Determination of Technetium-99 in Aqueous Solutions by Inductively Coupled Plasma Mass Spectrometry: Effects of Chemical Form and Memory† ROBERT C. RICHTER‡, S. ROY KOIRTYOHANN AND SILVIA S. JURISSON* Department of Chemistry, University ofMissouri, Columbia, MO 65211, USA The eects of chemical form and instrumental memory on the iently low for direct analysis of environmental samples, determination of technetium-99 (99Tc) in aqueous requiring preconcentration of the 99Tc.5 NAA methods, using environmental samples by ICP-MS were investigated. Using either thermal or fast neutron capture reactions, have also an assortment of cationic, anionic and neutral Tc and Re been found inadequate for the low 99Tc levels found in complexes, a comparison of the ICP-MS method with the environmental samples.8,9 established methods of liquid scintillation counting (LSC) for ICP-MS has been used successfully in environmental trace Tc and neutron activation analysis (NAA) for Re gave lower analysis and recently has been applied to 99Tc determithan expected Tc and Re values by ICP-MS owing to loss of nation.6,10–17 The published methods use preconcentration sample in the delivery system.Oxidation of the complexes techniques to increase 99Tc levels above the blank limited prior to analysis and the addition of Triton X-100 to the detection limit.12,17 High blanks result primarily from instrusample solution eliminated this problem. Instrumental mental memory, an increase in the background count rate memory, resulting from interactions of 99Tc with the peristaltic following the analysis of a solution containing 99Tc.pump tubing and the alumina injection port tube, caused Although the pertechnetate ion dominates in aqueous significant increases in the background count rate during environmental samples, the presence of reducing agents and/or analysis. Aspiration with a nitric acid solution between sample complexing agents may alter the chemical form of 99Tc.If 99Tc runs to clean the system eectively eliminated this problem. is reduced in the absence of complexing ligands, it forms TcO2 These techniques were applied to simulated tap water and which can adsorb on any surfaces in contact with the sample. actual river water samples, and the accuracy was assessed 99Tc has a high anity for sulfhydryl ligands, which results in through LSC and spike recovery experiments. The detection absorption by microorganisms (approximately 10–20% of the limit of the ICP-MS method was found to be 0.6 ppt with an 99Tc that enters the river or ground water may be found in RSD of less than 10%, and these results were within 4% of the microorganisms).4,5 99Tc also complexes with naturally occur- LSC results.The sensitivity of the ICP-MS method for the ring ligands such as humic acid.18 Title 10, Chapter 1, Part 20 determination of 99Tc is much superior to that of the of the US Nuclear Regulatory Commission Rules and alternative radioanalytical methods when accounting for the Regulations allows the release of 99Tc resulting from medical data acquisition time for identical, low-concentration samples applications into the sanitary sewer system.This 99Tc is usually such as are often found in the environment. bound to a ligand or protein. This study was undertaken to develop a procedure that Keywords: T echnetium-99 ; inductively coupled plasma mass spectrometry ; radioenvironmental analysis; technetium-99 eliminates instrumental memory and allows the quantification speciation eects; technetium-99 memory eects of the 99Tc in aqueous environmental samples independent of chemical form and which requires minimal sample pretreatment.To minimize instrument contamination, rhenium (a non- Technetium-99 (99Tc) is a low-energy beta emitter (0.292 MeV) radioactive chemical analog of 99Tc) was used in the initial with a half-life of 2.1×105 yr which has entered the environ- studies and method development.Rhenium is often used as a ment through nuclear weapons testing, nuclear power pro- non-radioactive chemical analog for technetium because their duction, medical applications