10

  46. Specialty Gas Analysis Software (SPGAS) • IRGAS 100 system • Collection & quantification • Qmax • Quantification manager • IRGAS Configuration Manager • Configures parameters • Quantification Reprocessing Tool • Recalculating spectra

  47. IRGAS 100 System • After opening the software the first window is the monitor screen • On the right side there is the available species • On the bottom is the legend of the species that are being shown in the top window • The top shows the concentration of all the species over time

  48. IRGAS 100 Monitor Screen Concentration of species over time Available Species

  49. IRGAS 100 System • Collecting a background • After opening the program, pressing the start button will automatically send the spectrometer to collect a background and then begin collecting a sample • Seeing the sample • Clicking on the desired species tab at the top will show you that species in real time • That screen shows the fast concentration tracker (FCT) and the averaged sample

  50. IRGAS Configuration Manager

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