The problem with loss of resolution can occur due to following reasons:
a) Mobile phase contaminated/deteriorated (causing retention times to change). Solution: Check make-up of mobile phase. b) Obstructed guard or analytical column. Solution: If present, remove guard column and attempt analysis. Replace guard column if necessary. If analytical column is obstructed, reverse and flush. If problem persists, column may be clogged with strongly retained contaminants. Use appropriate restoration procedure. If problem still persists, change column.