16 1260 Infinity Binary Pump User Manual
1 Introduction to the Binary Pump
Overview of the Hydraulic Path
What is Solvent Compressibility Compensation?
Although the compressibility of liquids is orders of magnitude lower than
the compressibility of gases, without correction a noticeable volume error
would be seen if typical chromatographic solvents are compressed to
operating pressures as high as 600 bar. In addition, the compressibility
depends on pressure, temperature and the amount of dissolved gas. In
order to minimize the influence of the latter, the use of a vacuum
degasser is mandatory for a high flow and composition precision.
Unfortunately, the influence of the temperature on compressibility is
non- linear and cannot be calculated.
The Agilent 1260 Infinity Binary Pump features a multi point
compressibility calibration. The compressibility of a solvent is determined
at different pressures from 0 – 600 bar and stored in an XML file. This
file can be distributed to other pumps because the solvent compressibility
is independent from the pump.
The binary pump and ChemStation come with predetermined solvent
compressibility data for the most common HPLC solvents like water,
acetonitrile, methanol, etc. Users can calibrate their own solvent mixtures
with the help of an easy to use calibration procedure in the Agilent Lab
Advisor software.
Let us use the practical example from the last section once again to
understand how compressibility compensation works:
Piston 1 draws solvent at ambient pressure. The movement direction is
reversed and piston 1 now compresses the solvent until the operating
pressure of the HPLC system is reached. The outlet valve opens, and
solvent is pumped by piston 1 into pump chamber 2.
Without any compensation, the delivered volume at operating pressure
would be too low. In addition, it would take a noticeable amount of time
to recompress the solvent to operating pressure. During this time frame,
no solvent would be delivered into the system and as a result a high
pressure fluctuation (known as pressure ripple) would be observed.
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