Highly negative Y-intercept

[ricopalazo]

Hi all!
What are root causes of a highly negative Y-intercept?
How to explain a highly negative intercept based on a linear regression of standards solutions through a range of 20-50ug/ml API? What can cause that?
Conditions: AcNH4 20mM pH 9.2/ACN 70:30 isocratic
Samples: Decapeptide in triethylaminphosphat solution pH 2.3
Column: Phenomenex Kinetex UPLC column

Here are basic informations, ask for more if nedeed.

Thx all

[HW Mueller]

How about the high concentration standards being OK, while at the low end the standards are too low, etc.

[danko]

Poor sensitivity or/and poor recovery (some of the stuff loaded stays in the column – is it new?), inadequate integration method, injection inaccuracy……………..
For more concrete suggestions, more data are needed - e.g. number of standard curve levels, number of determinations at each level (and variation). And representative chromatogram/s is/are always of great help.

Best Regards

[Peter Apps]

The calibration range (20 - 50 ug/ml) seems very narrow to me - is this usual practise in peptide HPLC ?

It makes the intercept very vulnerable to small variations in the upper and lower points.

Peter