Adsorption, Negative Intercepts and Calibration Curves

Chromatography Forum: GC Archives: Adsorption, Negative Intercepts and Calibration Curves
Top of pagePrevious messageNext messageBottom of pageLink to this message  By Donna Sirenski on Thursday, August 12, 2004 - 03:07 pm:

I have been challenged with the analysis of low concentrations of Triethanolamine in aqueous samples. I have observed a large negative intercept for my calibration curve. In fact, the negative intercept is larger than the response for the TEA in the samples. Surprisingly, my final result (TEA content) for several samples compares well with an analysis performed using LC/MS. My peer suggests that the method is still valid. I should point out that the curve is actually quite linear (r2>0.997) over the calibration range (100-500ppm) and I prepared my standards using the sample matrix, which is loaded with non-volatile material.

I can't find any information regarding large negative intercepts and I wonder if anyone can share their opinions regarding the validity of a calibration curve with large negative intercepts. I am thinking that the intercept is negative due to adsorption in the inlet which I can't seem to overcome and I do not want to have to derivitize the samples.


Top of pagePrevious messageNext messageBottom of pageLink to this message  By anonymous on Friday, August 13, 2004 - 10:10 am:

Could you post your line equation so we can see how large is "large"?


Top of pagePrevious messageNext messageBottom of pageLink to this message  By carla on Sunday, August 15, 2004 - 03:18 pm:

What do you mean with "negative intercepts"?

Do you mean the calibration curve crosses the amount/concentration axis or negative peaks?


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