Validation of continuous flow analysis for determining total nitrogen in plants compared to the Kjeldahl method

Major elements, also known as macro-elements, are present in significant amounts and are essential for plant growth and development. In agronomic, environmental, and fertilization studies, the total nitrogen content of plants is a key indicator. Assessing soil fertility and nitrogen availability requires a rapid and straightforward determination of total nitrogen. For this study, eight plant samples with varying nitrogen concentrations and different plant matrices were selected. A comparison was made between the nitrogen content, as determined by a continuous flow analyser (CFA), and the content obtained using the Kjeldahl method. The aim was to evaluate the feasibility of rapidly and accurately determining the total nitrogen content of plants. Analytical validation (linearity, precision, detection limits, and accuracy) was conducted in accordance with ISO 13528, ISO 17034, and NF T90-210 standards. Statistical assessment included regression analysis and one-way ANOVA at a 95% confidence level. A strong correlation was observed between the CFA and Kjeldahl results (R2 = 0.9972; p > 0.05), indicating no statistically significant differences between the methods. Both exhibited high precision (RSD < 5%) and accuracy across nitrogen concentrations ranging from 2.5 to 40 g·kg⁻1. The continuous flow analyser (CFA) provides a quick, precise, and environmentally friendly alternative to the Kjeldahl method for determining the total nitrogen content of plants. The CFA’s strong analytical equivalence with the reference procedure is demonstrated by its superior speed and automation, which reduces reagent use. Its robustness across different plant matrices and experimental conditions makes it a reliable and sustainable option for routine nitrogen analysis in agricultural and environmental laboratories.