Over time, the mineral oil overlay will basically void the medium of 
all lipophilic components (vitamin E, for instance). This may or may 
not be a problem, but you need to be aware of it and do the proper controls.

If you want to check for evaporation, just weigh your sample before 
and after the imaging.

Beat

At 23:23 12-02-2009, you wrote:
>My Guess is still evaporation of media is killing your 
>cells..  Overlay the cell media in each compartment with mineral 
>oil.  It stops all evaporation but allows CO2 gas exchange to occur 
>to maintain pH..  I do this with all my chamber systems and it works 
>great.  No need to humidify flowing air or gas.
>
>
>Joe Goodhouse
>Confocal Core Lab Manager
>Dept. of Molecular Biology
>Princeton University
>609-258-5432
>
>Visit us at 
><http://www.molbio/>http://www.molbio1.princeton.edu/facility/confocal/
>
>
>
>----------
>From: Confocal Microscopy List 
>[mailto:[log in to unmask]] On Behalf Of Paul Herzmark
>Sent: Thursday, February 12, 2009 4:36 PM
>To: [log in to unmask]
>Subject: Re: CO2, humidity, temp sensors
>
>
>I knew I would not get away with out details!
>
>I have an Invivo (company) plexiglass incubator box around my 
>inverted microscope. 5% CO2 is piped inside to a small space (about 
>50 ml) around the multiwell-Labtech (company)-coverslip. The small 
>space is created by a glass plate with a frame around it that goes 
>over the coverslip.The CO2 passes into the small space via special 
>tubing.The tubing goes under incubator-warmed water where it is 
>supposed to pick up water vapor without bubbling.
>
>1. The whole incubator, with most of the microscope is warmed to 37 degrees
>2. Only the small space surrounding the cells is humidified  and has CO2.
>
>
>
>
>On Thu, Feb 12, 2009 at 11:30 AM, Goodhouse, Joseph G. 
><<mailto:[log in to unmask]>[log in to unmask]> wrote:
>Paul,
>     Could you describe in detail your heating system. Do you 
> overlay your cells with mineral oil? This prevents evaporation 
> which will alter your salt concentration.
>
>  I use a Recordable Temp sensor from Fisher Scientific.  Cat No 
> 15-007-26. Inexpensive and works well.
>
>
>Joe Goodhouse
>Confocal Core Lab Manager
>Dept. of Molecular Biology
>Princeton University
>609-258-5432
>
>Visit us at 
><http://www.molbio/>http://www.molbio1.<http://princeton.edu/facility/confocal/>princeton.edu/facility/confocal/ 
>
>
>
>
>----------
>From: Confocal Microscopy List 
>[mailto:[log in to unmask]] On Behalf Of Paul Herzmark
>Sent: Thursday, February 12, 2009 2:24 PM
>To: <mailto:[log in to unmask]>[log in to unmask]
>Subject: CO2, humidity, temp sensors
>
>I have a cell dying problem in my microscope when I take pictures of 
>them overnight or longer. I suspect the humidity is failing and I 
>want to monitor that, CO2 and temperature.(It is not photodamage. 
>Cells die in areas away from the objective.)
>
>Can anyone suggest a supplier of recording sensors that I can get 
>next to the well slides on my stage?
>
>Thank you!
>
>Paul Herzmark
>Specialist
><mailto:[log in to unmask]>[log in to unmask]
>
>Department of Molecular and Cell Biology
>479 Life Science Addition
>University of California, Berkeley
>Berkeley, CA  94720-3200
>(510) 643-9603
>(510) 643-9500 fax
>