[Histonet] Microwave use

wlove <@t> att.net wlove <@t> att.net
Tue Oct 11 13:52:29 CDT 2005

Hello, this is my first response to a Histonet discussion - what an excellent method to communicate - I do not believe I have seen anything like it.  However, as I am unfamiliar with it, I am not sure that this will reach the Histonet.

We do research and provide microwave heating and processing devices for laboratories and light industrial applications including research tissue processors and other microwaves for staining, etc...

Microwaves are great time savers as the energy adsorbs into the material being heated differently that the way conventional heating does.  They can be quite consistent as well once people understand how to use them and how they operate.  Looking for hot spots with a bulb array is not a great method for finding hot spots as Rene J. pointed out.  She accurately also pointed out that the hot spot will change with a load in it.  By the way, if you can control power well, you do not need a separate water load.  But the introduction of any material in the microwave cavity will certainly change the energy distribution pattern and thus the so called hot spot.

Consistency is important to consistent processing.  Factors that affect consistency include:

Line voltage - always use a microwave oven that compensates for line voltage changes.  Most do.

Load - do not use a 50 ml sample and think you will get the same results with a 500 ml sample.  Nor will 10 - 50 ml samples vs. a 500 ml sample as the samples will be in different locations within the cavity and thus change the energy density.

Starting temperature of the sample will make differences in results

Location in the microwave will change results.  Mark with a marker a location and always use it.

I have heard of other methods to get consistent results as I am sure you have.

Here is one that I have never heard with regard to histoprocessing.  The temperature of the magnetron and the power supply transformer (major microwave generator components) makes just about the biggest single differences (can be over 10% variations) in process consistency.  The heating of the magnetron is quick, in about 3 minutes of operation, but the transformer can take 15 minutes or more as it is a large thermal mass.  

One way to reduce the variation is to operate the microwave with a liter or two of water on full power for 20-30 minutes to pre-warm the microwave.  The other way is to use a microwave that uses the temperature of the sample to control the process.

We are not biologist but are microwave engineers and understand the operation of microwaves and how they heat.  Hope this makes sense to all of you.

Caution - If I understand it correctly, you are using the microwave to heat the HIER solution to boiling and then putting it into the steamer.  This would greatly decrease the initial heating time.  Be very careful as it is possible to superheat, but not boil liquids in a microwave and then have it vigorously boil explosively when the liquid is move or stirred causing potential injuries.  

Tips to prevent:  
Do not use a container with a small mouth!
Stir the solution every couple of minutes.
Leave the solution in the container undisterbed for a period of time before removing.
Protect you face and body (arms and hands also) with face shields nad proper clothing 

Best regards 

Wayne Love 
Microwave Research and 
Applications, Inc. 
8685 Cherry Lane 
Laurel, MD 20707 
Phone 301-953-1771 
Fax 301-369-0523 
WebSite www.microwaveresearch.com 
Email info <@t> microwaveresearch.com 
Cell 630-269-5158 
Direct email: wlove <@t> att.net

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