Chromatography Forum

dear all
I am new in LC field.
my task is to monitor 2,4-TDI and 2,6-TDI in air sample. I use: eluent: 0.2M ammonium-acetate buffer, pH=6-6.2 with acetic acid; aceto-nitrile 70:30.
Column: Philips cyano 250 x 4.6, 5um
Flow: 1ml/min
Det: fluorescence, ex: 240nm, em: 370nm
This column has not been used for a long time and while measuring the baseline fluctuates. How can I stabilize the baseline? Furthermore, I have different concentrations of 2,4 , 2,6-TDI and on the chromatogram there are 6 peaks and I do not know which belongs to them. Unfortunately I don't have pure standards.
What would you suggest to identify them? Thank you.

You can but 2, 3 and 2, 6 TDI Stds from Aldrich

When you say that the baseline fluctuates, exactly what do you mean? Is the fluctuation regular (ie. every 30 sec) or is it constantly increasing or is it a more random fluctuation?

Hi sassman
It is a random fluctuation. I don't know if it is a mistake of the column or anything else. After a peak the baseline drops down below zero and stays there until next peak. Maybe there is a bubble in detector because I'm only using ultrasonic bath to eliminate the bubbles from the eluent.
Sorry for my english.

You need to check if your LC system works properly. I would bypass the column and run the same method with injection. If the similar fluctuation is observed, you will need to trouble-shoot the instrument.
Did you use premixed mobile phase? If not, try to so. Malfunctioned proportining valve affects detection.
To verify the column, it is better to run the same method on a known good instrument.
As for the application, I am attaching a link which leads to the same application we did on a Acclaim Mixed-Mode HILIC-1 column: http://www.dionex.com/en-us/images/pdf- ... hod-42.pdf