Determination of Depleted Uranium in Urine via Isotope Ratio Measurements Using Large-Bore Direct Injection High Efficiency Nebulizer—Inductively Coupled Plasma Mass Spectrometry

Abstract

Inductively coupled plasma mass spectrometry (ICP-MS), coupled with a large-bore direct injection high efficiency nebulizer (LB-DIHEN), was utilized to determine the concentration and isotopic ratio of uranium in 11 samples of synthetic urine spiked with varying concentrations and ratios of uranium isotopes. Total U concentrations and (235)U/(238)U isotopic ratios ranged from 0.1 to 10 microg/L and 0.0011 and 0.00725, respectively. The results are compared with data from other laboratories that used either alpha-spectrometry or quadrupole-based ICP-MS with a conventional nebulizer-spray chamber arrangement. Severe matrix effects due to the high total dissolved solid content of the samples resulted in a 60 to 80% loss of signal intensity, but were compensated for by using (233)U as an internal standard. Accurate results were obtained with LB-DIHEN-ICP-MS, allowing for the positive identification of depleted uranium based on the (235)U/(238)U ratio. Precision for the (235)U/(238)U ratio is typically better than 5% and 15% for ICP-MS and alpha-spectrometry, respectively, determined over the concentrations and ratios investigated in this study, with the LB-DIHEN-ICP-MS system providing the most accurate results. Short-term precision (6 min) for the individual (235)U and (238)U isotopes in synthetic urine is better than 2% (N = 7), compared to approximately 5% for conventional nebulizer-spray chamber arrangements and >10% for alpha-spectrometry. The significance of these measurements is discussed for uranium exposure assessment of Persian Gulf War veterans affected by depleted uranium ammunitions.

Sample introduction systems for the analysis of liquid microsamples by ICP-AES and ICP-MS

“…µm [238]. With this modification of the LB-DIHEN, good precisions and accuracies were obtained when U was determined in synthetic urine samples.…”

“…As regards the long term stability of the ICP-MS signal, the MCN6000 was able to provide only a 10-15% drift over a three day period of operation [175]. The determination of 239 Pu and the 240 Pu/ 239 Pu isotopic ratio are problematic due to the interference caused by 238 UH + and the tailing of the uranium peak. By using an Aridus TM , this kind of analysis can be efficiently performed in urine samples without suffering from the problem of hydride generation [176,177].…”

“…Furthermore, the precision reached with the LB-DIHEN was worse than that afforded by a pneumatic nebulizer coupled to a spray chamber [224]. The LB-DIHEN is suitable for the analysis of high salt content solutions [238] and slurries, and for this reason it has been applied to the analysis of biological samples [239] having a high concentration in cell agglomerations with diameters ranging from 16 to 18 µm. In order to improve the liquid and gas generation while preventing the nebulizer tip blockage, the inner diameter of the sample capillary has been reduced from 320 to 205…”

“…[175] MCN6000 239 Pu and 240 Pu in seawater / Sequential injection ICP-SFMS 3-10 l of sample were preconcentrated to 7 ml thus affording LODs of 0.64 and 0.19 fg/ml for 239 238 U ratios in uranium minerals / ICP-SFMS With a 100 µl/min sample consumption rate, the uranium isotope ratio was measured down to the level of 10 -7 .…”

Direct solution introduction using conventional nebulizers with a short torch for plasma mass spectrometry

“…Additionally, the DIHEN and DIN, like all micronebulizers, are more susceptible to nebulizer clogging due to the smaller dimensions for the solution capillary and gas annulus area. While this drawback has been overcome through the use of a large bore-DIHEN (LB-DIHEN) [25][26][27], analytical performance is reduced due to the larger average droplet size of the primary aerosol. A low-cost, demountable-DIHEN (d-DIHEN) was recently introduced [28] that provides similar or improved analytical performance compared to the DIHEN along with replaceable components.…”