Introduction to Time-of-Flight Mass Spectrometry and Deconvolution Nicholas Hall Speaker Mark Libardoni, Pete Stevens, Joe Binkley Life Science & Chemical Analysis Centre St. Joseph, Michigan, USA
e-seminar Goals Overview of a Time-of-Flight mass spectrometer Comparison to scanning instruments LECO s TOF MS Instruments Spectral reproducibility Fast spectral acquisition rates Increased linear dynamic range Deconvolution Overview Experimental Studies for: Sampling Rate Deconvolution Capability Usage as a High-Speed GC and GCxGC detector
Time-of-Flight Mass Analyzer A Time-of-Flight (TOF) is a non-scanning mass analyzer which emits pulses of ions (or transients) from the source. These pulses are accelerated so that the ions have equal kinetic energy as they are directed into a flight tube. Since kinetic energy is equal to 1/2 mv 2,wheremisthemassof the ion and v is the ion velocity, the lower the ion's mass, the greater the velocity and shorter its flight time. The travel time from the ion source through the flight tube to the detector, measured in microseconds, can be transformed to the m/z value through the relationships described above. Because all ion masses are measured for each transient, TOF mass spectrometers offer high sensitivity as well as rapid acquisition. A non-scanning instrument such as TOF MS offers many advantages including fast acquisition rates, exceptional dynamic range, spectral continuity, the ability to acquire full mass range spectra without sacrificing speed or sensitivity, and capability to perform quantitative analyses across a wide dynamic range in the presence of complex matrices. LECO s Pegasus TOFMS
Quadrupole Ion Path Molecules Detector Successful Ion Path Quadrupole Ion Analyzer Electron Ion Beam The strength and frequency of the RF field determines whether or not an ion of a certain mass passes through the rods (and is counted by the detector) or smashes into a nearby surface. For example, in a 120 volt field at a radio frequency of 2 MHz, only ions of 16 Daltons (Da) will navigate through the rods and into the detector. Heavier or lighter ions do not survive the journey to the detector. In this manner, you can control the mass of the ions that the detector collects. The quadrupole mass spectrometer is made with 4 rods of hyperbolic surfaces. A direct current field is applied to 2 rods and a radio frequency (RF) field is applied to the other 2 rods. These rods generate an electric field through which the ions can move.
Benefits of Quads and TOFs Quadrupole Time-of-Flight Inexpensive Robust Good for Qualitative and Quantitative work Excellent Qualitative and Quantitative results in single run No Spectral Bias (skewing) Excellent Detection Limits Enhanced Detection Limits Very Fast acquisition rates when operating in SIM (up to 500 spectra/s)
Sampling Rate Quadrupoles Time-of-Flight Scanning Instrument at 10,000 u/sec (~20 Hz) Duty Cycle Time Increase Scan Rate by Limiting Mass Range (40 200 amu) Non-Scanning Instrument Full Mass Range Acquisition All Masses are Collected Acquisition Rates up to 500 spectra/s (500 Hz) Sampling Rate is important for properly defined peaks and deconvolution
Proper Sampling Rates Literature defines the proper sampling rate of a chromatographic detector to have an acquisition speed capable of delivering at least 10 points across a fully resolved peak to deliver accurate quantitative data Therefore if you have a: 1 second wide peak, you will need a detector speed of 10 Hz 0.5 second wide peak (500 ms), you will need 20 Hz 0.2 second wide peak (200 ms), you will need 50 Hz 0.1 second wide peak (100 ms), you will need 100 Hz 0.05 second wide peak (50 ms), you will need 200 Hz
LECO Separation Sciences Delivering the Right Results Pegasus 4D and HT TruTOF TOF HT - Fastest GCMS Available - Market s only GCxGC-TOFMS - 2 nd Fastest GCMS Available - All the advantages of TOF at quad prices
Proper Sampling Rates Most samples are complex and do not contain fully resolved chromatographic peaks therefore some method of deconvolution is needed. d LECO has published results showing that 18-20 data points are necessary for accurate quantitative deconvolution of overlapped peaks.
Rel. Abund. 1000 750 500 250 Spectral Bias (Skewing) TOFMS GC Peak Scanning MS Inte ensity 8000 6000 4000 2000 Rel. Abund. 1000 750 500 250 0 60 80 100 120 140 m/z 0 42.5 43.0 43.5 Time (sec) 0 60 80 100 120 140 m/z Rel. Abund. 1000 750 500 250 Intensity 8000 6000 4000 2000 Rel. Abund. 1000 750 500 250 0 60 80 100 120 140 m/z 0 42.5 43.0 43.5 Time (sec) 0 60 80 100 120 140 m/z Rel. Abu nd. 1000 750 500 250 Intensity 8000 6000 4000 2000 Rel. Abun nd. 1000 750 500 250 0 60 80 100 120 140 m/z 0 42.5 43.0 43.5 Time (sec) 0 60 80 100 120 140 m/z
Proper Sampling Rate Metolachlor 238 Malathion 158 Fenthion 278 Chlorpyrifos 199 Parathion 291 DCPA 301 Cyanazine 68 Isodrin 193 Ti Trichloronat 269 40 spectra/s 9 peaks located
Proper Sampling Rate 10 spectra/s 6 peaks located
Proper Sampling Rate 5 spectra/s 5 peaks located
Proper Sampling Rate 2 spectra/s 0 peaks located
40 spectra/s 9 peaks located 10 spectra/s 6 peaks located 2 spectra/s 0 peaks located
True Signal Deconvolution A correlated set of ions reaches the detector Caliper
True Signal Deconvolution er Calipe
True Signal Deconvolution er Calipe
True Signal Deconvolution A new correlated set of ions reaches the detector t er Calipe
True Signal Deconvolution The first pack of correlated ions have apexed ChromaTOF lays down a peak marker er Calipe
True Signal Deconvolution er Calipe
True Signal Deconvolution The second pack of correlated ions have apexed ChromaTOF lays down another peak marker er Calipe
True Signal Deconvolution er Calipe
True Signal Deconvolution er Calipe
Coelution of 3 Pesticides Fenthion 278 Chlorpyrifos 199 Parathion 291 < 550 ms >
Spectral Coelution of Pesticides * * Fenthion * ** * Chlorpyrifos Parathion * * * *
Spectral Deconvolution of Pesticides Deconvoluted Spectra of Chlorpyrifos NIST Library Spectra of Chlorpyrifos
For More Information Contact LECO at: World Headquarters/United States In United States: 800-292-6141 or 269-985-5496 Outside U.S.A.: 269-983-5531 Email: info@leco.comcom www.leco.com