Peaks slightly shift by 0.1 min in standard vs sample, Why?

[chemist23]

Hello,

I am injecting sugar standards and tobacco samples on HPLC-RID. The standard is prepared in pure water and the sample is extract in pure water. When I compare the peaks found in the standard vs sample, there is a slight shift of about 0.1 min in the sample. Why is this even though diluent is the same?

[James_Ball]

One thing I can think of is tobacco has a lot of salts in it, so maybe that is creating a slight buffer solution with a different pH than the standards and causing the retention time shift.

Have you tried using a buffer solution for both extracts and standards? It might be what is needed to stabilize the retention times.

[pwm]

Are the peaks youre comparing the same area?

[lmh]

… and if you need to demonstrate that the shift is caused by the chemistry of the sample, and isn't merely that you're looking at the wrong peak, you can run a mixed vial containing a mix of standard and sample. If the sample is causing the standard to elute at a slightly different retention time, you will get one peak. If the peak in the sample isn't the same as the standard, you will get two peaks.