Homemade sambar powder always have a nice aroma and fresh flavor infused in it, when compared to store bought ones. I never use store bought sambhar powder for preparing sambar in my home, since am not compromised with the taste. I always and always love homemade ones. The ingredients included in sambar powder may vary from home to home and everyone of them has different taste. My mom use to make sambar powder in her own way and we all love the Sambhar made out of it. Am also following the same recipe of my mom and always prepare in large quantity and store it in air tight containers.
This sambhar powder, if prepared and stored as mentioned here, shelf life will be about 6 months with its fresh aroma.