Sample diluents should match your starting mobile phase - Tips & Suggestions
For best results, it is always best to try to dissolve your samples in as close as possible to your isocratic eluent or the start of your chosen gradient.
If this is not possible gradually increase the percentage of the solvent in your eluent in which the target is most soluble.
If this is not possible gradually increase the percentage of the solvent in your eluent in which the target is most soluble.