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<DIV dir=ltr align=left><SPAN class=339131919-13062012><FONT color=#0000ff
size=2 face=Arial>Debby,</FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=339131919-13062012><FONT color=#0000ff
size=2 face=Arial></FONT></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN class=339131919-13062012><FONT color=#0000ff
size=2 face=Arial>Not sure any of these explain negative readings, but here are
some things to consider:</FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=339131919-13062012><FONT color=#0000ff
size=2 face=Arial></FONT></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN class=339131919-13062012><FONT color=#0000ff
size=2 face=Arial>(1) Did you remember to rotate the lever on the monochromator
to filter out the stray light below 400 nm? Either way,
<DIV dir=ltr align=left><SPAN class=339131919-13062012><FONT color=#0000ff
size=2 face=Arial>you may want to take a scan in intensity mode to see whether
you really have enough light going through to make a reasonable measurement. The
lamp outputs very little light in the visible compared to the
UV.</FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=339131919-13062012></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN class=339131919-13062012>(2) Could the wavelength
calibration be way off in the visible region?</SPAN></DIV></FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=339131919-13062012><FONT color=#0000ff
size=2 face=Arial></FONT></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN class=339131919-13062012><FONT color=#0000ff
size=2 face=Arial>(3) Is it possible your particles sediment so fast they had
simply already pelleted by the time you could take a
measurement?</FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=339131919-13062012><FONT color=#0000ff
size=2 face=Arial></FONT></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN class=339131919-13062012><FONT color=#0000ff
size=2 face=Arial></FONT></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN class=339131919-13062012><FONT color=#0000ff
size=2 face=Arial>John</FONT></SPAN></DIV><BR>
<DIV dir=ltr lang=en-us class=OutlookMessageHeader align=left>
<HR tabIndex=-1>
<FONT size=2 face=Tahoma><B>From:</B> rasmb-bounces@rasmb.bbri.org
[mailto:rasmb-bounces@rasmb.bbri.org] <B>On Behalf Of </B>Deborah
Pheasant<BR><B>Sent:</B> Wednesday, June 13, 2012 12:10 PM<BR><B>To:</B>
rasmb@server1.bbri.org<BR><B>Subject:</B> [RASMB] Nanoparticle absorbance
question<BR></FONT><BR></DIV>
<DIV></DIV>
<DIV class=WordSection1>
<P class=MsoNormal>Hi all,<o:p></o:p></P>
<P class=MsoNormal>We had a suspension of nanoparticles (metal oxides) in
culture medium with FBS proteins and it measured 0.5 AU at 530 nm in a UV/VIS
spec. When we put it into SV centerpieces, it read that it had an A530 of
about -0.1 or -0.2. We are perplexed as to why this should be. Have
you had similar experiences or do you have an idea about what might be going
on?<o:p></o:p></P>
<P class=MsoNormal>Thanks very much,<o:p></o:p></P>
<P class=MsoNormal>Debby Pheasant<o:p></o:p></P></DIV></BODY></HTML>