Direct Analysis in Real Time (DART) Mass Spectrometry
Background: Mass spectrometry (MS) is one of the most powerful analytical methods available for exact structural identification of organic compounds. This includes organic compounds found in documents (such as paper, film or tape) in the form both of original components and of degradation products. The use of MS in preservation science has traditionally required the investment of time (for sample preparation) and solvents (for extraction). New, more efficient methods are now available for evaluation at the Library of Congress, using Direct Analysis in Real Time (DART) mass spectrometry.
Contributing Study:
Arnaud, C.H. (cover story interview of Jeanette Adams), "Taking Mass Spec Into The Open:
Open-air Ionization Methods Minimize Sample Prep and Widen Range of Mass Spectrometry Applications", Chemical & Engineering News, October 8, 2007 Cover, Vol. 85, Issue 41, pp 13‑18. http://pubs.acs.org/cen/coverstory/85/8541aboutcover.html
Project Description: An open-air ionization method called direct analysis in real time (DART) can provide alternative methods of mass spectrometric analysis that can either eliminate or significantly reduce the need for destructive sampling. Ionization in MS has traditionally been done within the vacuum system of the MS. However, in "open-air ionization" using DART, the sample is placed in a stream of helium that contains ionized atmospheric gases (such as water vapor and oxygen), and the analytes in the sample are ionized in the open air of the laboratory environment. This means that organic compounds in the sample can be directly, and in real time, determined without time-consuming analytical protocols and thus with high sample throughput. What makes DART particularly attractive for cultural heritage applications is that:
- An intact collection object can be held in the sample gap—or the housing containing an object can be opened in front of the gap—and volatile analyte molecules can be determined using a room-temperature stream of helium so that no destructive sampling is required.
- In cases in which destructive sampling is needed (for analyses of semi- or non-volatile molecules), micro-samples can be analyzed using a higher-temperature stream of helium in real time without the need for time-consuming sample manipulations such as extractions or chromatographic separations.
- DART is capable of detecting femtomoles (10-15 moles) and perhaps smaller quantities of analytes.
- DART can ionize not only low-mass volatile compounds but also higher mass compounds that contain reactive functional groups that cannot be readily determined by GC-MS.
Outcomes/Findings: Preliminary research and development is underway to evaluate the feasibility of using DART-MS to analyze a variety of library collection materials, including the following:
- determination of volatile acids from the decomposition of paper and cellulose acetate materials;
- the comprehensive analysis of different types of papers containing different additives including gums, glues, and size;
- the determination of chemical markers that are diagnostic of "sticky deterioration" of analog magnetic tapes; and
- the determination of contaminants in housing materials and housing environments.
Support: Library of Congress Preservation Directorate
Update and Images: Descriptions of the Library's research using DART-MS have been presented at the following venues: Users Group for Mass Spectrometry and Chromatography (MaSC) [Winterthur and Philadelphia Museum of Art], September 2007; British Library Meeting “VOCs in Paper Conservation Research", London, UK, February 2008 Pittsburgh Conference in Analytical Chemistry and Spectroscopy (PittCon), March 2008; 10th Annual Graduate Research Fair, Eastern Michigan University, Ypsilanti, MI, March 2008 [Sigma Xi Keynote Speaker]; Summit of Research Scientists (SORS) in Preservation Science, Library of Congress, Washington, DC, July 2008; American Institute for Conservation Annual Meeting, Richmond, VA, April 2007; American Chemical Society Middle Atlantic Regional Meeting, Collegeville, PA, May 2007; 55th American Society for Mass Spectrometry Conference, 2007; Eastern Analytical Symposium, Somerset, NJ, November 2007; 18th Triennial Meeting International Association of Forensic Sciences, New Orleans, LA, July 2008; US Secret Service Forensic Services Division, Washington, DC, July, 2008.
The images are of (A) the JEOL JMS-AccuTOF mass spectrometer with the (blue) DART ion source installed; (B) a leaf from a book being non-destructively sampled and analyzed in real time for volatile organic acids; and (C) the DART mass spectrum of acetic acid vapors in the housing microenvironment of a historic cellulose acetate motion picture film.
