Making changes in RT of peak

[sanS]

We have a method with Buffer:ACN as mobile phase.

As per method main peak should be between 15-18 minutes. What changes we should do in mobile phase if RT of main peak is at 12 minutes or if at 19 minutes?

Further if resolution requirement of two peaks is 2 but it is coming 1.6, what modification in mobile phase is required?

Thanks

[tom jupille]

In reversed phase chromatography, increasing the organic solvent content of the mobile phase decreases retention.

The resolution question is more complex. Resolution is controlled by three factors: retention, selectivity, and efficiency. If it's simply a retention effect, then, see the previous paragraph. If it's a question of selectivity, then you have to know something about the robustness of the method with respect to organic solvent content, pH, temperature, buffer conentration, and column chemistry in order to make an informed judgement. If it's a loss of efficiency, the replacing the column is usually the most cost-effective solution.