Rafael do Nascimento Oliveira¹, Wilkins Oliveira de Barros¹, Maria Elvira Lima da Silva¹, Joselson Rodrigues da Silva^1,2, Heloisa França Maltez², Herbert de Sousa Barbosa¹, Cícero Alves Lopes Júnior¹, Igor da Silva Constantino¹, Benedito Batista Farias Filho¹

Rapadura is a traditional homemade sweet widely produced in Brazil’s Northeast region. It has an interesting mineral composition, including magnesium, potassium, calcium, iron, manganese, copper, and zinc, along with reducing and non-reducing sugars, proteins, lipids, phenolic acids, and flavonoids. Because of its high content of inorganic species, combined with the fact that it is a minimally processed, mostly artisanal food, a detailed analysis of its nutritional composition is necessary—particularly regarding micro- and macronutrients, as well as the possible presence of heavy metals. The aim of this study is to develop a methodology for quantifying K, Ca, Fe, Cu, and Zn using Portable X-Ray Fluorescence Spectrometry (p-XRF). This technique presents itself as an alternative to the more established methods of elemental analysis described in the literature (ICP-OES, AAS), which, while highly reliable, are costly, time-consuming, and require wet sample preparation. The spectral scan confirmed the presence of K (Kα = 3.31 keV), Ca (Kα = 3.69 keV), Fe (Kα = 6.40 keV), Cu (Kα = 8.05 keV), and Zn (Kα = 8.64 keV). Optimization of operational parameters aimed at improving the signal-to-noise ratio for these five elements showed that reducing the scan area (spot size) weakened the analytical signal by an average of 22%. Granulated rapadura produced results with lower relative standard deviations (1.4–19.5%) compared to block rapadura (3.0–23%), as granulation reduces sample heterogeneity and the shadowing effect caused by radiation–sample interactions. Short analysis times (30–60 s) resulted in peaks with high relative standard deviations (1.7–18%), indicating that the interaction time between the radiation and the analyte strongly influences the analytical response, with 90 s emerging as the optimal analysis time. Furthermore, using a small fraction of the sample (0.5 g) improved analytical signal and precision, as it reduces the critical depth effect associated with thicker samples. Signal stability analyses revealed fluctuations for all five elements within the same day, likely influenced by element concentration, spectral interference regions (Cu/Zn), and variations in device temperature. However, results remained statistically consistent with those obtained on different days, demonstrating that the method is reliable for inter-day analyses. To strengthen the methodology, Standard Addition (SA) calibration will be carried out for each element, combined with the use of the Compton Effect as an Internal Standard (IS). Results will also be compared with those obtained by the reference method (Inductively Coupled Plasma Mass Spectrometry, ICP-MS) to establish correlations with the spectral data generated by p-XRF. This study will enable the quantification of minerals in rapadura samples produced in different Northeastern states, contributing to food safety while also adding value to local commerce.

Agradecimentos: Thanks to the Federal University of Piauí (UFPI), Federal University of ABC (UFABC), the Graduate Program in Chemistry (PPGQ-UFPI), the Coordination for the Improvement of Higher Education Personnel (Capes), and the Piauí State Research Support Foundation (FAPEPI).