and negligence. The release of chemistries are similar.19,20 The lanthanide contraction makes 99Tc into the environment is of concern because, in addition analogous Tc and Re compounds virtually identical from a to its long half-life, it is highly mobile in aerobic environments structural standpoint.19 The main dierence is in their redox as the pertechnetate ion (TcO4-), its predominant form.2–5 potentials; Re is much more dicult to reduce than Tc and This element does not occur naturally and has no non- thus much easier to oxidize.19,20 The dierence in the redox radioactive isotopes.The current concentration guideline set potentials suciently aects the chemistries in some cases such by the US Department of Energy (DOE) for public exposure that any method developed based on Re must be validated to 99Tc in drinking water in the USA is 4 nCi l-1 (148 Bq l-1 with Tc.or 0.24 mg l-1).6,7 The extent and causes of instrumental memory were deter- Radiometric techniques are the most common methods used mined using standard perrhenate solutions, and a cleaning for the determination of 99Tc. Methods based on beta counting method was developed which eectively eliminates the reten- require the separation of 99Tc from other radionuclides before tion of Re and Tc associated with analyses.The chemical form analysis and long counting times (often 12 h or more) for low- of Tc may not be pertechnetate in all waste streams, so several concentration environmental samples. In addition, the detec- coordination complexes of Re and Tc were analyzed by tion limits for beta counting methods usually are not suc- ICP-MS to assess the impact of metal oxidation state, the complex charge and the coordinated ligand.A pretreatment † See ref. 1. method which eectively oxidizes all complexes to pertechnet- ‡ Present address: New York State Department of Health, ate was developed such that there was good agreement between Wadsworth Center, Room D-349, P.O. Box 509, Albany, NY 12201-0509, USA. the ICP-MS results and either NAA (for Re) or liquid scintil- Journal of Analytical Atomic Spectrometry, May 1997, Vol. 12 (557–562) 557lation counting (LSC) (for 99Tc) for the various samples.The final test for any method developed is the analysis of real samples. Two types of samples were tested using the methods developed: (1) the various 99Tc complexes were prepared in tap water (to simulate sanitary sewer water) to insure that there was no interference from the matrix itself; and (2) actual river water samples known to contain 99Tc were obtained from the Savannah River site in South Carolina. All samples were validated using LSC.EXPERIMENTAL Materials Radiation safety Caution. The samples used for this work present radiological hazards. Proper radiation safety measures for handling, shielding, storage and disposal of these materials were strictly observed. Reagents Trace metal grade nitric acid (Fisher Scientific, Rochester, NY, USA) was used to prepare ICP-MS calibration and sample solutions. Analytical reagent grade acids (Fisher Scientific) were used to prepare cleaning solutions. Triton X-100 was purchased from Aldrich (Milwaukee, WI, USA).Rhenium Fig. 1 Structures of the various Tc and Re complexes. (1000 mg ml-1 ReO4-), tungsten (1000 mg ml-1 WO42-), and chromium (1000 mg ml-1) ICP-MS standards were purchased from Fisher Scientific. NH499TcO4 was purchased from Oak netium complexes were prepared in either water or acetonitrile. Ridge National Laboratory (Oak Ridge, TN, USA) and puri- The rhenium concentrations were determined by accurate fied prior to use (either by filtration to remove 99TcO2 or by weighing and the technetium concentrations by LSC.All H2O2 oxidation to convert 99TcO2 into 99TcO4-). A 99Tc samples analyzed by ICP-MS were 0.16 M in HNO3 and standard (0.289 mg ml-1 99TcO4-) was obtained from the contained 10.0 ppb of tungsten as an internal standard. Missouri University Research Reactor (MURR). Optifluor scintillation cocktail was purchased from Packard (Meriden, Instrumentation CT, USA). The reagents used for the syntheses of