ASTM 3612/TOGA/DissolvedGasGC
RevisedOcober 2013
Gas calibration standards are readily availa-
ble, but liquid standards ( known amounts of
gases dissolved in liquids ) are not easily
found, so youmight have tomake your own.
ASTM 3612 has a procedure, but it is cum-
bersome. Another standard preparation
method is to bubble calibration gas through
a liquid until the liquid and calibration gas
are in equilibrium. Suppliedwith theTOGA
GC system is a pressure regulator, restrictor
tube, silicone tubingwith Luer lock, and two
needles for this purpose.
Connect the regulator to the calgas cylinder
as shown and adjust the pressure so a slow
stream of bubbles comes out of the needle
which is positioned below the surface of the
liquid. Youmay have to lay theVOA vial
down on its side. The 2nd needle
( 27gage ) is inserted to vent the calgas
from the top of the vial. After one hour or
so, the calgases dissolved in the liquid
should have reached equilibrium. From the
Internet you can get a tablewhich shows
the amount of each gaswhichwill be dis-
solved in the liquid once equilibrium is
achieved, at least for water.
The solubility of gases in transformer oil is
assumed to be the same as for water, alt-
hough this is not completely accurate, and
different oil typeswill exhibit different solu-
bilities.
Slowbubbles
