Have a look on this method:

https://cfpub.epa.gov/si/si_public_record_report.cfm?dirEntryId=103917

Regards

great answer dr.mohamed

It is not equivalent directly, but you can use COD (chemical oxygen demand) to estimate the amount of organic carbon present in a sample. If you set up your calibration for the COD in terms of dissolved carbon you might be able to extrapolate a usable correlation.

Note that the reference from Dr. Hassaan is for TOC/DOC, not a substitute. The 254 absorbance does not directly correlate with TOC but rather with humic and fluvic acids.