the rhenium and technetium complexes were obtained from Sigma (St.ICP-MS Louis, MO, USA), Aldrich and Fisher Scientific. Distilled, A Perkin-Elmer SCIEX (Thornhill, ON, Canada) ELAN 5000 deionized water was used for sample preparation. River water ICP-MS instrument equipped with either a cross-flow pneu- samples were obtained from Westinghouse Savannah River matic nebulizer with a Scott-type spray chamber or an ultra- Company (Savannah River, SC, USA). sonic nebulizer (CETAC Technologies, Omaha, NE, USA) for sample introduction was utilized.The ICP-MS operating con- T echnetium and rhenium complexes ditions and sample acquisition parameters are given in Table 1. Potassium hexachlororhenate(IV) (K2ReCl6),21 bis(ethylenediamine) dioxorhenium(V) chloride {[ReO2(en)2 ]Cl},22 dioxote- NAA tra(pyridine)rhenium(V) chloride {[ReO2(py)4]Cl},23 tetra- Samples were irradiated at MURR using the parameters given butylammonium (mercaptoacetyltriglycine)oxorhenate(V) {Bu4N in Table 2.Known amounts of sample and chromium (used as [ReO(MAG3)]},24 bis[cyclohexane-1,2-dione dioximato an internal standard) were placed in 2 ml polyethylene vials, (-1)-O][(cyclohexane-1,2-dione dioximato)(-2)-O]methyl- sealed and transported to reflector positions in the reactor borato(-2)-N,N¾,N,N+,N¾¾,N¾¾¾chlororhenium(III ) [ReCl core with a pneumatic tube system. Irradiated samples were (CDO)3BMe],25 bis[cyclohexane-1,2-dione dioximato(-1)- decayed for 3 d and then counted for 10 min at the appropriate O][(cyclohexane-1,2-dione dioximato)(-2)-O]methylborato energies (Table 2) using a high-purity germanium detector (-2)-N,N¾,N,N+,N¾¾,N¾¾¾chlorotechnetium(III) [99TcCl (CDO)3BMe],26 oxo[(3,3,9,9-tetramethyl-4,8-diazaundecane- Table 1 ICP-MS operating conditions 2,10-dione dioximato)(-3)]technetium(V) (99TcOPnAO)27 and tetrabutylammonium tetrachlorooxotechnetate(V) [Bu4N ICP conditions— (99TcOCl4)]28 were synthesized using literature methods. Fig. 1 Rf power 1000 W illustrates the structures of the complexes. Plasma Ar flow rate 15.00 l min-1 Auxiliary Ar flow rate 0.770 l min-1 Nebulizer Ar flow rate 0.900 l min-1 Solutions Solution uptake rate 1.00 ml min-1 A 4.00 ppb rhenium solution, 1.45 ppb 99Tc solution, internal Data acquisition parameters— Dwell time 150 ms standard solution and ICP-MS calibration solutions were Sweeps per reading 250 prepared by diluting the standards with 0.16 M HNO3.HNO3 Readings per replicate 1 (0.8 M), H2SO4 (0.9 M), HCl (0.8 M), H3PO2 (0.9 M) and Number of replicates 3 HNO3–HCl (0.8 M in each) were prepared as potential cleaning Points per peak 1 solutions. Stock standard solutions of the rhenium and tech- 558 Journal of Analytical Atomic Spectrometry, May 1997, Vol. 12Table 2 NAA parameters for irradiation and counting Sample Analysis Eect of chemical form Thermal flux 4.0×1013 n cm-2 s-1 Epithermal flux 1.0×1012 n cm-2 s-1 The eect of chemical form on the quantification of 99Tc was Fast flux 4.0×1012 n cm-2 s-1 investigated by analyzing a variety of rhenium and technetium Irradiation time 1 h Decay time 3 h complexes (see below) for the content of the given metal.The Counting time 10 min Re samples were prepared as described above and analyzed by ICP-MS and NAA for validation of the results (Table 3). Nuclear reactions Gamma energy/keV Half-life The agreements between the results obtained from ICP-MS 185Re (n,c) 186Re 137 3.7 d and NAA were optimized by the addition of detergents and/or 187Re (n,c) 188Re 155 16.9 h oxidants to the samples and subsequent heating of the samples 50Cr (n,c) 51Cr 320 27.0 d prior to ICP-MS analysis(Table 4).The optimumpretreatment procedures developed for the Re samples were then used to analyze the Tc samples by ICP-MS. LSC was used for validation (Table 5). Additional optimization was necessary for the Tc samples because of the dierences in the redox potentials equipped with a multi-channel analyzer (EG&G Technologies, between Tc and Re.The optimization was achieved by heating Omaha, NE, USA). the 99Tc sample solutions (to ensure oxidation to pertechnetate) prior to ICP-MS analysis. L