Saving ARGB 32 Bits BPM in Photoshop

Ok, I have an Image in 8 bits per channel mode on Photoshop. When I try to save it doesn't let me select the A8 R8 G8 B8 option.

Why I can't do it? There's a special mode that I have to choose to make this option available?

Here's a screenshot. Only the XRGB (leading zero) it's availabe and I need the leading Alpha option.

Sorry for any misspelling