Preparation and evaluation of a new reference material for macro- and micronutrients in fish feed

A new reference material for inorganic constituents analysis in fish feed was produced and characterized according to the ISO Guides 30-35. The evaluation of the estimated minimum mass, homogeneity, and short- and long-term stability of the material was performed using microwave-assisted digestion and inductively coupled plasma optical emission spectroscopy as an in-house validated technique for Ca, Cu, Fe, K, Mg, Mn, Na, P, and Zn analysis. The accuracy of the measurements results was confirmed by analyzing the certified reference materials Oyster Tissue and Tomato Leaves, NIST SRM 1566b and SRM 1573a. The chemical characterization concerning elemental composition was performed through a collaborative trial with the participation of 35 laboratories by using spectroscopic and instrumental neutron activation analysis techniques. One-way analysis of variance (ANOVA) and regression analysis were the statistical methods applied to achieve the consensus values and their combined uncertainty, and the homogeneity and stability of the material presented averages within the 95% confidence interval. The expanded uncertainty considered all the instability observed during the stability, homogeneity, and characterization tests. The certified values and expanded uncertainties (k = 2) for the candidate reference were (28.65 ± 1.84) g kg−1 Ca, (10.51 ± 0.87) mg kg−1 Cu, (231.97 ± 20.17) mg kg−1 Fe, (5.86 ± 0.31) mg kg−1 K, (1.55 ± 0.16) g kg−1 Mg, (19.46 ± 2.12) mg kg−1 Mn, (2.16 ± 0.19) g kg−1 Na, (16.06 ± 0.97) g kg−1 P, and (129.56 ± 6.79) mg kg−1 Zn. The produced material proved its suitability for internal instrumental quality control or for the quality assurance of Ca, Cu, Fe, Mg, Mn, Na, P, and Zn analysis in fish feed for evaluation the laboratories quality control.