Fig. 4From: The pH-Dependent Stucture and Properties of Au and Ag Nanoparticles Produced by Tryptophan ReductionOptical spectra of silver and gold nanoparticles after 6 month of storing (a); mass spectra of Ag NPs under consideration in mass range 40 to 1000 Da for positive ions (b). The inset shows the color of silver colloidBack to article page