HPLC with fluorescense detector

[shareena]

Hi, i have problem with my chromatography result. my result for external quality control was high. i tried to find the cause step by step but still didnt get. My standard was ok. But for the external QC,all the values which have been submited were high (+2sd to +3sd).Im using the internal standard and it was ok. (still in the range). From my observation, the only thing that changed is the hplc itself. We are still using the same detector,column and reagents.Please help me.
Thank you

[Alexandre]

Your STD may be diff. from std used in external QC sample, looks like you have higher res. so your std may degraded or ext. QC sample was wrong.

If you have any old PT with known result e.g. FAPAS, try to analyze it or buy CRM or at least a standard of different origin.
2 possibilities –
a. all this works OK
b. nothing work
Conclusions
a. – bad external QC or more clean up is needed
b. – all above and/or new instrument bias and/or std is went off

[shareena]

Thank you very much for your suggestion. I had analyze new standard which is newly prepared and the third party QC material.
And the QC result was ok, but the external QC result was still high. Maybe as u suggested, the new instrument bias should be highlighted.

I will try to transfer the FLD detector to another instrument and see how it will works..
Many thanks