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<div>One more thing to check: does your protein absorb at the LS laser wavelength? This is not uncommon when a metal ion is incorporated. In that case, if you are using a Wyatt detector and ASTRA software, you can apply the correction algorithm for absorbing
samples.</div>
<div><br>
</div>
<div>A small protein should not be an issue. MALS regularly measures sub-10 kDa and even sub-1 kDa. Insulin measurements are spot on.</div>
<div><br>
</div>
<div>With best regards,</div>
<div>Dan Some</div>
<div>Wyatt Technology Corp.</div>
</div>
<div class="elided-text">On Mar 18, 2016 4:09 AM, Kevin Jackson <wyattuk@runbox.com> wrote:<br type="attribution">
<blockquote class="quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div><font size="2"><span style="font-size:10pt"></span></font>
<div>Oh...and having the correct mass recovery does not necessarily mean the MALS<br>
has been recently calibrated....but does show the concentration response is<br>
probably correct...and thus that the dn/dc has to be close to the correct<br>
value (assuming you are using DRI as a concentration detector).<br>
<br>
<br>
Kevin<br>
<br>
<br>
<br>
<br>
<br>
Dr Kevin Jackson<br>
Technical Director<br>
Wyatt Technology UK Ltd<br>
Tel: 01440 705229<br>
Mob: 07747038083<br>
Skype: wyattuk<br>
<br>
<br>
<br>
<br>
<br>
-----Original Message-----<br>
From: RASMB [<a href="mailto:rasmb-bounces@list.rasmb.org">mailto:rasmb-bounces@list.rasmb.org</a>] On Behalf Of Mattia Rocco<br>
Sent: 18 March 2016 10:32<br>
To: Stephen McLaughlin; Andrew Leech<br>
Cc: rasmb@rasmb.org<br>
Subject: Re: [RASMB] dn/dc<br>
<br>
<br>
.... and the MW should not be constant along the peak, I forgot to add, if<br>
oligomerization is going on....<br>
<br>
<br>
-----Original Message-----<br>
From: Stephen McLaughlin [<a href="mailto:stephenm@mrc-lmb.cam.ac.uk">mailto:stephenm@mrc-lmb.cam.ac.uk</a>]<br>
Sent: Fri 3/18/2016 10:55 AM<br>
To: Mattia Rocco; Andrew Leech<br>
Cc: jphilo@mailway.com; rasmb@rasmb.org<br>
Subject: Re: [RASMB] dn/dc<br>
<br>
Dear Mattia, Andrew and John, <br>
<br>
The BSA standard recovery is as expected. Hence, given that the Zn ions are<br>
not going to effect the dn/dc significantly, I think you are all right in<br>
suggesting that the error will be a compound of inaccuracy in dn/dc<br>
calculation coupled with lower light scattering for a small protein giving<br>
rise to an larger error that would be expected when analysing much larger<br>
proteins. <br>
<br>
Many thanks<br>
<br>
Stephen <br>
<br>
<br>
On 17 Mar 2016, at 16:08, Mattia Rocco wrote:<br>
<br>
> I agree with John regarding the dn/dc, but maybe the absolute calibration<br>
of the instrument could also be an issue... or the on-line concentration<br>
determination... as Andrew Leech pointed out this morning, do you recover<br>
the approximately correct molecular weight for, say, BSA?<br>
> <br>
> Mattia<br>
> <br>
> ________________________________<br>
> <br>
> From: RASMB on behalf of John Philo<br>
> Sent: Thu 3/17/2016 4:22 PM<br>
> To: 'Stephen McLaughlin'; rasmb@rasmb.org<br>
