AOAC Methods for Review in Codex STAN 234_11-2018

AOAC Official Methods Listed in CXS 234 for Milk and Milk Products

57

50.1.15

analyte uptake rate (w/pump), 0.8 mL/min; observation height: 16 mm above load coil (optimized for Mn). ( b ) Controllable heating mantle and acid scrubber. —Labconco 60301 (Labconco, 8811 Prospect, Kansas City, MO 64132, USA), or equivalent. ( c ) Glassware. —Soak overnight in 10% HNO 3 and thoroughly rinse with H 2 O. D. Procedure Vigorously shake container of infant formula to ensure complete mixing. Measure 15.0 mL of ready to feed (10.0 mL if concentrated, 1.5 g if powdered) infant formula into 100 mL Kjeldahl flask. Add 30 mL HNO 3 ⋅ HClO 4 (2 + 1) to flask along with 3 or 4 glass boiling beads. Let test portions sit overnight in acid. Carry 2 reagent blanks through entire procedure along with test portions. Before starting digestion, have ice bath available for cooling Kjeldahl flasks. HNO 3 should also be readily available. To start digestion, place each Kjeldahl flask on heating mantle set at low temperature. Once boiling is initiated, red-orange fumes of NO 2 will be driven off. Continue gentle heating until HNO 3 and H 2 O have been driven off. At this point effervescent reaction occurs between organic material and HClO 4 . Place flask on cool heating mantle and let digestion proceed with occasional heating from mantle. It is important that reaction between organic material and HClO 4 not go too fast, because charring will occur. If charing occurs, immediately place flask in ice bath to stop digestion. Add 1 mLHNO 3 and resume gentle heating. After reaction of test portion with HClO 4 is complete (identified by cessation of effervescent reaction between organic material and HClO 4 ) apply high heat for ca 2 min; do not heat to dryness because this can cause explosion. Remove flask from heating mantle and let cool. Transfer each digest to 50 mL volumetric flask and dilute to volume with H 2 O. Some precipitation is likely to occur (especially with high salt content products) after dilution. Precipitate will dissolve if shaken and allowed to sit overnight. Final acid content of digests is ca 20% HClO 4 . Elemental determination is accomplished by inductively coupled plasma (ICP) emission spectroscopy ( see Table 984.27 for parameters). Calibration of instrument is done through use of known calibration standards. Calibration standards may be used as single standards (i.e., one element per standard) or as mixed standard containing 2 or more elements. Whether single or mixed standards

AOAC Official Method 984.27 Calcium, Copper, Iron, Magnesium, Manganese, Phosphorus, Potassium, Sodium, and Zinc in Infant Formula Inductively Coupled Plasma Emission Spectroscopic Method First Action 1984 Final Action 1986 Caution: See Appendix B , safety notes on wet oxidation, nitric acid, and perchloric acid. A. Principle Test portion is digested in HNO 3 /HClO 4 and elements are determined by ICP emission spectroscopy. B. Reagents ( a ) Water. —Distilled, deionized. Use throughout. ( b ) Perchloric acid. —Double-distilled (G. Frederick Smith Chemical Co., PO Box 245, Powell, OH 43065, USA; www.gfschemicals.com, or equivalent). Dilute 10 mL to 50 mLwith H 2 O. ( c ) Standards. —All preparations yield 1000 µ g/mL. ( 1 ) Calcium. —Place 2.4973 g CaCO 3 in 1 L volumetric flask with 300 mL H 2 O, add 10 mL HCl, and after CO 2 has been released, dilute to 1 L. ( 2 ) Copper. —Dissolve 1.000 g Cu in 10 mL HCl plus 5 mL H 2 O to which HNO 3 is added dropwise until dissolution is complete. Boil to expel fumes, cool, and dilute to 1 L with H 2 O. ( 3 ) Iron. —Dissolve 1.000 g Fe wire in 20 mL 5M HCl; dilute to 1 L with H 2 O. ( 4 ) Potassium. —Dissolve 1.9067 g KCl in H 2 O and dilute to 1 L with H 2 O. ( 5 ) Magnesium. —Dissolve 1.000 g Mg in 50 mL 1M HCl and dilute to 1 L with H 2 O. ( 6 ) Manganese. —Dissolve 1.000 g Mn in 10 mL HCl plus 1 mL HNO 3 and dilute to 1 L with H 2 O. ( 7 ) Sodium. —Dissolve 2.5421 g NaCl in H 2 O and dilute to 1 L with H 2 O. ( 8 ) Phosphorus. —Dissolve 4.263 g (NH 4 ) 2 HPO 4 in H 2 O and dilute to 1 L with H 2 O. ( 9 ) Zinc. —Dissolve 1.000 g Zn in 10 mL HCl and dilute to 1 L with H 2 O. Commercially available certified standards may be substituted for any of the above element solutions. ( d ) Calibration standards. —Prepare to concentration indicated in Table 984.27 , using standards above. All calibration standards should be prepared to contain 20% HClO 4 to approximate HClO 4 concentration in diluted digest. C. Apparatus ( a ) ICP emission spectrometer. —Model 975 Plasma Atom Comp (Jarrell-Ash Corp., 27 Forge Pkwy, PO Box 9101, Franklin, MA 02038-9101, USA), or equivalent, capable of simultaneous or sequential determination of Ca, Cu, Fe, K, Mg, Mn, Na, P, and Zn. Minipuls 2 peristaltic pump (Gilson Medical Electronics, PO Box 27, 3000 W. Beltline Highway, Middleton, WI 53562, USA), or equivalent, used to feed glass crossflow nebulizer. Suggested operating parameters: warm-up time (plasma on), 30 min; exposure time, 5 s; integration cycles, 1 cycle (2 on line exposures, 1 off line exposure); forward power, 1.1 KW; reflected power, <5 watts;

Table 984.27. Suggested operating parameters for ICP emission spectroscopy

Standard, µ g/mL Low High

Wavelength, nm

Background correction a

Element

Ca Cu Fe Mg Mn Na K

317.9 324.7 259.9 766.5 383.2 257.6 589.0 214.9 213.8

N H N N N N N N H

0 0 0 0 0 0 0 0 0

200

5

10

200

5 5

200 100

P

Zn

5

a H = High side; N = no correction.

 2005 AOAC INTERNATIONAL

10/9/2018