Capillary electrophoresis fingerprinting of 8-aminopyrene-1,3,6-trisulfonate derivatized nitrocellulose after partial acid depolymerization

•Intact nitrocelluloses cannot be representatively derivatized by APTS.•Partial acid depolymerization by hydrochloric acid was considered prior to derivatization.•Cellodextrin oligomers are the major peaks appearing in electrophoretic fingerprints.•Their presence was confirmed by MALDI-TOF MS.•MALDI-TOF MS so far fails to detect nitrated residues.

Fine characterization of nitrocellulose (NC) remains a challenge, especially in forensic analysis, and a strategy consisting in obtaining representative fingerprints by a separation technique, as for proteins, is of prime interest. In this work, we first established that NCs (especially of high molar mass) cannot be representatively derivatized by 8-aminopyrene-1,3,6-trisulfonic acid (APTS), because of their poor solubility in the medium required for APTS derivatization. Therefore, a partial acid depolymerization step was considered, prior to derivatization by APTS, in an attempt to generate a mixture of oligosaccharides retaining information on the initial NC sample and/or on the cellulose used to prepare it. Acid depolymerization conditions (time and acid concentration) as well as APTS derivatization conditions (time, temperature, APTS/NC and reducing agent/APTS molar ratios) were investigated for lowly-nitrated NCs. The best compromise between depolymerization yields, speed, and pertinency of the resulting oligosaccharidic mixture was obtained using fuming hydrochloric acid (37%, w/w) at 50 °C for 30 min. The most effective procedure for APTS derivatization of oligosaccharides obtained after partial acid depolymerization of NC was achieved at 70 °C for 2 h. The resulting APTS-derivatized oligosaccharides were then separated by capillary electrophoresis (CE) using a background electrolyte composed of 60 mM 6-aminocaproic acid, pH 4.5 (adjusted with acetic acid) + 0.02% hydroxypropyl methyl cellulose. Finally, for the first time, they were identified using APTS-derivatized cellodextrin standards and by matrix-assisted laser desorption-ionization time-of-flight mass spectrometry (MALDI-TOF MS).