Can anyone recommend the best circuit for skin to electrode impedance measurement using the AD5933.

I wouls think the App note that describes "measuring Grounded impedances" would work well,

You need to make sure that the Return voltage is correctly biased to match the imput circuit of the Ad5933

The IA does this nicely with the ref cct. You can set it to the right level,

AC coupling the output will keep the DC bias at zero irrespective of the output selected.

The only thing left is t use a Isolator such as the 4Ch isolator with built in Pwr reg. I forgot th part.

This gives 2W and Isolation is good enough for you i think. If you need more you could use  Te ADUM2401 and a max845 plus halo transformer.

I have used this for medical devices and it will pass regs

I wouls think the App note that describes "measuring Grounded impedances" would work well,

You need to make sure that the Return voltage is correctly biased to match the imput circuit of the Ad5933

The IA does this nicely with the ref cct. You can set it to the right level,

AC coupling the output will keep the DC bias at zero irrespective of the output selected.

The only thing left is t use a Isolator such as the 4Ch isolator with built in Pwr reg. I forgot th part.

This gives 2W and Isolation is good enough for you i think. If you need more you could use  Te ADUM2401 and a max845 plus halo transformer.

I have used this for medical devices and it will pass regs