variable peak area in replicate injections

[debby hsu]

Dear All
I got RSD% close to 2% in replicate injections of standard solution for system suitability test.
The chromatographic system includes C18 HPLC column, mobile phase with pH 3.5 buffer and acetonitrile, 15 uL injection volume. And the pKa of analyt compound is about 6.8.
This situation seemed to be better under another chromatographic system including C8 column and mobile phase with pH 2.3 buffer and acetonitrile.

I would like to know what may cause high RSD% in replicate injections?

The buffer consists of ammonium phosphate monobasic, 1-octanesulfonic acid Na salt, triethylamine and then adjust pH with phosphoric acid.

Thanks for attention.
Debby

[kubowicz.tomasz]

Hello

Possible reasons:

-poor integration (if you're using automatic integration try to integrate peaks manually)
-sampler issue (leak, worn out rotor seal, syringe/needle problem)

Regards

Tomasz Kubowicz

[danko]

Try and qualify the injector by weighing the the vial your injecting from.
It's the first step end then other options could be considered.

Best Regrds

Funny mobile phase by the way