Chromatography Forum

Dear All,
I am trying separate Caffeine with HPLC using a C18 column. I would like to avoid using buffers if possible but I am getting distorted peaks and even split peaks in some chromatographic conditions. I found it difficult to get good retention with good peak shape using Methanol and Water only as the mobile phase. I have an access to a C8 columns if it may help.

I appreciate your suggestions.

Many thanks in advance.

What is your sample dissolved in? Using your mobile phase as the diluent can minimize peak shape problems.

Thanks Tom.
I tried the MP and Water but I found no clear difference.

try 70:30 MeOH:H2O as both diluent and mobile phase. on a C18, 4.6x75mm column with 10ul injection, you get a nice clean peak, in under 3 minutes; using a 1ml/min flow rate. Waters uses this method for some of their instrument qualification analysis.

I use a mobile phase of methanol/water 70:30 with 1% acetic acid to analyze caffeine and benzoic acid from direct injections of soda pop. This makes a great demonstration for school classrooms.

Methanol: Water 70:30 and a Standard C18 column, directly from a coffee mug, inject and you should get a nice Peak. Or you take a sample from Coca Cola, ultrasonic a Little bit and inject. Also a nice Peak.

Many thanks for all of you!

The job seems to be easier than what I thought!
I tried a new C18 column after reading your suggestions and every thing went well!
I think the OLD column is reaching its lifetime end!

Thanks again.