Re: Signal detection and sensitivity

From: Joseph Webster (J.Webster@centenary.usyd.edu.AU)
Date: Thu Jun 01 2000 - 18:53:20 EST


At 04:51 26/05/2000, Robert Adair McGilp wrote:
>Hello all,
>I would like some input regarding an issue I should probably be able to
>answer, but ...
>I have an investigator who has been using a FACSort to analyse his FITC/
>PE/Cychrome labelled samples and gets good resolution of the populations
>of interest (dual positives). He feels that we have been unable to
>reproduce the results on our Vantage SE.

I expect (and experience) higher sensitivity on the FACScan
than on the FACStar Plus, the same comparison should apply
to the FACSort vs the Vantage.
The optically coupled "stream-in-quartz" detection setup is
inherently more sensitive &/or more efficient than the
stream-in-air system.

By fine-tuning the alignment I have been able to improve the sorter
sensitivity, but the FACScan is still better.

>We have moved the z axis so that
>the nozzle is a good inch above the laser intercept and this gives a good
>approximation of the results he has seen on the analyser.

I don't know what's going on with a 1" nozzle-intercept gap; I'm
quite surprised you can get any usable results like that!
Can you still sort with the nozzle up there? I would expect the
stream vibration from drop drive to make it unusable.
I can't test that on my machine, can't physically move the
nozzle up that far....

>I have no
>problems with other samples and the sorter is performing very well. Is
>there something I can do to increase the sensitivity without rearanging
>the entire laser set up? The laser involved is an Enterprise II, with the
>primary power (UV) set to 25mW. This gives approx 300mW of 488 line.
>Thanks in advance,
>Rob McGilp



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