Methods to be Reviewed by OMB in 2016

AOAC Official Method 2015.06

Minerals and Trace Elements

in Infant Formula and Adult/Pediatric Nutritional Formula

ICP/MS Method

First Action 2015

(Applicable for determination of Na, Mg, P, K, Ca, Cr, Mn, Fe, Cu, Zn, Se, and Mo in infant

formula and adult/pediatric nutritional formula.)

Caution:

Chemicals employed are common-use solvents and reagents, harmful if inhaled,

swallowed, or absorbed through the skin. Refer to adequate manuals or Materials Safety Data

Sheets (MSDSs) to ensure that the safety guidelines are applied before using chemicals.

Microwaveoperationinvolveshot pressurizedacidsolution. Use appropriate personal protective

equipment such as a laboratory coat, safety glasses, rubber gloves, and a fume hood. Dispose of

all materials according to federal, state, and local regulations.

A. Principle

This method is an extension of AOAC Final Action Method

2011.19

to determine nine additional

elements. Nitric acid, ISTD, and hydrogen peroxide are added to the sample in microwave

vessels, and the samples are digested using preprogrammed temperature control. The addition

of hydrogen peroxide helps reduce carbon and nitrous oxide levels in the digestate. The

presence of carbon in the samples causes signal enhancement of Se. Therefore, to matrix match

the samples, carbon in the form of methanol is added to both the standard solutions and the

digestate before analysis. Ge (for 11 elements) and Te (just for Se) are used as ISTDs. Analysis is

performed by ICP/MS. Polyatomic interferences with the low mass elements are reduced or

eliminated by analyzing in the He collision mode using kinetic energy discrimination (KED). For

Se measurements, the H

gas mode is preferred for increased sensitivity. Quantitation of 12

elements is achieved essentially simultaneously by comparing the analyte/ISTD response ratios

in the unknown samples to a standard curve constructed from response ratios of calibration

standards.

B. Apparatus

(

)

ICP mass spectrometer.—

With quartz spray chamber, quartz torch, Ni/Pt sample cone, Ni/Pt

skimmer cone, autosampler, and printer. The ICP mass spectrometer must have collision

reaction cells (CRCs). In a limited multilaboratory testing study, four different ICP/MS instrument

models from three major vendors delivered equivalent performance.

(

)

Microwave oven.—

Commercial microwave designed for laboratory use at 0–300°C, with

closed vessel system and controlled temperature ramping capability. Use manufacturers’

recommended vessels. (

Caution

: microwave operation involves hot pressurized acid solution.

Use appropriate face protection and laboratory clothing.)

(

)

Hydrogen generator (hydrogen is recommended for better Se sensitivity).—

Parker Balston

(Haverhill, MA) Model H2PD-150, or equivalent. Alternatively, a high pressure cylinder (99.999%

purity) may be used.

Candidates for 2016 Method of the Year