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Chinese Journal of Chromatography
2021, Vol. 39, No. 11
Online: 08 November 2021

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Recent research highlights of metabolomics analysis methods based on nanoelectrospray direct-infusion mass spectrometry GUO Yinlong 2021, 39 (11):  1149-1150.  DOI: 10.3724/SP.J.1123.2021.08026 Abstract ( 132 )   HTML ( 217 )   PDF (824KB) ( 100 )

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Determination of two quaternary ammonium salts in disinfector by portable capillary electrophoresis device based on smartphone WANG Yuanyu, ZHANG Ruihua, ZHANG Qiang, CAO Chengxi, FAN Liuyin, LIU Weiwen 2021, 39 (11):  1151-1156.  DOI: 10.3724/SP.J.1123.2021.04030 Abstract ( 149 )   HTML ( 47 )   PDF (1572KB) ( 83 )   The existing miniature capillary electrophoresis (CE) devices use a tablet or a computer for data processing and analysis, which hinders their portability. In order to solve this problem, a smartphone-based CE device was proposed, which allowed for real portable quantitative analysis. The device integrated the functions of capacitively coupled contactless conductivity detection (C4D) and Bluetooth communication. Furthermore, a Kotlin language-based application with a user-friendly interface was developed. The application could not only control the electrophoresis run in the CE device but also receive the data from the C4D detector in real time, display the electrophoretogram, and process the data. The peak areas could be calculated automatically on the smartphone, and the migration time could be obtained. The size of the developed device was 20 cm×20 cm×15 cm, and its weight was 2 kg. Quaternary ammonium salts (QAs) in disinfectors (dodecyl dimethyl benzyl ammonium bromide (DDBAB) and dodecyl trimethyl ammonium bromide (DTAB)) were used as the analytes to verify the performance of the developed device. The experimental data showed that the linear ranges of DDBAB and DTAB were from 20 to 1000 and from 30 to 1000 μmol/L, respectively. The correlation coefficients (R2) of DDBAB and DTAB were 0.9995 and 0.9989, respectively, indicating good linearity between the peak area and concentration. The limits of detection (LODs) of DDBAB and DTAB were 10 and 13 μmol/L, respectively. The intra-day relative standard deviations (RSDs, n=3) of DDBAB and DTAB were 1.9% and 2.7% respectively, revealing good repeatability. In addition, a mixture of DDBAB and DTAB was tested. Two QAs were separated within 8 min, showing good selectivity. Finally, QAs in a bromo geramine disinfector used in the field were tested to further validate the performance of the designed device. The recoveries of DDBAB and DTAB were 100.5%-101.5% and 96.2%-99.3%, respectively, indicating good accuracy. The developed device has the advantages of good linearity, low LOD, good repeatability, high accuracy, and real portability, and it can be used for the quantitative detection of QAs in disinfectors.

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Research progress in the application of external field separation technology and microfluidic technology in the separation of micro/nanoscales CUI Jiaxuan, LIU Lu, LI Donghao, PIAO Xiangfan 2021, 39 (11):  1157-1170.  DOI: 10.3724/SP.J.1123.2020.12032 Abstract ( 98 )   HTML ( 31 )   PDF (9139KB) ( 55 )   The micro/nanoscales concerns interactions of entities with sizes in the range of 0.1-100 μm, such as biological cells, proteins, and particles. The separation of micro/nanoscales has been of immense significance for drug development, early-stage cancer detection, and customized precision therapy. For example, in recent years, rapid advances in the field of cell therapy have necessitated the development of simple and effective cell separation techniques. The isolation technique allows the collection of the required stem cells from complex samples. With the development of materials science and precision medicine, the separation of particles is also critical. The key physicochemical properties of micro/nanoscales are highly dependent on their specific size, shape, functional group, and mobility (based on the charged characteristics), which control their performance in the separation system. The current demand has made the simultaneous innovation of a separation system and an on-line detection platform imperative. Accordingly, various analytical methods involving the use of external forces, such as the flow field, magnetic field, electric field, and acoustic field, have been used for micro/nanoscales separation. Based on the physical and chemical parameters of the separation materials, these analytical methods can select different external force fields for micro/nanoscales separation, enabling real-time, accurate, efficient, and selective separation. However, at present, most of the applied field separation technologies require complex equipment and a large sample amount. This makes it crucial to miniaturize and integrate separation technologies for low-cost, rapid, and accurate micro/nanoscales separation. Microfluidic technology is a representative micro/nanoscales separation technology. It requires only a small volume of liquid, making it cost-effective; its high throughput enables continuous separation and analysis; its fast response in a microchip can allow many reactions; and finally, the miniaturization of the device allows the coupling of multiple detectors with the microchip. With the continuous growth and progress of microfluidic technology, some microfluidic platforms are now able to achieve the non-destructive separation of cells. They also enable on-line detection, offer high separation efficiency, and allow rapid separation for different biological samples. This review primarily summarizes recent advances in microfluidic chips based on flow field, electric field, magnetic field, acoustic field, and field separation technologies to improve the micro/nanoscales separation efficiency. This review also discusses the various external force fields of micro/nanoscales, such as a microparticle, single cell separation of substances classified introduction, and summarizes the advantages and disadvantages of their application and development. Finally, the prospect of the combined application of external field separation technology and microfluidic technology in the early screening of cancer cells and for precise micro/nanoscales separation is discussed, and the advantages and potential applications of the combined technology are proposed.

