Multidimensional Mass Spectrometry Coupled with Separation by Polarity or Shape for the Characterization of Sugar-Based Nonionic Surfactants

Abstract

Mass spectrometry (MS) and tandem mass spectrometry (MS/MS) were interfaced with ultra-performance liquid chromatography (UPLC) and ion mobility (IM) separation to characterize a complex nonionic surfactant, consisting of a methylated glucose core (glucam) conjugated with poly(ethylene oxide) (PEO(n)) branches that were partially esterified with stearic acid to form ethoxylated glucam (PEO(n)-glucam) stearates. Reverse-phase LC-MS afforded fast separation according to polarity into five major fractions. Accurate mass measurements of the ions in the mass spectra extracted from these fractions enabled conclusive identification of six components in the surfactant, including PEO(n)-glucam mono-, di-, and tristearates as well as free and esterified PEO(n) as byproducts. MS/MS experiments provided corroborating evidence for the fatty acid content in each fraction based on the number of stearic acid losses observed. With IM-MS, the total surfactant ions were separated according to charge and shape into four distinct bands. Extracted mass spectra confirmed the presence of two disaccharide stearates in the surfactant, which were undetectable by LC-MS. PEO(n)-glucam tristearates were, however, not observed upon IM-MS. Hence, LC-MS and IM-MS unveiled complementary compositional insight. With each method, certain components were particularly well separated from other ingredients (by either polarity or shape), to be detected with confidence. Consequently, combined LC-MS and IM-MS offer a superior approach for the characterization of surfactants and other amphiphilic polymers and for the differentiation of similarly composed amphiphilic blends. It is finally noteworthy that NH4(+) charges minimized chemical noise in MS mode and Li(+) charges maximized the fragmentation efficiency in MS/MS mode.

Ultra‐high performance supercritical fluid chromatography combined with quadrupole time‐of‐flight mass spectrometry for the characterization of pentaerythritol fatty acid esters

“…The product ion peaks of the [M + Na] + precursor ion at m/z 607.4180 were weak because this ion fragments only at high collision energy. However, one of these ions ( m/z 455.3384) was in accordance with the product ion formed from the [M + NH 4 ] + precursor, and the fragmentation mechanism is shown in Figure B . Another competitive dissociation channel of the sodiated molecule was the loss of heptanoic acid to form a product ion at m/z 477.3246 (C 26 H 46 O 6 + Na; mass error: 5.9 mDa).…”

“…However, one of these ions (m/z 455.3384) was in accordance with the product ion formed from the [M + NH 4 ] + precursor, and the fragmentation mechanism is shown in Figure 4B. 20 Another competitive dissociation channel of the sodiated molecule was the loss of heptanoic acid to form a product ion at m/z 477.3246 (C 26 H 46 O 6 + Na; mass error: 5.9 mDa). Because of the absence of the γ hydrogen in pentaerythritol fatty acid esters, hydrogen rearrangement could not take place; thus, this product ion may be produced by a dihydrogen rearrangement reaction.…”

“…The ion at m/z 455.3384 (C 26 H 47 O 6 ; mass error: 1.7 mDa) was formed by the neutral loss of the ammonium salt of the fatty acid from the [M + NH 4 ] + precursor ion at m/z 602.4606. The fragmentation mechanism is shown in Figure A . The product ion peaks of the [M + Na] + precursor ion at m/z 607.4180 were weak because this ion fragments only at high collision energy.…”

“…The postulated fragmentation mechanism is shown in Figure C, where the transfer of the hydrogen on the β carbon caused the neutral loss of the fatty acid molecule, producing a carbene ion. At the same time, the hydrogen on the carbon chain of another fatty acid ester transferred, forming a six‐membered ring structure with the β carbon . Neutral loss of 112.0862 Da from the peak at m/z 455.3384 (C 26 H 47 O 6 ; mass error: 1.7 mDa) to form the ion at m/z 343.2522 (C 19 H 35 O 5 ; mass error: 4.3 mDa) was due to the rearrangement of hydrogen, followed by cleavage of the bond that linked carbonyl and oxygen, and loss of a ketene (Figure D).…”

“…The fragmentation mechanism is shown in Figure 4A. 20 The product ion peaks of the [M + Na] + precursor ion at m/z 607.4180 were weak because this ion fragments only at high collision energy.…”