In 1982 Bøyum [1] published a new method for the isolation of human PBMCs that employed a medium of the same density as Lymphoprep™ containing no polysaccharide. This medium containing 14.1% (w/v) Nycodenz®, 0.44% NaCl, 5 mM Tricine-NaOH, pH 7.0 (ρ = 1.077 ± 0.001 g/ml; osmolality = 295 mOsm) is commercially produced by Axis-Shield as Nycoprep™ 1.077. 

This solution was subsequently modified [2] to provide a simple method for the preparation of mononuclear cells (MCs) from rodent and rabbit blood, which have a higher density than those from human blood. 

The solution contained 14.1% (w/v) Nycodenz®, 0.30% (w/v) NaCl, 5 mM Tricine-NaOH, pH 7.2 (ρ = 1.077 ± 0.001 g/ml; osmolality 265 mOsm). Reducing the osmolality of the solution causes the MCs, but not the polymorphonuclear leukocytes (PMNs), to gain water, thus their density decreases. This strategy gives better resolution of the MCs from PMNs than using a barrier of raised density.