ELECTROCHEMICAL SAMPLE PRETREATMENT COUPLED ONLINE 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 preconce ntration and matrix elimination on-line with ICP-MS detection. Analyte levels ranging from 20 mu g/L to subnanogram per liter were determine d in matrix-free standards with good linearity and precision. Detectio n 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 conc entrations as low as 5.0 mu g/L. High levels of salt matrix moderately suppressed uranium deposition efficiency, and therefore stripping pea k 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 9 0-s cell washout time. Uranium was quantified in a certified seawater matrix, NASS-4 (certified uranium level-2.68 +/- 0.12 mu g/L), at seve ral 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 af finity for anodized GC, and simultaneous measurement of thorium and ur anium was demonstrated.