The compressibility compensation default setting is 100 × 10-6 /bar for the pump. This setting represents an average value. Under normal conditions the default setting typically reduces the pressure pulsation to values below 1 % of system pressure that are sufficient for most applications and for all gradient analyses. The compressibility settings can be optimized by using the values for the various solvents described in Solvent compressibility. If the solvent in use is not listed in the compressibility tables, when using isocratic mixtures of solvents and if the default settings are not sufficient for your application the following procedure can be used to optimize the compressibility settings.
NOTE
When using mixtures of solvents it is not possible to calculate the compressibility of the mixture by interpolating the compressibility values of the pure solvents used in that mixture or by applying any other calculation. In these cases the following empirical procedure has to be applied to optimize your compressibility setting.
Inappropriate settings would mainly affect retention times of peaks eluted at the beginning of a gradient. Therefore optimize settings for the solvent at the beginning of the gradient. For mixtures containing up to 50 % water, use compressibility settings of water.
Start the pump with the required flow rate.
Before starting the optimization procedure, the flow must be stable. Check the tightness of the system with the pressure test.
Your pump must be connected to a data system or Instant Pilot with which the pressure and %-ripple can be monitored, or connect an external measurement device to the analog pressure output (see Electrical connections).
Starting with a compressibility setting of 40·10-6 /bar increase the value in steps of 10. Re-zero the signal display as required. The compressibility compensation setting that generates the smallest pressure ripple is the optimum value for your solvent composition. If ChemStation (classic view) is used and the ripple shown is positive, then the compressibility setting should be decreased. If it is negative, it should be increased.
Solvent (pure) | Compressibility (10-6/bar) |
|---|---|
Acetone | 126 |
Acetonitrile | 115 |
Benzene | 95 |
Carbon tetrachloride Footnote: Please check section Solvent information | 110 |
Chloroform Footnote: Please check section Solvent information | 100 |
Cyclohexane | 118 |
Ethanol | 114 |
Ethyl acetate | 104 |
Heptane | 120 |
Hexane | 150 |
Isobutanol | 100 |
Isopropanol | 100 |
Methanol | 120 |
1-Propanol | 100 |
Toluene | 87 |
Water | 46 |
[1]Please check section "Solvent Information" for compatibility to your specific LC system.
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