In-source decay of hyperbranched polyesteramides in matrix-assisted laser desorption/ionization time-of-flight mass spectrometry

Hyperbranched polyesteramides (DA(2)), prepared from hexahydrophthalic anhy dride (D) and diisopropanolamine (A) have been characterized, by use of mat rix-assisted laser desorption/ionization time-of-flight mass spectrometry ( MALDI-TOF-MS), field desorption (FD)-MS, and electrospray ionization (ESI)- MS. MALDI of polyesteramides produces protonated molecules. The spectra sho w a complex chemical composition distribution and end-group distribution wh ich are mainly composed of two series of homologous oligomers D(n)A(n+1) - mH(2)O and D(n)A(n) - mH(2)O, where m = 1-2. Signals from protonated molecu les D(n)A(n+1) and D(n)A(n) are almost absent in the MALDI spectrum, wherea s these ions are responsible for the base peak of D(n)A(n+1) - mH(2)O and D (n)A(n) - mH(2)O(m = 1-2) clusters in the ESI spectrum. The absence of -OH end-groups signals in the MALDI spectrum is due to a metastable decay of pr otonated D(2)A(n+1) and D(n)A(n) ions in the ion source of the MALDI mass s pectrometer prior to ion extraction. In-source decay results in the formati on of protonated lower D(n)A(n+1) - mH(2)O and D(n)A(n) - mH(2)O oligomers and their corresponding neutrals, leading to wrong conclusions concerning t he relative end-group distribution as a function of the degree of polymeriz ation and the chemical composition. (C) 2000 American Society for Mass Spec trometry.