improving voltage reference noise performance

Hi,

I want to sample a 4Hz signal with 100 samples per period ie sample every 2.5 msec. Now I want to have a good reference for this and think of improving the currently used ADR380. At the moment we just use a 100nF at the reference output = ADC ref input. Could I be better with a lowpass before the ref in or a lowpass and a buffer opamp?

ADC is an ADuC847.

Thanks for any hint and suggestion

Martin