In this post, I’m going to explain how DART-MS and ambient ionization can simplify and speed up chemical analysis by mass spectrometry.
What is ambient ionization?
Mass spectrometry is one of the most sensitive and versatile methods for chemical analysis. For almost a century, if you wanted to analyze chemicals by mass spectrometry, you could only analyze samples that could be introduced into a vacuum chamber and evaporated by heating. The development of atmospheric pressure ion sources like atmospheric pressure chemical ionization and electrospray ionization in the 1970’s and 1980’s greatly expanded the range of samples that could be analyzed by MS. However, samples still had to be injected into a sealed ion source. The introduction of ambient ionization with DART-MS (Direct Analysis in Real Time mass spectrometry) and DESI (desorption electrospray ionization) in the early 2000’s made it possible to analyze samples in open air, with little or no sample preparation.
Introducing the DART ion source
We developed DART at JEOL USA in late 2002 and early 2003, and JEOL introduced the AccuTOF-DART mass spectrometer at PittCon in 2005, winning the Pittcon Editors’ Gold Award for Best New Product.
Very briefly, DART-MS uses a high voltage needle to create a glow discharge plasma in a gas such as helium, argon, or nitrogen. The gas flowing out of the glow discharge chamber (“flowing afterglow”) contains highly energetic excited-state atoms or molecules. Long-lived excited-state atoms (“metastable atoms”) produce charged particles (“ions”) that can be introduced into a vacuum system and analyzed by mass spectrometry. Typically, the DART-MS source reacts with water or oxygen in air. These atmospheric ions react with the sample to produce the ions that are detected by the mass spectrometer. The detailed reactions will be described in subsequent posts.
The DART gas is often heated to evaporate chemicals that have low volatility. In thermal desorption DART (TD DART-MS), the sample is heated directly and the vapors are introduced into the DART-MS gas stream. Because DART-MS analysis can be carried out in open air, the chemist can quickly analyze objects held in front of the mass spectrometer. This has led to widespread use of the JEOL AccuTOF-DART system in fields such as forensics, materials analysis, chemical synthesis, and plant biochemistry.
Analyzing a smokeless gunpowder particle.
DART-MS is one of many chemical analysis tools that are available with the JEOL AccuTOF-DART mass spectrometer. If you’d like to learn more about JEOL mass spectrometers and the AccuTOF-DART system, please visit us here.