Donghui Luo

The application of stable isotope ratio analysis to determine the geographical origin of wheat.

In this work, in order to discriminate the geographical origin of wheat, δ(13)C and δ(15)N values of 35 wheat samples originated from different regions were determined, using the method of element analyser-stable isotope ratio mass spectrometry. The results indicated that wheat from Australia, the USA, Canada and China could be potentially discriminated by using analyte δ(13)C and δ(15)N. δ(13)C values of wheat were ranged from -25.647‰ to -22.326‰, the δ(15)N values of 35 wheat samples were calculated between 1.859‰ and 7.712‰. Moreover, the results illustrated regional distributions of δ(15)N values of wheat as Australia>The USA>Jiangsu province of China>Shandong province of China>Canada. So δ(13)C and δ(15)N analysis would be potentially useful for rapid and routine analyses of geographical origin of wheat, even the cereal grains. In order to confirm the discrimination capability of δ(13)C and δ(15)N, a follow-up work will use this method to analyse a larger set of samples.

Geographical origin of cereal grains based on element analyser-stable isotope ratio mass spectrometry (EA-SIRMS).

The stable carbon and nitrogen isotopic compositions (δ(13)C and δ(13)N) of different cereal grains from different regions were determined, using element analyser-stable isotope ratio mass spectrometry (EA-SIRMS) as the key method. Systematically, δ(13)C and δ(13)N of 5 kinds of cereal grains of different origins, 30 wheat samples from different cultivation areas and 160 rice samples of different cultivars from Guangdong province of China were examined. The results indicated that the δ(13)C values of rice, soybean, millet, wheat and corn were significantly (P < 0.05) different within different origins (Heilongjiang, Shandong and Jiangsu province of China), respectively, while δ(13)N values were not. Interestingly, there exists discrimination between these 5 kinds of cereals grains, no matter C-3 or C-4 plants. Further study showed that the δ(13)C values of wheat from Australia, the USA, Canada, and Jiangsu and Shandong province of China were also significantly (P < 0.01) different. Furthermore, the P-value test for 160 rice samples of 5 cultivars was not significant (P > 0.05), which indicated that the cultivar of cereal grains was not significant based on δ(13)C value. Thus, the comparison of δ(13)C would be potentially useful for rapid and routine discrimination of geographical origin of cereal grains.

Adulteration Identification of Commercial Honey with the C-4 Sugar Content of Negative Values by an Elemental Analyzer and Liquid Chromatography Coupled to Isotope Ratio Mass Spectroscopy.

According to the AOAC 998.12 method, honey is considered to contain significant C-4 sugars with a C-4 sugar content of >7%, which are naturally identified as the adulteration. However, the authenticity of honey with a C-4 sugar content of <0% calculated by the above method has been rarely investigated. A new procedure to determine δ(13)C values of honey, corresponding extracted protein and individual sugars (sucrose, glucose, and fructose), δ(2)H and δ(18)O values, sucrose content, and reducing sugar content of honey using an elemental analyzer and liquid chromatography coupled to isotope ratio mass spectroscopy, was first developed to demonstrate the authenticity of honey with a C-4 sugar content of <0%. For this purpose, 800 commercial honey samples were analyzed. A quite similar pattern on the pentagonal radar plot (isotopic compositions) between honey with -7 < C-4 sugar content (%) < 0 and 0 < C-4 sugar content (%) < 7 indicated that honey with -7 < C-4 sugar content (%) < 0 could be identified to be free of C-4 sugars as well. A very strong correlation is also observed between δ(13)C honey values and δ(13)C protein values of both honey groups. For the δ(18)O value, the C-4 sugar content (%) < -7 group has lower (p < 0.05) values (16.30‰) compared to other honey, which could be a useful parameter for adulterated honey with a C-4 sugar content (%) < -7. The use of isotopic compositions and some systematic differences permits the honey with a C-4 sugar content of <0% to be reliably detected. The developed procedure in this study first and successfully provided favorable evidence in authenticity identification of honey with a C-4 sugar content of <0%.

