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- Posts: 28
- Joined: Fri Mar 11, 2016 3:41 pm
I hope it is alright to not open a new topic for every minor question. So I am doing it in this thread.
I am using a waters alliance 2695 coupled to a DAD coupled to a mass spectrometer equipped with an ESI source.
1) My gradient delay time is around 6 min. This seems to be very long. I don't know if it is correct but I once read that HPLCs with a gradient proportioning valve generally have higher gradient delay times. Is is true? What could I do to decrease the gradient delay time? I thought about decreasing the inner diameter of the tubings and also about shortening them.
2) When exactly do you run a blank? Right now I do it in the beginning, before every new set of samples and after all samples. Obviously if I have a sample with profound carry over I mix blanks in between. What is your advice?
3) Where excatly does an HPLC measure the pressure? If my HPLC for example says 100 bar it only means that this pressure exists in the tubing before the column, right? Downstream of the column is not a 100 bar, is it?
4) Would you ever run an isocratic method for an analyte in a biological matrix i.e. cell remnants? The reasoning behind my question is the following: In my opinion the isocratic method could lead to hydrophobic compounds accumulating on the column leading somewhen to a sudden elution. Do you agree?
5) I recently measured an API in a biological matrix. In certain cases the compound displayed severe peak tailing and reduced peak height and in other cases the peaks looked "perfect". What could be the reason?
Thanks in advance people!