Separation of analytes

Separation of analytes - context
Analyte mixtures and separation - 1
Analyte mixtures and separation - 2
Analyte mixtures and separation - 3
Introduction to chromatography
Chromatographic columns
Principle setup of a chromatographic unit
Example of separation
Chromatographic system - 1
Chromatographic system - 2
Standard gas chromatograph
(Old) liquid chromatography unit
(New) liquid chromatography unit
HPLC columns
Comparison GC and HPLC
Selftest
     1) Purpose of chromatographic process
           Answer
     2) Unsuitable compounds
           Answer
     3) HPLC vs. GC
           Answer
     4) Detectors
           Answer
     5) Solvent properties
           Answer
     6) Retention time
           Answer
     7) Analyte identification
           Answer
     8) Irreversible or reversible sorption process
           Answer
     9) Short analysis time
           Answer
     10) Retention factor
           Answer
     11) Breakthrough-curve
           Answer
Problems
End of lesson

5) Solvent properties

 

Question:

What properties should a solvent have that is used for injecting an extract into a GC?
Which solvents should be used for HPLC?

 

Answer:

For GC: The solvent should be so volatile that it elutes from the column well before the first analyte. In other words, the retention factor R of the solvent should be smaller than that of the analytes. If solvent and analytes were to co-elute, their peaks would overlap. Accurate quantification of the analyte is then impossible, particularly because the solvent peak is typically much larger than the peaks of the analytes (as substantially more solvent than analyte molecules are delivered into the chromatographic system per injection).

For HPLC: First and foremost, the solvents need to be "HPLC-grade". That is a very high level of purity. Only slight impurities (less than 1 vol%) would create peaks in the chromatogram. Second, the solvent needs to be adapted to the mobile phase that is running through the column and the sample port. For instance, if the mobile phase is water, one looks for a solvent that is miscible with water (i.e., a solvent that does not create a separate phase in the HPLC).