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FOR EXPERT REVIEW PANEL USE ONLY
NOT FOR DISTRIBUTION
1
Expert Review Panel for Infant Formula and Adult Nutrition
Evaluation of Method _AOAC 2015.06
Title:
Milk, milk products, infant formula and adult nutritionals – determination of calcium, copper, iron,
magnesium, manganese, phosphorus, potassium, sodium and zinc contents – Inductively coupled plasma
mass spectrometric method (ICP-MS)
Author:
Joseph Thompson and Lawrence Pacquette
Summary of Method:
Nitric acid, internal standard, and hydrogen peroxide are added to the sample in microwave vessels and the
samples are digested at 200 °C using a preprogrammed temperature control digestion. Germanium (Ge, for
11 elements) and tellurium (Te, just for Se) are used as internal standards. Analysis is performed by
inductively coupled plasma mass spectrometry (ICP-MS). Polyatomic interferences on the low mass
elements are reduced or eliminated by analyzing in He collision mode using kinetic energy discrimination
(KED). For Se measurements the H2 gas mode is preferred for increased sensitivity. Quantitation of 12
elements is achieved essentially simultaneously by comparing the analyte/internal standard response ratios
in the unknown samples to a standard curve constructed from response ratios of calibration standards.
Method Scope/Applicability:
Quantitation of 12 elements is achieved. These 12 elements include calcium, copper, iron, magnesium,
manganese, phosphorus, potassium, sodium, zinc, and chromium, selenium, and molybdenum. / in butter,
cheese, whey powder, liquid whole milk, whole milk powder, whey protein concentrate powder, and infant
formula
General comments about the method:
Method is well written;
The MLT result presented to the ERP demonstrates that this AOAC 2015.06 method is a sensitive, accurate,
ad reliable method for the determination of calcium, copper, iron, magnesium, manganese, phosphorus,
potassium, sodium and zinc contents in milk, milk products, infant formula and adult nutritionals. The test
results with the AOAC samples have shown that all the reproducibility results met the SMPR in general.
The difference between this ICP-MS data and the alternative method ICP-AES data are also low, within 5%,
except the copper and zinc, the differences are -9% and -7%, respectively.
A closer look at the AOAC sample result for copper and Iron near the SMPR low analytical range limit (or
the LOQ) show an interesting observation. The reproducibility data near the LOQs of copper and iron
seems larger than the SMPR.
Method Clarity:
Method is well written, clear to follow