Comparison of primary monoatomic with primary polyatomic ions for the characterisation of polyesters with static secondary ion mass spectrometry

Abstract

Static secondary ion mass spectrometry (S-SIMS) emerges as one of the most adequate methods for the surface characterisation of polymers with an information depth of essentially one monolayer. The continuing search for increased analytical sensitivity and specificity has led to exploring the use of polyatomic primary ions as an alternative to the traditionally applied monoatomic projectiles. As part of a systematic investigation on polyatomic bombardment of organic and inorganic solids, this paper focuses on selected polyesters. Mass spectra and ion yields are compared for layers deposited on silicon wafers by spincoating solutions with different concentrations of poly(epsilon-caprolactone) (PCL), poly(butylene adipate) (PBA) and poly(ethylene adipate) (PEA). Accurate mass measurements have been used to support the assignment of the ions and link the composition of the detected ions to the analyte structure. Use of polyatomic projectiles increases the yield of structural ions with a factor of +/-15, +/-30 and +/-10 for PCL, PBA and PEA, respectively, in comparison to bombardment with Ga+ primary ions, while the molecular specificity is improved by the detection of additional high m/z ions.

A comparison of the static SIMS and G‐SIMS spectra of biodegradable homo‐polyesters

“…The strong presence of the Si + mass peak indicates the polymer film was a thin layer, in the order of 1 nm, or there was patchy coverage. Nevertheless, the SSIMS spectrum was in close agreement to those obtained in the previous studies [9,17] -3) and 'C t ' = mass peaks which are unrelated to PHB (see text).…”

“…[17]. It is interesting to note that fragments with n > 1 were not seen in PCL for m/z 120-300, as shown in Fig.…”

“…[25,26] Furthermore, configuration of the polymer may also play a major part in the fragmentation, as van Royen et al proposed the possibility of undergoing McLafferty rearrangement with PCL. [17,27] Consistency of the type of fragment ions observed were also interesting, as [ [28] has also speculated the formation of the [nM + H] + ions for PLA, PHB and PCL via McLafferty rearrangement followed by olefin elimination is also possible to form R-C( OH + )-OH. The molecular weight of the polymer will also affect the relative abundance of fragments from the main-chain and end-of-chain regions.…”

“…The SSIMS spectrum was in close agreement with previous studies. [9,17] The most intense peak in the SSIMS spectrum was Si + at m/z 28, which was from the substrate. The strong presence of the Si + mass peak indicates the polymer film was a thin layer, in the order of 1 nm, or there was patchy coverage.…”

Cluster secondary ion mass spectrometry of polymers and related materials

“…Some examples include work by Davies et al (2003), who found enhancement in signals characteristic of PET and polypeptides when employing Au þ 3 clusters, Nagy and Walker who observed similar enhancements using Au (Nagy, Gelb, & Walker, 2005) and Bi (Nagy & Walker, 2007) clusters for bombardment of polystyrene and other organic materials, and several others [Au clusters (Bryan et al, 2004;Aimoto et al, 2006;Zhu & Kelley, 2006), C 60 Hill & Blenkinsopp, 2004), SF þ 5 (Gillen & Roberson, 1998;Stapel, Thiemann, & Benninghoven, 2000;Stapel & Benninghoven, 2001;Boschmans, Van Royan, & Van Vaeck, 2005;Van Royen, Taranu, & Van Vaeck, 2005)]. …”