Characterization of poly(ethylene glycol) esters using low energy collision-induced dissociation in electrospray ionization mass spectrometry

Abstract

A method of characterizing polyglycol esters, an important class of industrial polymer, has been developed using electrospray ionization ion trap mass spectrometry (ESI ITMS). The fragmentation behavior of polyglycol esters is found to be different from that of polyglycols whose functional end groups are linked to the polymer chain via ether bonds (i.e., polyglycol ethers). The fragmentation pattern of an oligomer ion generated by low-energy collisioninduced dissociation is strongly dependent on the type of cation used for ionization. It is shown that structural information on the polymer chain and end groups is best obtained by examining the fragment ion spectra of oligomers ionized by ammonium, alkali, and transition metal ions. T andem mass spectrometry using either matrixassisted laser desorption ionization (MALDI) or electrospray ionization (ESI) is being developed as a tool for polymer structural characterization [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16]. We are particularly interested in characterizing functional polyglycols, including poly(ethylene glycol) (PEG), poly(propylene glycol) (PPG), and their copolymers [12][13][14][15][16][17][18][19]. Structural characterization of this type of polymer is important because polyglycols are widely used in industry with their properties strongly depending on not only molecular weights, but also structures and compositions. Recently, polyglycols have also been increasingly used in biotechnical and biomedical applications such as the development of slow releasing drugs [20,21]. Traditionally, polyglycols were thought to be difficult to fragment in low-energy CID tandem MS. In our recent work, we demonstrated that lithium and transition metal ions could form adduct ions with polyglycol in ESI, and these adduct ions could readily undergo fragmentation [15,16]. The resulting fragment ion spectra were very informative for the structural characterization of polyglycol. Our previous study was focused on alcohol ethoxylates whose end-groups are linked to polyglycol chains via ether-type C™O bonds (i.e., polyglycol ethers). The results generated therein were compared to earlier studies of the same type of polyglycols employing fast atom bombardment (FAB) MS/MS by Latimer and coworkers [22][23][24][25].Poly(ethylene glycol) ester, especially fatty acid methyl ester ethoxylate (FAMEE), is another class of polyglycol which can be used as an alternative to alcohol ethoxylates in many industrial applications. With varying alkyl chain lengths in the fatty acid moiety, a wide range of hydrophilic lipophilic balance (HLB) values can be achieved to suit different applications [14]. They are extensively used as non-ionic bases for cosmetics and pharmaceuticals, non-ionic emulsifiers for vegetable and mineral oils, thickening agents for creams, anti-static agents for plastics, and non-ionic surfactants. Despite active MS study on alcohol ethoxylates [12][13][14][15][16][17][18][19], the literature on ester ethoxylates is scarce [5,16,63].In this work, we report a metho...

Microstructural study of a nitroxide-mediated poly(ethylene oxide)/polystyrene block copolymer (PEO-b-PS) by electrospray tandem mass spectrometry

“…Dissociation of this m/z 1198.7 precursor ion gave rise to an unexpectedly simple spectrum where only three main series could be observed. Indeed, a more complex MS/MS spectra was expected since, following Lattimer's pioneering work [16,26], all CID studies of PEO homopolymers have described four main fragment ion series [27][28][29][30][31][33][34][35][36], and Jackson [27,37,38] and others [39 -42] have reported nine fragment ion series arising from dissociation of PS oligomer ions.…”

“…Such PEO-b-PS diblock copolymer with well defined structure has CH 3 -as the ␣ end-group, SG1 nitroxide as the end-group and a linkage group between the two blocks, as illustrated in Scheme 2. Fragmentation pathways of PEO oligomers have already been demonstrated, using fast atom bombardment (FAB) [16,26], MALDI [27][28][29][30][31][32], ESI [33][34][35], or desorption electrospray ionization (DESI) [36] to generate oligomer adducts. Structural characterization of PS ions produced by MALDI has been reported using collision-induced dissociation (CID) [27,[37][38][39][40][41][42], sustained off-resonance irradiation (SORI)-CID [43], or PSD [39], and fragmentation pathways were described.…”

Tandem mass spectrometry of poly(methacrylic acid) oligomers produced by negative mode electrospray ionization

“…Dissociation pathways have been studied for a large variety of polymers, such as PEO [11][12][13][14][15][16][17][18][19][20][21][22][23][24], PS [20,[23][24][25][26][27][28][29][30], or poly(methylmethacrylate) (PMMA) [20, 21, 23, 30 -32]. In contrast, few MS studies have been reported for PMAA and most of them focused on the analysis of volatile thermal degradation products of the polymer [33,34].…”

Systematic MALDI‐TOF CID Investigation on Different Substituted mPEG 2000

“…The very prominent and distinct fragmentation can be explained by a McLafferty þ 1 rearrangement (1,5 hydrogen-transfer) [21] that involves the sulfonic acid ester bond leading to the cleavage of the toluene sulfonic acid and the formation of a vinyl ether end group at the PEG chain with a m/z value of 1710.048, as observed previously by different groups (Figure 1d). [22][23][24][25] This peak at m/z 1710.048 marks the beginning of the fragment series B that can be followed down to m/z 125.020. The B series, as well as the C series, are part of different fragment distributions forming eye catching regular structures in the middle molar mass region of the CID spectrum that are certainly much lower in intensity in comparison to the 1,5 hydrogen-transfer (Figure 1e).…”

“…As this mass loss of m/z 170.013 and m/z 172.010 corresponds to the p-(chloromethyl)-benzoic acid with 35 Cl and 37 Cl, respectively, a 1,5 hydrogen-transfer is proposed leading, like in the case of tosylated mPEG, to the fragment with m/z 1710.102 (Figure 2d). [22][23][24][25] Furthermore, the loss of the chlorine atom within the acid is underlined by the loss of the chlorine isotopic pattern.…”