Yes u can use UV-Vis. spectrophotometer to differentiate between chelated and non-chelated solutions  

1 Analysis of chelated and non-chelated product by UV/Vis detection (without HPLC separation)

This may also possible. But, before the study, you have to study UV/Vis spectrums of Fulvic acid and chelated products of them separately. If there are deferent λ max for deferent products this method also possible. If λ max is same for chelated and non-chelated molecules, UV/Vis analysis methods are not useful to identify the (without separation).

1. Analysis of Fulvic acid by HPLC

HPLC (with UV/Vis or ECD detection) can be used to determine Fulvic acid in an aqueous solution.

Please refer methods attached. (Also, you can find many methods from literature).

Some time you may able to use HPLC to separate chelated and non-chelated product and can be quantify the each products (with UV/Vis detection). However, you have to scan each peak of spectrum (of chelated product) to find out possible λ max to quantify them.

However, be careful about the pH of buffers because those buffers may affect the yield of chelated products (may decompose)

1 Analysis of chelated and non-chelated product by UV/Vis detection (without HPLC separation)

This may also possible. But, first of all, you have to study UV/Vis spectrums of Fulvic acid and chelated products of them separately. If there are deferent λ max for deferent products this method also possible. If λ max is same for chelated and non-chelated molecules, UV/Vis analysis methods are not useful to identify and quntify them (without separation).

1. Analysis of Fulvic acid by HPLC

HPLC (with UV/Vis or ECD detection) can be used to determine Fulvic acid in an aqueous solution.

Please refer methods attached. (Also, you can find many methods from literature).

Some time you may able to use HPLC to separate chelated and non-chelated product and can be quantify the each products (HPLC with UV/Vis detection). However, you have to scan each peak of spectrum (of chelated product) to find out possible λ max to quantify them.

However, be careful about the pH of buffers because pH s may affect the yield of chelated products (may decompose)

Uv and HPLC methods can involve in the % identification of most of the organic molecule of low molecular weight.

Thanking You