The warm beauty of amber has been captivating and inspiring people since ancient times.

Even today, some secrets remain locked inside the fossilized tree resin. Some of the oldest recovered samples predate the rise of dinosaurs — and could outlast even the most advanced materials that science can make today. That extreme durability has made amber's internal structure so difficult to understand. 

Millions of years ago, this resin exuded from trees and then fossilized over time and techniques to probe the inner molecular architecture of amber seemed to destroy evidence of certain relationships between compounds. 

Studying this Canadian amber from the Late Cretaceous period, scientists have revealed one of its long-held secrets. © Government of Canada, Canadian Conservation Institute, CCI 123773-0025

Jennifer Poulin and Kate Helwig of the Canadian Conservation Institute built on past attempts to use pyrolysis-gas chromatography-mass spectrometry by slowing down the pyrolysis phase, which essentially uses heat to break down a substance.

By doing so, the researchers were able to show that specific groups of atoms within their samples were bound to succinic acid, known historically as "spirit of amber."

For the first time, molecular evidence of the structural role played by succinic acid within the macromolecular structure of Class Ia and Class Id resinite is presented. Using a novel gas chromatographic methodology, communol (Class Ia) and ozol (Class Id) moieties within the polylabdane matrix are shown to be cross-linked with succinic acid. Samples were analyzed using pyrolysis-gas chromatography–mass spectrometry with in situ hexamethyldisilazane derivatization, using a thermal separation probe to perform the pyrolysis and sample introduction. The relatively slow rate of heating and prolonged pyrolysis of resinites using this new methodology, combined with the use of a mild derivatization reagent, allowed communol pyrolysates from Class Ia resinite and ozol pyrolysates from Class Id resinite to elute with unbroken succinyl ester cross-linkages. These results provide direct molecular evidence that the key role of succinic acid within Class Ia and Class Id resinite is to cross-link the macromolecular structure. In the Class Id resinite, the methodology also allowed the detection of succinyl ester linkages between ozol pyrolysates and dehydroabietol, thus demonstrating that nonpolymerized diterpenes contribute structurally to the macromolecular structure of Class Id resinite. 
DOI: 10.1021/ac501073k

"There can be no doubt that much of the stability and durability of certain kinds of amber comes from the succinic acid cross-linking within the matrix," the researchers said. 

So at least one of the puzzles that has perplexed amber research for decades has been solved.

Citation: Jennifer Poulin, Kate Helwig, 'Inside Amber: The Structural Role of Succinic Acid in Class Ia and Class Id Resinite', Anal. Chem. June 19, 2014, DOI: 10.1021/ac501073k. Source: American Chemical Society