> Subject: Re: [RASMB] dn/dc<br>
> <br>
> <br>
> <br>
> Stephen, I think it is unlikely the dn/dc for your protein differs by more<br>
than 5% from your calculation. If there is a "major" discrepancy then<br>
calibration is not the issue. <br>
> <br>
> John<br>
> <br>
> <br>
> <br>
> -----Original Message-----<br>
> From: RASMB [<a href="mailto:rasmb-bounces@list.rasmb.org">mailto:rasmb-bounces@list.rasmb.org</a>] On Behalf Of Stephen<br>
McLaughlin<br>
> Sent: Thursday, March 17, 2016 5:08 AM<br>
> To: Mattia Rocco <mattia.rocco@hsanmartino.it><br>
> Cc: rasmb@rasmb.org<br>
> Subject: Re: [RASMB] dn/dc<br>
> <br>
> <br>
> <br>
> Dear Mattia, <br>
> <br>
> <br>
> <br>
> at the minute, it would be good to know if the dn/dc increases or<br>
decreases and roughy how much. There is a significant discrepancy between<br>
the molar mass measured by SEC-MALS and the expected mass from mass-spec. <br>
> <br>
> <br>
> <br>
> Best <br>
> <br>
> <br>
> <br>
> Stephen<br>
> <br>
> <br>
> <br>
> <br>
> <br>
> <br>
> <br>
> On 17 Mar 2016, at 09:53, Mattia Rocco wrote:<br>
> <br>
> <br>
> <br>
>> Dear Stephen,<br>
> <br>
>> <br>
> <br>
>> it likely will. But calculating a dn/dc is not that reliable anyway...<br>
and what's the level of precision you need, after all?<br>
> <br>
>> <br>
> <br>
>> Best - Mattia<br>
> <br>
>> <br>
> <br>
>> ________________________________<br>
> <br>
>> <br>
> <br>
>> From: RASMB on behalf of Stephen McLaughlin<br>
> <br>
>> Sent: Thu 3/17/2016 10:40 AM<br>
> <br>
>> To: rasmb@rasmb.org <<a href="mailto:rasmb@rasmb.org">mailto:rasmb@rasmb.org</a>>
<br>
> <br>
>> Subject: [RASMB] dn/dc<br>
> <br>
>> <br>
> <br>
>> <br>
> <br>
>> Dear all, <br>
> <br>
>> <br>
> <br>
>> I have a small three fingered Zn binding protein. Will the presence of<br>
Zn ions affect the refractive increment that can be caluculated from<br>
sequence?<br>
> <br>
>> <br>
> <br>
>> <br>
> <br>
>> Best <br>
> <br>
>> <br>
> <br>
>> Stephen<br>
> <br>
>> <br>
> <br>
>> <br>
> <br>
>> ______________________________<br>
> <br>
>> <br>
> <br>
>> Stephen McLaughlin, Ph.D.<br>
> <br>
>> <br>
> <br>
>> Biophysics<br>
> <br>
>> MRC Laboratory of Molecular Biology<br>
> <br>
>> Francis Crick Avenue<br>
> <br>
>> Cambridge Biomedical Campus<br>
> <br>
>> Cambridge, CB2 0QH<br>
> <br>
>> <br>
> <br>
>> Tel.: +44 (0) 1223 267891 (office)<br>
> <br>
>> <br>
> <br>
>> Email:stephenm@mrc-lmb.cam.ac.uk<br>
> <br>
>> _____________________________<br>
> <br>
>> <br>
> <br>
>> <br>
> <br>
>> <br>
> <br>
>> <br>
> <br>
>> <br>
> <br>
>> <br>
> <br>
>> <br>
> <br>
> <br>
> <br>
> _______________________________________________<br>
> <br>
> RASMB mailing list<br>
> <br>
> RASMB@list.rasmb.org <<a href="mailto:RASMB@list.rasmb.org">mailto:RASMB@list.rasmb.org</a>>
<br>
> <br>
> <a href="http://list.rasmb.org/listinfo.cgi/rasmb-rasmb.org">http://list.rasmb.org/listinfo.cgi/rasmb-rasmb.org</a><br>
<<a href="http://list.rasmb.org/listinfo.cgi/rasmb-rasmb.org">http://list.rasmb.org/listinfo.cgi/rasmb-rasmb.org</a>>
<br>
> <br>
<br>
<br>
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