analytical vs. high sensitivity flow cell

Santi
Santi
in Instrumentation and Mass Spectrometry
<p><span>Hello,</span></p><p></p><p><span>I have a question about the different flow cell types.</span></p><p></p><p><span>I´m looking for to change my flow cell from an analytical to a high senstivity one. </span><span>I know that my signal will increase x2.5 with the high sensitivity flow cell.</span></p><p><span>Can I use the same methods like now (up to 960 bar) or must I be more carefully with the new one?</span></p><p><span>Are there any papers which compares both flow cells? </span></p><p><span>Because I only have found that my signal will increase and that I will lose resolution. But how much resolution will I really lose?</span></p>

Answers

  • lizh
    lizh

    The backpressure ratings on the flow cells are identical and the high sensitivity actually has a larger volume and so will be even less effected. HAve you ahd issues before?

    The increased vflow cell volume is because the cell is basically 2.5 x longer, using a 2.5 times longer light guide.

    Therefore the biggest issue could be linearity. The detector's linearity range will not change, but you will get 2.5 times the increase in sensitivity, so your larger peaks could be outside 2.5 AU linearity spec. That may or may not be an issue for you, but check the absorbance of your largest peak and see what it is and then if you have to stay linear for all the peaks you can dilute or simply choose a smaller injection volume to get the peak within the linear range, but not too much so you get the benefits of the increased pathlength.

    The question about resolution is interesting...You have two items in your favor, first you get 2.5 times more signal, but also you get a longer residency time too. Make sure to adjust your data rate to get just enough points across the peak, but not too many and you may need to adjust the filtering down as the peaks are bigger. The noise of the two cells is about the same, the eficiency of light transfer is about the same, as same mechanism, but again residency is longer. And you are right dispersion goes up, but it seems like your detector is the only one so you will not pay too high a penalty, your peaks will disperse more in the larger flow cell, but it is still quite a small volume. By the time you think about all this it might be simpler to make a trial injection. BAsically if the peak heights go up 2.5 times will a little more peak width offset that? We have found this not to be the case, but I have not seen the tiny shoulder that you are trying to resolve in your chromatogram! All things being equal you should visualize the peak better. That will not be true of a second detector in line which will pay the dispersion price.

    Hope that helps. In the menatime I will work on getting you a reference that shows the comparsion which as you suspect show you what really happens. It vacation week and the best person to get me the example is away, so bear with me.

    Liz

  • Santi
    Santi

    Hi Liz,

    thanks for your answer.

    Linearity should not be the problem. What I do is Metabolite Identification and we work with a concentration of 10µM for the parent compound. The biggest issue is to detect also very small metabolites in the UV Trace, and not only in the MS.

    So it is important for us that we don´t loss so much resolution. I think it should be no big problem the higher dispersion.

    Thats the reason why I open this discussion, to see if somebody has experience with it or have some data which compares both.

    I will wait for your examples.

    Thanks in advance.

    Santi

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