As one possible solution to unexpected retention times is to ensure that the mobile phase solvent lines currently contain the mobile phase solvents you want to use. A previous user may have used a different mobile phase on the instrument and there can be some residual solvent left in the lines. In this case, simply purge the solvent lines to waste with your mobile phase and you will have the correct solvent for your application. Do not let the unwanted solvents enter your column.