Wayne R. Wolf

Preparation of a mixed human diet material for the determination of nutrient elements, selected toxic elements and organic nutrients: A preliminary report

Using 201 foods from the United States Food and Drug Administrations Total Diet Study (FDA TDS), a mixed diet composite (USDIET-I) was prepared to represent the intake of 25-30-year-old males in the United States. Proximate analyses, phytate determination, and assays for nutrient elements and selected toxic elements, as well as organic nutrients were carried out on this composite. As part of a quality control exercise for a coordinated research program, atomic absorption spectrophotometry, inductively coupled atomic emission spectrometry, colorimetry and neutron activation analysis were used to determine up to 30 elements in this diet material. A comparison of the daily intakes of As, Ca, Cd, Cu, Fe, Hg, K, Mg, Mn, Na, P, Se and Zn from the composite USDIET-I shows excellent to good agreement with FDA TDS values calculated from results of single food analyses. These USDIET-I results demonstrate the feasibility of the mixed diet concept as a viable approach for a reliable assessment of daily intakes, especially for a number of elements such as Cd, Cr, Hg and Mo that occur at low concentrations in individual food products. Simultaneously, stability of some organic nutrients during storage was also investigated. Initial findings suggest that this program may also be useful in the development of reference materials for organic nutrients, for which there is a great need. These aspects are discussed.

Simultaneous determination of water-soluble vitamins in SRM 1849 Infant/Adult Nutritional Formula powder by liquid chromatography–isotope dilution mass spectrometry

AbstractAssessing dietary intake of vitamins from all sources, including foods, dietary supplements, and fortified foods, would be aided considerably by having analytical methodologies that are capable of simultaneous determination of several vitamins. Vitamins naturally present in foods may occur in different chemical forms, with levels ranging over several orders of magnitude. Vitamins in dietary supplements and fortified foods, however, are typically added in a single chemical form, and matrix issues are usually not as complex. These sources should thus be relatively amenable to approaches that aim for simultaneous determination of multiple vitamins. Our recent work has focused on development of liquid chromatography (LC)–UV/fluorescence and LC–tandem mass spectrometry methods for the simultaneous determination of water-soluble vitamins (thiamine, niacin, pyridoxine, pantothenic acid, folic acid, biotin, and riboflavin) in dietary supplement tablets and fortified foods, such as formula powders and breakfast cereals. As part of the validation of our methods and collaboration in characterization of a new NIST SRM 1849 Infant/Adult Nutritional Formula powder, we report data on SRM 1849 using isotope dilution mass spectrometric methods. Use of available NIST Standard Reference Materials® as test matrices in our method development and validation gives a benchmark for future application of these methods. We compare three chromatographic approaches and provide data on stability of vitamin standard solutions for LC-based multiple vitamin determinations. FigureExtracted ion chromatograms of seven vitamins using RP chromatography treatment

Coupled gas chromatography-atomic absorption spectrometry

The specific, precise detection of volatile metal chelates has been obtained by coupling the effluent from a gas chromatograph directly to the burner head of a commerical atomic absorption spectrometer (AAS). Quantitation of chromium in the nanogram range has been accomplished with a detection limit of 1.0 ng. The chelation-extraction-gas chromatographic separation procedure coupled with the selective detection by AAS gives a relatively interference-free system that has been used to quantitatively analyse for chromium in standard biological materials NBS SRM 1571 Orchard Leaves and SRM 1569 Brewers Yeast. Metal chelates of iron, copper and cobalt have also been detected by this system.

Determination of selenomethionine in yeast using CNBr derivatization and species specific isotope dilution GC ICP-MS and GC-MS

A comparison of several published and in-house methods for quantitation of selenomethionine (SeMet) in yeast was undertaken using species specific isotope dilution (ID) with a 74Se enriched SeMet. An in-house method was based on digestion of samples by refluxing for 16 h with 4 M methanesulfonic acid, derivatization of SeMet with cyanogen bromide and extraction into chloroform for determination by GC ICP-MS. Concentrations of 3434 ± 19 and 3419 ± 15 μg g−1 (one standard deviation, n = 6) with relative standard deviations of 0.55% and 0.42% for SeMet were obtained in yeast based on measurement of 78Se/74Se and 82Se/74Se ratios, respectively, in agreement with a value of 3417 ± 27 μg g−1 (one standard deviation, n = 6) obtained using ID GC-MS detection based on the ratio of 106/100 of SeCN+ ion. The SeMet accounts for 67% of the total Se in the sample. A method detection limit (three standard deviations) of 0.9 μg g−1 was estimated for SeMet based on a 0.25 g subsample. Significantly lower concentrations of 2220 ± 7 and 2215 ± 9 μg g−1 (one standard deviation, n = 4) with RSDs of 0.30 and 0.41% were obtained by ID GC ICP-MS using 78Se/74Se and 82Se/74Se ratios, respectively, following digestion with 2% SnCl2 in 0.1 M HCl and reaction with CNBr to form volatile CH3SeCN. Similar SeMet concentrations of 3415 ± 200 and 3447 ± 198 μg g−1 (one standard deviation, n = 6) and significantly degraded precisions of 5.86 and 5.74%, respectively, were obtained in yeast using 78Se/74Se and 82Se/74Se ratios, respectively, following digestion with 4 M methanesulfonic acid and derivatization with methyl chloroformate.

