SR XRF in identification of trace elements in trace amounts of humic acids
Humic acids (humic and fulvic acids) are natural substances that perform a number of functions in the biosphere to maintain its stability. This is due to the ability of humic acids to accumulate, deposit, and store carbon and a wide range of trace elements for long, geologically-comparable periods, as well as inhibiting chemical compounds toxic to living organisms. The content of humic acids in soils and natural and man-made deposits is ambiguous. The amount of humic acids can often be deciles (or even less) of percent. This means handling of very large masses, up to a kilogram or more, of soil samples to study. This, in turn, limits the possibility of quantitative research to identify the ecological state of the environment. Since the extracted preparations of humic acids have a weight of milligrams, there arises a problem of non-destructive methods for their investigation and creation of base of preparations of humic acids for their further study. Testing of different methods of analysis (NAA, two-jet arc plasma AES etc.) for determination of the trace element content in humic acids resulted in a conclusion that X-ray fluorescence analysis using synchrotron radiation (SR XRF), which a non-destructive and multi-element method, fits the best to a wide range of problems concerning the condition of the natural environment. It is particularly important to identify elements such as As, Se, Br, Rb, Sr, Y, Zr, Mo, I, Pb, Th, and U, determination of which in humic acids by other methods may be difficult or unreliable. Thus, the use of SR XRF in identifying a wide range of trace elements in humic acids enables, first, using weights of a few milligrams, secondly, extension of the possible range of elements to identify, and, finally, storage of preparations of this natural component, which is very significant in the functioning of the biosphere, for further research.