Xindong Guo

QuEChERS-based purification method coupled to ultrahigh performance liquid chromatography–tandem mass spectrometry (UPLC–MS/MS) to determine six quaternary ammonium compounds (QACs) in dairy products

QuEChERS-based purification coupled with UPLC-MS/MS method, was developed for six quaternary ammonium compounds (QACs) determination in dairy products. Powder samples were firstly dispersed by water. Protein in liquid milk was precipitated and sample solution was extracted by acetonitrile. QuEChERS-based purification was used to purify the solution. QACs were finally separated by HILIC column and detected in MRM mode of MS/MS under ESI(+). The stable isotope benzyl-2,3,4,5,6-d5-dimethyltetradecylammonium bromide (C14-BAC-d5) was used as an internal standard. This method was validated in terms of linearity, sensitivity, precision, accuracy. Linear relations were favorable for QACs over the selected concentration ranges of 0.2-50μg/L, with correlation coefficients greater than 0.999. The limits of detection (LODs) were in the range of 0.4-14.5μg/kg. Recoveries were between 91.2% and 115% with RSDs of 2.8-7.5% for intra-day precision and 3.7-6.7% for inter-day precision. This validated method was successfully applied to determine the QACs concentrations in dairy products.

A salting out-acetonitrile homogeneous extraction coupled with gas chromatography-mass spectrometry method for the simultaneous determination of thirteen N-nitrosamines in skin care cosmetics.

A sensitive gas chromatography-mass spectrometry method was established for the simultaneous determination of thirteen N-nitrosamines (NAs) in skin care cosmetics. The cosmetics samples were firstly dispersed by water and subsequently extracted and purified using salting out-acetonitrile homogeneous extraction method. Finally, the extracting solution was concentrated by slow nitrogen gas blowing. All of the samples were separated by INNOWAX capillary chromatographic column, and detected by selected ion monitoring (SIM) mode of gas chromatography-mass spectrometry (GC-MS) and quantified by isotope internal standard method. The method was validated for linearity and range, accuracy, precision and sensitivity. Under the optimized condition, the calibration curves were linear over the selected concentration ranges of 2-500μg/L for all the thirteen analytes, with calculated coefficients of determination (R(2)) of greater than 0.996. The limits of detection (LODs) and the limits of quantitation (LOQs) of the method were 3-15μg/kg and 10-50μg/kg, respectively. Recoveries were calculated at three levels of concentration spiked in two kinds of cosmetics (skin care cream and water). The values were found between 93.8% and 121.0% with relative standard deviation (RSD) values of 2.5-7.2% for intra-day precision (n=6) and 3.3-6.7% for inter-day precision (n=5). The method was successfully applied to analyze twenty-two cosmetics samples and N-nitrosodimethylamine (NDMA) was detected in one sample with the concentration of 207μg/kg.

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%.

Determination of three fluorescent whitening agents (FWAs) and their migration research in food contact plastic packaging containers and food simulants by UPLC-MS/MS method

In order to determine three fluorescent whitening agents (FWAs), including FWA184, FWA368 and FWA 393 in migration solutions of food contact plastic packaging containers, a sensitive UPLC-MS/MS method was developed based on the migration tests using food simulants. Under the optimized conditions, the calibration curves were linear over the selected concentration ranges of 0.03–200 μg L−1 for all three analytes, with calculated coefficients of determination (R2) greater than 0.999. The limits of detection (LODs) and the limits of quantitation (LOQs) of the method were 0.01–0.03 μg L−1 and 0.03–0.09 μg L−1, respectively. Recoveries were calculated at three levels of concentration spiked in a negative sample. The values were found between 96.1% and 111.4% with relative standard deviation (RSD) values of 3.0–6.1% for intra-day precision (n = 6) and 2.6–6.4% for inter-day precision (n = 5). The developed method was applied to study the migration trend of target analytes in different migration temperatures and times, and corresponding migration equations with correlation coefficients more than 0.991 were obtained. Finally, the method was successfully applied to analyze migration solutions of twenty samples and FWA184 was detected only in samples with a concentration 0.57 μg L−1 at 25 °C and 0.21 μg L−1 at 5 °C, respectively.

