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).