Piperazine is not the same chemical as the buffer PIPES (piperazine-N,N'-bis-(2-ethanesulfonic acid). You should use piperazine if you want to duplicate the solution in the protocol.
siderophore test using CAS assay is effective but, instead of CAS assay if your organism is able to grow on Luria agar then you can go for the method described below.
1. prepare the blue dye and Luria agar separately and autoclave it.
2. Mix the autoclaved blue dye 4ml to 6ml/100ml of autoclaved Luria agar (until you see the perfect color).
3. pour the solution and keep it for solidification.
4. streak or spot your microorganism and keep it for incubation in required temperature.
5. After 48-72 hours you can see the orange layer on plate if microorganism is able to produce siderophores.