MALDI-TOF MS Imaging evidences spatial differences in the degradation of solid polycaprolactone diol in water under aerobic and denitrifying conditions

Abstract

Degradation of solid polymers in the aquatic environment encompasses a variety of biotic and abiotic processes giving rise to heterogeneous patterns across the surface of the material, which cannot be investigated using conventional Matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF-MS) that only renders an "average" picture of the sample. In that context, MALDI-TOF MS Imaging (MALDI MSI) provides a rapid and efficient tool to study 2D spatial changes occurred in the chemical composition of the polymer surface. Commercial polycaprolactone diol (average molecular weight of 1250Da) was selected as test material because it had been previously known to be amenable to biological degradation. The test oligomer probe was incubated under aerobic and denitrifying conditions using synthetic water and denitrifying mixed liquor obtained from a wastewater treatment plant respectively. After ca. seven days of exposure the mass spectra obtained by MALDI MSI showed the occurrence of chemical modifications in the sample surface. Observed heterogeneity across the probe's surface indicated significant degradation and suggested the contribution of biotic processes. The results were investigated using different image processing tools. Major changes on the oligomer surface were observed when exposed to denitrifying conditions.

A mass spectrometry imaging method for visualizing synthetic polymers by using average molecular weight and dispersity as indices

“…It is also considered to be a powerful tool for synthetic polymers; however, MALDI-MSI in polymer applications is still limited, although the number of reports is increasing. [18][19][20][21][22][23][24][25][26][27] Conventional MALDI-MSI visualizes the spatial distribution of target compounds, which have specified m/z values, by extracting their mass images from the MSI raw data. This method is not suitable for synthetic polymers because they have a mass distribution.…”

“…However, the differences in spatial distribution were discussed in previous reports by comparing the mass images of several degrees of polymerization. [21][22][23]26,27 Kune et al suggested drawing the sum of mass images of chemically related compounds using KMD analysis. 28 They have successfully applied the method to find lipids, tetraalkylammoniums, polymers and lipopeptides in complex imaging mass data.…”

Using MALDI-TOF MS imaging and LC-HRMS for the investigation of the degradation of polycaprolactone diol exposed to different wastewater treatments

“…Recently, we performed a comparative study on the degradation of a polyester, PCLD, in two aquatic environments, a river and a laboratory mesocosm, applying MALDI-ToF-MS [18]. In a follow-up study [19], we explored the capability of MALDI-MSI as an analytical tool for investigating modifications in the chemical composition at the polymer surface after exposure to either sterile, aerobic, or denitrifying conditions, using PCLD as a probe polymer.…”

Improving the analyte ion signal in matrix‐assisted laser desorption/ionization imaging mass spectrometry via electrospray deposition by enhancing incorporation of the analyte in the matrix

“…Matrix‐assisted laser desorption/ionization (MALDI) imaging mass spectrometry (IMS) is a powerful technique which allows for both the determination and visualization of the spatial distribution of analytes within a sample . A variety of analytes can be detected, including small molecules, noncovalent complexes, peptides and proteins, lipids, and synthetic polymers . MALDI‐IMS experiments have been performed on a variety of systems, including three‐dimensional cell cultures, animal tissue, whole animal sections, plant tissue, and bacterial biofilms .…”

“…[2,3] A variety of analytes can be detected, including small molecules, [4,5] noncovalent complexes, [6] peptides and proteins, [7][8][9][10] lipids, [11,12] and synthetic polymers. [13,14] MALDI-IMS experiments have been performed on a variety of systems, including three-dimensional cell cultures, [15] animal tissue, [9,10] whole animal sections, [16,17] plant tissue, [7,18] and bacterial biofilms. [19] A constant push to be able to resolve smaller and smaller spatial features has resulted in the use of smaller laser spots in order to collect MALDI images using the smallest step size possible, with the current state of the art being a 2.5 micron step size.…”