Determination of actinide elements at femtogram per gram levels in environmental samples by on-line solid phase extraction and sector-field-inductively coupled plasma-mass spectrometry

An on-line solid phase extraction method has been developed for the determination of 232Th, 237Np, 238U, 239Pu, 240Pu, 241Am and 243Am in biological certified reference material using a column containing TRU-Spec(TM) resin coupled with sector-field inductively coupled plasma-mass spectrometry. Absolute detection limits were 0.7, 0.85, 0.6, and 0.65fg for 237Np, 239Pu, 241Am and 243Am, respectively. The 239Pu was determined in NIST Human Liver (963±297fgg-1 compared with a certified value of 848±161fgg-1) using a dry and wet ashing sample preparation method, and in a spiked cabbage reference material (394±54fgg-1 compared to an indicative value of 467fgg-1) using microwave digestion. Sequential separation of Pu and U was achieved by on-column reduction of Pu with titanium(III) chloride and elution in 4M HCl to facilitate the determination of 239Pu in samples containing high levels of 238U, thereby eliminating the interference of 238U1H+ at m/z 239. The sequential elution procedure was used to determine 239Pu in NIST human lung (814±55fgg-1 compared with a certified range of 227-951fgg-1) and NIST Rocky Flats Soil (2423±137fgg-1 compared with a certified value of 3307±248fgg-1).