Developing an Uncertainty Budget for Polymer MALDI-TOF MS
What are the keys to quantitation?
Mass Bias in Ion Formation?
MALDI Process Characterization
Vary Matrix:Analyte:Salt Ratios
Traditional (Serial) and Combinatorial Methods
Mass Bias in Ion Separation/Detection?
Optimize Instrument Settings
Factorial Design of Experiments
Operator Bias in Data Analysis?
Operator Independent Data Analysis Methods MassSpectator
Can the uncertainties for each step be ascertained?
Type A ("Random") Uncertainty
Type B ("Systematic") Uncertainty
Obtained by Repeat Measurements
Obtained through study of the method itself
Mass Axis: relatively small uncertainty
Least important MMD determination
(Very important for species identification!)
Mass Axis: three calibration strategies
Biopolymers (i.e. secondary standards)
Repeat unit calibration (Caution regarding isotope
effects)
Voltage, time, distance (Absolute but not precise)
Signal Axis: larger uncertainty than mass axis
Most important axis for MMD measurement
Relative peak area (not absolute) is the measurand
Signal axis
Desorption probability
Ionization probability
Detection efficiency
Sample preparation
Approach
Experiments will revolve around the gravimetric mixing of
polymers with closely-matched molecular mass distributions and
comparing the gravimetric results with the mass spectrometric
results.
Combinatorial
Sample Preparation
Rastering X-Y Stage
Programmable Syringe Pump
Gas Nebulizer to Deposit Sample
First Libraries Have Been Produced
In Conjunction with NCMC “Combi for NIST”
Instrument
Optimization
The orthogonal factorial 25-1 design used required 16 observations
at parameter extrema, with an additional three middle-range
observations for comparison
Factors studied: laser energy, detector voltage, ion extraction
delay time, ion extraction first stage voltage, lens voltage
Response variable: signal to noise ratio
Characterization and Measurement Group
Polymers Division
Materials Science and Engineering Laboratory