SC Simulated sanitary sewer samples A Tracor Analytic (Elk Grove Village, IL, USA) Delta 300 liquid scintillation counter was used to determine 99Tc concen- Tap water was used as the diluent to simulate samples from trations in samples consisting of 9 ml of Optifluor liquid sanitary sewers.Aliquots were taken from each of the 99Tc scintillation cocktail and 1 ml of sample solution. The samples complex stock solutions, placed in two 100 ml polymethylpen- were equilibrated in the absence of fluorescent light for 1 h tene flasks, filled to the mark with 0.16 M HNO3, and heated before counting. at 35 °C for 45 min. These samples were analyzed by LSC to determine their 99Tc concentrations and then diluted by a factor of 10000 with tap water and analyzed by ICP-MS Instrumental Memory (Table 6).To minimize instrument contamination from radioactivity, the extent and sources of Tc retention in the ICP-MS system were Environmental Samples determined using Re, the non-radioactive chemical analog for The application of the method developed for the quantification Tc, and Tc was then evaluated beginning with the optimized of 99Tc by ICP-MS was extended to an environmental river conditions. water sample obtained from the Savannah River site in South The extent of Re retention was evaluated by measuring the Carolina.LSC and standard addition experiments were used initial background count rate for Re at m/z 187 while aspirating to validate the ICP-MS results. a 0.16 M HNO3 blank solution, then aspirating the 4.00 ppb Re solution for 2 min, rinsing with water for 30 s and remeasuring the 0.16 M HNO3 blank solution to determine the apparent River water analysis by L SC background count rate.This procedure was repeated nine Duplicate samples (200 ml) of river water were evaporated to consecutive times (Fig. 2). dryness by heating at 60 °C, the residue was dissolved in 10 ml The sources of Re retention were determined by measuring of 2.0 M HNO3 and the solution was transferred into 20 ml the background count rate of the 0.16 M HNO3 blank solution LSC vials and again evaporated to dryness. The residues at m/z 187 before and after individually cleaning each compo- remaining were dissolved in 1 ml of 0.16 M HNO3 and scintil- nent of the ICP-MS system following a 30 min aspiration with lation cocktail (9 ml) was then added.Each sample was the 4.00 ppb rhenium solution and a 30 s rinse with water. The counted for 12 h. The elapsed time for 99Tc quantification sampler and skimmer cones were removed, rinsed with dilute was 72 h. HNO3 and sonicated in an ultrasonic bath to remove any Re deposits.The injection port tube (quartz or alumina) and spray chamber were cleaned by soaking in 2 M HNO3 for 1 h. The River water analysis by ICP-MS peristaltic pump tubing (standard or SolventFlex from Perkin- Direct sample analysis. A sample (1.5 l) of river water was Elmer, Norwalk, CT, USA) was replaced rather than cleaned. acidified with 15 ml of concentrated HNO3, heated at 75 °C The optimum cleaning solution composition was determined for 75 min and filtered to remove undissolved sediment.Twelve by comparing the initial background count rate of the 100 ml aliquots were then analyzed by ICP-MS. Three hours 0.16 M HNO3 blank solution at m/z 187 with that measured were required for quantification of 99Tc using this method, after a 2 min aspiration with the 4.00 ppb rhenium solution with 2 min for sample acquisition and 4 min rinsing between followed by 8 min of rinsing with one of the cleaning solutions samples. (see below). The count rate at m/z 187 was measured every 2 min during the continuous aspiration with one of the rinse Standard addition method. A sample (300 ml) of river water solutions to determine the time course of the cleaning (Fig. 3). was treated as above and used to prepare two 100 ml samples The most eective cleaning solution, as determined for Re, was for standard addition analysis. Dierent aliquots (75 and validated for 99Tc by comparing the initial background count 100 ml) of a 289 pg ml-1 99Tc standard solution were added