Determination of ⁹⁹Tc in Urine using EIChroM TEVA^® discs

Buzz Vickery and Tabitha A. Liebrecht

Severn Trent Laboratories Richland

2800 George Washington Way

Richland, WA 99352

As a commercial laboratory STL Richland has the need for methods that are both cost- and time-efficient. This presentation will focus on a separation scheme for ⁹⁹Tc in urine using EIChroM TEVA^® discs and present the improvements in tracer yield, turnaround time, waste minimization and cost savings as compared to ion exchange columns.

A sample size of 300 mL of urine is poured into a flask with the appropriate tracers added. The sample is then subjected to evaporation, wet acid digestion and muffling. The sample is treated to ensure oxidation of Tc to the +7 oxidation state. Each sample is then passed through an EiChrom TEVA^® disc. The TEVA^® disc is rinsed with 0.01M HNO₃ to remove all possible alpha-emitting interferences. The TEVA^® disc is rolled into a LSC vial, mixed with 15 mL of Beckman Ready-Gel and counted for 60 minutes by liquid scintillation counting.

Tracer yields have improved ~10% (ave=96.1%, n=63, σ=0.066), with a ~15% improvement in MDA. The range for tracer yields are 70% - 104% with 85.7% of the samples being above 90%. There is also 60% less acidic waste being generated with the TEVA^® disc method as compared to the ion exchange method. The analysis time decreased from 48 hours to 12 hours after switching to the TEVA^® disc method.

Different sample preparation variables were experimented with in this study, which occurred between 11/30/99 – 1/13/00. Some of the samples were repeatedly wet-ashed with 30% H₂O₂ and concentrated HNO₃ (batches 9340413, 9340415, 9344288, 0007198). Other samples were wet-ashed and heated between 200°C and 500°C (batches 9348468, 9348470 and 0007201). Some samples were less than 2 weeks old (batches 9340413, 9340415, 9344288, 9347455 and 9347454) while others were 12-months old (batches 0007201 and 0007198). Samples were either spiked at the beginning of sample preparation (batches 9340413, 9340415 and 9344288) or at the beginning of chemical separation (batches 9344290, 9347455 and 9347454), there was very little difference between recoveries of these samples. Muffled samples had excellent recoveries (ave.=94.5%, n=16, σ=5.19) at all temperatures tested. Non-muffled urine had an average percent recovery of 95.7%, tSIE of 316, and a Luminescence (Lm) value of 6.8 (Table 1), while muffled samples had average values of 94.8%, 407.1 and 1.7, respectively (Table 3). The most noticable advantage of muffling samples (old or new) is that they have higher tSIE and lower Lm values, which translates into higher efficiency and lower interference. Another test was to see if one (1) liter of urine would overwhelm and cause breakthrough of ⁹⁹Tc on the TEVA^® disc (Table 2). There were a total of 52 samples tested, 16 of these samples were matrix blanks. These 52 data points are shown graphically in Figure 1. There were also 22 instrument blanks, which were used to calculate the MDA (Figure 2). The distribution coefficient for the TEVA^® disc was developed by EIchroM Industries.

Table 1: Table of Tracer Recovery (artificial, fresh, and 12 month old urine)

R%yield = Radiochemical Yield = Tc99 recovered / Tc99 added * 100

Figure 2: Table of Tracer Recovery for High-Volume Samples

Figure3: Table of Tracer Recovery for High-Temperature Samples

Figure 1: Plot of all urine data points

Figure 2: MDA caluculation

Based on initial calculations the MDA is 4.69 pCi/L for a 300ml urine sample, and 1.47 pCi/L for a 1000ml urine sample. The mean and the standard deviation of the blanks used to calculate the MDA is:

R_B = 22.86, 0.717

E = 0.8871, 0.0233

V_A = 0.3101, 0.0104

Where MDA = Minimum Detectable Activity of the sample

R_B = Count rate of detector background (in cpm)

E = Detector efficiency

t_s = Count time for analysis

TF = Transmission factor = 1

V_A = Sample aliquot volume