Quantitative determination of nonylphenol polyethoxylate surfactants in marine sediment using normal-phase liquid...

A new comprehensive analytical method based on normal-phase liquid chromatography-electrospray ionization mass spectrometry (LC-ESI-MS) has been developed for the quantitative determination of individual nonylphenol ethoxylate (NPEO) surfactants in complex environmental matrices. Clean-up of sample extracts was performed on cyanopropyl silica solid-phase extraction cartridges. Complete NPEO oligomer separation was achieved by using normal-phase LC. Because the non-polar solvents used in normal-phase LC are incompatible with ESI, unique LC-ESI-MS interface conditions were adopted that provided a functional interface and also enhanced the detection response of NPEOs. These provided enhanced ESI signal intensity and stability and facilitated the detection of NPEOs as sodium adducts at parts-per-billion concentration levels. The overall analytical method was validated for accuracy and precision by analyzing sediment samples spiked with known amounts of NPEOs. The method is superior to those currently used for NPEO analysis (LC-UV, LC-fluorescence, LC-thermospray-MS, LC-field desorption-MS, LC-particle beam-MS and GC-MS) in terms of detection limits, specificity and speed of analysis. The validated method was successfully applied to determine levels of NPEOs in sediments from the Strait of Georgia, British Columbia. This work also demonstrates that by proper selection of normal-phase LC-ESI-MS interface conditions this technique is capable of solving separation problems which are not amenable with reversed-phase LC-ESI-MS.