title: Solvent-based and solvent-free characterization of low solubility and low molecular weight polyamides by mass spectrometry: a complementary approach.
abstract: BACKGROUND
  Polyamides (PA) belong to the most used classes of polymers because of their attractive chemical and mechanical properties. In order to monitor original PA design, it is essential to develop analytical methods for the characterization of these compounds that are mostly insoluble in usual solvents.
  
  
  METHODS
  A low molecular weight polyamide (PA11), synthesized with a chain limiter, has been used as a model compound and characterized by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS). In the solvent-based approach, specific solvents for PA, i.e. trifluoroacetic acid (TFA) and hexafluoroisopropanol (HFIP), were tested. Solvent-based sample preparation methods, dried-droplet and thin layer, were optimized through the choice of matrix and salt. Solvent-based (thin layer) and solvent-free methods were then compared for this low solubility polymer. Ultra-high-performance liquid chromatography/electrospray ionization (UHPLC/ESI)-TOF-MS analyses were then used to confirm elemental compositions through accurate mass measurement.
  
  
  RESULTS
  Sodium iodide (NaI) and 2,5-dihydroxybenzoic acid (2,5-DHB) are, respectively, the best cationizing agent and matrix. The dried-droplet sample preparation method led to inhomogeneous deposits, but the thin-layer method could overcome this problem. Moreover, the solvent-free approach was the easiest and safest sample preparation method giving equivalent results to solvent-based methods. Linear as well as cyclic oligomers were observed. Although the PA molecular weights obtained by MALDI-TOF-MS were lower than those obtained by (1)H NMR and acido-basic titration, this technique allowed us to determine the presence of cyclic and linear species, not differentiated by the other techniques. TFA was shown to induce modification of linear oligomers that permitted cyclic and linear oligomers to be clearly highlighted in spectra.
  
  
  CONCLUSIONS
  Optimal sample preparation conditions were determined for the MALDI-TOF-MS analysis of PA11, a model of polyamide analogues. The advantages of the solvent-free and solvent-based approaches were shown. Molecular weight determination using MALDI was discussed.
authors.affiliation: Université de Rouen, Laboratoire COBRA UMR 6014 & FR 3038, IRCOF, 1 Rue Tesnière, 76821 Mont St Aignan Cedex, France.
authors.forename: Caroline
authors.initials: C
authors.lastname: Barrère
authors.forename: Marie
authors.initials: M
authors.lastname: Hubert-Roux
authors.forename: Catherine M
authors.initials: CM
authors.lastname: Lange
authors.forename: Majed
authors.initials: M
authors.lastname: Rejaibi
authors.forename: Nasreddine
authors.initials: N
authors.lastname: Kebir
authors.forename: Nicolas
authors.initials: N
authors.lastname: Désilles
authors.forename: Laurence
authors.initials: L
authors.lastname: Lecamp
authors.forename: Fabrice
authors.initials: F
authors.lastname: Burel
authors.forename: Corinne
authors.initials: C
authors.lastname: Loutelier-Bourhis
mesh_terms: D002851:Chromatography, High Pressure Liquid; D005841:Gentisates / Q000737:chemistry; D008970:Molecular Weight; D009757:Nylons / Q000737:chemistry* / Q000145:classification; D012974:Sodium Iodide / Q000737:chemistry; D012995:Solubility; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization / Q000379:methods
chemical_list: D005841:Gentisates; D009757:Nylons; D012974:Sodium Iodide; C010925:2,5-dihydroxybenzoic acid