It's so simple I can't believe I didn't find out until now. Just put a teaspoon of baking soda in your hand, add a little water and rub your hands together and voila, rub on armpits. I found it to last all day and right through to the next day. You also get the added bonus of softer hands.
I already used baking soda for cleaning and toothpaste and now I'm also testing it out in place of shampoo. What a great find!!
(Part 2 to follow)