KPA Analysis Brief - Uranium Sample Types

The following methods of treating sample types will permit analysis in the low parts-per-trillion (µg/l) range. Samples with higher levels of uranium may be diluted instead of wet-ashed.

Urine, Vegetation, Tissue

Sample treatment is complete destruction of organic content by slow wet-ashing with either nitric/perchloric acid or nitric acid/hydrogen peroxide. The ash is dissolved in dilute nitric acid and diluted to a pH above 1.

Soils, Leachable Uranium

Leach soil in hot 8 M nitric acid, preferably with stirring, for several hours. Boil to reduce the acid volume. Cool somewhat and add 30% hydrogen peroxide to complete destruction of organic components. Stir well and heat. Cool and dilute at least ten-fold with deionized water. Centrifuge leachate or let solids settle. Analyze with the KPA. Further dilution may be beneficial or necessary.

Air Filters

Leach filters with hot 8 M nitric acid. Cellulose filters may totally dissolve. Leachate of soluble filters must be wet-ashed like urine to eliminate degradation compounds. Wet-ash to near dryness, then dilute to about 5 Ml. Analyze with the KPA. If significant, the uranium blank of the filters must be monitored.

Water

Drinking water may usually be analyzed without pretreatment. If present, organic luminophors, e.g. from decayed vegetation, may produce non linearity in the data. Make sample about 10% nitric acid and boil to dryness. Dissolve residue with warm, 4 M nitric acid and dilute at least four times to original volume. Swamp water may require more rigorous wet-ashing. If a lower detection limit is required, dilute less as desired. This pretreatment should be followed in general unless experience indicates that it is not necessary. Natural water may contain chloride and/or reducing organic compounds which can cause severe quenching. Either the nitric acid boil down treatment or sample dilution will be appropriate. D-5174, TRACE URANIUM IN WATER BY PULSED-LASER PHOSPHORIMETRY, is the ASTM method for uranium assay with the Chemchek KPA. The EPA has adopted the ASTM method in the National Primary Drinking Water Regulations (40 CFR Part 141, sec. 141.25).