Development of a GC/MS method for the qualitative and quantitative analysis of mixtures of free fatty acids and metal soaps in paint samples

Jacopo La Nasa; Francesca Modugno; Matteo Aloisi; Anna Lluveras-Tenorio; Ilaria Bonaduce

doi:10.1016/j.aca.2017.11.017

Development of a GC/MS method for the qualitative and quantitative analysis of mixtures of free fatty acids and metal soaps in paint samples

Anal Chim Acta. 2018 Feb 25:1001:51-58. doi: 10.1016/j.aca.2017.11.017. Epub 2017 Nov 14.

Authors

Jacopo La Nasa¹, Francesca Modugno², Matteo Aloisi³, Anna Lluveras-Tenorio⁴, Ilaria Bonaduce⁵

Affiliations

¹ Department of Chemistry and Industrial Chemistry, University of Pisa, Via Giuseppe Moruzzi 13, 56124, Pisa, Italy. Electronic address: jacopo.lanasa@for.unipi.it.
² Department of Chemistry and Industrial Chemistry, University of Pisa, Via Giuseppe Moruzzi 13, 56124, Pisa, Italy. Electronic address: francesca.modugno@for.unipi.it.
³ Department of Chemistry and Industrial Chemistry, University of Pisa, Via Giuseppe Moruzzi 13, 56124, Pisa, Italy. Electronic address: matteoaloisi2610@gmail.com.
⁴ Department of Chemistry and Industrial Chemistry, University of Pisa, Via Giuseppe Moruzzi 13, 56124, Pisa, Italy. Electronic address: anna.lluveras@for.unipi.it.
⁵ Department of Chemistry and Industrial Chemistry, University of Pisa, Via Giuseppe Moruzzi 13, 56124, Pisa, Italy. Electronic address: Ilaria.bonaduce@unipi.it.

PMID: 29291806
DOI: 10.1016/j.aca.2017.11.017

Abstract

In this paper we present a new analytical GC/MS method for the analysis of mixtures of free fatty acids and metal soaps in paint samples. This approach is based on the use of two different silylating agents: N,O-bis(trimethylsilyl)trifluoroacetamide (BSTFA) and 1,1,1,3,3,3-hexamethyldisilazane (HMDS). Our experimentation demonstrated that HMDS does not silylate fatty acid carboxylates, so it can be used for the selective derivatization and GC/MS quantitative analysis of free fatty acids. On the other hand BSTFA is able to silylate both free fatty acids and fatty acids carboxylates. The reaction conditions for the derivatization of carboxylates with BSTFA were thus optimized with a full factorial 3² experimental design using lead stearate and lead palmitate as model systems. The analytical method was validated following the ICH guidelines. The method allows the qualitative and quantitative analysis of fatty acid carboxylates of sodium, calcium, magnesium, aluminium, manganese, cobalt, copper, zinc, cadmium, and lead and of lead azelate. In order to exploit the performances of the new analytical method, samples collected from two reference paint layers, from a gilded 16th century marble sculpture, and from a paint tube belonging to the atelier of Edvard Munch, used in the last period of his life (1916-1944), were characterized.

Keywords: Free fatty acid; Gas chromatography/mass spectrometry; Hexamethyldisilazane; Metal soaps; N,O-bis(trimethylsilyl)trifluoroacetamide; Painting; Silylation.