Chemical distinctions between Stradivari's maple and modern tonewood

Violins made by Antonio Stradivari are renowned for having been the preferred instruments of many leading violinists for over two centuries. There have been long-standing questions about whether wood used by Stradivari possessed unique properties compared with modern tonewood for violin making. Analyses of maple samples removed from four Stradivari and a Guarneri instrument revealed highly distinct organic and inorganic compositions compared with modern maples. By solid-state ¹³C NMR spectroscopy, we observed that about one-third of hemicellulose had decomposed after three centuries, accompanied by signs of lignin oxidation. No apparent changes in cellulose were detected by NMR and synchrotron X-ray diffraction. By thermogravimetric analysis, historical maples exhibited reduced equilibrium moisture content. In differential scanning calorimetry measurements, only maples from Stradivari violins, but not his cellos, exhibited unusual thermooxidation patterns distinct from natural wood. Elemental analyses by inductively coupled plasma mass spectrometry suggested that Stradivari's maples were treated with complex mineral preservatives containing Al, Ca, Cu, Na, K, and Zn. This type of chemical seasoning was an unusual practice, unknown to later generations of violin makers. In their current state, maples in Stradivari violins have very different chemical properties compared with their modern counterparts, likely due to the combined effects of aging, chemical treatments, and vibrations. These findings may inspire further chemical experimentation with tonewood processing for instrument making in the 21st century.

Negative ion mode atmospheric pressure ionization methods in lignin mass spectrometry: A comparative study

RATIONALE

Mass spectrometry with atmospheric pressure ionization is the most promising method for studying the structure of natural lignin, which is the second most abundant biopolymer in nature. The goal of this study is to compare the efficiency and characteristics of different types of ionization techniques (ESI, APCI, and APPI) in the negative ion mode by the example of softwood lignin.

METHODS

As the subjects of the study, we selected a preparation of spruce dioxane lignin and several phenols, simulating the basic structural fragments of the lignin macromolecule. High-resolution mass spectra were recorded using an Orbitrap mass spectrometer. Acetone was used as a solvent for samples and a dopant in photoionization mode. The ionization conditions were optimized to achieve the maximum intensity of the mass spectra.

RESULTS

The formation of deprotonated lignin molecules is characteristic of all the studied types of ionization; partial fragmentation of the biopolymer occurs in all ionization modes. ESI in the presence of ammonia yields low-intensity signals, leads to a significant decrease in ionization efficiency with increasing molecular weight of lignin oligomers, gives high-intensity impurity peaks in the mass spectra, and demonstrates selectivity for more polar structures. The ionization efficiency increases sharply in the order of ESI < APCI < APPI. The two latter methods are characterized by similar mechanisms of ionization; they ensure detection of approximately 1900 spruce lignin oligomers in the range of molecular weights up to 1.8 kDa. The determination of the elemental composition of oligolignols enabled the four main groups of compounds to be distinguished.

CONCLUSIONS

Photoionization using acetone as a dopant is distinguished by a significantly higher intensity of signals and the lowest sensitivity to contaminants present in the lignin preparation. This ionization method can be considered as preferred for studying the dioxane lignin preparations of woody plants. Copyright © 2016 John Wiley & Sons, Ltd.