Determination of micronutrient minerals in coconut milk by ICP OES after ultrasound-assisted extraction procedure

• Factorial and Doehlert designs for ultrasound-assisted extraction optimisation.
• The sample preparation is rapid, easy, inexpensive and reproducible.
• Information about micronutrient concentrations in coconut milk samples is provided.

In this paper, multivariate optimisation was applied to the development of an ultrasound-assisted multi-elemental extraction procedure to measure micronutrient minerals in coconut milk samples by inductively coupled plasma optical emission spectrometry (ICP OES). The factorial and Doehlert designs were applied to optimise the process variables. Using this approach, the optimal experimental condition for 1.0 g of coconut milk was determined: 10 min sonication time; 20.0 mL of HNO3 (1.0 mol L−1); and 5 min centrifugation time at 2000 rpm. The extraction percentage was calculated using the analyte concentration obtained by a total digestion procedure as a reference. Accuracy was assessed by analysing a certified reference material (NIST 1549). The proposed procedure was applied to the analysis of commercial samples of coconut milk, and the resulting concentration ranges, in μg g−1, were as follows: 5.8–131 (Ca), <0.27–1.56 (Cu), 0.76–5.52 (Fe), 212–1781 (K), 14.9–201 (Mg), <0.11–3.88 (Mn), 274–625 (Na), 26–341 (P) and <0.74–3.2 (Zn). The method described offers a rapid, easy and efficient sample preparation method for direct determination of micronutrient minerals in coconut milk by ICP OES.