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

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.

Extreme Phenotypic Plasticity in Metabolic Physiology of Antarctic Demosponges

“…The range of values, 2-10% nitrogen for sponges in this study, encompasses the 6% nitrogen found in other sponges, such as Hymeniacidon heliphila (Barbarino and Lourenco, 2009) and Spongilla lacustris (Sandjensen and Pedersen, 1994). S. lacustris also had a carbon content (30%) within the range of those found in the current study (9-41%).…”

“…CHN values obtained for sponges in the current study were at the lower end of those recorded in marine ectotherms (Barbarino and Lourenco, 2009;Obermüller et al, 2013). The range of values, 2-10% nitrogen for sponges in this study, encompasses the 6% nitrogen found in other sponges, such as Hymeniacidon heliphila (Barbarino and Lourenco, 2009) and Spongilla lacustris (Sandjensen and Pedersen, 1994).…”

Proximate composition of marine invertebrates from tropical coastal waters, with emphasis on the relationship between nitrogen and protein contents

“…The animals were grouped by their respective taxonomic phyla, but many species that belong to different orders or classes of a same phylum were analyzed. Thus, within the same phylum, part of the variations in chemical profiles can be assumed as a consequence of phylogenetic traits (Barbarino & Lourenço, 2009). It is also important to point out that our results are expressed as percentage of substance to the total mass, thus the occurrence of large amounts of structural inorganic contents contribute to diminish the tissue concentrations of nitrogen and all other substances measured here (phosphorus, protein, carbohydrate, and lipid).…”

“…In contrast to protein analysis, total nitrogen (TN) is relatively simple to measure, and it is very accurate (Barbarino & Lourenço, 2009). For virtually all species chemically known, most of the nitrogen content is found in proteins, which means that both total protein and TN tend to vary in a proportional fashion (Huet et al, 1988;Mariotti et al, 2008).…”

“…Analyses of substances such as proteins, lipids and carbohydrates, as well as total nitrogen and phosphorus, have great importance, since they are major constituents of living matter (Barbarino & Lourenço, 2009;Diniz et al, 2012). Carbohydrates are complex biomolecules that perform structural roles in cells, but they also serve as a fundamental reservoir of chemical energy (Lairson et al, 2008).…”