Direct Analysis in Real Time (DART)

Contributors: Catherine H. Stephens, Asher Newsome

Overview

Technique: DART-MS
Formal name: direct analysis in real time-mass spectrometry
Sample image of the data
DART is a technique to introduce a sample into an analytical device. The following is a mass spectrum from introducing a sample into the flow of the DART.

DART-MS of ca. 8th century BCE textile fragment with alizarin dye. (image provided by Asher Newsome)

What this technique measures: The mass of organic small molecules, generally under 1000 Da, that are gaseous or can be (thermally) desorbed from the surface of a solid or liquid. Works best when the analyte molecule includes a heteroatom (oxygen, nitrogen, etc.) but depending on the mass spectrometer and specific techniques can also detect saturated hydrocarbons.
Limitations of this technique: Without chromatography, low-abundance analytes among a great variety of background species may be detected by the instrumentation but overlooked by the analyst unless the ion of interest is known in advance or can be found by combing through spectra. Large, intact samples surfaces can be analyzed but require special considerations.
Can/how can this technique be made quantitative? Isotopically-labeled standards for a known analyte can be purchased for use with a well-designed experiment.

Samples

Phases it can be used to examine: gas, liquid, solid.
Is this technique non-destructive? As an ionization method for mass spectrometry, a small amount of material is unavoidably consumed. The high-temperature gas may cause melting, discoloration, or scorching of a sample surface in a conventional experiment, but the degree of destructiveness may be limited or practically non-existent depending on the design of experiment and preparation/ingenuity of the analyst.
How invasive is this technique? Dependent on the nature of the analyte and the ability to sample material.
Minimum size of sample necessary to use this technique? Micrograms, single fibers, or other, depending on sample.
Sample preparation methods: little to none necessary, but compatible with solid phase microextraction.

Applications

Examples of how this technique is used in the field? Common analytes include dyes, residues, volatiles, pesticides, synthetics, metabolites, and many more.
Risks associated with using this technique? None aside from potential damage to sample, noted above.

Budgetary Considerations

Approximate cost to purchase equipment for this technique? A commercial DART ionization system with common peripherals may be purchased for +$40k, although various low temperature plasma and flowing afterglow ionization systems can be built by an experienced instrumentalist or a dedicated chemistry/physics/engineering student for considerably less. Various new and used mass spectrometers with respective resolution capabilities may be purchased from vendors for +$100k.
Annual cost to maintain this equipment? DART consumes helium or nitrogen gas at ~2 L/min while in operation (or less depending on peripherals) and may be teed of mass spectrometer gas supplies. Mass spectrometry maintenance fees vary with instrument manufacturer and age but are small compared to employment of an expert operator.
Sample analysis costs? Little to none.

Case Studies

Alizarin dye on textile fibers: C.S. DeRoo and R. A. Armitage, “Direct Identification of Dyes in Textiles by Direct Analysis in Real Time-Time of Flight Mass Spectrometry” Analytical Chemistry 2011, 83, 18, 6924–6928.
Ink identification on paper: Roger W. Jones, Robert Cody, John F. McClelland, “Differentiating Writing Inks Using Direct Analysis in Real Time Mass Spectrometry” Journal of Forensic Sciences (2006): 51 (4): 915-8
Smoke residue on large, intact wooden object with a modified DART system: Timothy P. Cleland, G. Asher Newsome, R. Eric Hollinger, “Proteomic and direct analysis in real time mass spectrometry analysis of a Native American ceremonial hat” Analyst 2019 144 (24): 7437-7446
Pesticide in food matrix using sample extraction peripherals: Germán Augusto Gómez-Ríos, Emanuela Gionfriddo, Justen Poole, and Janusz Pawliszyn, “Ultrafast Screening and Quantitation of Pesticides in Food and Environmental Matrices by Solid-Phase Microextraction–Transmission Mode (SPME-TM) and Direct Analysis in Real Time (DART)” Analytical Chemistry 2017, 89, 13, 7240–7248.

• IonSense Application Notes

Additional Information

Complementary Techniques: Ambient mass spectrometry: DESI, DAPPI, paperspray, etc. R. Javanshad and A. R. Venter, "Ambient ionization mass spectrometry: real-time,proximal sample processing and ionization", Analytical Methods 2017, 9, 4896.
Variations of this technique: other post-plasma ambient ionization methods LTP, FAPA, etc.

References

• R. B. Cody, J. A. Laramée, H. D. Durst, “Versatile new ion source for the analysis of materials in open air under ambient conditions”, Analytical Chemistry 77 (2005) 2297-2302.
  
• Jürgen H. Gross, “Direct analysis in real time--a critical review on DART-MS” Analytical Bioanalytical Chemistry (2014); 406 (1): 63-80.
  
• G. Asher Newsome, Ikumi Kayama, Shannon A. Brogdon-Grantham, “Direct analysis in real time mass spectrometry (DART-MS) of discrete sample areas without heat damage” Analytical Methods (2018); 10 (9): 1038-1045.

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