A team of researchers, led by Sichun Zhang of Tsinghua University in Beijing, has developed a new imaging mass spectrometric (IMS) process that can analyze works of art without causing any damaging to the art itself. The key to the method is a new IMS approach that uses a low-temperature plasma probe to carefully remove molecules from the surface of the art.
Published in the journal Angewandte Chemie [Liu et al., Angewandte Chemie (2010) doi: 10.1002/anie.200906975], the research was based on the team’s interests in developing a new ambient ionization method. They then built a low-temperature plasma probe ion source that works at ambient conditions without perceivable damage to the sample. In addition, the spatial resolution of the IMS technique is sufficiently high to allow characterization of the spatial distribution of analytes.
The probe has a fused capillary and two electrodes created with aluminum foil, which is then subjected to extremely strong alternating voltage. The voltage induces a dielectric barrier discharge in the helium that is placed inside the capillary. This has the effect of making helium atoms form into separate ions, electrons and exited atoms – a plasma – which only reaches a temperature of 30°C. The helium plasma that leaves the capillary ejects molecules from the surface of the sample and ionizes them, which ensures the artwork under investigation is undamaged.
The researchers first applied the new ion source to the analysis of seals – the stamps used as signatures and means of authentication on Chinese paintings and calligraphy. As some components in paintings are organic compounds, the probe was able to show variations in the composition of the ink of individual seals, and therefore identify those seals that were authentic from those that weren’t. This breakthrough meant the technique could be applied to an examination of paintings, and their identification, conservation and restoration.
The next step in the research will focus on the application of this new ion source for mass spectrometry in various fields, including the direct analysis of pesticide residue on vegetables, searches for traces of explosive on the surface of luggage, the analysis of cancer biopsies, as well as other new applications in the chemical and drug industries.