There was an issue with the Guanine HCl analysis by reverse phase HPLC. The first 6 injections of the Guanine standard were fine with % RSD of 0.34. In the subsequent guanine control injection, the third injection has a higher than expected peak area and height resulting in failure of its % recovery. Next, the Guanine drift injection was ok again.

The baseline of the above chromatograms were expanded and examined. They looked fine or consistent.

The lambda max (275 nm) was examined in the absorbance spectrum of Guanine and concluded not likely to be the cause.

So, we are going to re-inject the trouble control sample five times with a known control with supporting data into the Waters HPLC to ensure that the problem was not the sample and something else. We would be able to see the results sometime this week.

If sample is not the cause, then the issue can be the HPLC system. Your suggestion is needed.

Instrument: Waters 717 HPLC with a PDA detector
Mobile phase: 1 % Methanol in 50 mM Sodium Acetate, pH 4.5
Column: Phenomenex C18, 150 x 4.6, 5 micron, 110A
Flow rate: 1 mL/min
RT of peak: 7 min


The HPLC is old, so plumbing can be an issue with a 1% mobile phase on a C18?


Thanks