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Preparation of liquid crystal-based molecularly imprinted monolith and its molecular recognition thermodynamics WEI Qin, CHEN Xiuxiu, BAI Lihong, ZHAO Liang, HUANG Yanping, LIU Zhaosheng 2021, 39 (11):  1171-1181.  DOI: 10.3724/SP.J.1123.2021.01017 Abstract ( 77 )   HTML ( 21 )   PDF (989KB) ( 43 )   Molecularly imprinted polymers (MIPs) incorporated with liquid crystalline monomers can imprint and recognize templates at a very low level of crosslinking, thus addressing challenges associated with conventional MIPs, such as the embedding of the imprinted sites, low binding capacity, and slow mass transfer due to the high degree of crosslinking. Compared with traditional MIPs, the prepared MIPs have a greater number of easily binding sites, which can effectively overcome the embedding and low utilization of imprinting sites. Simultaneously, with a decrease in the level of chemical crosslinking, the mass transfer of template molecules can be significantly improved. However, the imprinting effect of liquid crystalline MIPs is generally weaker than that of traditional MIPs due to the low degree of crosslinking. Therefore, to obtain liquid crystalline MIPs with a good imprinting effect, a series of low-crosslinked liquid crystalline molecularly imprinted monoliths were prepared by graft polymerization and evaluated by high performance liquid chromatography (HPLC) to systematically determine the relation between the polymerization parameters and the affinity of the resulting liquid crystalline MIPs. In this experiment, trimethylolpropane trimethacrylate (TRIM) was used to synthesize a monolithic column skeleton with toluene and dodecyl alcohol as porogens. (S)-Naproxen was used as a template and liquid crystalline monomer 4-(4-cyanophenyl)-cyclohexyl ethylene (CPCE) was added for grafting to synthesize the liquid crystalline MIP monolith. The influence of the acetonitrile content and pH in the mobile phase on the chromatographic retention of the template molecule was investigated. The results showed that the main force of MIP recognizing naproxen changed from hydrogen bonding to hydrophobic interaction by the addition of the liquid crystalline monomer. Frontal analysis and adsorption isotherm fitting, including Langmuir, Freundlich, and Scatchard fitting, showed that when the crosslinking degree was 15%, the liquid crystalline MIPs exhibited the highest imprinting factor and heterogeneity, and the specific adsorption was stronger than non-specific adsorption. By analyzing the stoichiometric displacement model, the total affinity of the MIP monoliths for the template molecules (ln A) was determined to be 0.645, significantly higher than that of its analogues, indicating that the liquid crystalline imprinted monolith had a higher total affinity for the template molecule. The spatial matching degree (nβ) of the template molecule to the cavity structures of MIPs was also very high, and only inferior to that of ketoprofen. Nevertheless, the ln A value of ketoprofen was only 0.242, which indicated that the spatial effect was not the key factor in determining the recognition ability of liquid crystalline imprinting systems. An analysis of the separation thermodynamics revealed that the separation of the liquid crystalline MIPs was an entropy-controlled process, while that of conventional liquid crystalline-free MIPs was an enthalpy-controlled process. Based on the above results, the addition of a liquid crystalline monomer may alter the recognition mechanism of MIPs, and an appropriately low crosslinking degree can significantly improve the recognition performance of liquid crystalline MIPs, paving the way for a new generation of MIPs.

