Uranium in urine

As discussed before, quadrupole based ICP-MS allows multi-element determination at the trace and ultratrace level and/or isotope ratios in aqueous solutions in a few minutes as a routine method with detection limits of elements in the sub pgml-1 range and a precision for determined trace element concentration in the low % range (RSD - relative standard deviation). The precision for isotope ratio measurements varies between 0.1% and 0.5% RSD. This isotope ratio precision is sufficient for a multitude of applications, e.g., for evidence of contamination of sample with depleted or enriched uranium in urine (this technique is used in the author s laboratory in a routine mode14) or the isotope dilution technique for the quantitative determination of trace element and species concentration after doping the sample with enriched isotope spikes. 

TIMS has been used for many years as the benchmark technique especially for uranium isotope analysis. Instrumental improvements have enabled ICP-MS to approach the accuracy and precision obtained by TIMS in measuring data. In addition, due to time consuming sample preparation steps and the need for a large volume of urine, the method has been replaced by the more powerful ICP-MS in many laboratories. An interlaboratory analytical exercise on the determination of natural and depleted uranium in urine was carried out by different ICP-MS instruments, by thermal ionization mass spectrometry (TIMS) and instrumental neutron activation analysis. TIMS has also been employed to determine fg quantities of Pu and °Pu in bioassay samples (such as human urine and artificial urine), ° in an interlaboratory comparison for the analysis of the Pu and Pu/ °Pu atomic ratios in synthetic urine by TIMS and AMS as reported in reference. ... 

Ejruk, J.W., Carmichael, A. J., Hamilton, M.M., McDiarmid, M., Squibb, K., Boyd, P., Tardiff, W. (2000). Determination of the isotopic composition of uranium in urine by inductively coupled plasma mass spectrometry. Health Phys. 78 143-6. 

Gwiazda, R.H., Squihh, K., McDiarmid, M., Smith, D. (2004). Detection of depleted uranium in urine of veterans Jrom the 1991 Gulf War. Health Phys. 86 12-18. 

According to USNRC Regulatory Guide 8.22, the acceptable methods for the quantification of uranium in urine must have a detection limit of 5 pg/mL and a precision of 30% (Kressin 1984). A urinary concentration >100 pg/L is indicative of recent absorption, while a concentration of <40 pg/L may be due either to slow uptake from the site of absorption or to bone mobilization (Butterworth 1955). Variations in background levels of uranium from drinking water in different locations may also result in higher or lower urinary concentrations of uranium. 

An alternate method for estimating uranium intake is to measure the daily excretion of uranium in urine and feces. Using this method in a study of 12 subjects in Utah, it was estimated that the average dietary intake for the Salt Lake City population was 4.4 0.6 pg, an intake that is higher than that reported for New York City, Chicago, and San Francisco residents (1.3-1.4 pg) (Singh et al. 1990). 

Several methods that do not require chemical separation are available for measuring uranium in urine (in units of total mass or total activity). These methods include spectrophotometric (total mass), fluorometric (total mass), kinetic phosphorescence analysis (KPA) (total mass), and gross alpha (total activity) analyses (Wessman 1984). The most widely used methods for routine uranium analysis are a-spectrometry and liquid scintillation spectrometry. These methods utilize the natural radioactivity of uranium and are sensitive and require little sample preparation. Photometric techniques such as fluorometry and phosphorometry are less widely used, but kinetic phosphorescence analysis is becoming more widely used. Measurements of total uranium do not provide the relative isotopic abundance of the uranium isotopes, but this may only be important when converting between activity and mass when the isotopic ratios are uncertain. 

Butterworth A. 1955. The significance and value of uranium in urine analysis. Trans Assoc Ind Med Offrs 5 30-43. 

Hinton ER Jr. 1983. Development of a multi-purpose alpha-detection procedure for enriched uranium in urine. Anal Lett 16 367-380. 

Karpas Z, Halicz L, Roiz J, et al. 1996. Inductively coupled plasma mass spectrometry as a simple, rapid, and inexpensive method for determination of uranium in urine and fresh water Comparison with lif. Health Phys 71(6) 879-85. 

Kressin IK. 1984. Spectrophotometric method for the determination of uranium in urine. Anal Chem 56 2269-2227. 

Arsenazo III was used to determine natural uranium in urine [6] and simultaneous determination of uranium and plutonium at trace levels in process streams by derivative spectrophotometry [7]. 

Haldimann, M., Baduraux, M., Eastgate, A., Froidevaux, P., O Donovan, S., Von Gunten, D., and Zoller, O. 2001. Determining picogram quantities of uranium in urine by isotope dilution inductively coupled plasma mass spectrometry. Comparison with alpha-spectrometry. J Anal Atom Spectrom 16(12), 1364—1369. 

