Question five: Alkyl amines, such as those listed below, are difficult to separate by HPLC using silica-based C18 columns. The amine groups are relatively polar and the pKa values are given for their conjugate acids.
ethanolamine pKa = 9.50
butylamine pKa = 10.64
A. Indicate why separations are difficult with standard silica-based C18 columns.
B. Indicate an alternative way of using a type of liquid chromatography to separate them - indicate the type of column and the type of eluent needed (including pH) for successful separation.
Question six:
The gas chromatogram shown below was for the analysis of 1 ̄µL of liquid sample (reaction products) injected using a split ratio of 1:4 (one part in 4 injected into the column), with separation on a 0.25 mm x 15 m open tubular column with 0.2 ̄µm film thickness (normally a high efficiency column).
Indicate:
a) A problem in how the GC was run the quality of the chromatogram.
b) A change in conditions which could result in an improved chromatogram.