We have to optimize a separation with HPLC, we have an solute containing 4-hydroxybenzoic acid, 3-hydroxybenzoic acid, 4-hydroxy-3-methylbenzoic acid, benzoic acid, 2-Chloorbenzoic acid, 3-Chloorbenzoic acid and were using an eluent with acetonitile and water and a (standard) C-18 column.
The only possibilities that we have is to change flow rate and de ratio of acetonitrile and water.
Does someone have some advice how to do this because otherwise we have to do it over and over again and we have just a few hours.

Thank you in advance!

Jorim

We have a method and a column for the separation of various benzoic acids, if you need it in a future. Please check our website at www.primesep.com. Here is the link to the separation of hydroxybenzoic acids. I think that you be able to separate yor mixture by usinhg our Primesep B or Primesep B2 column
http://allsep.com/makeChr.php?chr=Chr_023

Jorim,

Flow rate won't do anything for you, if the selectivity is not right. You may be able to improve selectivity with the acetonitrile content, but also possibly at the expense of analysis time. Neither one of these techniques are good for methods development.
Why are you stuck with these changes? Is this a Pharmacopoeia procedure? If this is the case, you will be better off to find out, what the column was on which the method was developed.