Can I use a classical HPLC column in combination with an UHPLC system?

Yes, HPLC columns can also be used with UHPLC systems and due to the smaller system dead volume the column performance in plate numbers will be higher. UHPLC systems are especially endowed to endure high pressures caused by the small particle sizes. Classical HPLC columns produce a lower back pressure because of the bigger particles and therefore are compatible to UHPLC systems.