Thorium In Environmental Samples Research Articles

Fully automated lab-on-valve-multisyringe flow injection analysis-ICP-MS system: an effective tool for fast, sensitive and selective determination of thorium and uranium at environmental levels exploiting solid phase extraction

An on-line solid-phase extraction method linked to inductively coupled mass spectrometry (ICP-MS) has been developed for the determination of low levels of uranium and thorium in environmental samples. The hyphenation of lab-on-valve (LOV) and multisyringe flow injection analysis (MSFIA), coupled to an ICP-MS, allows the simultaneous determination of thorium and uranium in different types of environmental sample matrices achieving high selectivity and sensitivity levels. On-line separation and preconcentration of thorium and uranium are carried out by means of UTEVA resin. The potential of the LOV-MSFIA makes possible the full automation of the system by the on-line regeneration of the column. The limits of detection reached are 0.4 ng L−1 of uranium and 2.8 ng L−1 of thorium. The reproducibility of the LOV-MSFIA-ICP-MS is 1.7% of RSD. Moreover, a high sensitivity, a wide working range (0–200 μg L−1 for uranium and thorium) and an injection frequency up to 9 h−1 (depending on the sample volume) should be highlighted. Different water sample matrices (seawater, well water, freshwater, tap water and mineral water), a phosphogypsum sample with natural uranium and thorium content and a channel sediment reference material were satisfactorily analyzed with the proposed method.

Micro-column solid phase extraction to determine uranium and thorium in environmental samples

Extraction chromatographic separation techniques based on U/TEVA and TEVA resins were utilized to separate uranium and thorium isotopes in complex matrices from environmental samples. This approach has the advantages of ease of quantitative analysis, small sample size, an absence of mixed waste solvents, complete separation of U/Th isotopes, acceptable chemical yields and good energy resolution in the alpha spectrum. The procedure for analyzing alpha-emitting isotopes of uranium and thorium in geothermal water from Peito, Taiwan, is illustrated in detail. It involves sample pre-concentration, filtration and separation by highly selective extraction chromatographic resins, followed by electroplating and alpha-spectroscopy. The analytical results show a chemical recovery exceeding 55% for U and 65% for Th, respectively, under optimized conditions. The efficient and cost-effective use of recyclable columns makes the analytical methods simple, accurate, rapid, reliable and robust.

An improved radiochemical separation of uranium and thorium in environmental samples involving peroxide fusion

A radiochemical procedure for the accurate determination of uranium and thorium using peroxide fusion followed by ion exchange and extraction chromatography is described. The method of extraction of the element from solid samples is the most important factor in the investigation. It is demonstrated, by measuring a number of reference materials, that fusion with Na 2O 2 ensures a complete destruction of the mineral lattice and greatly improves the determination of the true activity of actinides.

Determination of natural uranium and thorium in environmental samples by ETV-ICP-MS after matrix removal by on-line solid phase extraction

An on-line solid phase extraction method has been developed for the determination of 238 U and 232 Th biological certified reference material using inductively coupled plasma mass spectrometry (ICP-MS). Absolute detection limits were 2.7 pg and 3.1 pg for the determination of 238 U and 232 Th respectively, both being blank limited. The result for the determination of 238 U in NASS-4 Open Ocean Sea Water was 2.13±0.28 ng ml –1 compared with a certified value of 2.68±0.12 ng ml –1 . The results for the determination of 238 U in SLRS-3 River Water was 0.043±0.002 ng ml –1 compared with an indicative value of 0.045 ng ml –1 . Results for the determination of 238 U and 232 Th in NIST 1575 Pine Needles were 14.6±3.4 ng g –1 and 28.3±4.5 ng g –1 respectively compared with certified values of 20±4 ng g –1 and 37±3 ng g –1 , using a dry and wet ashing sample preparation method. Results for the determination of 238 U and 232 Th in NIST 1566a oyster tissue were 121±21 ng g –1 and 29±8 ng g –1 for 238 U and 232 Th compared to certified and indicative values of 132±12 ng g –1 and 40 ng g –1 , using the same method. When a lithium metaborate fusion method was used, results for 238 U and 232 Th were 23.3±2.0 ng g –1 and 36.2±5.6 ng g –1 respectively in NIST 1575 Pine Needles. The application of electrothermal vaporisation ICP-MS (ETV-ICP-MS) to NASS-4 Open Ocean Sea Water gave 2.81±0.54 ng ml –1 and SLRS-3 River Water 0.045±0.004 ng ml –1 for 238 U. When the fused NIST 1575 samples were analysed using ETV-ICP-MS, results for 238 U and 232 Th were 19.5±1.7 ng g –1 and 38.8±2.2 ng g –1 respectively. Absolute detection limits for ETV-ICP-MS were 30 fg and 9 fg for 238 U and 232 Th respectively, both being blank limited.

Optimizing the results in alpha-spectrometry of very low-level activity samples when the spike used is present in the sample

Determination of very low-level activity in samples using α-spectrometry is possible due to the low background. In order to determine the chemical yield in the separation of the element of interest, a spike must be added to the sample. In many practical cases there is no adequate spike or it is not available in the laboratory. In these cases a spike of the radionuclide already pesent in the sample can be used as the so-called inner standard method. In order to achieve the best results the optimal quantity and the spike to choose must be determined to reduce the uncertainties associated with the activities. The present work is a systematic study of these problems. These considerations were used to the determination of thorium in environmental samples.

Accurate determination of uranium and thorium in environmental samples using alpha track-etch technique

A theory of the methods of uranium determination in environmental samples based on the measurement of alpha activity of radon and its daughters and on the total alpha activity of all the members of the uranium decay chain using the track-etch technique is given in this paper. It is shown that for samples in which there is radioactive disequilibrium, these methods cannot be used to obtain meaningful and accurate results. It also follows from the theory that an accurate estimate of uranium and thorium-232 in environmental samples, such as soils, foodstuffs, flora and fauna, cannot be obtained from the measurement of the radioactivity of radon daughter nuclides in view of the radioactive disequilibrium in these open systems.

Determination of cerium, yttrium and thorium in environmental samples

A method for the determination of Ce, Y and Th in sea water, pore water, suspended matter, sediments and biota is reported. The method involves a double coprecipitation with Mg(OH)2 and CaC2O4 to pre-concentrate Ce, Y and Th from sea and pore water and acid digestion in open vessels to solubilise sediments, suspended matter and biota. The measurement was performed by inductively coupled plasma atomic emission spectrometry. Radiotracers (144Ce, 88Y and 228Th) were used in different steps to check the chemical yield of the method. Detection limits of 44 ng g–1(0.005 ng ml–1) for Ce, 0.62 ng g–1(0.0003 ng ml–1) for Y and 15 ng g–1(0.003 ng ml–1) for Th in biota and sediments (water) were obtained. Results for the determination of Ce, Y and Th in sea water, pore water, suspended matter, sediments and biota for samples collected in the Tyrrhenian Sea are given. High concentration factors and recoveries were obtained for Ce, Y and Th in various marine environmental samples. Larger sample volumes can be used to increase the concentration factors and to improve the detection limits.