Nitric acid and hydrogen peroxide in milk and cheese digestion for the detection of metals


Numa Castro Gonzalez
Marcos Pérez-Sato
Eutiquio Soni-Guillermo
Edgar Valencia-Franco
Martín Carmona-Victoria
Francisco Calderón-Sánchez


Acid digestion, Metal contamination in milk, Cheese


Objective:  To determine the concentration of arsenic (As), cadmium (Cd), copper (Cu), chromium (Cr), lead (Pb), and zinc (Zn) in milk and cheese by comparing the use of nitric acid (HNO3) and a mixture of nitric acid and hydrogen peroxide (HNO3 + H2O2) in acid digestion.

Design/methodology/approach: The milk for the study was collected from storage tanks in various localities of Huejotzingo, and the different types of cheese came from Santa Ana Xalmimilulco, Huejotzingo, Puebla, Mexico. Digestion was carried out in a CEM MarsX microwave. Elemental concentrations were determined by Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES).

Results: The combination of HNO3 + H2O2 in milk digestion resulted in higher concentrations of Cd, Pb, and Zn. Conversely, the concentration of As was higher when using only HNO3 for digestion. No significant differences were found for Cr and Cu between the two digestion methods. In the case of Oaxaca cheese, digestion with HNO3 resulted in higher concentrations of As. Acid digestions did not affect the concentrations of the remaining elements. The same behavior was observed for Ranchero cheese, since the digestion combining HNO3 + H2O2 resulted in lower As concentrations, as compared to the digestion with only HNO3. Pb and Zn were not significantly affected by the treatments, while the concentrations of Cd, Cr, and Cu could not be determined when samples were treated with the HNO3 + H2O2 combination.

Limitations: In this work we were able to determine the concentration of a number of metals present in milk and cheese using nitric acid and hydrogen peroxide in acid digestion. However, we recommend more tests are carried out to establish which acid or combination of acids allows for a broader detection of metals.

Findings/Conclusions: According to the results obtained in this work, we can conclude that there is specificity for metal detection, with HNO3 being the most efficient.

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