The answer to your question is yes, but I do store stock concentrated
buffer in the refrigerator, and dilute when needed.  

You can make up 0.5M TRIS, pH 7.6, then dilute 1 part 0.5M TRIS in 9 parts
0.9% sodium chloride for final working buffer of 0.05M TRIS in 0.9% sodium
chloride solution for a TRIS buffered saline. I store concentrated stock
for 1 year at 4C.  Working buffer can sit out at RT, but if I don't use it
within a week, I do store working in refrig and usually use working buffer
within a week. 

I know that labs also make up 10X PBS buffers and do the same thing.  



  
Gayle Callis
MT,HT,HTL(ASCP)
Histopathology Supervisor
Veterinary Molecular Biology - Marsh Lab
Montana State University - Bozeman
19th and Lincoln St
Bozeman MT 59717-3610

406 994-6367
406 994-4303 (FAX)