UV resonance Raman detection and quantitation of domoic acid in phytoplankton

Cultures of the phytoplankton diatom, Pseudonitzischia multiseries, have be en harvested under controlled growth conditions ranging from late logarithm ic to late stationary phase (17-58 days). The amount of domoic acid (DA) pr esent in the growth media and in the homogenized cells has been determined by HPLC. Defined samples of media, homogenized cells, whole cells, and whol e cells in media have been laser excited at 251 nm for the purpose of selec tively exciting intense UV resonance Raman spectra from DA in the samples. Neither media nor cell component spectra from algae seriously interfere wit h DA spectra. The spectral cross sections for the dominant 1652-cm(-1) mode of DA have been determined for 242-, 251-, and 257-nm excitation, Maximum sensitivities are achieved with 251-nm excitation because cross sections fo r DA are maximum, and interference from other algal components becomes very small. DA concentrations that have been determined with 251-nm excitation by resonance Raman methods correlate closely with values determined indepen dently with HPLC, especially at higher DA concentrations. The UV resonance Raman analysis of DA in phytoplankton algae is shown to be very sensitive a nd quantitative as well as rapid and nonintrusive.