There are basically de-ionized water (diH2O), distilled water
(dH2O) and double-distilled water (ddH2O) that use in the laboratory.
diH2O
water, as the name suggests, has had the charged molecules (ions) in
the solution removed by filtration through a bed of ion exchange resins.
These small plastic beads with a positive or negative charge, attract
the undesirable molecules and replace them with either a H+ ion or an
OH- ion, which combine to form pure water. The process does not remove
anything without a charge, including viruses and bacteria. diH2O, due to
the lack of ions, has very low electrical conductivity. The process is
relatively inexpensive, as there is minimal hands-on time, the plastic
beads can be ‘recharged’ multiple times with strong acids and bases, and
the tanks require infrequent cleaning.
dH2O
is produced by heating water to boiling and gathering the resulting
water vapor in a clean container. Any contaminants and undesirable
molecules are left behind in the original container as precipitated
solids. The boiling process sterilizes the water, meaning viruses and
bacteria are killed during the procedure. It is the oldest method of
purification and is still in common usage. However, some dissolved
impurities can have a lower boiling temperature than water and may be
gathered in the secondary container along with the purified water vapor.
The distillation process requires more hands-on time and cleaning of
the solid contaminants out of the distillation chamber after every
procedure, which can be challenging or even hazardous depending on the
initial cleanliness of the water.
ddH2O
is traditionally considered the ‘most pure’ type of laboratory-grade
water. This is simply the secondary distillation of the water vapor of a
prior distillation procedure. This process is the most time-consuming
out of the three and does not necessarily avoid the risks of potential
impurities being carried along with the vapor.
hear is the basic flow diagram of double distillation process..
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