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ANALYSIS OF PERFLUORINATED CARBOXYLIC ACIDS IN SOILS II: OPTIMIZATION OF CHROMATOGRAPHY AND EXTRACTION
Citation:
WASHINGTON, J. W., W. M. HENDERSON, J. J. ELLINGTON, T. JENKINS, AND J. J. EVANS. ANALYSIS OF PERFLUORINATED CARBOXYLIC ACIDS IN SOILS II: OPTIMIZATION OF CHROMATOGRAPHY AND EXTRACTION. JOURNAL OF CHROMATOGRAPHY A. Elsevier Science Ltd, New York, NY, 1181(1-2):21-32, (2008).
Impact/Purpose:
The general goals of this research are to meet OPPT's need for data and information regarding the stability of TBPPs in soils. We plan to address these needs with a series of lab experiments in which FBPs are exposed to selected natural and amended soils. We anticipate that, as we learn about the general behavior of FBPs in soils, we will develop a protocol for testing FBPs in soils that has procedures similar to the guidelines described in OECD 307.
Description:
With the objective of detecting and quantitating low concentrations of perfluorinated carboxylic acids (PFCAs), including perfluorinated octanoic acid (PFOA), in soils, we compared the analytical suitability of liquid chromatography columns containing three different stationary phases, two different liquid chromatography tandem mass spectrometry (LC/MS/MS) systems, and eight combinations of sample-extract pretreatments, extractions and cleanups on three test soils. For the columns and systems we tested, we achieved the greatest analytical sensitivity for PFCAs using a column with a C18 stationary phase in a Waters LC/MS/MS. In this system we achieved an instrument detection limit for PFOA of 270 ag/µL, equating to about 14 fg of PFOA on-column. While an elementary acetonitrile/water extraction of soils recovers PFCAs effectively, natural soil organic matter also dissolved in the extracts commonly imparts significant noise that appears as broad, multi-nodal, asymmetric peaks that coelute with several PFCAs. The intensity and elution profile of this noise is highly variable among soils and it challenges detection of low concentrations of PFCAs by decreasing the signal-to-noise ratio. In an effort to decrease this background noise, we investigated several methods of pretreatment, extraction and cleanup, in a variety of combinations, that used alkaline and unbuffered water, acetonitrile, tetrabutylammonium hydrogen sulfate, methyl tert-butyl ether, dispersed activated carbon and solid-phase extraction. For the combined objectives of complete recovery and minimization of background noise, we have chosen: 1) alkaline pretreatment; 2) extraction with acetonitrile/water; 3) evaporation to dryness; 4) reconstitution with Tetrabutylammonium-hydrogen-sulfate ion-pairing solution; 5) ion-pair extraction to methyl-tert-butyl ether; 6) evaporation to dryness; 7) reconstitution with 60/40 acetonitrile/water (v/v) and; 8) analysis by LC/MS/MS. Using this method, we detected in all three of our test soils, endogenous concentrations of all of our PFCA analytes, C6 through C10 -- the lowest concentrations being roughly 30 pg/g of dry soil for perfluorinated hexanoic and decanoic acids in an agricultural soil.