Electrochemical Sample Pretreatment Coupled On-Line with ICP-MS:  Analysis of Uranium Using an Anodically Conditioned Glassy Carbon Working Electrode

Uranium may be accumulated at an anodized glassy carbon (GC) electrode at −0.15 V and stripped at +1.15 V, allowing electrochemical preconcentration and matrix elimination on-line with ICP-MS detection. Analyte levels ranging from 20 μg/L to subnanogram per liter were determined in matrix-free standards with good linearity and precision. Detection limits (3s y / x /slope) determined from standard addition plots were 0.12 ng/L with 10-min accumulation time, permitting the minor isotopes of uranium to be determined with good precision at total uranium concentrations as low as 5.0 μg/L. High levels of salt matrix moderately suppressed uranium deposition efficiency, and therefore stripping peak height, but could be compensated for by extended accumulation times. Matrix elimination of up to 20 000 mg/L Na was complete with just a 90-s cell washout time. Uranium was quantified in a certified seawater matrix, NASS-4 (certified uranium level 2.68 ± 0.12 μg/L), at several levels of dilution: recoveries ranged from 100.4 to 119.4% and all agreed with the true value within 95% CL. Thorium showed a similar affinity for anodized GC, and simultaneous measurement of thorium and uranium was demonstrated.