Fig. 2.

Optimization of acquisition conditions for confocal resonance Raman microscopy to distinguish zeaxanthin from lutein. Zeaxanthin and lutein standards were dissolved in methanol at 10-μM concentrations. Of four Raman gratings, (A) 600, (B) 1,200, (C) 1,800, and (D) 2,400 grooves/mm, the 1,800 and 2,400 grooves/mm gratings were the best. The Raman shifts of the peaks of the C = C bond vibrations of zeaxanthin and lutein were distinguishable at 1,528 and 1,532 cm⁻¹, respectively.