two questions

[moon704520]

1)how can I increase the retention of the interested peak(actually there is no any retention )?here I only got one common RP-C18 column,250*4.6,5u,120A,
2) I find someone use some THF sometime they use DMF combined with ACN or MeOH,just interested in the fuction of the THF/DMF?
many thanks !

[shaun78]

1. Generally in reversed phase chromatography the retention time in increased by decreasing the amount of organic in the mobile phase and increasing the amount of water.

2. Adding something like DMF or THF to ACN or MeOH generally serves to increase the strength of the organic mobile phase. In RP chromatography, this will help compounds that are retained on the column for long periods of time elute more quickly. Small amounts of DMF or THF might also have been added to the organic mobile phase to keep small impurities from building up on the head of the analytical column.

Cheers,

Shaun

[yangz00g]

1) No retention on C-18 means the compound is too polar or ionized. If adjust pH can make the compund neurtal, you can see some retention. If pH adjust fails and you have only this column, ion-paring may work.

2) agree with Shaun.

[Consumer Products Guy]

Sometimes THF delivers selectivity different than methanol or acetonitrile.