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Precise identification of O-linked β-N-acetylglucosamine peptides based on O-mesitylenesulfonylhydroxylamine elimination reaction GUO Zhixin, LI Hang, QIN Weijie 2021, 39 (11):  1182-1190.  DOI: 10.3724/SP.J.1123.2020.12024 Abstract ( 116 )   HTML ( 27 )   PDF (2237KB) ( 59 )   Supporting Information O-linked β-N-acetylglucosamine (O-GlcNAc), an important post-translational modification of proteins, plays an essential role in maintaining normal biological activities of organisms. Studies have shown that the disruption of O-GlcNAc homeostasis is closely associated with various human diseases. Therefore, large-scale enrichment and identification of O-GlcNAc proteins is important for exploring diagnostic biomarkers of clinical diseases. O-GlcNAcylation is substoichiometric, and its glycosidic bond is unstable; hence, the enrichment and identification of O-GlcNAc proteins remains a challenge. Recently, metabolic labeling technology with per-O-acetylated unnatural monosaccharides has been introduced to enrich O-GlcNAc proteins or peptides in cells. However, azidosugars can also react with the thiol group of cysteine to form cysteine thiol-azidosugar artificial modification as a byproduct in cell metabolism, which interferes with the identification of O-GlcNAc proteins or peptides. Therefore, the development of a methodology for the specific and complete removal of cysteine thiol-azidosugar artificial modification is necessary. O-Mesitylenesulfonylhydroxylamine (MSH) is an oxidizing and aminating reagent with great potential to oxidatively eliminate the cysteine thiol modification to dehydroalanine. Hence, it is worthwhile to probe whether MSH can eliminate cysteine thiol-azidosugar artificial modification. Two cysteine thiol-azidosugar artificial modifications were synthesized successfully by incubating thiol standard peptides with tetraacetylated N-azidoacetylgalactosamine (Ac4GalNAz) in sodium carbonate buffer (200 mmol/L, pH 10) at 37 ℃ for 90 min. Then, the reaction conditions for MSH oxidative elimination were optimized to completely remove cysteine thiol-azidosugar artificial modification. Sodium phosphate buffer (50 mmol/L, pH 8.0) was selected to protect the O-GlcNAc modification due to its mild nature. After extensive investigation, the optimized reaction conditions were established as 95 ℃ (reaction temperature) and 30 min (reaction time). Both cysteine thiol-azidosugar artificial modifications could be removed completely under these conditions. Furthermore, two azide-labeled O-GlcNAc (N3-O-GlcNAc) peptides were used to assess whether MSH destroyed the O-GlcNAc modification at the same time. The results showed that the two N3-O-GlcNAc peptides were stable after treatment with MSH at 95 ℃ for 30 min. In short, with excess MSH, the N3-O-GlcNAc peptides were stable, but the cysteine thiol-azidosugar artificial modification was exhausted in sodium phosphate buffer (50 mmol/L, pH 8.0) at 95 ℃ for 30 min. Moreover, both O-GlcNAc modification and cysteine thiol-azidosugar artificial modification exist in cell metabolism. This method can not only remove cysteine thiol-azidosugar artificial modification but also ensure the stability of O-GlcNAc modification. There is growing evidence that O-GlcNAcylation mainly occurs in proteins in the cytoplasm and nucleus, and that most O-GlcNAc proteins are involved in important biological signaling pathways. The nuclear and cytoplasmic proteins incubated with Ac4GalNAz in HeLa cells were selected as a model system. After the nuclear and cytoplasmic proteins were digested into peptides, MSH was applied to remove cysteine thiol-azidosugar modification. In addition, 51 peptides for the elimination of the cysteine thiol-azidosugar artificial modification were identified, indicating that MSH can remove the interference of cysteine thiol-azidosugar artificial modification in cell metabolism. Biotin probe and streptavidin dynabeads were subsequently used to label and enrich N3-O-GlcNAz peptides in cell metabolism. Finally, 157 O-GlcNAc peptides attributed to 130 proteins were identified. To better understand the functional roles of O-GlcNAc proteins, gene ontology analysis was performed. Cell component analysis showed that the identified O-GlcNAc proteins were mainly distributed inpostsynaptic density, cytoplasm, and condensed nuclear chromosome. The proteins were mostly involved in biological processes, including cell division, excitatory postsynaptic potential, and microtubule-based movement. The proteins responsible for transferase activity, transferring acyl groups, histone acetyltransferase activity, and microtubule binding were highly enriched, indicating that O-GlcNAc proteins play important roles in cells. In summary, this work developed an approach to enrich O-GlcNAc peptides precisely in metabolic labeling by removing cysteine thiol-azidosugar artificial modification with MSH. This methodology provides a new strategy for the application of metabolic labeling technology with unnatural monosaccharides in glycoproteomics analysis.

