Solvent mismatch isn't only a GC issue: solvent mismatch effects on peak shape for LC analyses

When working with dilute samples, larger injection volumes can be used to increase on-column analyte mass. Often, if our sample solvent differs from our mobile phase, it results only in an injection artifact at the beginning of the run. Especially when using smaller columns, injection volume can have a larger effect than expected, especially for early-eluting compounds. Three injections were made of caffeine in methanol. We can see that as injection volume increases, peak shape for caffeine suffers dramatically to the point where some of the analyte elutes in the void. Since the column used is a 50mm x 2.1mm column packed with 5µm silica, the volume of this column is only about 100µL, so an injection volume of even 10µL accounts for 10% of the total column volume. In contrast, we can see that even large injection volumes of caffeine in mobile phase (Water:ACN) have little effect on peak shape. Feel free to contact me for more information, or if you have any comments on this phenomenon.