Why would curcumin not pass through a 0.45μm syringe filter?

Hello everyone,

In order to measure curcumin with a spectrophotometer during dissolution in a medium (water, NaCl and HCl =>pH 1.2), I would pass the curcumin sample through a filter of 0.45μm.

However, when the sample passes through the filter, the resulting solution contains very limited curcumin conc., as if the filter is retaining it. This is weird, since in literature everyone passes curcumin through this filter. When I centrifuged the sample and passed the supernatant of high conc. through the filter, again the resulted solution would very extremely low in conc.

I've tried different volumes and concentrations of the sample, but the result is the same. When I re-use a filter, then suddenly the concentration is rising, as if the new sample going through the filter washes off some curcumin left from the previous one.

Any ideas?