[RASMB] density meter accuracy/precision
Steve Shire
shire.steve at gene.com
Thu Feb 21 09:54:39 PST 2008
Hi Steve,
As Jo mentioned if you wish to obtain densities of buffer
solutions directly then 3 places are sufficient. We use the hand held
version all the time and have compared measurements of buffers with
picnometer measurements and have gotten the same results. Overall the
portable unit will save you time and get you accurate readings.
Steve
On Feb 21, 2008, at 5:30 AM, Stephen Eyles wrote:
> Thank you everyone for the advice. Seems the DMA5000 is really
> worth its weight in gold....and seems to cost almost as much!
> So the portable ones on the market (in the ~US$2k range) really
> aren't worth spending the money on?
>
> ------------------------------------------------
> Dr Stephen J. Eyles
> University of Massachusetts - Amherst
> Polymer Science & Engineering
> Amherst, MA 01003, USA
> eyles at polysci.umass.edu
> Tel: (413) 577-1528
> Fax: (413) 545-0082
> ------------------------------------------------
>
> On Feb 21, 2008, at 6:08 AM, Antje Voelkel wrote:
>
>> Dear Steve,
>>
>> the DMA 5000 has already a thermostat included. It has a
>> temperature stability up to 0,001 °C.
>> The calibration procedure is very easy air (air pressure
>> dependent) and water measurement. Because the density is shown
>> directly, it is also easy to check, if there is cleaning or
>> recalibration necessary.
>>
>> I can absolutely recommend this instrument.
>>
>> best regards
>> Antje
>>
>>
>> Jo Butler schrieb:
>>> Dear Steve,
>>>
>>> Christine is of course absolutely correct and reminded us of an
>>> important point. In fact, we also use a thermostatting bath
>>> rated to a constancy of temperature of 0.01°C. The precision of
>>> setting is more like 0.1°C, but the really important point is
>>> that we always make the measurements of the buffer and solution
>>> (s) together, so that the constancy of temperature means that
>>> their temperatures will be very close. This is important because
>>> of the great variation of water density with temperature in the
>>> ranges of interest to most biologists.
>>> One practical point is that I have found that when one loads a
>>> new sample, you can use the Paar to watch it reach temperature
>>> equilibrium by simply starting to time counts. At first the time
>>> varies rapidly, but then (usually within a few minutes) it slows
>>> and settles to the point where there is essentially random
>>> variation in the last decimal point. Once this happens, one can
>>> take a series of readings to give a mean and SD for the value.
>>>
>>> Best wishes,
>>>
>>> Jo
>>>
>>> Christine Wandrey wrote:
>>>> 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 <mailto:eyles at polysci.umass.edu>
>>>>>> Tel: (413) 577-1528
>>>>>> Fax: (413) 545-0082
>>>>>> ------------------------------------------------
>>>>>>
>>>>>> _______________________________________________
>>>>>> RASMB mailing list
>>>>>> RASMB at rasmb.bbri.org <mailto:RASMB at rasmb.bbri.org>
>>>>>> http://rasmb.bbri.org/mailman/listinfo/rasmb
>>>>>
>>>>> --
>>>>> Dr P.J.G. Butler,
>>>>> MRC Laboratory of Molecular Biology,
>>>>> Hills Road, Cambridge, CB2 0QH, UK.
>>>>> Tel. +44 (0)1223 402296
>>>>>
>>>>> _______________________________________________
>>>>> RASMB mailing list
>>>>> RASMB at rasmb.bbri.org <mailto:RASMB at rasmb.bbri.org>
>>>>> http://rasmb.bbri.org/mailman/listinfo/rasmb
>>>>
>>>> -------------------------------------------------------------------
>>>> -------------
>>>> 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 <mailto:christine.wandrey at epfl.ch>
>>>>
>>>> Postal address:
>>>> EPFL-SV-IBI-LMRP
>>>> AAB 042, station 15
>>>> CH-1015 Lausanne
>>>> Switzerland
>>>>
>>>>
>>>>
>>>>
>>>>
>>>>
>>>>
>>>
>>
>>
>> --
>> ===============================================================
>>
>> Antje Voelkel
>> Max-Planck-Institute of Colloids and Interfaces
>> Colloid Chemistry
>> Am Muehlenberg 1
>> 14476 Golm
>> Germany
>>
>> Tel: +49 331 567 -9528/ -9531
>> Fax: +49 331 567-9502
>>
>>
>
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