Like anything, if sodium citrate or extender get old it does not work as well.
We are probably talking about two weeks maximum for keeping a solution of sodium citrate in a bottle, after that there could be a problem with crystallization. Sure you can use fresh extender as well, as long as it contains sodium citrate (sodium citrate is a clarifying agent) and you zero out the spec to that reagent. To keep a fresh sodium citrate solution you can make it up in small batch sizes, for example 500 ml.