rate for the 0.16 M HNO3 blank solution at m/z 99 with that to these samples and they were then analyzed by ICP-MS.measured after a 3 min aspiration with the 1.45 ppb 99Tc solution followed by a 4 min rinse with 0.8 M HNO3. This Statistical Analysis procedure was repeated six consecutive times. SolventFlex tubing and an alumina injection tube were used in these The values reported for the Re complexes by NAA are the average of four sample irradiations. With the exception of the experiments.Journal of Analytical Atomic Spectrometry, May 1997, Vol. 12 559river water, for which 12 samples were analyzed, all ICP-MS oxoanions are known to have an anity for alumina).20 The use of a quartz injection tube eliminated this memory eect. results are the average of six sample analyses. LSC samples were analyzed in triplicate for the routine analyses and in duplicate for the lengthy river water samples. All errors are Eectiveness of Cleaning Solutions reported as plus or minus one standard deviation from the mean.Dismantling the system to clean the components between sample runs is an unrealistic approach to minimizing the background count rate. A more practical approach is aspir- RESULTS AND DISCUSSION ation of a cleaning solution through the system between samples to remove any residual analyte. A variety of acids Instrumental Memory were tested as cleaning agents and their eectiveness was Instrumental memory eects have been reported for the determined by monitoring the background count rate while ICP-MS determination of 99Tc by a number of groups, but aspirating a cleaning solution following a simulated analysis the solution to the high backgrounds observed for these (Fig. 3).The background count rate decreased rapidly for all analyses has generally been the use of tedious and time- the cleaning solutions except H3PO2. The formation of col- consuming preconcentration procedures.11,12,14–16 As precon- loidal ReO2 and its adsorption to the spray chamber walls, centration increased the analyte concentration, the 99Tc signal accumulation in the dead volume of the spray chamber or was increased and the accompanying increase in background precipitation on to the pump tubing may be responsible.HCl signal was apparently tolerable. Instrumental memory eects more eectively reduced the background count rate, perhaps arise from the retention of 99Tc in the ICP-MS system, perhaps through the formation of mobile Re–Cl complexes or by the from analyte build-up on the cones, adsorption to a surface displacement of perrhenate by chloride in the pump tubing en route to the plasma or retention in the dead volume of the and injection port tube.The most eective cleaning solution spray chamber. The background count rate between sample was found to be 0.8 M HNO3. runs was measured during a simulated analysis to study the The optimum rinse time was determined from Fig. 3. Using eects of instrumental memory. Fig. 2 shows the increase in 0.8 M HNO3 as the rinse solution, aspiration for 4 min reduced the apparent background count rate for 187Re (a non- the count rate to its minimum value and continued rinsing did radioactive chemical analog for 99Tc). After just one run the not further improve the background count rate. apparent background count rate had nearly doubled and after The same cleaning procedure was found suitable for minimiz- nine runs it was 20 times the original value.This sharp increase ing the 99Tc background count rate during analysis. The in the background could result in significant error when background count rate for the 0.1 M HNO3 blank solution analyzing solutions with concentrations near the limit of was found to be 16.2±0.6 counts s-1 prior to and detection. 