Chromatographic separation and mass spectrometric analysis of N-acetyl-l-cysteine-protected palladium nanoparticlesElectronic supplementary information (ESI) available. See DOI: 10.1039/c7ay01146f

In this study, water-soluble N -acetyl- l -cysteine-protected palladium nanoparticles (NAC-PdNPs) were synthesised. The obtained NAC-PdNPs were well characterised by UV-vis absorption spectroscopy, infrared spectroscopy, X-ray photoelectron spectroscopy, and transmission electron microscopy. The as-synthesised NAC-PdNPs were found to be polydisperse in nature with an average particle size of 2.17 ± 0.20 nm. As such, a reverse-phase high-performance liquid chromatographic (RP-HPLC) methodology coupled with UV-vis absorption detection has been developed for separating and analysing this as-synthesised NAC-PdNPs product. A gradient elution program with mobile phase mixtures of methanol/water containing 50 mM tetrabutylammonium fluoride was successfully applied to separate the as-synthesised NAC-PdNPs sample. The spectral characteristics of each RP-HPLC-separated NAC-PdNPs fractions were captured online using a diode array detector. In addition, most major RP-HPLC fractions were collected and further characterised by matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry (MALDI-TOF MS) in order to elucidate their chemical compositions. The mass spectra suggest that the NAC-PdNPs as-synthesised product is indeed a complex mixture of small PdNPs comprising Pd 10 (NAC) 7 , Pd 11 (NAC) 7 , Pd 11 (NAC) 8 , Pd 12 (NAC) 9 , Pd 13 (NAC) 6 , Pd 13 (NAC) 9 , Pd 14 (NAC) 5 , Pd 14 (NAC) 9 , Pd 15 (NAC) 9 , Pd 17 (NAC) 11 , and Pd 20 (NAC) 11 . The UV-vis spectral characteristics of the separated NAC-PdNPs are closely related to the number of Pd atoms. This study highlights the values of using high-resolution chromatography together with UV-vis absorption spectroscopy and MALDI-TOF MS for revealing the hidden properties of each individual PdNPs species in a PdNPs product. The NAC-PdNPs product was successfully separated by reverse-phase HPLC, and the collected NAC-PdNPs fractions were characterised by MALDI-TOF MS.