Optimized MALDI-TOF MS Strategy for Characterizing Polymers

Abstract

In recent years, matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) plays an essential role in the analysis of polymers. To acquire a more reliable strategy for polymer profiling, we characterized four representative polymers including polyethylene glycol 6000, polyvinylpyrrolidone K12, polymer polyol KPOP-5040, and polyether polyol DL-4000. The preparation methods of these four polymer samples have been optimized from six aspects, including matrix, cationization reagent, solvent, mixing ratio of cationization reagent to polymer, mixing ratio of matrix to polymer, and laser intensity. After investigating the effects of seven commonly used matrices on the ionization efficiency of four polymers, trans-2-[3-(4-tert-butylphenyl)-2-methyl-2-propenylidene] malononitrile (DCTB) was found to be the only matrix suitable for the analysis of all the four polymers. Our experimental results suggested that different polymers showed a certain preference for different cationization reagents. For example, the polymer polyol KPOP-5040 was suitable for sodium iodide as the cationization reagent, while polyvinylpyrrolidone K12 was more suitable for silver trifluoroacetate (AgTFA). For the choice of solvent, tetrahydrofuran is a reagent with rapid evaporation and a wide range of dissolution which can achieve the best results for the analysis of four polymers. The optimized method was successfully applied to the identification of DSPE-PEG-NH₂ with different polymerized degrees. This MALDI-TOF strategy potentially provided the supplementary function through the polymer's application in biomedical and visible probing.

Keywords: MALDI-TOF MS; polyether polyol DL-4000; polyethylene glycol 6000; polymer; polymer polyol KPOP-5040; polyvinylpyrrolidone K12.

FIGURE 1

Experiment scheme. Workflow of the study.

FIGURE 2

MALDI-TOF MS spectrums of PEG-6000 with different matrices including CHCA (A), DHB (B), DCTB (C), dithranol (D), 9AA (E), 2,3,4-THAP (F), and 2,4,6-THAP (G). Effect of the matrix on polymer ionization efficiency (H). Blue, orange, gray, and yellow colors indicate the peak intensity of PEG-6000, PVPK12, KPOP-5040, and DL-4000, respectively.

FIGURE 3

MALDI-TOF MS spectrums of PEG-6000 with different cationization reagents including AgTFA (A), NaTFA (B), and NaI (C). Intensities of four polymers with different cationization reagents (D). Effect of solvent on the polymer ionization efficiency (E). Blue, orange, gray, and yellow colors indicate the peak intensity of PEG-6000, PVPK12, KPOP-5040, and DL-4000, respectively.

FIGURE 4

MALDI-TOF MS spectrums of polymers with the cationization reagent (A) and without the cationization reagent (B). The effect of different ratios of the cationization reagent (C), different ratios of the matrix (D), and laser energy (E) on the polymer ionization efficiency. Blue, orange, gray, and yellow colors indicate the peak intensity of PEG-6000, PVPK12, KPOP-5040, and DL-4000, respectively.

FIGURE 5

Identification of DSPE-PEG-NH2-2000 (A) and DSPE-PEG-NH2-3400 (B) with the optimized strategy.