1
Q
Calculate “z”
A
z = 1/delta(m/z)
2
Q
Mass Analyzer Function and Characteristics
A
- separate ions of different (m/z)
- important characteristics
- mass resolution
- mass accuracy
- speed
3
Q
Mass Resolution
A
- the observed m/z value divided by the smallest difference (delta m/z) for two ions that can be separated
- two common definitions
- FWHM- full width at half max peak (single peak)
- 10% valley - the separation between two adjascent equal magnitude peaks such that the valley between them is a specified fraction of the peak height
4
Q
Mass Accuracy
A
- the measured error in m/z divided by the theoretical value
((experimental(m/z)-theoretical(m/z))/theoretical (m/z))*106 yields mass accuracy in ppm
5
Q
Mass Range
A
- maximum allowable m/z ratio amenable to analysis
6
Q
Linear Dynamic Range
A
- range over which an ion signal is linear with the analyte concentration
7
Q
Speed
A
- number of scans per unit time
8
Q
Filtering Mass Analyzer
A
- mass analyzer which functions as a filter allowing only ions of a singel specific m/z to exit while all others are discarded
- low fraction of generated ions are detected
- filtering analyzers need to be scanned to generate the full spectrum
- select ion monitoring (SIM) of a selected m/z value allows for more precise measurement of ion abundance
9
Q
Quadrapole Mass Analyzer
A
- assembly of four parrallel equidistant spaced rods
- masses are separated by their vibratory motion in a high-frequency oscillating field which is created by applying direct current and radio frequency potentials to the electrodes
- mass spectrum is obtained by changing both the direct current and the radio frequency while keeping their ratio constant
- ions which are unstable under these conditions will crash into the rods
- fast scan speeds but has low mass resolution R=200 at m/z 200
- can be operated as a mass analyzer or mass filter
10
Q
Three Dimensional Quadrapole Ion Trap
A
- mass separation is achieved by storing ions in the trapping space and manipulating their motion in time rather than space
- traps all ions in a radio frequency field consisting of two end cap electrodes and a ring electrode
- by scanning different radio frequency voltages ions with different m/z are ejected (slow ejection allows for better mass resolution)
- low levels of detection than quadrapole
- capable of MS/MS
- is only able to trap a limited number of ions and has a low mass resolution delta m/z = 1
11
Q
Quadrapole Ion Trap Operational Principles
A
- instrument creates stable trajectories for ions of certain m/z or m/z range while removing unwanted ions by letting them collide with the walls or removing them through axial ejection due to unstable trajectories
12
Q
Linear Quadrapole Ion Trap (LIT)
A
- shoebox composed of quadrapoles plus trapping potentials at both ends of the box
- mass is analyzed by trapping and ejection of desired ions depending upon their m/z
- can trap more ions (increased sensitivity) and has a high scan rate approx 20Hz
- still has low resolution delta m/z = 1
13
Q
FT-ICR
A
- Fourier-Transform Ion Cyclotron
- traps ions using a static magnetic field
- ions circle with radius r (unchanged kinetic energy) which is effected by their m/z ratio
- by applying a broadband pulse certain m/z are synchronized and become excited thereby increasing their radius while maintaining the same frequency of rotation
- as the orbit of the ions nears the walls of the device the ions pass by electrodes inducing an image current
14
Q
Cyclotron Detection
A
- image current induced by ions passing electrodes on the walls of the instrument creates a potential which can be amplified and measured
- Fourier transform is performed on the time dependent current to yeild frequencies for various ions which can be related to their m/z
- allows for high mass resolution in excess of 1,000,000 and accuracy <1ppm of error despite long aquision times
- increasing the scan speed lowers the resolution to approximately 600,000
15
Q
A
Mass Spectrometry
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