Solution: Check system for loose fittings. Check pump for leaks, salt build-up, and unusual noises. Change pump seals if necessary.
b) Change in mobile phase composition. Small changes can lead to large changes in retention times.
Solution: Check make-up of mobile phase. If mobile phase is machine mixed, hand mix and supply from one reservoir.
c) Air trapped in pump. Retention times increase and decrease at random times.
Solution: Purge air from pump head or check valves. Change pump seals if necessary. Be sure mobile phase is degassed.
d) Column temperature fluctuations.
Solution: Use reliable column oven or insulate column.
e) Column overloading. Retention time usually decreases as mass of solute injected on column exceeds
Solution: Inject smaller volume or dilutions of the sample.
f) Sample solvent incompatible with mobile phase.
Solution: Adjust solvent. Whenever possible, inject samples in mobile phase.
g) Column problem. Not a common cause of erratic retention. As a column ages, retention times gradually decrease.
Solution: Substitute new column of same type to confirm column as cause. Discard old column if restoration procedures fail.