Fatty Acids of Ten Commonly Consumed Pulses.

Gas chromatography (GC) with flame ionization detection (FID) and mass spectrometry (MS) detection were used to characterize the fatty acid (FA) compositions of ten commonly consumed (i.e., market class) pulses. Lipids from ground pulses were extracted using a classical chloroform/methanol extraction and quantified by GC-FID with structural confirmation by GC-MS. Principal component analysis (PCA) was applied to FA compositions of the pulse extracts, and the pulses clustered into three distinct groups: one rich in linolenic acid, 18:3 (carbon number:unsaturation, C:U), one rich in 16:0, and one in which 18:1 was highest, along with predominant 18:2. These ten pulses averaged 46.1% linoleic acid (18:2), 22.7% oleic acid (18:1), 18.0% palmitic acid (16:0), and 7.6% linolenic acid (18:3). Individual values ranged widely, with 18:2 ranging from 26.0% in black beans to 48.4% in garbanzo beans. The greatest difference was in 18:3, which ranged from 2.2% in garbanzo beans to 38.8% in pinto beans. Oxo-FA were observed in all ten samples, and the distribution of oxo-FA in the samples also varied. Overall, the very different FA compositions of pulses lead to the possibility of breeding and genetic modification between pulses to produce the most desirable FA composition for nutritional benefit.

Determination of pyridoxine in dietary supplements by liquid chromatography with UV, fluorescence, and mass spectrometric detection: single-laboratory validation.

A single-laboratory validation was performed for a method that determines pyridoxine, one of the B6 vitamers, in dietary supplements using LC and UV, fluorescence, or MS detection. The method was adapted for use with either HPLC or ultra-performance LC (UPLC). Pyridoxine is extracted from samples using 0.1 M formic acid, and specific conditions are adjusted for each of the different types of supplement materials examined. Reversed-phase chromatography with C18-based columns is used in both HPLC and UPLC. Fluorescence detection, often used in chromatographic analyses of vitamin B6 in foods, was successfully used here, but offered no great advantages over UV detection in the supplement materials tested. MS detection was also satisfactory, although use of an internal standard was required. Accuracy of the method was demonstrated in several ways, including use of a standard reference material. Precision and repeatability of the method were found acceptable by analysis of variance and HorRat repeatability calculations.

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

Assessing 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(R) 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.

Determination of niacin in food materials by liquid chromatography using isotope dilution mass spectrometry.

The availability of deuterium-labeled nicotinic acid makes stable isotope dilution mass spectromerty (MS) coupled with liquid chromatography (LC) an attractive option for the determination of the water-soluble B-vitamin niacin in food samples. A method was developed based on acid digestion, solid-phase extraction with a strong cation exchange column, and reversed-phase chromatography with a C18 column. Detection is by positive ion electrospray MS. Analysis in selected ion recording mode is subject to interference problems similar to those found with other LC determinations of niacin, but the additional selectivity of multiple reaction monitoring mode largely eliminates interference problems. The method was applied to 6 different food matrixes and to appropriate reference materials, including milk samples with niacin levels near 1 ppm. The method exhibited good accuracy, based on levels obtained for the reference materials, and relative standard deviations in the range of 0.5-5%.

Updated estimates of the selenomethionine content of NIST wheat reference materials by GC-IDMS.

Updated estimates of the selenomethionine content of four NIST wheat reference materials have been obtained by use of a revised gas chromatography-stable-isotope dilution mass spectrometric method. The revised method makes use of digestion with methanesulfonic acid, which enables more complete recovery of endogenous selenomethionine than was previously achieved by overnight denaturing treatment in 0.1 mol L(-1) HCl. The NIST wheat reference materials each contain approximately 55% of their total Se content as selenomethionine. Information about forms of Se in reference materials adds value to these materials in Se speciation studies. Estimates of selenomethionine content are also provided for other wheat samples, including several grown under conditions of exposure to high Se levels. These samples also contain approximately 55% of their total Se content as selenomethionine. The consistent level of 55% of total selenium occurring in the form of selenomethionine when the total selenium content varies by a factor of 500 is suggestive of an active mechanism of incorporation of selenium into wheat grain. Figure Selenomethionine content of wheat samples.

Certification of a new selenized yeast reference material (SELM-1) for methionine, selenomethinone and total selenium content and its use in an intercomparison exercise for quantifying these analytes.

A new selenized yeast reference material (SELM-1) produced by the Institute for National Measurement Standards, National Research Council of Canada (INMS, NRC) certified for total selenium (2,059+/-64 mg kg(-1)), methionine (Met, 5,758+/-277 mg kg(-1)) and selenomethionine (SeMet, 3,431+/-157 mg kg(-1)) content is described. The +/-value represents an expanded uncertainty with a coverage factor of 2. SeMet and Met amount contents were established following a methanesulfonic acid digestion of the yeast using GC-MS and LC-MS quantitation. Isotope dilution (ID) calibration was used for both compounds, using 13C-labelled SeMet and Met. Total Se was determined after complete microwave acid digestion based on ID ICP-MS using a 82Se spike or ICP-OES spectrometry using external calibration. An international intercomparison exercise was piloted by NRC to assess the state-of-the-art of measurement of selenomethione in SELM-1. Determination of total Se and methionine was also attempted. Seven laboratories submitted results (2 National Metrology Institutes (NMIs) and 5 university/government laboratories). For SeMet, ten independent mean values were generated. Various acid digestion and enzymatic procedures followed by LC ICP-MS, LC AFS or GC-MS quantitation were used. Four values were based on species-specific ID calibration, one on non-species-specific ID with the remainder using standard addition (SA) or external calibration (EC). For total selenium, laboratories employed various acid digestion procedures followed by ICP-MS, AFS or GC-MS quantitation. Four laboratories employed ID calibration, the remaining used SA or EC. A total of seven independent results were submitted. Results for methionine were reported by only three laboratories, all of which used various acid digestion protocols combined with determination by GC-MS and LC UV. The majority of participants submitted values within the certified range for SeMet and total Se, whereas the intercomparison was judged unsuccessful for Met because only two external laboratories provided values, both of which were outside the certified range.

Selenomethionine contents of NIST wheat reference materials.

Values of the total selenium and selenomethionine (Semet) content of four wheat-based reference materials have been obtained by gas chromatography-stable isotope dilution mass spectrometry methods. The total Se method is an established one, and the results obtained with it are consistent with previously-assigned values. The Semet method (previously reported by our laboratory) is based on reaction with CNBr. Our data indicate that the four wheat samples (wheat gluten, durum wheat, hard red spring wheat, and soft winter wheat), though having a 30-fold range in total Se content, all have about 45% of their total Se values in the form of selenomethionine. Investigation of the CNBr-based method suggests that additional experiments are needed to verify that all selenomethionine in the wheat samples is accounted for, but also indicates that the values obtained are within 15% of the true values. As the form in which Se occurs in foods and dietary supplements is important from a nutritional perspective, adding information about Se speciation to total Se values in appropriate reference materials makes these materials more valuable in relevant analytical work.