Concentration levels measurement of uranium and thorium in cenote water from Yucatan

Uranium (U) and thorium (Th) are radioactive elements of natural origin and these are found in low concentrations (U < 30 ng mL^-1 and Th < 1 ng mL^-1). Methods used for measurement total U and Th in groundwater samples show a poor sensitivity, especially alpha spectrometry, due to that this technique needs a pre-concentration of the sample, radiochemical purification, and a long measurement time. We propose in this work a direct quantification of the total Th and U in natural water samples using inductively coupled plasma mass spectrometry (Icp-Ms), where we evaluated the detection limits, accuracy, precision, matrix effects of measure isotopes in method (²2³²Th, ²³⁴U, ²³⁵U, and ²³⁸U) and spectral interferences. Sample treatment was performed through acidification and filtration of the samples, as well as a direct analysis in Icp-Ms. Recovery percentage values varied between 98 and 107% and accuracy and precision were below 5%. Results obtained of cenote water samples from Yucatan show Th and U concentrations lower than reported in the other studies that are focused on quality water. In conclusion, the developed method has an excellent performance in routine analysis with very good sensitivity in the analysis of U and Th in water. (author)