Un tampon de charge est systématiquement ajouté à la solution d'ADN ; il va permettre à la solution de se déposer au fond du puits et de visualiser la migration de l'échantillon grâce à des colorants.
L'exemple ci-dessous est extrait de la fiche technique du tampon de charge Promega
Promega Blue/Orange Loading Dye, 6X
The dye is used for loading DNA samples into non denaturing gel electrophoresis wells and tracking migration during electrophoresis. The buffer is designed to be used at a 1X final concentration.Composition of Blue/Orange Loading Dye, 6X: 0.4% orange G, 0.03% bromophenol blue, 0.03% xylene cyanol FF, 15% Ficoll® 400, 10mM Tris-HCl (pH 7.5) and 50mM EDTA (pH 8.0).Migration characteristics: In a 0.5–1.4% agarose gel in 0.5X TBE, xylene cyanol FF migrates at approximately 4kb, bromophenol blue at approximately 300bp and orange G at approximately 50bp.