15.9±0.7 counts s-1 following the analysis of a 1.45 ppb The ICP-MS system was systematically dismantled, the 99TcO4- solution (7439±86 counts s-1 count rate).The individual components were cleaned and the background count absence of any significant change in the background count rates before and after cleaning were compared to determine rate during the simulated analysis indicated that the cleaning the sources of 99Tc and Re retention. The spray chamber and procedure eectively removed any residual 99Tc from the sampling cones had no significant eect on system memory, system.since the apparent background count rate did not change after cleaning. The peristaltic pump tubing, on the other hand, played a major role. When the used piece of standard tubing Eect of Chemical Form on 99Tc Determination was replaced with a new piece, a 10-fold decrease in the The eect of chemical form on 99Tc analysis was probed using apparent background count rate was observed. This suggested a number of dierent Re and 99Tc complexes (Fig. 1). Rhenium that the tubing was permeable to Re or that surface sites was again used as the non-radioactive chemical analog of existed to which the Re bound.The use of SolventFlex tubing 99Tc during method development. The complexes used for this minimized the increases in the apparent background count rate. study exhibited a range of metal oxidation states and overall The injection tube was also involved in the retention of complex charge. Additionally, the 99mTc analogs of rhenium. Cleaning the alumina injection tube resulted in a (Bu4N)[ReO(MAG3)] and MCl(CDO)3BMe (M=Re or 99Tc) fourfold decrease in the background count rate, indicating that are used in nuclear medicine departments for renal and myocar- the Re had adsorbed on the alumina (perrhenate and other Fig. 3 Eectiveness of cleaning solutions. The background count rate at m/z 187 is shown while aspirating each of the cleaning solutions Fig. 2 Eect of instrumental memory on background count rate. The ($, 0.9 M H3PO2; (, 0.9 M H2SO4; #, 0.8 M HCl; ', 0.8 M HNO3; 2, 0.8 M HCl+0.8 M HNO3) immediately following analysis of a 4.00 ppb background count rate for the blank solution at m/z 187 is shown following consecutive analyses of a 4.00 ppb ReO4- standard solution.ReO4- standard solution. 560 Journal of Analytical Atomic Spectrometry, May 1997, Vol. 12Table 3 Comparison of NAA and ICP-MS results for rhenium com- Table 5 Comparison of LSC and ICP-MS results for 99Tc complexes.All values in mg ml-1 (ppm) plexes. All values are percentage of rhenium in the complex Complex Calculated NAA ICP-MS Complex LSC ICP-MS K2ReCl6 39.0 39.7±0.2 38.9±0.5 Bu4N99TcOCl4 1.29±0.06 1.14±0.02 99TcOPnAO 1.99±0.01 1.98±0.05 ReO2(en)2Cl 49.8 48.0±0.8 48.1±1.4 ReO2(py)4Cl 32.6 33.0±0.7 32.4±0.8 99TcCl(CDO)3BMe 0.531±0.005 0.453±0.011 ReCl(CDO)3BMe 27.8 26.9±0.4 5.12±0.09 Bu4N[ReO(MAG3)] 26.4 1.07±0.02 1.08±0.03 Table 6 Comparison of LSC and ICP-MS results for 99Tc complexes Table 4 Optimization of solution conditions for ReCl(CDO)3BMe in a tap water matrix.All values in pg ml-1 (ppt) Solution conditions Re (%) ICP-MS 0.16 M HNO3 5.12±0.09 Sample LSC PN* USN* 0.01% (v/v) Triton X-100 Complex Mix 1 26.1±0.1 25.4±0.8 — 0.16 M HNO3 23.3±0.3 Complex Mix 2 57.0±0.1 56.1±0.6 — 0.08% (v/v) Triton X-100 Bu4N99TcOCl4 5170±20 — 5150±50 0.16 M HNO3 24.8±0.5 99TcOPnAO 550±2.0 — 549±7.0 99TcCl(CDO)3BMe 56.1±0.7 — 55.9±1.0 0.16 M HNO3 30 min oxidation 26.2±0.2 * PN=pneumatic nebulization; USN=ultrasonic nebulization. 5.0% (v/v) H2O2 0.16 M HNO3 23.1±0.2 0.01% (v/v) Triton X-100 0.16 M HNO3 26.7±0.3 which already contained an oxidant (HNO3), were allowed to 30 min oxidation stand for 30 min prior to analysis. This led to an improvement NAA result 26.9±0.4 over the Triton X-100 method (Table 4). The use of hydrogen peroxide as oxidizing agent failed to improve the correlation. Since the ICP-MS results for the HNO3 oxidation of ReCl(CDO)3BMe were found to lie just outside one standard dial imaging, respectively, and an isomer of TcOPnAO is used deviation of the NAA values, a small amount (0.01%) of Triton for cerebral blood flow imaging.29 X-100 was added to improve the correlation. This combination The values obtained from ICP-MS analysis were compared resulted in excellent agreement with the NAA data (Table 4) with the results from NAA and LSC to probe the eects of and was used to analyze the 99Tc complexes.chemical form.The Re analyses are reported as percentage of The LSC and ICP-MS results for the 99Tc complexes are Re since accurate masses were obtained. To minimize sample given in Table 5. Good correlation between LSC and ICP-MS handling and potential contamination, the concentrations of was observed only for 99TcOPnAO. The low values for the the 99Tc samples were determined by LSC and the results are other complexes resulted from insucient oxidation of the reported as ppm of 99Tc in solution. 