Spectrometric determination of L-cysteine and its enantiomeric purity using silver nanoparticles

The system containing silver nanoparticles (similar to 45 nm) and L-cysteine at the concentration range from 10(-9) to 10(-2) mol L-1 was studied by absorption and electronic circular dichroism spectroscopy in the UV-vis range and surface enhanced Raman spectroscopy at different pH and ionic strength. By later one the presence of L-cysteine was clearly detectable even at 10(-9) mol L-1. The analysis of circular dichroism spectra by statistical methods, namely two-step cluster analysis, principal component analysis, and partial least square regression, allowed determination of L-cysteine in the range from 10(-5) to 10(-3) mol L-1. Moreover this system is very sensitive to addition of D-cysteine; hence, the enantiomeric ratio can be estimated and the presence of o-cysteine in the system is clearly detectable even at 10(-6) mol L-1, i.e. the content of this enantiomer is as low as 2% in the mixture. (C) 2013 Elsevier B.V. All rights reserved.