Successive injection in microstructured-capillary electrophoresis for rapid pairwise comparisons. Application to questioned documents

Herein we propose a successive double injection in microstructured-capillary electrophoresis for a fast, simple and easy-to-interpret comparison of samples. First, injection was optimized through three capillaries (conventional capillary of 28.5 μm id, microstructured capillary (MSC) of 6 holes of 32.8 μm each, and MSC of 61 holes of 8.9 μm each). The 6-hole MSC was selected, as it provided reproducible results, and higher volume capacity, which allowed larger injection volumes. Then, the method was applied to the analysis of different types of inks present in questioned documents. After the criterion to establish a MATCH or No match between two successive samples, a blind test with 20 pairwise comparisons between questioned signatures was finally made to demonstrate the potential of the method. The method proved to be useful in pairwise comparison analyses, as it: i) provides a fast and practical analysis; ii) maintains the same CE conditions for both samples; iii) uses simple data treatment which puts on easy interpretation on the results, interesting in court.