GC065 Column Quality Testing: The Grob Test Mix

 Even though fused silica columns were thought to be inert, it has active “hot spots” of silanol groups, and polar compounds, particularly basic amines, can be adsorbed strongly to its surface, producing peak tailing and poor quantitative results. The Grob test can be used to evaluate the effectiveness of the deactivation process. The test proposes a mixture of six classes of compounds, that would probe for any unwanted column adsorption:

1)      Hydrocarbons. They are neutral compounds and always should produce sharp and symmetrical peaks. If not, they indicate a poorly installed column.

2)      Fatty acid methyl esters. Used to determine separation efficiency of the column. Small peak heights indicate adsorption losses in the system.

3)      Alcohols. They interact if there is presence of silanol in the injection port liner or the column, producing reduced peak heights, due to hydrogen bonding.

4)      Aldehydes. Reduced heights or symmetrical peaks imply adsorption of aldehydes.

5)      Acids. Adsorption can be caused by basic adsorption sites or hydrogen bonding, due to free silanol groups. The column may be used for other types of analytes.

6)      Bases. Poor peak shape or reduced heights indicate the column has an acidic nature. It can be used for other types of analytes.

The elution order of Grob-type test mixtures is also used to determine the polarity of liquid phases. Column manufacturers use these mixtures for quality assurance.

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