[RASMB] averages from SV

[Kristian Schilling]

Hi Borries, hi Holger,

no doubt, if I have absorbance detection and one chromophore group per 
molecule, I have number proportional detection. Every datapoint is number 
weighted, and if I sum up according to standard formulae, I can calculate 
number, weight and z averages.

If detection is mass proportional, as with interference, then every 
datapoint is mass weighted. I reckon that if I sum up according to the 
formula for number average I get weight average, and using weight average 
formula I get z average. Because every single datapoint is already mass 
weighted due to the mode of detection.

If all is correct until here, the interesting question is: how do I 
calculate number weighted average from mass proportional detection data?

This just my reckoning - I'm not quoting, so don't take this for granted!

Cheers,
Kristian

At 10:28 23.01.2006 -0600, you wrote:
> >
> > Hi everybody,
> >
> > we're looking for the pertinent reference for calculating number- and
> > z-averages from dc/dt-distributions - any hints? Furthermore, are
> > there formula for getting these averages from c(S)- and vHW-distributions?
> >
>
>Holger,
>
>to get number averages, I presume you want number of molecules, right?
>I guess in that case you need to make some assumptions about how the
>measured s-value relates to mass so you can make the conversion to
>numbers.  The exact conversion of course would then of course also depend
>on the measurement mode (i.e, interference, or particular wavelength
>and absorbance properties). All molecules in your mix better have the
>same signal properties, for example, if you have a mixture of molecules
>that have a different ratio of trp/MW, and you use absorbance at 280 nm
>as mass measure, then your conversion is going to be wrong. Otherwise,
>standard formulas for calc. Mw, Mn and Mz apply.
>
>-Borries



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