99Tc (Re is easier to oxidize than Tc).20 Heating the 99Tc- The NAA and ICP-MS analyses for the Re complexes are containing solutions for 45 min at 35 °C prior to ICP-MS shown in Table 3. The results from the two methods compare analysis resulted in good agreement between the two methods. favorably with each other and with the known percentage of Re, except for (Bu4N)[ReO(MAG3)] and ReCl(CDO)3BMe. The low value observed for the analysis of (Bu4N) Analysis of Water Samples [ReO(MAG3 )] by both NAA and ICP-MS compared with the theoretical value resulted from the presence of a Bu4NBr The above techniques were applied to the determination of 99Tc in simulated sewer water and river water.Tap water was impurity. The good agreement between the NAA and ICP-MS results for this complex indicated that the chemical form had used as a model for sanitary sewer water. Reliability was validated by LSC and direct and standard addition ICP-MS not aected the analysis.The low value observed for the ICP-MS analysis of ReCl(CDO)3BMe was accompanied by analysis. The results for tap water analysis using pneumatic and ultrasonic nebulization are given in Table 6. There is good an increase in the background count rate, suggesting adsorption to the walls of the pump tubing, spray chamber or sample agreement with LSC for both nebulization methods. Since satisfactory nebulization conditions could not be found when flask, probably resulting from the high lipophilicity of this compound.Triton X-100 was present, it was omitted from the ultrasonic nebulization method. Additional heating (75 min) successfully Several procedural modifications were examined to minimize the adsorption of this neutral, lipophilic analyte. A detergent, compensated for this change. There is excellent agreement between all methods of analysis. Direct ICP-MS analysis Triton X-100, was added to improve the dispersion of the complex in aqueous solutions.Addition of 0.01% (v/v) Triton of the river water sample gave a concentration of 1.72±0.14 pg ml-1 of 99Tc, ICP-MS standard addition analysis X-100 improved the correlation with the NAA data signifi- cantly (Table 4). Even though the correlation was further gave 1.76±0.36 pg ml-1 and LSC gave 1.78±0.09 pg ml-1. These results suggest that LSC is comparable to ICP-MS, but improved by increasing Triton X-100 to 0.08% (v/v), a 50% reduction in the Re count rate was observed along with carbon the dierences in the times for data acquisition per sample (2 min for ICP-MS and 12 h for LSC) and the fact that the deposits on the sampling cones.The reduction in the Re count rate aected the precision, accuracy and detection limit of the LSC sample was concentrated by a factor of 20 illustrate the much superior sensitivity of the ICP-MS method for this low method and the carbon deposits could eventually obstruct the sampler orifice.Hence higher concentrations of Triton X-100 specific activity radionuclide. The large standard deviations for the ICP-MS analysis of the river water sample result were not used to further improve the correlation. Oxidation of ReCl(CDO)3BMe to ReO4-, a more soluble because the analyte concentration is close to the detection limit of 0.6 ppt (3s of the blank), which is equivalent to chemical form of Re, was evaluated as an alternative method. The ReCl(CDO)3BMe solutions used for ICP-MS analysis, 0.6 ng l-1 (0.37 Bq l-1 or 0.01 nCi l-1).Journal of Analytical Atomic Spectrometry, May 1997, Vol. 12 5619 Ikeda, N., Seki, R., Kamemoto, M., and Otsuji, M., J. Radioanal. CONCLUSION Nucl. Chem., 1989, 131, 65. The use of these simple preoxidation and cleaning