question archive In a chromatographic experiment you use a C18 column with a mobile phase mixture of acetonitrile and water (30:70 mixture)
In a chromatographic experiment you use a C18 column with a mobile phase mixture of acetonitrile and water (30:70 mixture)
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In a chromatographic experiment you use a C18 column with a mobile phase mixture of acetonitrile and water (30:70 mixture). After preliminary testing you determined that your analytes are well separated but the retention time is too long and peaks are too broad. What is your next step optimising chromatographic conditions?
A. Increase the column temperature by 100°C.
B. Change the injection volume.
C. Change the mobile phase mixture to increase the fraction of acetonitrile.
D. Change the mobile phase mixture to increase the fraction of water.
E. Change the stationary phase of the column to make it less polar.
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What is your next step optimising chromatographic conditions?
E. Change the stationary phase of the column to make it less polar.
Step-by-step explanation
The surface of C18 as the stationary phase in chromatographic separation has a particular disadvantage. C18 always has unreacted silanol groups that may actually form secondary polar interactions with the analyte. This therefore leads to broadening of the peaks. In order to avoid this, a procedure known as capping is used where the C18 is changed by reacting with chlorosilane to make it less polar hence reduced interaction with the analyte