Hydrogen (2H/1H) Combined with Carbon (13C/12C) Isotope Ratios Analysis to Determine the Adulteration of Commercial Honey

In this study, δ2H values of honey were detected and then applied to the identification of honey adulteration. In the meantime, δ13C values of honey, its protein fraction, and individual sugar (glucose and fructose) were also determined by EA-IRMS and LC-IRMS, which combined with δ2H values of honey, have been developed to improve isotopic methods devoted to the research of honey authenticity. For this purpose, 58 Chinese commercial honey samples from various origins were analyzed. The results indicated that the ranges of δ13Choney and δ13Cprotein of these samples were from −28.833 to −10.886 ‰ and −28.327 to −21.632 ‰, respectively. Interestingly, a very strong correlation was observed between δ13Choney value and δ13Cprotein value of pure honey. Moreover, δ2H values of the honey samples were calculated between −156.725 and −170.029 ‰. The comprehensive procedure has advantages over existing methods in terms of time and sensitivity.

Multi-Element (C, N, H, O) Stable Isotope Ratio Analysis for Determining the Geographical Origin of Pure Milk from Different Regions

In order to identify the geographical origin of pure milk, different proteins and milk water were extracted from pure milk originated from Australia and New Zealand, Germany and France, the USA, and China. Then, δ13C and δ15N values of the extracted proteins and δ2H and δ18O values of milk water were determined by element analyzer-isotope ratio mass spectrometry (EA-IRMS). The results indicated that pure milk from these regions could be potentially discriminated by using analyte δ13C, δ15N, δ2H, and δ18O. The P value analysis of them was highly significant (P < 0.01) considering the origins. 3D distribution of δ13C, δ15N, δ2H, and δ18O can also clearly present regional concentration phenomena according to the regions of pure milk. Therefore, it can be concluded that δ13C, δ15N, δ2H, and δ18O analysis could potentially be rapid and routine for origin discrimination of pure milk.

Application of QuEChERS-based purification coupled with isotope dilution gas chromatography-mass spectrometry method for the determination of N-nitrosamines in soy sauce

A sensitive and rapid method involving an improved approach called the quick, easy, cheap, effective, rugged, and safe (QuEChERS) purification method and isotope dilution gas chromatography-mass spectrometry (GC-MS) was established to determine six N-nitrosamines (NAs) in soy sauce. Samples were firstly extracted by ethyl acetate. Then the extraction solution was concentrated by slow nitrogen gas blowing and subsequently purified using the QuEChERS-based purification method. Separation of six target NAs was performed on an INNOWAX polar capillary chromatographic column. All of the samples were detected by selected ion monitoring (SIM) mode of GC-MS and N-nitrosodimethylamine-d6 (NDMA-d6) and N-nitrosodipropylamine-d14 (NDPA-d14) were used as internal standards. The developed method was validated in terms of the linearity, limit of detection (LOD), matrix effects, specificity, accuracy and precision. Results indicated that this method is of good specificity with almost negligible matrix effects. Linear relations of six NAs were favourable in the range of 2.0–200 μg L−1 and the correlation coefficients were greater than 0.9994. The LODs were lower than 1 μg kg−1 (0.4–0.9 μg kg−1) and the limits of quantitation (LOQs) of the method were within the range of 1.2–3.0 μg kg−1. The mean recoveries for negative light and dark soy sauce samples at three spiked concentration levels were in the range of 80.2–112% with overall relative standard deviation (RSD) values (n = 6) of 2.5–6.8%. The validated method was simple and rapid, with good repeatability, and was successfully applied to determine the concentrations of NAs in soy sauce.

Simultaneous determination of 11 restricted dyes in cosmetics by ultra high-performance liquid chromatography/tandem mass spectrometry

A simple, fast, and sensitive method was developed for the simultaneous determination of 11 restricted water-soluble colorants (including Tartrazine, Amaranth, Ponceau 4RC, Sunset Yellow, Allura Red AC, Acid Red 2G, Ponceau SX, Brilliant Blue FCF, Orange I, Acid Black 1, and Acid Orange 7) in eye shadow, lipstick, lip gloss, and other cosmetics by using ultra-high performance liquid chromatography/tandem mass spectrometry (UPLC–MS/MS). The conditions of sample preparation and separation were optimized. The UPLC separation was performed on a UPLC HSS T3 column with acetonitrile-water as the mobile phase. The results showed that the 11 investigated dyes displayed good peak shape within 4 min. The linear ranges were between 0.1 and 50 μg L−1, and the linear correlation coefficients were high (≥0.9942). The limits of quantification were in the range of 4.1–100 μg kg−1. Dyes that spiked in eye shadow, lipstick, and lip gloss in the range of 0.005–2.0 mg kg−1 were tested in terms of sensitivity, repeatability, and recovery. Recoveries obtained for the dyes ranged from 81.6% to 118.2%. Intraday and interday precisions (relative standard deviations) were less than 8%. The results confirmed that UPLC–MS/MS method could be a fast and quantitative technique for the simultaneous determination of restricted dyes in cosmetics.

