Stability impact salt concentration

Several detergents, including Brij-35, Tween20 or Triton X-100, have been tested and did not negatively impact assay performance. Optimal buffer composition (salt concentration, ionic strength, pH, additives to stabilize proteins, detergents) and its effects on the fluorophore used to label the protein should be determined for each new labeled kinase. 

Inaeasing precursor salt concentration increases the ion occupancy number per reverse micelle, which promotes intramicellar nucleation and growth and leads to higher uptake. On the other hand, high-ionic strength inside water pools of reverse micelles impacts the stability of the (w/o) microemulsions [63,64]. Moreover, the stabihty of the (w/o) microemulsions depends on the surfactant counterion, which results from ion exchange between the solubilized metal salt and sodium. Since the focus of this work was on nanoparticle uptake by (w/o) microemulsious, the concentrations of the metal precursors were limited to values which maintained stable reverse-micellar structures. 

For liquid formulations, the choice of using either a salt or a carbohydrate to adjust the osmolality of the solution is made by the impact on protein stability. Sodium chloride is one of the most commonly used salts in the formulation of both traditional pharmaceutics as well as biological pharmaceutics. It is extremely safe, well tolerated, and inexpensive. However, the presence of sodium chloride in a formulation of rhuMAb HER2 was found to increase oxidation when the formulation was stored in stainless steel containers, presumably because the sodium chloride promoted corrosion of the stainless steel. Interactions of salts with the proteins must be investigated on an individual basis because the type and concentration of salt may lead to protein aggregation. 

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