A system for defining reference materials applicable to all food matrices

Recently the subcommittee on Food Definition of the AOAC INTERNATIONAL Task Force on Methods for Nutrition Labeling proposed a “Food Matrix Organizational System” [4] to systematically judge the applicability of collaboratively studied methods over a range of food matrices. This system describes a food matrix by its location in one of nine sectors in a triangle, with each point of the triangle defined as representing 100% and the opposite side representing 0% of the normalized contents of each of three major components of FAT, PROTEIN and CARBOHYDRATE. Foods falling within the same sector would be chemically similar and thus should behave in a similar analytical manner. This same scheme can be used to select one or two food matrices representing each sector, for development of a series of reference materials representing all foods. The list of 5250 foods contained in the USDA Nutrient Data Base for Standard Reference has been sorted and matched to this schematic to determine the scope of the selection process. In addition the list of foods in the “USDA Data Base for Food Consumption Surveys” has been examined. Results and progress of this selection process are reported.

A LC/UV/Vis method for determination of cyanocobalamin (VB12) in multivitamin dietary supplements with on-line sample clean-up

A HPLC-UV/Vis method using a two-column strategy with a switching valve for on-line sample clean-up was developed for the determination of cyanocobalamin (CN–Cbl/Vitamin B12) in multivitamin dietary supplement tablets. The method uses two columns: an Agilent Zorbax C8 (150 mm × 4.6 mm, 5 μm particle size) reversed-phase column and a Waters Symmetry C18 (150 mm × 4.6 mm, 5 μm particle size) reversed-phase column. Chromatographic separation was achieved using a programmed gradient mobile phase consisting of (A) 0.1% formic acid in water and (B) 0.1% formic acid in acetonitrile. Because of the low levels of Vitamin B12 in the samples, large injection volumes, and thus much interfering material, must be used to exceed the limit of quantitation (LOQ) by UV detection. A switching valve was used to divert most of these early eluting interfering materials to waste, effecting on-line sample clean-up without excessive sample preparation steps. The recovery of CN–Cbl in the method was 99.5% and the LOQ was 10 ng per injection. The method was successfully applied to the analysis of the NIST SRM 3280 multivitamin/multimineral dietary supplement tablet. The method is specific, precise, and accurate for the intended use. Compared to off-line sample clean-up procedures, it offers the advantage of being easier, more economical, and less time-consuming.

Selex : an expert system for evaluating published data on selenium in foods

Abstract Providing consistent and objective evaluation of published data on nutrient composition is critical for planning future analytical studies and for effective use of data. Based on a commercial expert system shell, a computer system of approximately 200 rules has been created to evaluate and ratre quantitatively published data on selenium in foods. The evaluation scheme uses five general categories for its rule-making process: number of samples, analytical method, sample handling, sampling plan, and analytical quality control. For each selenium value to be evaluted, rating ar assigned in each category by the expert system based on input which is derived from the information reportedin a given paper. A quality index, which is derived from the ratings, is a measure of the reliability of a given selenium value over all categories for a given study. The concepts used in developing SELEX have the potential of establishing criteria for evaluation of proposed analytical methods prior to their publication.

Ion-exchange high performance liquid chromatographic determination of selenomethionine by reaction with cyanogen bromide

Abstract A sensitive and simple ion-exchange HPLC procedure is described for the separation and analyses of selenomethionine from coeluting naturally occurring amino acids. Cyanogen bromide selectively reacts with selenomethionine in the absence of stannous chloride to form an unknown reaction product, formation of which is quantitative. A calibration curve is obtained over a linear dynamic range of 30 nmoles to 500 nmoles of selenomethionine.

Potentiometric and spectroscopic study of selenomethionine complexes with copper(II) and zinc(II) ions

SummaryThe stepwise stability constants of 1:1 and 2:1 complexes of selenomethionine (SeMet) with CuII and ZnII ions have been determined in NaNO3 (0.1m) supporting electrolyte by potentiometric titration at 25 °C. The overall log stability constant (logβML2 = [ML2]/[M2+][L−1]2) for CuII and ZnII complexes are 14.50 and 8.75, respectively. Two new solids were prepared and identified by elemental microanalysis as (SeMet)2Cu and (SeMet)2Zn. I.r. and Raman spectral studies indicated metal coordination with the nitrogen and oxygen atoms of the amino acidato group of SeMet. The corresponding stretching bands were assigned at 341.1cm− for Cu-O, 352.9 cm− for Zn-O, 497.3 cm− for Cu-N and 475.2 cm− for Zn-N bonds.

Rapid Trichloroacetic Acid Extraction and Liquid Chromatography Method for Determination of Nicotinamide in Commercial Cereals

ABSTRACT Determination of niacin in fortified infant and dairy products has been accomplished using a variety of analytical liquid chromatography (LC) methods. Applications of these LC techniques to other food matrices suffer due to the presence of endogenous absorbing peaks at 260 nm that co-chromatograph with the nicotinic acid and nicotinamide vitamers. We have successfully adapted the LC method of Woollard and Indyk for the determination of nicotinamide in reference and commercial cereal products. Unbound nicotinamide in fortified cereal was extracted with 0.6M tri-chloroacetic acid and chromatographed on a C18 reversed-phase column using a mobile phase of 75% methanol and water (pH 2.8, with formic acid) with sodium dioctylsulphosuccinate (0.1%) as the ion-pairing agent. Using Spectral Analysis ChromQuest software, a three-dimensional view showed only nicotinamide under the LC peak. Similarity index spectral matches of nicotinamide standard and the LC peak were ≈100%, indicating the absence of interf...