Detection of poly(ethylene glycols) and related acidic forms in environmental waters by liquid chromatography electrospray mass spectrometry

Poly(ethylene glycols) (PEGs) and related mono-and di-carboxylated forms constitute one of the most abundant classes of contaminants in natural waters. Because of the lack of efficient analytical methods, only one study has been devoted to estimate levels of these analytes in some river waters. The present method involves analyte extraction from 50 mt of raw sewage, 100 mi of treated sewage, 500 mt of river water and seawater, and 2000 mt of groundwater by a 0.5-g Carbograph 4 cartridge. Isolation of acidic analytes from co-extracted neutral ones was accomplished by differential elution. During removal of the HCl-acidified CH2Cl2/CH3OH eluent mixture, carboxylated PEGs were purposely allowed to convert into their methyl esters. This offered the advantage of analyzing for all the species of interest using the same instrumental arrangement. Extracts were analyzed by liquid chromatography/electrospray/mass spectrometry operated in the positive-ion mode. For species with ethoxy chain lengths greater than or equal to 4, analyte recoveries were better than 83%, while lower homologues were poorly recovered, and thus, they were not considered when analyzing environmental aqueous samples. Under full-scan conditions, analytes in real water samples could be quantified at few tens of nanograms per liter, while data acquisition in the selected ion monitoring mode afforded limits of quantification of 0.1-0.3 ng/L. Analyses of influents and effluents of activated sludge wastewater treatment facilities showed that even high molecular mass PEGs, so far considered rather resistant to biodegradation, were very efficiently removed from sewages. The ubiquitous nature of PEG-type compounds was evidenced by the fact that they were detected at parts per trillion levels in marine waters 16 nautical miles from the Italian coast and in five groundwaters samples collected from subsurface depths ranging between 60 and 208 m.