Liquid Mixtures
Standard Cylinder with Single-Port Valve and Precharged Pressure Pad
Liquid mixtures using a standard size cylinder, a single-port valve and a precharged pad are gravimetrically prepared with GRAVSTAT™ using balances calibrated with weights traceable to NIST. The head space above the liquid is initially pressurized (precharged) with an inert gas such as helium. Liquid is withdrawn from the cylinder using the pressure in the head space.
Advantages
This set-up is used with less volatile components (i.e. those with a lower vapor pressure) even though the cylinder pressure decreases as liquid is withdrawn from the bottom of the cylinder via a dip tube.
Disadvantages
More volatile components (i.e. those with a higher vapor pressure) tend to accumulate in the inert gas head space. Buildup of volatile components in the head space lowers the accuracy and consistency of the calibration standard. The total cylinder pressure declines as liquid is withdrawn and results in changing sample delivery pressure.
Recommended Uses
Adequate for mixtures with components having low volatility.