Determination of Niacin in Infant Formula by Solid-Phase Extraction and Anion-Exchange Liquid Chromatography
Abstract:A peer-verified, solid-phase extraction (SPE)/anion exchange liquid chromatographic method is presented for the determination of niacin in milk-based and soy-based infant formula. Analysis is in 3 steps: test sample digestion, extraction/cleanup, and liquid chromatography (LC). Digestion uses a standard AOAC digestion procedure that involves autoclaving at 121°C for 45 min in (1 + 1) H2SO4 to free endogenous niacin from protein and to convert added niacinamide to niacin. The digest solution is adjusted to pH 6.5 with 7.5M NaOH. Acidification to pH <1.0 with (1 + 1) H2SO4 precipitates the protein. The clarified solution is then filtered, and the filtrate is brought to volume. SPE of niacin is accomplished by passing an aliquot of the digest solution through an aromatic sulfonic acid–SPE (ArSCX–SPE) column. After the column is washed with methanol and water to remove extraneous material, the niacin is eluted with 0.25M sodium acetate/acetic acid buffer at pH 5.6. An anion-exchange polystyrene–divinylbenzene column with 0.1M sodium acetate/acetic acid buffer at pH 4.0 is used for LC. Niacin is determined by UV detection at 260 nm. A standard curve is prepared by passing known amounts of niacin through the ArSCX–SPE columns used for niacin extraction. The following values for x_bar and relative standard deviation (RSD) were obtained for National Institute of Standards and Technology Standard Reference Material (NIST SRM) 1846 Infant Formula with a certified value for niacin of 63.3 ± 7.6 μg/g: Submitting laboratory.— x_bar = 59.7 ± 4.0 μg/g; RSD = >6.7%; confidence interval (CI) = ± 1.4 μg/g; n = 27. Peer laboratory.— x_bar = 56.6 ± 6.6 μg/g; RSD = >11.7%; CI = ± 4.1 μg/g; n = 8.
Document Type: Research Article
Affiliations: 1: U.S. Department of Agriculture, Beltsville Human Nutrition Research Center, Food Composition Laboratory, 10300 Baltimore Ave, Beltsville, MD 20705-2350. 2: U.S. Food and Drug Administration, Atlanta Center for Nutrient Analysis, 60 8th St, NE, Atlanta, GA 30309. 3: U.S. Food and Drug Administration, 22201 23rd Dr, SE, Bothwell, WA 98021. 4: AgriQuality NZ, 131 Boundary Rd, PO Box 41, Auckland, NZ.
Publication date: May 1, 2001
- The Journal of AOAC INTERNATIONAL publishes refereed papers and reviews in the fields of chemical, biological and toxicological analytical chemistry for the purpose of showcasing the most precise, accurate and sensitive methods for analysis of foods, food additives, supplements and contaminants, cosmetics, drugs, toxins, hazardous substances, pesticides, feeds, fertilizers and the environment available at that point in time. The scope of the Journal includes unpublished original research describing new analytical methods, techniques and applications; improved approaches to sampling, both in the field and the laboratory; better methods of preparing samples for analysis; collaborative studies substantiating the performance of a given method; statistical techniques for evaluating data. The Journal will also publish other articles of general interest to its audience, e.g., technical communications; cautionary notes; comments on techniques, apparatus, and reagents.
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