procedures 10 Igarashi, Y., Kim, C. K., Takaku, Y., Shiraishi, K., Yamamoto, M., and Ikeda, N., Anal. Sci., 1990, 6, 157. to analyze successfully river water samples for 99Tc demon- 11 Kim, C.K., Otsuji, M., Takaku, Y., Kawamura, H., Shiraishi, K., strates that in the absence of a significant isobaric 99Ru Igarashi, Y., and Ikeda, N., Radioisotopes, 1989, 38, 151. interference or high concentrations of dissolved solids, the 12 Morita, S., Kim, C. K., Takaku, Y., Seki, R., and Ikeda, N., Appl. tedious preconcentration and separation procedures previously Radiat. Isot., 1991, 42, 531. reported are unnecessary.13,15–17 If 99Ru is present, a correction 13 Morita, S., Tobita, K., and Kurabayashi, M., Radiochim.Acta, 1993, 63, 63. based on the amount of 101Ru present can be applied.6 When 14 Momoshima, N., Sayad, M., and Takashima, Y., Radiochim. Acta, the 99Ru concentration is orders of magnitude higher than that 1993, 63, 73. of 99Tc or the sample is taken from an area where the natural 15 Nicholson, S., Sanders, T. W., and Blaine, L. M., Sci. T otal abundance ratios may have been altered (the fission yields of Environ., 1993, 130, 275.the ruthenium isotopes do not correspond to the natural 16 Sumiya, S., Morita, S., Tobita, K., and Kurabayshi, M., J. Radioanal. Nucl. Chem., 1994, 177, 149. abundances), the 99Ru must be separated from the 99Tc prior 17 Garcia Alonso, J. I., Sena, F., and Koch, L., J. Anal. At. Spectrom., to analysis. If the sample contains only a high concentration 1994, 9, 1217. of dissolved solids, on-line separation can be used to remove 18 Sekine, T., Watanabe, A., Yoshihara, K., and Kim, J.I., Radiochim. the matrix prior to 99Tc determination.30,31 Acta, 1993, 63, 87. 19 Deutsch, E., Libson, K., Vanderheyden, J.-L., Ketring, A. R., and Maxon, H. R., Nucl. Med. Biol., 1986, 13, 465. We acknowledge Perkin-Elmer SCIEX for providing the 20 Cotton, F. A., and Wilkinson, G., Advanced Inorganic Chemistry, ICP-MS system and the Missouri University Research Reactor Wiley, New York, 5th edn., 1988, pp. 850–867. for financial support and the use of their facilities. We thank 21 Watt, W., and Thompson, R. J., Inorg. Synth., 1963, 7, 189. 22 Murmann, R. K., Inorg. Synth., 1966, 8, 173. Dr. Donna Beals (Westinghouse Savannah River Co.) for 23 Ram, M. S., and Hupp, J. T., Inorg. Chem., 1991, 30, 130. providing the river water sample, Dr. Alan Ketring for assist- 24 Rao, T. N., Adhikesavalu, D., Camerman, A., and Fritzberg, ance with the NAA analysis and Dr. Jack Lydon, Teri Parsons A. R., Inorg. Chim. Acta, 1991, 180, 63. and Martha Halihan for help with the syntheses of the 25 Jurisson, S., Treher, E. H., Francesconi, L. C., Malley, M. F., complexes. Gougoutas, J. Z., and Nunn, A. D., Inorg. Chem., 1991, 30, 1820. 26 Treher, E. H., Francesconi, L. C., Malley, M. F., Gougoutas, J. Z., and Nunn, A. D., Inorg. Chem., 1989, 28, 3411. 27 Jurisson, S., Schlemper, E. O., Troutner, D. E., Canning, L. R., REFERENCES Nowotnik, D. P., and Neirinckx, R. D., Inorg. Chem., 1986, 25, 543. 28 Davison, A., Trop, H. S., Depamphilis, B. V., and Jones, A. G., 1 Abstracted in part: Richter, R. C., PhD Thesis, University of Inorg. Synth., 1982, 26, 160. Missouri–Columbia, 1995. 29 Jurisson, S., Berning, D., Jia, W., and Ma, D., Chem. Rev., 1993, 2 Holm, E., Radiochim. Acta, 1993, 63, 57. 93, 1137. 3 Yanagisawa, K., Muramatsu, Y., and Kamada, H., Radioisotopes, 30 Hollenbach, M., Grohs, J., Mamich, S., Kroft, M., and Denoyer, 1992, 41, 397. E. R., J. Anal. At. Spectrom., 1994, 9, 927. 4 Lieser, K. H., Radiochim. Acta, 1993, 63, 5. 31 Shabani, M. B., and Masuda, A., Anal. Chim. Acta, 1992, 261, 315. 5 Lieser, K. H., and Bauscher, C. H., Radiochim. Acta, 1987, 42, 205. 6 Crain, J. S., and Gallimore, D. L., Appl. Spectrosc., 1992, 46, 547. Paper 6/06483C 7 Order Number 5400.5, 8 February 1990, Chapters II and III, Received September 20, 1996 United States Department of Energy, Washington, DC. 8 Trautmann, N., Radiochim. Acta, 1993, 63, 37. Accepted December 12, 1996 562 Journal of Analytical Atomic Spectrometry, May 1997, Vol. 12