Microwave-Assisted Extraction and Quantitative LC/ID-MS Measurement of Total Choline and Free Carnitine in Food Standard Reference Materials

Abstract The Stakeholder Panel on Infant Formula and Adult Nutritionals of AOAC INTERNATIONAL has declared both choline and carnitine to be priority nutrients in infant formulas, and ongoing efforts exist to develop or improve Official Methods of AnalysisSM for these nutrients. As a result, matrix-based certified reference materials are needed with assigned values for these compounds. In this work, traditional acid and enzymatic hydrolysis procedures were compared to microwave-assisted acid hydrolysis, and conditions optimized to provide complete sample hydrolysis and recovery of total choline from four food standard reference materials (SRMs): whole milk powder, whole egg powder, infant formula, and soy flour. The extracts were analyzed using LC on a mixed-mode column (simultaneous RP and ion exchange) with isotope dilution-MS detection to achieve simultaneous quantification of total choline and free carnitine. Total choline has been determined in these four food matrixes with excellent precision (0.65 to 2.60%) and accuracy, as confirmed by use of SRM 1849 Infant/Adult Nutritional Formula as a control material. Free carnitine has been determined in two of these food matrixes with excellent precision (0.69 to 2.19%) and accuracy, as confirmed by use of SRM 1849 Infant/Adult Nutritional Formula as a control material. Limitations in simultaneous determination of total choline and free carnitine resulted from extreme differences in concentration of the two components in egg powder and soy flour (at least three orders of magnitude). Samples required dilution to prevent poor LC peak shape, which caused decreased precision in the determination of low concentrations of free carnitine. Despite this limitation, the described method yields results comparable to current AOAC Official Method 999.14 Choline in Infant Formula, with a decrease of more than 2 h in sample preparation time.

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Heat-assisted slurry sampling GFAAS method for determination of lead in food standard reference materials

Journal of Food Composition and Analysis ◽

10.1016/j.jfca.2015.03.007 ◽

2015 ◽

Vol 42 ◽

pp. 78-83 ◽

Cited By ~ 7

Author(s):

Yue'e Peng ◽

Wei Guo ◽

Ping Zhang ◽

Lanlan Jin

Keyword(s):

Reference Materials ◽

Standard Reference Materials ◽

Slurry Sampling ◽

Food Standard

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Determination of Ultratrace Levels of Lead in Infant Formula by Isotope Dilution Inductively Coupled Plasma Mass Spectrometry

Journal of AOAC International ◽

10.1093/jaoac/76.6.1378 ◽

1993 ◽

Vol 76 (6) ◽

pp. 1378-1384 ◽

Cited By ~ 3

Author(s):

Joseph J Thompson

Keyword(s):

Mass Spectrometry ◽

Infant Formula ◽

Reference Materials ◽

Isotope Dilution ◽

Inductively Coupled Plasma ◽

Standard Reference Materials ◽

Inductively Coupled ◽

Relative Standard ◽

Plasma Mass Spectrometry

Abstract A simple method was developed for the accurate and precise determination of low- and sub-ppb (ng/g) concentrations of lead in infant formula by isotope dilution inductively coupled plasma mass spectrometry using ultrasonic nebulization. After addition of a known amount of 207Pb, samples were microwave digested and the ratio 207Pb/208Pb was measured in the digests. Agreement with certified values for lead in milk powder standard reference materials was good, and isotope dilution analysis using 206Pb yielded identical results for the standard reference materials. Lead concentrations determined for several infant nutritional products were verified by an independent method. Typically, relative standard deviations of <4% were obtained with this method for lead concentrations above 2 ppb. The recovery of 2 ng of lead from an aqueous standard carried through the microwave digestion was 104 ± 4%. Infant formula (containing 0.6 ppb lead) to which 0.4 ng of natural-abundance lead had been added, to simulate a formula containing 0.9 ppb lead, was analyzed by isotope dilution, and the result was 96 ± 18% of the theoretical value. Thus, differences of 0.3 ppb lead could be clearly distinguished, and the detection limit was estimated to be 0.1 ng lead per gram of infant formula. The keys to accuracy for this method are minimizing contamination and accurately determining the concentration of lead in the isotopically enriched standard.

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