title: A microdestructive capillary electrophoresis method for the analysis of blue-pen-ink strokes on office paper.
abstract: This manuscript describes the development of a capillary electrophoresis (CE) method for the detection of acid and basic dyes and its application to real samples, blue-pen-ink strokes on office paper. First, a capillary zone electrophoresis (CZE) method was developed for the separation of basic and acid dyes, by studying the separation medium (buffer nature, pH and relative amount of additive) and instrumental parameters (temperature, voltage and capillary dimensions). The method performance was evaluated in terms of selectivity, resolution (above 5 and 2 for acid dyes and basic dyes, respectively, except for two basic dye standards), LOD (lower than 0.4 mg/L) and precision as intraday and interday RSD values of peak migration times (lower than 0.6%). The developed method was then applied to 34 blue pens from different technologies (rollerball, ballpoint, markers) and with different ink composition (gel, water-based, oil-based). A microdestructive sample treatment using a scalpel to scratch 0.3mg of ink stroke was performed. The entire electropherogram profile allowed the visual discrimination between different types of ink and brands, being not necessary a statistical treatment. A 100% of discrimination was achieved between pen technologies, brands, and models, although non-reproducible zones in the electropherograms were found for blue gel pen samples. The two different batches of blue oil-based pens were also differentiated. Thus, this method provides a simple, microdestructive, and rapid analysis of different blue pen technologies which may complement the current analysis of questioned documents performed by forensic laboratories.
authors.affiliation: Department of Analytical Chemistry, Physical-Chemistry and Chemical Engineering, Multipurpose Building of Chemistry, University of Alcalá, Ctra. Madrid-Barcelona Km. 33.600, 28871 Alcalá de Henares (Madrid), Spain.
authors.forename: Matías
authors.initials: M
authors.lastname: Calcerrada
authors.affiliation: Department of Electronics, Polytechnic School, University of Alcalá, Ctra. Madrid-Barcelona Km 33.600, 28871 Alcalá de Henares (Madrid), Spain.
authors.forename: Miguel
authors.initials: M
authors.lastname: González-Herráez
authors.affiliation: Department of Analytical Chemistry, Physical-Chemistry and Chemical Engineering, Multipurpose Building of Chemistry, University of Alcalá, Ctra. Madrid-Barcelona Km. 33.600, 28871 Alcalá de Henares (Madrid), Spain. Electronic address: carmen.gruiz@uah.es.
authors.forename: Carmen
authors.initials: C
authors.lastname: Garcia-Ruiz
mesh_terms: D004396:Coloring Agents / Q000032:analysis*; D019075:Electrophoresis, Capillary; D044707:Forensic Sciences / Q000379:methods*; D007281:Ink; D010209:Paper; D015203:Reproducibility of Results
chemical_list: D004396:Coloring Agents
keywords: Blue ink; Blue pen; Capillary electrophoresis; Dyes; Ink differentiation; Profiling