Evaporative light-scattering detection in the quantitative analysis of semivolatile polycyclic aromatic compounds by high-performance liquid chromatography

Polycyclic aromatic compounds (PACs) with molecular weights lower than 300 were not considered in the past to be analyzable using an evaporative light-scattering detector (ELSD) due exclusively to their supposed volatility. We demonstrate that a variety of small, low-boiling, 3-6-ringed PACs (which include condensed PAHs, heteronuclear polycyclic compounds, and hydroxy-PAHs) can be analyzed using ELSD under mild working conditions without significant volatilization. Although area counts versus sample load can be linearized with adequate regression coefficients in the mass range studied, results obtained from the injection of pure and binary mixtures of PACs indicate that ELSD behaves nonlinearly at low sample loads, regardless of the volatility or involatility of each compound. Quite uniform response factors are obtained on the linear zone for the studied PACs, and analyses of mixtures are carried out with errors generally lower than 6%. Experimental data are better fitted to logarithmic regressions, which provide similar slopes for the studied PACs, which in turn suggest that ELSD operates in similar scattering domains for these compounds under our working conditions. The use of a mathematical simulation of particle size distributions after nebulization and evaporation confirms this and explains why response factors of PACs are similar.