Dear Alon,

Please define DOM for the answerers in your question always  for the first time. Why?

Not all people are familiar with DOM (Dissolved Organic Matter) and don't adopt a child or chemicals. Please read your question again prior to write the right terminology  before posting and , important, you must do a google search . Why??

- give please the following :

adsorption of DOM on clay

and you' ll obtain  a plenty of answers.

DO YOU MEAN the ADSORPTION  of Na Citrate  and Na oxalate on clay (Adsorption is pH and TEMPERATUR depending)( What a kind of clay?) 

or

the UV-Vis   ( in this case the ABSORPTION) of the above cited Na salts in  water.? You must buy and measure  the PURE salts at first .

Reformulate and post your question again.

JRG