Comparison of different methods used for phosphorus determination in aquatic organisms

The reliable determination of the total phosphorus (P) content stored in aquatic biota is essential for studies on nutrient stoichiometry, as well as for effective lake management measures. However, a variety of methods are found in the literature for sample P content determination, which renders it necessary to assess whether the data reported in different studies are comparable. We used different combinations of combustion durations, acid types and acid concentrations for sample digestion, and measured P concentrations subsequently with the standard colorimetric method. In addition, P contents of samples were assayed by ICP-OES and MP-AES methods. Our results confirmed that the variability among studies using different methods may explain some of the reported intraspecific and interspecific variation. We found that duration of combustion exerted the most important influence on the P retrieval, while acid type and acidity of the hydrolysing solution did not substantially influence the efficiency of sample digestion. We recommend using 8 h of combustion and 0.3 N HCl for acid hydrolysis prior to the colorimetric P analysis, and urge standardisation in the P analyses of biotic samples so as to obtain reliable results and data comparable among different studies.