B15 Silver Stained Polyacrylamide Gel

Description
A protein separation on a silver stained polyacrylamide gel is shown. Protein and peptide mixtures are frequently analyzed (by electrophoresis) by spotting them on a gel and separating them with a strong electrical field. Histidine in peptides and proteins reacts with formaldehyde and silver ions to initiate the reduction of silver ions to a dark elemental silver precipitate. The intensity and position of the bands may be used to determine the amount and identity of the proteins. Farmer's reagent oxidizes excess silver which forms on the surface of the gel and decreases the intensity of black bands to measurable levels. Thiosulfate promotes the oxidation by complexing silver ions.

Equation
2 Ag⁺ + HC=OH + H₂O -peptide or protein --> 2 Ag + HCOOH + 2 H⁺

Fe(CN)₆³^- + 2 S₂O₃²^- + Ag --> Ag(S₂O₃)₂³^- + Fe(CN)₆⁴^-

Farmer's reagent products

Reference
J. Heukeshoven and R. Dernick, "Electrophoresis", 6, (1985), p 103.