Bagatti D, Cantone MC, Giussani A, Veronese I, Roth P, Werner E, HoUriegl V (2003) Regional dependence of urinary uranium baseline levels in non-exposed subjects with particular reference to volunteers from Northern Italy. J Environ Radioact 65 357-364 Karpas Z, Halicz L, Roiz J, Marko R, Katorza E, Lorber A, Goldbart Z (1996) ICP-MS as a simple, rapid, and inexpensive method for determination of uranium in urine and fresh water comparison with LIE Health Phys 71 879-885... 

The differences in sample size, sample preparation procedures, counting time, accuracy, isotope composition, and minimum detectable limits (MDL) should be noted. Some of these methods will be briefly surveyed here. The methods for determining uranium in urine are nsually also suitable for measuring the concentration of uranium in water, and those that are described in detail in Section 4.4.1 will not be discussed here to avoid duplication. 

Table 4.8 summarizes the findings of some of the major studies that were carried out in Sweden by Rodnshkin et al., where reference valnes for the concentration of uranium in urine, whole blood, sernm, hair, and nails are given for populations that are not occnpationally exposed to nraninm componnds. 

As mentioned earlier, there are several analytical methods that have been developed for the analysis of uranium in urine. Some of the older methods required separation and preconcentration of the uranium from the urine sample, but modern methods, based mainly on ICPMS, allow direct determination of the uranium in raw urine or after simple dilution. In the following section, some of the older analytical methods for determining uranium in urine will be described. This section is based in part on a review that was carried out at Oak Ridge National Laboratory (Bogard 1996). 

Alpha spectrometry can be used to determine the concentration of uranium in urine samples, and a detailed description of one of these procedures is presented here in order to demonstrate its complexity and the amount of labor involved (IAEA 2000). The uranium in the urine sample must be separated, purified, and preconcentrated by ion exchange before being deposited on a thin metal disk for alpha spectrometry. The IAEA method uses a spike of as a tracer to determine the chemical yield. The schematic outline of the procedure is shown in Figure 4.10. 

FIGURE 4.10 Outline of radiochemical separation processes used to prepare uranium bioassay samples for alpha spectroscopy. (Adapted from training manual IAEA, Determination of Uranium in Urine by Alpha Spectroscopy, IAEA, Vienna, Austria, 2000.)... 

Solid pellet fluorometry (or fluorimetry) is one of the classic older methods that were widely used to determine the uranium content in urine (Centanni et al. 1956). The urine sample is added to solid NaF or NaF/LiF that is fused by heating so that water and volatile organic and inorganic compounds are evaporated. The sample is then excited by UV radiation at 320-370 nm and the fluorescence at 530-570 nm is measured (perpendicular to the incident beam). The sensitivity is about 30 pg L for a 0.1 mL sample, but after preconcentration by ion exchange detection limits of 0.1 0.1 pg L for a 10 mL have been reported (Dupzyk and Dupzyk 1979). Even this improved MDL is insufficiently sensitive for monitoring unexposed populations where the expected concentration of uranium in urine is below 0.02 pg L (20 ng L )-... 

Kinetic phosphorescence analysis (KPA) is another optical method that utilizes the fact that uranyl ions emit light after excitation by an energetic photon. The use of a pulsed laser for irradiating the sample affords time resolution to differentiate between the decay of uranyl ions (that follow first-order kinetics) and other compounds that may be present in the urine sample. Reportedly, the method has a limit of detection (LOD) of 10 ng L uranium in urine that is almost sufficient for measurement of background levels of unexposed populations (Moore and Williams 1992). 

Thermal ionization mass spectrometry (TIMS) is a sensitive mass spectrometric technique that has been deployed in some cases to measure trace amounts of uranium in urine and its isotopic composition (Kelly et al. 1987). The authors report measurement of one freeze-dried urine standard sample (SRM 2670) and two actual urine samples collected from children. For TIMS measurements, chemical separation has to be performed prior to the analysis. In an earlier work by the same author (Kelly and Fassett 1983), a spike of was used to implement isotope dilution measurements of picogram quantities of uranium in biological tissues. As mentioned earlier, a single urine sample tested by TIMS gave 3.4 ng L (Wrenn et al. 1992). 

The level of uranium in urine and blood plasma was determined by ICPMS in a group of 20 healthy French residents of Paris in one of the earliest published studies using this technology (Allain et al. 1991). The samples were diluted threefold by 1% nitric acid and europium (25 pg L ) was used as an internal standard. The time for analysis of a sample was 2 min and a conservative limit of quantification (5o) was reported as 35 ng L for uranium in urine and plasma. 

The use of a dynamic reaction cell to reduce interferences intended to identify the presence of DU in urine was described (Ejnik et al. 2005). The idea was to deploy a reagent gas (oxygen in this case) to convert the U ions into UO ions in order to shift the uranium isotopic peaks to masses that have no isobaric interferences from polyatomic species. The method did improve the detection limit for uranium in urine to 0.1 pg mL and the ratio can be measured accurately with uranium... 

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