Validation of nitrogen compounds in marine waters

Abstract

Nitrogen compounds in sea water (total nitrogen, ammonia, nitrates, and nitrites) belong to the nutrients involved in biochemical changes. Nutrients are transferred into the Baltic Sea e.g. from onshore point sources, from diffuse sources, from marine sediments, or from the atmosphere, which results in a water body’s becoming richer in nutrition elements, and finally in its eutrophication. Excessive eutrophication creates an imbalance in the ecosystem; among other things, it encourages massive phytoplankton blooms, increases the level of the organic matter as well as of its sedimentation, and it reduces the level of oxygen in the bottom water, which leads to the death of benthic organisms, and demersal fish. An analysis of marine waters constitutes a difficult task e.g. due to the small values of the biogenic substances (µmol/dm3), their short period of maintenance in a water sample, as well as the high salinity, which may hinder the examinations. An analysis made on a secured sample should be performed within a period not longer than 4-6 hours after the sample’s collection. In this article, you will find presented a validation of methods for determining nitrogen compounds (total nitrogen, ammonia, nitrates, and nitrites) in sea water via spectrophotometric method, in accordance with procedures recommended by the HELCOM [8,14]. In analytical chemistry, validation of methods is an important element. It is an obligatory affirmation that all the requirements of a specific intended use have been met. Due to the performed validation of the method, there were determined: limits of detection and quantification, the selectivity of the method, its linearity, precision within the repeatability and/or reproducibility limits, as well as recovery rate and accuracy of the method. Credibility and reliability of the testing procedures in question were confirmed by the positive results of certified reference materials analysis: the VKI Reference Material QC SW3.1B, and QC.SW3.2B, and of comparative (inter-laboratory) research. The methods developed in the process were incorporated into the routine analysis in the Laboratory of Environment Protection of the Maritime Institute in Gdansk, which was accredited by the Polish Centre of Accreditation in 2014 with respect to the discussed research methods.