An assessment of analytical performance of dissolved organic nitrogen and dissolved organic phosphorus analyses in marine environments: a review

To better understand the cycling of marine dissolved organic matter, analytical methods are required allowing for data on dissolved organic nitrogen and phosphorus (DON and DOP) to be acquired with high analytical performance. The coverage of documented DON and DOP analytical performance is very limited; instead analytical data are mostly available for total dissolved N and P (TDN and TDP) analyses. This substitution overestimates analytical performance for DON and DOP measurements due to the cumulative effect of Standard Deviation applied for detection limit and precision evaluations. The little available data obtained by photolytic, chemical, a combination of both, and high temperature combustion methods indicate that current detection limit is 0.30 µM for DON and 0.010 µM for DOP. Precision for both analytes, in general, is ≤4.5%. The data on accuracy is scarce despite availability of Reference Materials for TDN and NO₃^? + NO₂^? analyses, and for the TDN measurement is <5%; even fewer data exist for TDP due to a lack of reference material for this analysis. The Beer–Lambert law is linear up to 200 µM for TDN and 5–6 µM for TDP. Current analytical abilities for DON/DOP measurements are not ready yet to set the level of dissolved organic carbon analysis. The advance in the analytical performance for DON and DOP measurements depends upon the possibility to improve the analytical performance for dissolved inorganic N and P measurements involved in DON and DOP estimations. For the DOP analysis, an international standard method becomes necessary to develop and evaluate collaboratively. The chemical oceanographers’ community should reconsider requirements needed for the coverage of analytical performance for DON and DOP measurements to make this data more shareable and transparent. The lack of these data protracts marine analysts from attaining further methods improvement and development.