Amorphous Conjugated Polymers as Efficient Dual‐Mode MALDI Matrices for Low‐Molecular‐Weight Analytes

Abstract

Matrix‐assisted laser desorption/ionization mass spectrometry (MALDI MS) usually employs highly crystalline small‐molecule matrices, and the analyte is interpreted as being co‐crystallized with the matrix. We recently showed that semi‐crystalline polymers are efficient matrices for the detection of low‐molecular‐weight compounds (LMWCs) in MALDI MS and MALDI MS Imaging, and are dual‐mode, i. e., enabling both positive and negative modes. The matrix performances of two fluorene/napthalene diimide co‐polymers P(TNDIT‐Fl(C4C2)) and P(TNDIT‐Fl(C10C8)) were investigated and compared. Both are fully amorphous according to XRD measurements, show high relative absorption values at the wavelength of common MALDI lasers (λNd:YAG=355 nm: C4C2=73 %; C10C8=67 %), and are solution processable. As matrices, they are dual‐mode, and enable the detection of LMWCs while being mostly MALDI‐silent. Compared with semicrystalline polymer matrices, the amorphous matrices give similar or better signal intensities, thus indicating that analyte inclusion takes place in the amorphous part of the polymer matrix.

MALDI Matrices for the Analysis of Low Molecular Weight Compounds: Rational Design, Challenges and Perspectives

“…Also, the conjugated polymers discussed under subchapter 3.2 are excellent dual polarity mode matrices, enabling LMW compounds detection in positive as well as negative mode, while being vacuum stable and MALDI silent, i. e., not giving matrix-related signals when low laser intensities were used. [19,65]…”

“…By changing the sidechain length and type, we could obtain semicrystalline and fully amorphous derivatives of PNDI. The latter not only functions as matrix for LMW compounds, but even slightly outperforms the former, suggesting that for conjugated polymers the analyte incorporation most likely takes place in the amorphous phase [65] …”

Amorphous poly-N-vinylcarbazole polymer as a novel matrix for the determination of low molecular weight compounds by MALDI-TOF MS

“…Furthermore, achieving point-to-point reproducibility still faces challenges due to the “sweet spot” effect caused by the uneven co-crystallization between the crystalline matrix and the analyte. Recently, Horatz et al 18 synthesized two amorphous copolymers P(TNDIT–FI(C10C8)) and P(TNDIT–FI(C10C8)) as MALDI matrices from 9,9-bis(2-ethylhexyl)fluorene as the starting material for LMWC detection in positive and negative ion modes, respectively, and explored the relationship between matrix crystallinity and the performance as a matrix. The results show that amorphous matrices have obvious advantages in the LMWC signal intensity detection compared to semi-crystalline matrices.…”

Polymerization as a Strategy to Improve Small Organic Matrices for Low-Molecular-Weight Compound Analytics with MALDI MS and MALDI MS Imaging

“…We recently reported that conjugated homo- and heteropolymers are promising matrices for LMWC analytics with MALDI MS and MSI as they combine very low background interferences with HV stability and good ionization efficiencies in positive and negative modes . Furthermore, different from classic SOMs, for semicrystalline conjugated polymers, the analyte incorporation seems to take place in the amorphous region …”

“…43 Furthermore, different from classic SOMs, for semicrystalline conjugated polymers, the analyte incorporation seems to take place in the amorphous region. 44 Here, we apply polymerization as a new strategy to improve established SOMs. Adding vinyl groups to two well-known SOMs, DHB and harmine, followed by free-radical polymerization, resulted in two polymeric small organic matrices (P(SOMs)) carrying the respective SOMs as side chains: poly(vinyl dihydroxybenzoic acid) (P(VDHB)) and poly(vinyl harmine) (P(VHar)).…”