English to Spanish Science Chemistry; Chem Sci/Eng

Hola a todos, estoy con una patente química y no entiendo lo de "running" a gradient,
alguien tiene alguna sugerencia?

Algunos ejemplos donde aparece:

"The crude peptide was purified by semi-preparative RP-HPLC on a Phenomenex Gemini C18 column (5 μ, 110 Å, 10.0 x 250 mm) running a gradient of 5-50% (45% MeCN per min) and then 50-100%..."

"Purification was performed using semi-preparative Reverse Phase (RP) High-Performance Liquid Chromatography (HPLC) using a column and running a gradient as described per procedure for each peptide."

Muchísimas gracias!