Determination of Technetium-99 Activity in Water or Solid Samples using Extractive Disc Separations Followed by Proportional C

Determination of Technetium-99 Activity in Water or Solid Samples using Extractive Disc Separations Followed by Proportional Counting

William H. Hayes

O’Brien & Gere Laboratories, Inc.; Syracuse, NY

Summary

A rapid technique was developed for determining Tc-99 activity in water or solid samples. The technique involves the use of TEVA Discs™ for separation of technetium. Counting is performed using a low-background proportional counting system. Analyses are performed in duplicate for each sample: one sample is analyzed neat; the duplicate is spiked with a known Tc-99 activity for the purpose of determining the matrix-specific Tc-99 recovery.

Drinking water or surface water samples having insignificant suspended solids concentrations are passed through the TEVA Discs™ directly. Water samples having visible amounts of solids are filtered through a Whatman No.41™ filter prior to passing the filtrate through the TEVA Disc™. Solid samples are leached with 200 mL 0.1% sodium hypochlorite per a 20 g sample. The leachate is then filtered with a Whatman No. 41 filter. Its filtrate is then passed through the TEVA Disc™.

Filters are dried at 38EC for 2 hours and then counted for 200 minutes.

Results

For our proportional counter, the average beta background is 0.63 cpm. The efficiency determined for Tc-99 within the TEVA Disc™ is 24.6%.

Matrix

Volume or Mass

(mL or g)

Typical MDC

(pCi/(L or g))

Range of

Recoveries (%)

Average

Recoveries (%)

Std

Dev

# of

data

points

water

500

1.5

89.5 - 111

98.7

8.8

solids

0.03

56.2 - 111

93.2

17.6

Procedure

Solids

1 Weigh a 20g sample and duplicate into glass beakers

2 Spike the duplicate with Tc-99

3 Heat for 2 hr at approximately 85EC

4 Filter solids into a Whatman No 41 filter

5 Assemble TEVA filter into a Whatman filter assembly on vacuum flask

6 Filter filtrate from above through TEVA filter by gravity (no vacuum)

7 Rinse filter with 50 mL 0.05M HNO₃

8 Rinse assembly with minimal DI water

9 When reservoir is empty, turn on vacuum to complete the filtering process

10 Place the used TEVA filters into a 38EC incubator or oven and dry for 2 hours

11 Count in a proportional counter for 200 minutes

Water

1 Measure from 500 to 2000 mL depending on the detection level required

2 If water is clean, proceed from step 5 above

If visible solids are present, proceed from step 4 above

Miscellaneous Notes

As a means of testing the placement and stability of technetium on the filter media, a series of filters were spiked and counted right-side-up and up-side-down. The variable tested was volume of sample. Spikes were prepared having volumes ranging from 100 mL to 2000 mL. Data will be presented showing that no appreciable difference was noted in the count rate ratios attributable to sample volume.

Background and Conclusions

Development of the above method was necessitated as a result of the fact that, at the time of its development, O’Brien & Gere Laboratories did not have a liquid scintillation counter. After significant testing, it was determined that the method is a reliable, accurate, and simple method for assessing Tc-99 activity.

Though we do not envision this method replacing LSC counting techniques for Tc-99, it was determined that the method is capable of providing reliable data in situations, such as ours, where an LSC was not available or in analysis environments having limited resources such as a mobile lab.

™’s - TEVA Disk: trademark of EIChrom Industries, Inc.; Darien, IL

S Whatman No. 41: trademark of Whatman International Ltd.