Determination of nonylphenol ethoxylates in the aquatic environment by normal phase liquid chromatography–electrospray mass spectrometry

A comprehensive analytical method based on normal-phase liquid chromatography–electrospray ionization mass spectrometry (NPLC–ESI-MS) has been established for determination of nonylphenol ethoxylates (NPEOs) in the aquatic environment. Extraction and cleanup of samples were performed on graphitized carbon black (GCB) solid-phase extraction cartridges. Complete separation between each individual NPEOs was achieved by combining a C18 pre-column with a silica analytical column and using acetonitrile–water as eluent. Quantitative determination by LC–ESI-MS was achieved in the positive ionization (PI) mode at a ramped cone voltage for NPEOs using selected ion monitoring. Recoveries for NPEOs ranged between 91.9 and 117.5%, and the limits of detection varied between 0.5 and 2 ng/l for individual NPEOs with n longer than 2, and between 5 and 0.5 μg/l for NP1EO and NP2EO. This method was successfully applied to the investigation of residual NPEOs with n>2 in the Chongqing area of the Changjiang river. NPEOs with n ranging from 1 to 22 were found to vary between 0.1 and 2900 ng/l with a distribution depending on the depth of water.