Did you harden them off before putting them outside all day?

If so... perhaps you could create shade for your plants so that they do not get the harshest light from the west. Maybe putting in a thin trellis (you could make this yourself to fit your needs- wire, twigs wrapped together, etc) with some material on it to shade the plants.

I had the same problem last year on my south-west facing balcony. I get a bit of shade from the over head balcony. I reseeded later in the summer, and they did better. However, I learned to keep them in the shade of my patio table, and they did better in lighter colored 8-10" pots (1 Gal ice cream tubs work too). Spinach is a cool weather crop, so it's only natural that it would not tolerate full sun. I've just started putting mine out earlier this week, and I am keeping them in a shady corner. I've read that you can use a kind of mesh or cheesecloth over the top to keep them shaded.

Thanks for the advice. I'll have to create some shade on the balcony for my spinach since it's pretty much full sun all day.

I'm actually on my third attempt with this darn spinach. The sun took my first try, and then my cats got to the pot after I planted a second round of seeds. If it's not one thing, it's another. *Hopefully* I can keep my spinach sun and cat protected. lol

Good luck =). I'd like to know what you come up with for a shading device, if you get a chance to write about it!