[RASMB] density meter accuracy/precision

[Christine Wandrey]

Dear Steve,

a practical comment. The description of the instrument says a  
precision of 10-6. But practically it is very difficult to get. You  
need then  an excellent instrument calibration and high temperature  
stability, less than 0.01°C temperature fluctuation. The practical  
case is a precision of 10-5, but this you really need as mentioned by  
Jo.
Best,
Christine
On Feb 20, 2008, at 4:18 PM, Jo Butler wrote:

> Dear Steve,
>
> If all you want is a solvent density, then you really only need (at  
> most) 3 decimal places and the DMA5000 is over the top, since you  
> are most unlikely to know the partial specific volume to this  
> precision (since the product v-bar*rho will only have the precision  
> of the least precise term).
> However, if you think that you might ever want to get into the  
> business of measuring density increments, and hence being able to  
> calculate meaningful apparent partial specific volumes, then all the  
> precision you can get in density is wanted, as one is looking at  
> density differences between solution and solvent where the solute  
> concentration is likely to be only mg/ml (i.e. 10–3), so a precision  
> of 10–6 is by no means too high.
>
> Good luck,
>
> Jo
>
> Stephen Eyles wrote:
>> Hi AUCers.
>>
>> We are contemplating purchasing a densitometer to more accurately  
>> determine densities of our buffer solutions for AUC.
>> What precision/accuracy is really necessary? I know the de facto  
>> standard instrument seems to be the Anton Paar DMA5000 but is this  
>> overkill? Aside the significant extra expense, is there a real  
>> benefit to 6-decimal place measurement of density or could we do a  
>> reasonable job with a hand-held instrument? Weighing known volumes  
>> on a balance clearly isn't cutting the mustard!
>>
>> Thanks for any advice and helpful tips.
>>
>> Steve
>>
>> ------------------------------------------------
>> Dr Stephen J. Eyles
>> University of Massachusetts - Amherst
>> Amherst, MA 01003, USA
>> eyles at polysci.umass.edu
>> Tel: (413) 577-1528
>> Fax: (413) 545-0082
>> ------------------------------------------------
>>
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>
> -- 
> Dr P.J.G. Butler,
> MRC Laboratory of Molecular Biology,
> Hills Road, Cambridge, CB2 0QH, UK.
> Tel. +44 (0)1223 402296
>
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--------------------------------------------------------------------------------
PD Dr. habil. Christine Wandrey, MER
Ecole Polytechnique Fédérale de Lausanne (EPFL)
Laboratoire de Médecine Régénérative et de Pharmacobiologie (LMRP)
http://people.epfl.ch/christine.wandrey

tél.: (+41) 21 693 9661
fax: (+41) 21 693 9685
email: christine.wandrey at epfl.ch

Postal address:
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