By Anonymous on Monday, July 14, 2003 - 08:25 pm:
i am using Lichrosphere RP8 250 X 4.0 5um column for one of my application . with a mobile phase of
buffer : methanol : acetonitrile
in the composition 50:35:15
buffer is made up of 7ml triethyl amine in 1000 ml of water its ph adjusted to 3.0 with phosphoric acid .
what happens is we are getting one impurity eluting very closely to the drug main peak . its eluting first and than drug peak . i have almost 10 columns of same brand . we get seperation in two columns for this impurity that too 1.5 resolution . but in rest 8 columns impurity is completely merge with the main drug peak .
i check the chemistry of this column its spherical silica which is non encapped with 12.5 percentage of carbon load and with so much of ligand desity of 4.1 . with surface area of aroud 350 m2/g . so what can be the probleam is it so that this kind of specification can not be achieved in reproducibile manner or some problam with the mobile phase . can make my other 8 column to work for this application by giving some treatment or its not possible .
you can reply to me at shi_ri@indiatimes.com
shirish patel
By Anonymous on Tuesday, July 15, 2003 - 12:24 am:
I don't know if it is still valid today, but in earlier times we noticed that home-packing of Lichrosphere C8-columns is more difficult than C18. I.e. the columns showed a tendency to dead volume after a week or so. Dead volume control is very easy with that type of columns.
C18 are today the most popular RP-Phases.
PETER