By Anonymous on Thursday, September 26, 2002 - 02:12 am:
Does anyone know if it is possible to resolve by HPLC (C18 column) a mixture drug // complex(drug:b-cyclodextrin)??
I tried this, but I obtained a single peak at RT of drug. (It’s the hydrophobicity of column so strong that dissociate the complex and retain only the drug….and what I see is free drug plus the drug from the complex?? The spectra of drug is practically unchanged after the inclusion on cyclodextrin and I monitored at lambda specific for drug)
Thanks
By Fabiano on Thursday, September 26, 2002 - 03:44 am:
I already did a drug-cyclodextrin analysis and what I noted is that the inclusion(drug-cyclodextrin complex)is much more low that what I saw by DSC,problably because the organic solvent in the mobile phase compete with your drug for the cyclodextrin cavity.I think that the column force a separation from drug-cyclodextrin.
maybe your mobile phase are displacing all drug from cyclodextrin .what is your mobile phase?your drug?
bye
By bill tindall on Thursday, September 26, 2002 - 05:08 am:
When an analyte can exist in two forms, or two states, what you see in chromatography will depend on how rapid equilibration occurs between these two forms or states. You will only see a peak for each if the equilibration rate is much slower than the time scale of the chromatography. At an intermediate rate you will see a broad ugly looking peak. If equilibration is rapid you will see one peak which will represent an average of each form or state. therefore, unless the rate is very slow you will not be able to use chromatography to directly determine the fraction free and the fraction included.
Furthermore, the formation constant of the complex will be affected by the composition of the solvent, or lack of solvent. Therefore, you can't dissolve a sample in something and determine anything other than the fraction included in that solvent mixture.
Bottom line, generally can't use chromatography to determine how much compound is complexed in original sample.
By Anonymous on Thursday, September 26, 2002 - 05:16 am:
the drug is metoprolol and the mobile phase is 20% MeCN, 80% sol KH2PO4 pH3 with H3PO4
By Fabiano on Thursday, September 26, 2002 - 05:40 am:
I tryed with lysinopril in ß-CD,try to use MeOH in the same rate or decrese the organic solvent,maybe help ,here we had very bad cromatograms.but with less organic solvent we could see how much was getting complexed in ß-CD.
but what bill tindall says is true :generally can't use chromatography in this case.