If you find problems with separation when you use an autosampler, but not when you do a manual injection, it's important to understand how your autosampler is making each injection. If a large portion of your wash solution is being injected along with the sample, the separation will be affected in most cases. This is especially true for short columns with quickly eluting peaks (like our PP-ODS II) because a significant portion of the separation will occur before the true mobile phase condition is re-established.

Solution: The simplest option is to replace the wash solution with the same mobile phase, or at the least, with wash solution that has a composition more similar to the mobile phase. Be careful to wash the autosampler with pure water after you finish your analysis to avoid damage due to the precipitation of salt from the wash (mobile phase) solution.

Other adjustments can be made to your autosampler, but this will depend on your type of autosampler. For example, bubbles, size of sample loop, injection volume, length of needle line, syringe speed, etc