Comparison of CHN analysis and Hach acid digestion to quantify total nitrogen in marine organisms

Elisabete Barbarino, Sergio O. Lourenço

Limnol. Oceanogr. Methods 7:751-760 (2009) | DOI: 10.4319/lom.2009.7.751

ABSTRACT: The quantification of total nitrogen in biological samples has wide applications in marine sciences. Different methods are currently used to quantify nitrogen content, but their accuracies have not been extensively tested with samples of marine origin. In this study, we compared results for total nitrogen analysis generated by the Hach method, a relatively new and low-cost technique, with CHN elemental analysis, a widely accepted and costly technique. Sixty aquatic organisms were tested covering substantial biological diversity, including algae, invertebrates, fishes, mangrove plants, salt marsh plants, and seagrasses. Two pure protein standards (bovine serum albumin and bovine milk casein) were also tested. All materials were tested using freeze-dried samples. Fishes showed the highest concentrations of nitrogen, with values always higher than 14%, whereas leaves of mangrove plants showed the poorest N content among all species (<2.0%). In general, animals showed higher values for total nitrogen than algae and spermatophytes. Results obtained with CHN analysis and the Hach method were compared for each species based on triplicate analyses for each method. Comparisons for each species showed no statistical differences between the techniques, which yielded virtually identical nitrogen measurements. In addition, results obtained with both CHN analysis and the Hach method for the two pure protein standards were similar to data provided by the manufacturer. The set of results indicates that the Hach method is suitable for nitrogen analysis of marine organisms and should be considered as an inexpensive and accurate alternative for nitrogen quantification.