Which brings us back to the Hellma "TrayCell" solution where you can,
from the same spectrometer, have both the cuvette option and the
quickness of the NanoDrop/NanoVue system.
Anyone that can comment on the performance of the TrayCell from Hellma?
Cheers,
Martin
On Dec 5, 2008, at 9:06 AM, Gregor Witte wrote:
Agree!
I think for crystallographic use the nanodrop is perfectly okay to
see if the protein is 5mg/ml or 30mg/ml. But in fact I also do not
trust our instrument if it comes to more important issues like
preparing solutions for titrations or assays. And due to the small
pathlength I do not trust absorptions of small concentrated samples
at all. I always prefer a “real” 2-beam spectrophotometer
(monochromators) with a quarz-cuvette and a nice pathlength. Of
course, you cannot reliably measure solutions exceeding Abs 1 or
maybe 1.5 OD in a spectrophotometer with 1cm pathlength.
There’s also one quite strange thing about the nanodrop – they sell
the “calibration check solution” (which is some kind of yellow
chromate-solution with known absorption), then you check your
nanodrop with it and maybe find out that it’s off to some certain
extend: But then you’re stuck(!), because you cannot calibrate it on
your own. I guess it would be quite easy to integrate a calibration-
option into the software, but at the moment the instrument tells you
“calibration failure” and you have to call the service guys who then
carry it home and calibrate it by turning of the two small screws at
the top of it and then glue them with locktite.
Anyway, at least for our mid to high concentrated samples the
nanodrop is not showing large fluctuations so we are happy with it.
But everyone using a nanodrop should check it from time to time – as
I found out that ours was off more than 20% at one day - which
raised some trouble of course…
Cheers,
Gregor
Von: CCP4 bulletin board [mailto:[EMAIL PROTECTED] Im Auftrag
von Filip Van Petegem
Gesendet: Donnerstag, 4. Dezember 2008 22:20
An: CCP4BB@JISCMAIL.AC.UK
Betreff: Re: [ccp4bb] suggestions for UV spectrometer
I want to add I absotely hate the nanodrop. We've had a demo for
it, and found the readouts to be very unreliable. Fluctuations of
20% and more. Just leaving the same drop in and measuring the sample
multiple times gives different values (going in both directions, so
not only due to evaportations). Sure, it's easy and fast, and maybe
good to have a rough idea about your protein concentration, but I
would never want to use it for exact measurements such as needed for
e.g. a CD or an ITC instrument. I've heard other labs in our
department have similar issues. We've also had a demo for the
Nanovue from GE Healthcare: same issues - very large fluctuations
from one sample to another. I suppose this is simply an inherent
problem with small volumes...
Cheers
Filip Van Petegm
On Thu, Dec 4, 2008 at 12:48 PM, Patrick Loll <[EMAIL PROTECTED]>
wrote:
At the risk of dragging this discussion even further afield from
crystallography:
How can you get realistic numbers for concentrated solutions using
the Nanodrop? I understand that the instrument reduces absorbance
by using a very short path length. However, I thought that in order
for the Beer-Lambert formalism to be applicable, the solution needs
to be sufficiently dilute so that the chance of molecules
"shadowing" one another is negligible. Isn't this condition violated
for concentrated solutions (even with short path lengths)?
Pat
On 4 Dec 2008, at 1:27 PM, Michael Giffin wrote:
We also like the Nanodrop...
---------------------------------------------------------------------------------------
Patrick J. Loll, Ph. D.
Professor of Biochemistry & Molecular Biology
Director, Biochemistry Graduate Program
Drexel University College of Medicine
Room 10-102 New College Building
245 N. 15th St., Mailstop 497
Philadelphia, PA 19102-1192 USA
(215) 762-7706
[EMAIL PROTECTED]
--
Filip Van Petegem, PhD
Assistant Professor
The University of British Columbia
Dept. of Biochemistry and Molecular Biology
2350 Health Sciences Mall - Rm 2.356
Vancouver, V6T 1Z3
phone: +1 604 827 4267
email: [EMAIL PROTECTED]
http://crg.ubc.ca/VanPetegem/
.
B. Martin Hallberg, PhD
Assistant professor
Department of Cell and Molecular Biology
Medical Nobel Institute
Karolinska Institutet
Von Eulersv. 1
SE-171 77 Stockholm
Sweden
Fax: +46-8-339380
