principle of autoclaving - pressure ? (Dec/18/2010 )
Ok
Just to check if I am understanding it: higher pressure means that you need a higher temperature to boil (change from water to gasous phase), thus when raising the pressure you also raise the temperature by wich water boils and in this particular case you assure that you reach a certain pressure that you can savely sterilise the products at 121 without losing all the contents of the products (so you wont boil away everything).
Anyway, this in my mind, I have to following questions:
- When you drop the pressure too rapidly, then I would think that you would turn too much of your product into a gasous phase and thus boil away the producht (when looking at the phasediagram of water). Is this correct then?
(I do not understand what you mean by: "but the quick drop in pressure may allow them to eliminate any liquid which may have condensed (this is speculation on my part" , allow to elimitate the liquid that has condensed? You mean that the condensed liquid would turn into gas and this be lost? (loss of medium?))?
- I see why you need the pressure system for autoclaving medium, but what for solids?
If I would simply heat the autoclave untill I reach 121°C , then why wouldnt this work without the pressure? Is this because without the pressure all the water that turned into gas would be away? (escape , since you do not keep it under pressure, you do not close the autoclave)?
Or is it really physically impossble to heat the inside of the autoclave to 121°C at normal pressure?
- Why do people wrap so much in aluminumfoil? I would think that this foil would prevent a very good sterilisation? Since the steam might not be able to penetrate the foil as good as without foil?
Whats the idea behind the use of foil?
lyok on Wed Dec 22 14:12:42 2010 said:
Just to check if I am understanding it: higher pressure means that you need a higher temperature to boil (change from water to gasous phase), thus when raising the pressure you also raise the temperature by which water boils and in this particular case you assure that you reach a certain pressure that you can safely sterilize the products at 121 without losing all the contents of the products (so you wont boil away everything).
Anyway, this in my mind, I have to following questions:
- When you drop the pressure too rapidly, then I would think that you would turn too much of your product into a gaseous phase and thus boil away the product (when looking at the phase diagram of water). Is this correct then?
(I do not understand what you mean by: "but the quick drop in pressure may allow them to eliminate any liquid which may have condensed (this is speculation on my part" , allow to elimitate the liquid that has condensed? You mean that the condensed liquid would turn into gas and this be lost? (loss of medium?))?
i was talking about autoclaving solids when i said that. by reducing the pressure rapidly the temperature will be high enough to allow any liquid which had condensed from the steam to boil away.
If I would simply heat the autoclave until I reach 121°C , then why wouldn't this work without the pressure? Is this because without the pressure all the water that turned into gas would be away? (escape , since you do not keep it under pressure, you do not close the autoclave)?
Or is it really physically impossible to heat the inside of the autoclave to 121°C at normal pressure?
solids, such as surgical implements, used to be sterilized by placing them into boiling water for a period of time (remember sterilizers in doctors' offices?). by using the higher temperatures obtained with steam it takes less time and is more effective than simply boiling. if you don't close the vessel (autoclave) then the steam will cool too rapidly causing the solids to get wet and sterilization may not be efficient. of course you can heat without pressure (look at ovens) but steam gives you more thermal mass and may allow more even heating of the material being autoclaved (this is all supposition on my part, reality may differ from what i say).
Whats the idea behind the use of foil?
foil (and autoclave bags, wrapping paper, vessels) are used to ensure that what you are autoclaving remains sterile until you remove it from the package. the steam doesn't really need to touch the item, it just needs to heat it.
mdfenko on Wed Dec 22 16:32:44 2010 said:
solids, such as surgical implements, used to be sterilized by placing them into boiling water for a period of time (remember sterilizers in doctors' offices?). by using the higher temperatures obtained with steam it takes less time and is more effective than simply boiling. if you don't close the vessel (autoclave) then the steam will cool too rapidly causing the solids to get wet and sterilization may not be efficient. of course you can heat without pressure (look at ovens) but steam gives you more thermal mass and may allow more even heating of the material being autoclaved (this is all supposition on my part, reality may differ from what i say).
And also because you need a higher temperature then 100°C to kill the bacteria (I think? or not?)
Or can you kill bacteria at 100°C if you just let it boil long enough in stead of going up to 121°C?
Ok, but I have noticed that they put aluminum foil around boxes containing pipettetips? Seems rahter strange since they remove this foil right after autoclaving and they put the boxes without the foil in the cabinets or drycabinets..
I can understand you put foil around pieces of paper or material (needles or something) in order to keep it sterile, but putting it around closed boxes?
they're just wasting aluminum foil. i sterilize tip boxes held closed with autoclave tape.
mdfenko on Wed Dec 22 16:45:51 2010 said:
they're just wasting aluminum foil. i sterilize tip boxes held closed with autoclave tape.
you wrap the tape all around or just in the middle of the boxes to keep it closed?
I have seen them do the following thing: wrap tape all around and then aluminim foil.. and then when its done, they remove the foil, put it in the drychamber.. after a while take it out, use it and put it in a cabinet next to the flow for using it the next time..
For me this seems rather strange.. and not logical.. but heck, I am not a microbiologist...
just in the middle to keep the box closed (and to let me know that it has been autoclaved).
mdfenko on Wed Dec 22 16:56:52 2010 said:
just in the middle to keep the box closed (and to let me know that it has been autoclaved).
OK.
PS. they once told me that the indicator tape just means that the steam was there.. but it doenst necessary means its sterile.. no idea if this is true though
lyok on Wed Dec 22 16:59:50 2010 said:
PS. they once told me that the indicator tape just means that the steam was there.. but it doesn't necessary means its sterile.. no idea if this is true though
true. the tape indicates that it has been heated to autoclave temperatures, not necessarily long enough to kill everything.
keep in mind that some things are resistant to normal autoclaving (eg-prion proteins).