Methods to be Reviewed by OMB in 2016

1712

Thompson et al.:

ournal of

AOAC I

nternational

ol.

98, N

6, 2015

Specificity and linearity studies were conducted with pure

analyte (no matrix). For the specificity studies, individual

standards of each analyte were prepared at 50 mg/L. For

linearity, standards were prepared at nine concentrations of each

analyte, spanning a range from 50% of the lowest calibration

standard to 50% above the highest calibration standard. For

precision studies, the 11 SPIFAN matrixes (infant powder, milk;

infant powder, soy; infant powder, milk partially hydrolyzed;

infant powder, soy partially hydrolyzed; adult powder, low

fat; adult powder, milk; pediatric formula powder; infant

elemental powder; infant RTF, milk; adult RTF, high protein;

and adult RTF, high fat) were tested for all 12 elements on

8 days in duplicate each day, by two analysts using two Agilent

ICP/MS units. For accuracy/recovery studies, each SPIFAN

matrix was spiked with various concentrations of each analyte

and analyzed by the method in triplicate over 3 days. Finally,

Standard Reference Material (SRM) 1849a [National Institute

of Standards and Technologies (NIST), Gaitherburg, MD] was

used to verify accuracy. The SRM is a milk-based hybrid infant/

adult nutritional powder with certified values for Ca, Cu, Cr, Fe,

Mg, Mn, Mo, P, K, Se, Na, and Zn and was included as a QC

sample (QCS) in each run of the method.

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. Microwave operation involves hot

pressurized acid solution. 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 lowmass 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

Table 1. Summary of SLV acceptance criteria from SMPR 2011.009 and SMPR 2014.004

SMPR 2014.004

SMPR 2011.009

Parameter

Analytical range

0.001–1.0

0.001–1.2 0.01–20 0.1–18

3–110

15–800

10–850

20–1280

10–2000

20–1600 20–1000 10–500

LOD

LOQ

0.001

0.01

0.1

Repeatability

≤5% at >0.005

≤8% at <0.005

≤5%

Recovery

90–110% at >0.005

80–115% at <0.005

90–110% of mean spiked recovery over the range of the assay

Reproducibility (over

the analytical range)

≤10%

≤10% ≤10% ≤10% ≤10%

≤8%

≤15% ≤15% ≤15%

Concentrations apply to a) RTF liquids “as-is”; b) reconstituted powders (25 g into 200 g of water); and c) liquid concentrated diluted 1:1 by weight.

mg/100 g reconstituted final product for Mn, Cu, Fe, Zn, Mg, P, Na, Ca, and K; µg/100 g for Cr, Mo, Se.

NA = Not applicable.

Candidates for 2016 Method of the Year