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.

Simultaneous determination of fluorescent whitening agents (FWAs) and photoinitiators (PIs) in food packaging coated paper products by the UPLC-MS/MS method using ESI positive and negative switching modes

A sensitive ultra-high performance liquid chromatography tandem mass spectrometry (UPLC-MS/MS) method was established for the simultaneous determination of fluorescent whitening agents (FWAs) and photoinitiators (PIs) in food packaging coated paper products. Samples were firstly soaked in water and then ultrasonically extracted by using methanol–trichloromethane. The extraction solution was subsequently separated by using a Phenomenex Luna C18 (2) chromatographic column (50 mm × 2.00 mm, 3 μm) using methanol-5 mmol L−1 ammonium acetate as the mobile phase. The target analytes were ionized by the ESI positive and negative switching modes and detected using the multiple-reaction monitoring (MRM) mode. The method was validated for linearity and range, accuracy, precision and sensitivity. Under the optimized conditions, the calibration curves were linear over the selected concentration ranges of 10–1000 μg L−1 and 0.5–50 μg L−1 for four FWAs (FWA28, FWA85, FWA71 and FWA351) and the rest of the ten compounds, respectively, with calculated coefficients of determination (R2) greater than 0.99. The instrument limit of quantitation (ILOQ) and the corresponding method limit of quantitation (MLOQ) of fourteen target analytes were in the range of 0.5–10 μg L−1 and 6–125 μg kg−1, respectively. Recoveries were calculated at three levels of concentration spiked into negative samples and the values were found between 79.2% and 115% with relative standard deviation (RSD) values of 3.2–12.3% for intra-day precision (n = 6) and 4.5–11.5% for inter-day precision (n = 5) 2.5–7.2%. The method was successfully applied to analyse twenty-five food packaging coated paper product samples and FWA184 and 4-MBP were detected in only two samples with the concentrations of 151 μg kg−1 and 32 μg kg−1, respectively.

Dispersive micro solid phase extraction (DMSPE) using polymer anion exchange (PAX) as the sorbent followed by UPLC–MS/MS for the rapid determination of four bisphenols in commercial edible oils

The present work presents a novel and rapid analytical method for the simultaneous analysis of bisphenol A (BPA), bisphenol B (BPB), bisphenol F (BPF) and bisphenol S (BPS) in edible oil based on dispersive micro solid phase extraction (DMSPE) for the first time followed by isotope dilution-ultra high performance liquid chromatography tandem mass spectrometry (UPLC-MS/MS). The edible oil sample was dispersed by n-hexane and extracted with ammoniated methanol-water solution. Then the target analytes were dispersedly absorbed using the polymer anion exchange (PAX) as the sorbent and eluted by acidic methanol. After that, four bisphenols were separated on a C18 column by gradient elution with methanol and 0.05% ammonium hydroxide in water as mobile phase, detected by MS/MS under multiple reactions monitoring (MRM) mode and quantified by internal standard method. The PAX amounts, adsorption time, concentrations of formic acid in the elution solvent and volume of elution solvent for the DMSPE technique were optimized. The limit of detection and quantitation (LOD and LOQ), matrix effect, recovery and precision of the developed method were investigated. Results indicated that BPS and the rest three bisphenols displayed excellent linearity in the concentration ranges of 0.1-50μg/L and 0.5-250μg/L, respectively, with correlation coefficients (R2) all larger than 0.998. Achieved MLODs (S/N=3) varied between 0.1-0.4μg/kg for all bisphenols. The mean recoveries at three spiked levels in edible oil were in the range of 87.3-108%. Intra-day precision (n=6) and inter-day precision (n=5) were <9% and <11%, respectively. This method is of rapid-and-simple pretreatment, accurate and sensitive, and suitable for the simultaneous determination of bisphenols in edible oil.