State of the Art on Mass Spectrometry : Focus and Critical Quality Issues

Transcription

1 State of the Art on Mass Spectrometry : Focus and Critical Quality Issues Rudolph C Johnson, PhD Emergency Response Branch 26 June 2013 National Center for Environmental Health Division of Laboratory Sciences

2 Focus and Critical MS Quality Goals Focus Fingerprint spectra for bacteria Primarily in clinical microbiology Producing interpretable results on a representative number of samples as quickly as possible Quality Well characterized performance in a specific matrix Limits of detection, or minimum number of organisms Established, documented proficiency in a matrix

3 General Comments on Mass Spectrometry and New Applications Mass spectrometry is about 100 years old Most instrumentation is conserved between applications Introduction ion source mass/ion separation detection Large field State-of-the-art developments : If most mass spectrometers are not really new, then what is? How people are using them, modifying them o Sample preparation, introduction and ionization o Database leveraging Why is this important to me? Many areas of MS are mature, robust MS offers both universal and focused testing capability If you are looking for a new testing platform, really look here

4 General Comments on Mass Spectrometers and New Applications Portability Primarily an engineering issue - It can be done Portable is not the same as stand-alone Traditional issues persist that directly impact Quality Data is impressive, can be misunderstood The following slides introduce Issues to track on state-of-the-art technologies Where to focus for quality issues

5 Traditional Mass Spectrometry Sample Introduction Advancements This is a vacuum system, requires differential pumping, like entering BSL labs MALDI best for pathogens Less sample = better sensitivity Too much sample, binning issues, sensitivity Ion Source Advancements MS can t detect neutrals, requires ionization Ionization had traditionaly been too harsh on biomolecules Impurities compete during ionization, and reduce sensitivity Gas Phase Separation - Few changes Separation based on mass to charge ratio High voltage, vacuum based instruments (power, safety issues) Instruments can be portable to building-sized (accelerators) Gas phase separation is fast, generating large amounts of data, traditional limitation

6 Traditional Mass Specometry Selection of Instruments Few changes, year to year variation Low resolution to high resolution systems. Low resolution is more flexible, cheaper, more reliable Better is the enemy of good enough is key Detection Minor changes The mass spectrometer is a timing circuit Like ringing a bell, speed of acquiring data influences sensitivity Ions that arrive late are counted as different ions Quality issue Data Processing Advancements Databases for fingerprints Better computers have had a huge impact here

7 Biggest changes in MS: So this means Fingerprint identification vs. Interpretation Sample cleanup and introduction sensitivity and robustness issues Output database searching This translates into : Turning MS into a blackbox for the average user But if you don t understand the key issues, you will generate poor quality data

8 So this means Key Issues: How do you verify instrument performance, daily? What are your positive and negative controls? How do you characterize fingerprint spectra, and who controls database entries? What is a minimum threshold criteria for a positive result (statistical issues)? What is your matrix? How do you compensate for charge competition?

9 Summary Fingerprint spectra Key focus in microbiological applications MS instruments are established, some are portable Not usually stand-alone Quality is a cornerstone issue for MS Applications Don t let the technology carry you away, focus on the application issues Characterization of a system, limits, rates of false positive and negatives Established matrix Interpretation of results, and proficiency testing

10 Thank You For more information please contact Centers for Disease Control and Prevention 1600 Clifton Road NE, Atlanta, GA Telephone, CDC-INFO ( )/TTY: Web: The findings and conclusions in this report are those of the authors and do not necessarily represent the official position of the Centers for Disease Control and Prevention. National Center for Environmental Health Division of Laboratory Services