Dispersive Liquid-Liquid Microextraction Combined with Ultrahigh Performance Liquid Chromatography/Tandem Mass Spectrometry for Determination of Organophosphate Esters in Aqueous Samples

A new technique was established to identify eight organophosphate esters (OPEs) in this work. It utilised dispersive liquid-liquid microextraction in combination with ultrahigh performance liquid chromatography/tandem mass spectrometry. The type and volume of extraction solvents, dispersion agent, and amount of NaCl were optimized. The target analytes were detected in the range of 1.0–200 µg/L with correlation coefficients ranging from 0.9982 to 0.9998, and the detection limits of the analytes were ranged from 0.02 to 0.07 µg/L (S/N = 3). The feasibility of this method was demonstrated by identifying OPEs in aqueous samples that exhibited spiked recoveries, which ranged between 48.7% and 58.3% for triethyl phosphate (TEP) as well as between 85.9% and 113% for the other OPEs. The precision was ranged from 3.2% to 9.3% (n = 6), and the interprecision was ranged from 2.6% to 12.3% (n = 5). Only 2 of the 12 selected samples were tested to be positive for OPEs, and the total concentrations of OPEs in them were 1.1 and 1.6 µg/L, respectively. This method was confirmed to be simple, fast, and accurate for identifying OPEs in aqueous samples.

Determination of total maleic acid, fumaric acid, p-hydroxybenzoic acid and benzoic acid in food by ultra performance liquid chromatography-tandem mass spectrometry

Hydrolysis reaction coupling to ultra performance liquid chromatography-triple quadrupole tandem mass spectrometry (UPLC-MS/MS) was applied for the determination of total maleic acid, fumaric acid, p-hydroxybenzoic acid and benzoic acid in milk-based infant formula, soy-based infant formula, beef jerky, starch and cake. Samples were hydrolyzed by sodium hydroxide and then acidified. The hydrolysis solution was then precipitated by acetonitrile. After being centrifuged, a part of the supernatant was blown dry by nitrogen gas and then dissolved in water for testing. The testing solution was separated by a reverse phase column and then detected by triple quadrupole tandem mass spectrometry operated in a multiple-reaction-monitoring mode. Matrix-matched calibrations were used for quantification. Methyl esters of the acids were used to optimize the influential parameters of the hydrolysis reaction. The matrix effects of the samples on the four acids ranged from 45.7% to 157%. Most of the recoveries at the 50 mg kg−1 and 200 mg kg−1 levels were from 74.6% to 129%, with relative standard deviations ranging from 3.5% to 21%. The limits of detection ranged from 1.0 mg kg−1 to 10.0 mg kg−1. Fifty samples from the local market were tested.

Recent Developments in Application of Stable Isotope and Multi-element Analysis on Geographical Origin Traceability of Cereal Grains

With the development of cereal grain market and convenient transportation of food all over the world, the potential for distribution of mislabeled products increases accordingly, highlighting the need of consumers pursuing for high-quality cereal grains with a clear geographical origin identity. Appropriate analytical methods to ensure a fair competition among producers and to protect consumers against fraud are extremely required. Currently, stable isotope ratio analysis and multi-element analysis gradually become the promising approaches for cereal grain traceability. In recent years, a growing number of research papers have been published on tracing cereal grains by stable isotope ratio and multi-element analysis combining with other instruments. In these reports, the global variety of stable isotope compositions has been investigated, including light elements such as C, N, H, O, and S, and heavy isotopes variation such as Sr and B; in addition, more than 50 elements were applied in the geographical origin analysis of cereal grain and favorable results were obtained. In the present paper, an overview about geographical origin traceability of cereal grain by stable isotope ratio analysis and multi-element analysis is provided.