No Sample Prep MS
Conducted by O. David Sparkman
Using mass spectrometry to analyze a pure compound or a mixture of pure compounds is a relatively easy process. It usually involves putting the analyte(s) into solution and injecting them into a gas chromatograph-mass spectrometer (GC-MS) or a liquid chromatograph-mass spectrometer (LC-MS) and waiting for spectra of pure substances to be produced.
Unfortunately, this is not the case with most of the analyses presented to the analytical chemist. Someone wants to know what makes a chili pepper hot, whether or not a drug is present in a biological fluid such as blood plasma or urine, was that piece of burned carpet associated with an arson fire or not, did that bird die from pesticide poisoning or something more insidious such as VX nerve agent, or something else that will require sample preparation before the analyte can be introduced into an instrument to obtain a mass spectrum.
Often, this sample-preparation requirement and a need to separate analytes by chromatography results in long time delays in getting a result or even the statement, “Is all that work really worth it.” The capabilities long touted for mass spectrometry are veiled in this cloud of how-to-get-to-the-analyte.
Well, in the infamous words of the famous Peter Seller's character, Inspector Jacque Clouseau, “NOT-ANYMORE!” A new technique involving mass spectrometry has been introduced that takes advantage of mass spectrometry's ability to assign an accurate mass to an ion so that an elemental composition can be assigned and to confirm that elemental composition through the intensity of isotope peaks. This technique is called DART.
No, I am not talking about the Detroit Area Rapid Transit Authority. I am talking about the mass spectrometry technique named by its inventors Direct Analysis in Real Time. Most acronyms used in mass spectrometry relate to some descriptive aspect of the technique such as MALDI (matrix-assisted laser desorption/ionization) or DESI (desorption electrospray ionization). However, even when the acronym is explained, it is still not clear what DART is.
DART is an analytical technique that allows for the in situ mass spectral analysis of substances by “dangling” the material that has the substance on it in the instrument. Perhaps “dangle” is not an appropriate term to use when describing a sample position in an instrument's interface; however, to say that the sample is “placed in the interface” or “positioned in the interface” would detract from the casualness with which the sample position can be adjusted to obtain data in a DART instrument. The DART interface is such that an instrument could be placed in the produce section of a supermarket and used by concerned consumers to determine what pesticides were present on various fruits and vegetables.
DART is a mass spectrometry system that:
- can analyze samples in the gas, liquid, or solid phase
- operates at 0 potential
- operates in the open air (atmospheric pressure)
- does not require solvents
- obtains mass spectra from sample on the surface of anything imaginable; i.e. commodities, ball caps, glass rods, plastics, adhesive tape, etc.
This presentation will provide a brief discussion of how DART works and will provide a series of examples of the uses of DART. Even if you are not looking to add mass spectrometry capabilities or increase your existing capabilities, you need to know about this technique that could well be the next Nobel Prize-winning technology in mass spectrometry.
A detailed outline and Prof. Sparkman's qualifications follow below.
DART - A New Type of In Situ Mass Spectrometry:
No Sample Prep MS
Description of the DART Ionization Technique
- Definition of Direct Analysis in Real Time
- Operating pressures
- Sample placement
- Types of samples that can be analyzed
- Description of the physical ion source
- The mass analyzer requirement
Mechanisms of Ionization
- Penning ionization
- Protonation through water clusters
- Analysis cross section
- Negative-ion formation
- Calibration of the m/z scale
- Use of heat
- Role of dopants
- A practical forensics example
- The surface composition of currency
- How to use DART to tell where you were last night
- Explosive analysis and detection
- An illustration of DART with the analysis of finger prints
- Distinction between isobaric substances in counterfeit drugs
- What's on the skin of your fruit?
- In situ detection on bizarre surfaces like tire treads, bird feathers, and porous concrete
How DART might be useful to your specific applications
- An open discussion about your specific needs and how DART may be applied to them
O. David Sparkman
O. David Sparkman is currently an Adjunct Professor of Chemistry at the University of the Pacific in Stockton, California; an American Chemical Society Instructor in Mass Spectrometry; a Consultant to the National Institute of Standards and Technology Mass Spectrometry Data Center; President of ChemUserWorld.com; and the American Society for Mass Spectrometry Member-at-large for Education.
Dr. Sparkman holds positions on the Editorial Advisory Boards of the European Journal of Mass Spectrometry and the HD Science GC/MS Update - Part B; is on the Continuing Education Committee of the ACS; and is the Book Review Editor for the European Journal of Mass Spectrometry. He is the author of Mass Spectrometry Desk Reference (Global View Publishing: Pittsburgh, PA, 1st ed. 2000; 2nd ed. 2006). He is a member of the Editorial Boards of the John Wiley Encyclopedia of Environmental Analysis and Remediation and Encyclopedia of Analytical Chemistry, Editor of and a contributor to the Mass Spectrometry Section of the Encyclopedia of Analytical Chemistry, and a contributor to the Encyclopedia of Environmental Analysis and Remediation. Along with J. Throck Watson, he developed the Mass Spectral Interpretation Quick Reference Guide.