difference between distilled water and deionized water - (Oct/16/2005 )
Hi
Can any one tell me approximately which water ( ddH20 or MilliQ ) has greater ppm of ions.......and how much?????
plzzzzzzzzz
MilliQ water is much purer than any water made by distillation, no matter how many times the distillation is carried out. You can establish this by measuring conductivity. Really good water also has no organics -- because it is treated with UV to break them down and remove them as ionized products.
There are three grades of lab water (no, not dirty, tap and drinking). Grade three, minimum purity, is put through a base-exchange system, then activated carbon to remove chlorine & organics. Lastly it goes through reverse osmosis.
Grade 2 water (cleaning glass, making up buffers) is deionised reverse osmosed water.
Grade 1 water, which you use in chromatography, PCR etc, is continually circulated through the de-ioninized & reverse osmosis steps. It is also passed through UV disinfection and sub-micron filtration (0.2microns). This is the double deionized water you mention.
In UK purified water has to comply with BS EN ISO 3696, I'm not sure about the US system. When checking the system your lab uses bear in mind quality required and quantity. The longer you need to store the product the more chance it has of becoming contaminated. I think water purity is checked by the electric current that can pass through it, hence purity is reported in Mohm.cm. Simple distillation of water will remove organics and microbes but probably not the ions. The thing is, you need several techniques to get rid of the different size of particles.
Hope that helps.
does it make any sense to autoclave milliQ water?
No. MilliQ water is sterile when it comes out of the machine, and it's probably more pure than the steam used in the autoclave.
it may be sterile when it gets past the ultrafilter but then it has to travel through tubing (usually tygon) which may (and often does) have organisms growing on it.
so, you probably should sterilize. if you don't want to use an autoclave then you can filter sterilize.
my teacher told us that the difference between distilled and deionised water is :
distilled : free of microorganisms.
deionised: free of ions.
what you say ???
distilled : free of microorganisms.
deionised: free of ions.
what you say ???
distilled and deionized just refers to the method used to purify the water.
nothing related to microorganisms !!!!!????? 
u mean my teacher was wrong ???
well,thanks for the starter of this subject ....
so i can discover that we were fooled 
so, you probably should sterilize. if you don't want to use an autoclave then you can filter sterilize.
I've been told that water from the MilliQ is always sterile! Hmm. With our machine, the tubing is always full of water (air doesn't get in) so there should not be any way for the organisms to get in.
Here's another thought: is distilled water even available any more? I've never seen nor heard of anyone having a distiller. MilliQ seems to be the standard, and it's just as good (if not better).