DAD and Oxytetracycline

[Emi]

Hi Everyone,


I am using DAD (G1315B) to detect Oxytetracycline and I have to use a method which is basically the mobile phase consists of 15 % acetonitril and 85 % of 0.1 phosphoric acid at 355 nm and I got good results but after stop period 4 months, I got some samples to be analyzed the same way but I got weird results....... I found negative peaks all over the spectrum for each run for the standards! I did check the purity of the mobile phase and the column and it is clean however, when I run methanol with 100% ACN, I got good and clear spectrum.By the way, I tried 280 nm and it is positive but still find some peaks everywhere ... only 355 nm is negative.

Could you please help me to fix this problem

Thanks a lot in advance

Regards

[HPLCCONSULT]

Without any details, it sounds like you changed your Reference Wavelength Values/Bandwidth settings. Make sure the Reference Wavelength is OFF for ALL runs. Make sure you are using the same settings.

*Remove the column, insert a small back pressure restriction device (tubing) and wash the system down. Next, run a blank and check the full spectrum.

[Consumer Products Guy]

Without any details, it sounds like you changed your Reference Wavelength Values/Bandwidth settings.

Agree, most likely explanation.

[Emi]

Thanks for your rapid reply and I am going to follow your instructions and update you

Have a great day