A standard synthesis of silver nanoparticles in aqueous solution relies on the reduction of silver ions by sodium borohydride in the presence of sodium citrate. Nonetheless, the overall reaction has not been unambiguously determined. The focus of the current study is to identify and quantify the reaction products as well as investigate the mechanism of nanoparticle formation. To this end, we have constructed a mass spectrometer apparatus that allows us to sensitively monitor in real time gas phase species produced during the synthesis of the nanoparticles. One significant difference between some of the reactions that have been proposed in the literature is the production of H₂. We will present our results on the time evolution of H₂ as well as results of isotopic substitution experiments designed to determine the source of the evolved H₂. We have also used B¹¹ NMR to determine what boron species are present in the products.