[RASMB] Plateaus in Absorbance?

John Philo jphilo at mailway.com
Tue Jun 28 09:59:10 PDT 2011


Peter,
 
Yes, perhaps a slit sticking problem could explain what you are seeing, but
it looks like the instrument thinks the slit is moving along during the
'stuck' periods, which suggests the potentiometer is actually rotating,
which in principle it cannot do without the slit moving too. Thus it might
be a mechanical problem with the drive gear or other parts of the
motor-potentiometer assembly. The set screws on the shafts in the motor-pot
assembly can sometimes work loose, allowing slippage, and if memory serves
that effect is similar to what you are seeing. But clearly mechanical
slippage would be aggravated if the slit assembly cannot move freely, so you
could have two problems needing correction.
 
You could check yourself for dirt or a burr on the slit assembly (remember
to power off before you remove it so room light doesn't blow out the PMT
pre-amplifier). But if the problem is in the motor-pot assembly you'll need
your service tech.
 
John

  _____  

From: rasmb-bounces at rasmb.bbri.org [mailto:rasmb-bounces at rasmb.bbri.org] On
Behalf Of Peter Edward Prevelige Jr
Sent: Tuesday, June 28, 2011 8:25 AM
To: rasmb at rasmb.bbri.org
Subject: [RASMB] Plateaus in Absorbance?



Hi All -

 

We are observing what appear to be plateaus in the absorbance profile in
both equilibrium and velocity runs. The plateaus are seen with different
samples and different rotor speeds. Our current hypothesis is that the slit
in front of the detector is sticking and releasing.  It appears that these
are lost steps as after the slit releases the exponential is shifted along
the radial distance axis. Some representative data is attached showing
different speeds and cells. The superimposed scans (cell 1 35K, & cell 1
44K) are scans recorded about 10 hours apart in time.

 

Is it reasonable to think that the slit is sticking? How can we diagnose and
fix this problem?

 

Peter

 

Peter E. Prevelige Jr.

Professor

Dept. of Microbiology, BBRB 416/6

Univ. of Alabama @ Birmingham

845 19th St. South

Birmingham AL. 35294-2170

Phone 205 975-5327

FAX 205 975-5479

prevelig at uab.edu

http://www.microbio.uab.edu/faculty/prevelige/prevelige-p.htm

 

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