If the column back pressure is too high or higher than usual, please check the following suggestions.
a.) Problem in pump, injector, in-line-filter or tubing.
Solution: Disconnect column from system and replace with unions 0.010’’ ID or larger tubing to reconnect the injector to the detector. Run pump at high flow rate (2 - 5 ml/min). If pressure is minimal, see cause 2. If not, isolate cause by systematically eliminating system components. Start with the detector and work back to the pump.
b.) Obstructed column.
Solution: Remove guard column if present and check pressure. Replace guard column if necessary. If column is obstructed, reverse and flush the column while disconnected from the detector. If problem persists, use appropriate restoration procedure. If problem still persists, replace column.
c.) Wrong mobile phase.
Solution: Check mobile phase. Check make-up of mobile phase: Even small changes in composition can affect back pressure.