Analytical mass spectrometry of poly(ethylene glycol) additives in artists’ acrylic emulsion media, artists’ paints, and microsamples from acrylic paintings using MALDI–MS and nanospray-ESI–MS

Poly(ethylene glycol) (PEG) compounds in artists’ acrylic emulsion paint products from different paint manufacturers, ranging from base emulsions (Rohm and Haas, Rohm and Scott Bader), to modified emulsions and complete paints (Rowney, Winsor and Newton, Golden, Liquitex, Lascaux), were characterised with a newly developed mass spectrometric method which combines data from Matrix assisted laser desorption/ionisation mass spectrometry (MALDI–MS) and nano-electrospray ionisation mass spectrometry (nano-ESI–MS(MS)). MALDI–MS was used for the determination of the molar mass distribution (MMD) and calculation of the molar mass averages ( M w and M n ), the polydispersity index ( D ) and the relative amount of a specific distribution if multiple PEGs were present. Electrospray ionisation mass spectrometry was used for the end-group analysis. Three different classes of polymers was found being PEG, polypropylene glycol (PPG) and a block copolymer of polyethylene glycol/polypropylene glycol (PEG/PPG) with molar mass averages ranging from 400 to 4200 Da. PEG compounds with a nonylphenyl or an octylphenyl hydrophobic end-group are most common. The hydrophilic end-groups observed are hydroxide and/or sulphate. Water extracts of microsamples from a palette by David Hockney dating from 1970 and samples paintings by Patrick Caulfield (1936–2005) and John Hoyland (born in 1934) were investigated with the same technique. Although some artist paint manufacturers use the same specific base emulsions to make their paints, the composition of the PEG compounds present in the water extracts of the palette and paintings samples made it possible, in some cases, to suggest a specific brand of paint used by the artist.