You can use normal C18 column as RPHPLC for the analysis vitamin type of Thiamine, Riboflavin, Vitamin D3, Niacin etc. Would you please mention your vitamins name?
There are various type of carbon containing column available commercially like C4, C6, C8, C18, C30 etc. More the adjacent numerical number of C increases the carbon number increases.
In CANIA http://www.cania.org.ve/ we use Agilent Zorbax Rapid Resolution Hypersil ODS 4x250 mm 5um to analysis Vit A and E in plasme samples after hexane organic extraction with a good performance.
But we have had several analyticals problems to analysis Vit D in the same samples.