[Spm] Water quality

[Igor Sokolov]

Hi Don,

We have used quite successfully Ultrapure MilliQ water for imaging of
single molecules. If the filter cartridge/membrane were not changed as
recommended, there is a good chance that water gets contaminated. We do
not change those as frequently as the manufacturer recommends (too
expensive), and therefore, we have to monitor quality of this water. 

We found three quite simple tests: 

1. pH of good water should be around 7. If it is below ~6 or above ~7.5,
there is a good chance that it is contaminated. 

2. Light scattering: should be none. The device to check it is very
simple, and can be assembled within an hour. It is a cuvette for
fluorescence, which you fill with water to analyze. Put it under
anoptical microscope with an objective with working distance >~1mm (>
than wall thickness of the cuvette) . Then you illuminate water in your
cuvette from the side with a laser (a good laser pointer might be
sufficient). If there are any particulate contamination there, you will
see it (starting from the size of a few nm). (P.S. Definitely, one
should be caution about using lasers, and not trying to send it directly
to your eyes.)

3. (probably the most accurate), just look at Raman spectra (a regular
fluorescent spectrometer should work). Contaminated water has specific
signatures that are very easy to recognize.

Hope it helps.

Best regards,

Igor

 

_____________________________________

Igor Sokolov, Ph.D.

Professor,

Department of Physics,

Department of Chemistry and Biomolecular Science,

Director of Nanoengineering and Biotechnology Laboratories Center
(NABLAB), 

NY Center for Advanced Material Processing (CAMP)

Clarkson University, 

Potsdam, NY 13699

 

Phone:    315-268-2375

Fax:        315-268-6610

email:      isokolov at clarkson.edu

Web:       http://www.clarkson.edu/~isokolov

               http://www.clarkson.edu/~nablab

_____________________________________

 

From: Don Chernoff at ASM [mailto:donc at asmicro.com] 
Sent: Tuesday, April 07, 2009 11:36 PM
To: SPM List
Subject: [Spm] Water quality

 

I have found that the image quality of adsorbates on mica (e.g. DNA
molecules) depends on the purity of the water used to prepare solutions
and to rinse the mica disks.  I like to use water from a local Milli-Q
system, but sometimes the water quality is not good enough.  Can anyone
suggest a commercial source of water?

 

regards,
Don
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