SUPPLEMENTAL INFORMATION FOR THE PAPER

Effects of tailored surface chemistry on desorption electrospray ionization mass spectrometry: a Surface-Analytical Study by XPS and AFM

Andrea Penna†,§, Maria Careri†, Nicholas D. Spencer§ and Antonella Rossi*‡§

†Dipartimento di Chimica, Università di Parma, Parco Area delle Scienze 17/A, 43124, Parma, Italy

‡Dipartimento di Scienze Chimiche e Geologiche, Università di Cagliari, Complesso Universitario di Monserrato, Unità di Ricerca INSTM, 09042, Monserrato, Cagliari, Italy

§Department of Materials, ETH Zurich, Vladimir-Prelog-Weg 5, 8093 Zürich, Switzerland

* To whom correspondence should be addressed.

e-mail: and

Section 1 contains further XPS data, concerning g-MTES, g-OTES and g-FOTES, i.e. survey XP-spectra (Figure S.1) and O 1s high-resolution for each functionalized surface (Figure S.2). In addition, lists of the peak-fitting parameters for the high-resolution XP-spectra are given as well as quantitative surface analysis by apparent atomic concentrations for raw and functionalized glass surfaces (Table S.3).

Section 2 contains mass spectra of the mixture of analytes, i.e. melamine, lincomycin and tetracycline, when analyzed at setting different sprayer potentials (i.e. 3 kV and 1 kV).

Section 1

Survey spectra of each surface showed signals ascribable to glass, such as from Si and O as well as Na, K and Ca, which are naturally abundant as counter ions within the silicate glass network.

O 1s high-resolution spectra of g-MTES, g-OTES and g-FOTES, shown below in Figure S.2, were composed of a convolution of three contributions due to the presence of glass at 532.8 eV [1] together with the signals ascribable to the adsorption of silanes, and one at about 533.8 eV, attributed to unreacted alkoxy groups. Oxygen atoms belonging to metasilicates gave a contribution at about 531 eV [2].

The high-resolution spectrum of S 2p was fitted with two doublets whose maxima in their 2p3/2 components were at 164 and at about 168 eV (Figure S.3), assigned to the presence of well-ordered MTES layers having thiol groups on top [3] and to a minor contribution from oxidized sulfur [4–6].

Figure S.1. Survey XP-spectra of g-MTES (a), g-OTES (b) and g-FOTES (c)

Figure S.2. Curve-fitting of high resolution Si 2p XP-spectra of g-MTES (a), g-OTES (b) and g-FOTES (c).

Figure S.3. Curve-fitting of high-resolution S 2p XP-spectrum of glass surfaces functionalized with MTS.

Section 2

In this section mass spectra of a mixture of melamine, lincomycin and tetracycline (100 pmol) obtained by setting the sprayer potential to 3 kV and 1 kV are reported (Figure S.4a-b). It was observed, as expected, that even in the absence of any electrical field to activate the onset of an electrospray flow, protonated molecular ions of each analytes were observed [7, 8]. Differences in relative ion abundances were not observed, but a significant drop in total ion current was seen, at the lower sprayer-potential setting.

Figure S.4.Desorption electrospray ionization (sprayer voltage, 3kV, a) and desorption spray ionization (sprayer voltage, 1 kV, b) mass spectra of 100 pmol of melamine, lincomycin and tetracycline (on g-FOTES as an illustrative example).

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