The major form is UO2(2+) uranyl the best method is alpha spectrometry.

But can also be present as UO2(CO3)2 2- at normal pCO2 concentrations in seawater. Another sensitive method for determining uranium is by adsorptive stripping voltammetry.

ICP-MS is a much more sensitive and easier method for natural uranium analysis in environmental water samples.

Thank you Dr. Adeloju for your information regarding the the presence of UO2(CO3)2 2- in sea water. But what is the evidence of formation of such compound? How it can be identified as this particular species?

icp-ms use to find uranium but check the isotope

ICP-MS is a sensitive technique for assay of uranium at trace level. But it will not give any information regarding chemical speciation, i.e. in which oxidation form it remains in solution.

Using titration method to find the carbon amount

The main determinant for the formation of UO2(CO3)2 2- in seawater is the CO2 concentration present. If low UO2(2+) , uranyl ions, will predominate. In terms of speciation, adsorptive stripping voltammetry (AdSV) is definitely superior to other methods. At neutral/near neutral pH, it is well known in the literature that the UO2(CO3)2 2- species formed is relatively stable. So by judicious choice of complexing agent, it would be possible to detect free (residual) UO2(2+) directly in a sample by AdSV. Subsequently, by treating another portion of the sample to convert all uranium to UO2(2+) form, you can determine the total uranium concentration. The difference between the total and the free concentrations will give the concentration for UO2(CO3)2 2- present. This is assuming there is no other dominants anions such as chloride, phosphate, etc. This is only my suggestion, you may want to do a literature search to see if someone has done uranium speciation in water by this or similar approach.

Thank you Dr. Adeloju. Your answer helped me to get excellent information.