Table 1 Adopted method for the anoxic separation of U(IV)/U(VI) at micro-molar concentrations

1

Wash ~2-5 g of Dowex® 1x8 resin (100–200 mesh, chloride form) with ~20 mL 0.1 M HCl, repeat 4x

Pre-wash to remove any residual material from resin production that can interfere with uranium analysis via KPA

2

Use final rinse from Step 1 to slurry-pack a suitable column (such as a Thermo Scientific® Pierce polystyrene column, 0.7 cm ID with top and bottom frits) to 1.5-2 mL bed volume

Use a bed-height to column diameter ratio >3. In this study, bed-height to column diameter ratios between 5 and 7 were used with success

3

Flush resin-packed column with 4 M HCl (~10 bed volumes)

Pre-flush to ensure resin column is completely saturated with 4 M HCl

4

Add two successive flushes of 1x10^-2 M Ti(III) (2 bed volumes each) in 4 M HCl and, using end caps, seal in a final 1.5-2 bed volumes of Ti(III) and allow the packed resin column to soak for 3 or more days

Pre-treat resin to reduce oxidants associated with the resin that cause oxidation of U(IV)

5

Drain the resin column and flush with at least 10 bed volumes of 4 M HCl

To flush out residual Ti(III) prior to sample addition

6

Add uranium-containing solution in 4 M HCl (1 mL). Elute column with a total of 9 bed volumes of 4 M HCl and collect fraction(s)

To collect U(IV) fractions, which pass through the resin at 4 M HCl

7

Elute column with a total of 9 bed volumes of 0.1 M HCl and collect fraction(s)

To collect U(VI) fractions, which adsorb to resin at 4 M HCl but are eluted at 0.1 M HCl

8

Flush column with a total of 7 bed volumes of 0.1 M HCl

Post-flush to ensure all U(VI) is flushed away and clean resin for future use

9

Flush column with a total of 7 bed volumes of 4 M HCl

Post-flush to ensure all U(IV) is flushed away and resin column is in 4 M HCl state for future use

Column is ready to be re-used by repeating Steps 6–9 (Steps 1–5 need only be completed once)