A method of sorting a sperm cell sample comprising the steps of: a. staining a sperm cell sample with a first media; b. sorting the sperm cell sample to form at least one subpopulation contained in a second media; and c. freezing the at least one subpopulation in a third media; wherein the first media, the second media or the third media comprises alpha-ketoglutarate or a derivative thereof at a concentration of 0.01-5 mg/ml.