This may be a difficult problem if want to detect everything. Here are a few comments which may help you:

• The lipids will not "damage" your C18 column at all. They may foul it, so just as with all good chromatography methods, a strong wash solvent will be needed AFTER each analysis to wash the column down and prepare it for another analysis (a gradient of MeOH and Methylene chloride works well as a wash solution on some C18 for lipids). *Always use gradients to wash down the column as they allow you to change the polarity and solubility to dissolve the different types of material which are retained and clog the stationary phase over time.
• Fat soluble vitamin plus lipids in one solution... Saponification and liquid-liquid extraction are the simplest techniques to use (no chromatography needed).
• You may need to use in-line, 2D HPLC multidimensional chromatography to solve this problem. The lipids could be resolved (or captured and placed on "hold" using the 1st column, Dimension #1) and vitamin D could be resolved in the 2nd dimension (on column #2). This may be rather easy as the lipid can be captured with NP chromatography and the vitamin eluted onto the RP column for analysis.
• Have you thought about detection issues yet? Vitamin D is easy using UV. Phospholipids will require something else such as ELSD, CAD, MS or RID. If your concentrations are high enough, then 210nm will detect ("see") something, but 210nm is NOT selective so the method may be invalid. Also, UV would only be possible if the mobile phase used is transparent near 210nm (not very likely).

Some references which may help you:

(a) Standalone, 2D HPLC Multidimensional Column Switching Unit: Model CS3020. More info at this link: http://www.hplctools.com/switching.htm

(b) Simple method for separation of Vitamin D (This is a Prep example, but the method is the same on an analytical scale): https://www.researchgate.net/publication/21553707_Preparative_isolation_of_vitamin_D2_from_previtamin_D2_by_recycle_high-performance_liquid_chromatography

(c) Simple method to resolve Phospholipid classes apart using an HILIC hybrid NP HPLC method: https://www.researchgate.net/publication/239244583_A_Rapid_Method_For_Phospholipid_Class_Separation_by_HPLC_using_an_Evaporative_Light-Scattering_Detector?ev=prf_pub

Article Preparative Isolation of Vitamin D2 from Previtamin D2 by Re...

Article A Rapid Method For Phospholipid Class Separation by HPLC usi...

You can separate the lipid-soluble vitamins from the phospholipids via saponification with KOH 1N in 90% ethanol and a subsequent liquid-liquid extraction with hexane. Phospholipds can be saponified, vitamims and sterols can't. After that, you can separate your vitamin D with a C-18 column.

Saponification is a good technique to use, but select a method which does not involve heating the solution as you need to be cautious of any thermal breakdown which may result in isomerization or degradation of the vitamin D.

Thank you very much for your answers. Im going to consider first using UV-detection since it's the easier way. Then, saponification and the last one the method to clean the column in HPLC. Thanks again.