HPLC degasser techniques: Types of solvent degassing
HPLC solvent degassing
HPLC is a chromatography where in a liquid is allowed to flow over a solid phase under constant pressure. The solvents is pumped by a constant rate to achieve desired pressure.
This pressure determines the rate of separation of components in the mixture. If the particle size is small, then high pressure is required.
But in doing so, if there are air bubbles in solvents being pumped, then there is fluctuation of pressure. Also there can be problems like improper peaks, improper detection, clogging of column etc.Since water and other solvents can easily trap up air, they are to be devoid of gases.
Hence in HPLC degassing of solvents (mobile phase) is very essential for proper operation and retrieval of uniform data.
Degassing removes entrapped air and other gases from the solvents.
This degassing has to be done in a manner such that the volume of solvent should not change. Also there should be chemical damage to the solvent. That is the properties of solvents should not change after degassing.
For this we need such techniques which do not generate heat and also contaminate the solvent.
Hence degassing is done by very smart and safe methods.
Degassing using Sonicator-picture
Types of solvent degassing
Degassing is done by two techniques:
a) By ultra sonication
b) By filtration method.
1) Ultrasonication degassers: Here gas is removed by subjecting the solvent to ultrasonication,
This is done by two methods.
i). By placing ultrasonicator probe in the solvent. here the solvent to be degassed is taken in a beaker. The ultrasonicator probe is inserted into solvent and subjected to ultasounds. The sound waves burst the gas bubbles and gas is expelled.
ii). By placing in ultrasonicator trough: Here the solvent beaker is placed in a ultrasonicator trough. The water in the sonicator trough generates ultrasound waves. These help the gas bubbles in the solvent to burst. This is the commonest technique for degassing of HPLC solvents. The methods is less expensive and also less tedious than previous method.
Filteration method of degassing
2. Filteration degasser
Filtration degassing is not a commonly used technique but is highly effective one.
Here solvents are degassed by synergistic action of vacuum suction, filtration and also mechanical stirring.
The solvents are filtered under vacuum into a filtration flask through a 0.4 to 0.2 micron filter. This provide effective filtration plus exposure of entrapped air to vacuum during passage of solvent through filter pores.
Then the filtrate in the flask is subjected to rigorous stirring using magnetic stirrer with constant application of vacuum for definite period of time (half an hour is recommended). This provides effective degassing as the entrapped air forms bubbles due to stirring and there by removed by vacuum.
This method provides high quality degassing over the sonication method as it not only involves degassing but thorough filtration.
Further it is recommend to put the degassed solvents in refrigerator over night if your mobile phase is not a crystallizing buffer at low temperature. Cold enhances effective degassing.
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