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Proteomic analysis of serum and serum exosomes, and their application in intrahepatic cholangiocarcinoma YANG Kaige, WANG Weiwei, WANG Yan, YAN Chao 2021, 39 (11):  1191-1202.  DOI: 10.3724/SP.J.1123.2021.04009 Abstract ( 239 )   HTML ( 29 )   PDF (5557KB) ( 85 )   Exosomes are extracellular vesicles with a diameter in the range of 50-200 nm and a double-layer lipid membrane structure that are released by various types of cells under normal or abnormal physiological conditions. At present, according to their extensive biological functions, exosomes have been used in a wide range of research fields and applications, including as potential biomarkers and drug delivery vehicles. Intrahepatic cholangiocarcinoma is a malignant tumor of the biliary epithelium with the characteristics of cholangiocellular differentiation, which accounts for 10%-15% of all types of primary liver cancer. Intrahepatic cholangiocarcinoma has no obvious clinical symptoms in the early stages, which results in a low survival rate. Imaging equipment dependent diagnostic methods and currently commonly used diagnostic markers with low sensitivity/specificity have necessitated the development of new specific markers for intrahepatic cholangiocarcinoma. In this study, exosomes were isolated from serum using a commercial kit and characterized through nanoparticle tracking analysis, Western blotting analysis, and transmission electron microscopic analysis to prove the successful isolation of exosomes. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) showed that the protein profiles of the serum and serum exosome samples were significantly different. In particular, some high-abundance proteins in the serum samples were significantly reduced or disappeared in the serum exosome sample. Meanwhile, some protein bands (which may belong to exosomes) that did not appear in the serum samples appeared in the serum exosome samples, leading to the conduciveness of subsequent mass spectrometry analysis. The serum and serum exosome samples of the healthy control and intrahepatic cholangiocarcinoma groups were analyzed by liquid chromatography-mass spectrometry for label-free quantitative proteomics. In total, 547 proteins were identified in the serum exosome samples, of which 341 (more than 60%) could be found in the exosomal protein database. In addition, 271 and 430 credible proteins were screened from the serum and serum exosome samples for multi-dimensional statistical analysis and differential protein discovery. Unsupervised principal component analysis and supervised orthogonal partial least squares discriminant analysis based on the quantitative proteome of the serum and serum exosome samples could distinguish the healthy control and intrahepatic cholangiocarcinoma groups well, which illustrates that the two types of samples both have potential in the diagnosis of intrahepatic cholangiocarcinoma. There were 15 upregulated and 8 downregulated proteins screened in the intrahepatic cholangiocarcinoma group compared to the healthy control group based on the serum samples, while 33 upregulated and 18 downregulated proteins were screened in the intrahepatic cholangiocarcinoma group compared to the healthy control group based on the serum exosome samples, and only four of the differential proteins screened based on the two types of samples were duplicates. At the same time, 35 of the 51 differentially expressed proteins screened based on serum exosome samples belonged to the exosomal protein database. Finally, biological information analysis was performed according to these differential proteins. The molecular functions, biological processes, and signal pathways enriched by these differential proteins mainly involved the innate immune responses, inflammatory responses, and blood coagulation. This study provides a reference value for potential biomarker discovery and exploration of the process of occurrence, development, and metastasis of intrahepatic cholangiocarcinoma. Moreover, compared with proteomic analysis based on serum samples, proteomic analysis based on serum exosome samples can be used to identify more differential proteins and biological information, and although these differential proteins and biological information may show big differences, the specificity and sensitivity of exosome-based diagnosis and the superiority of exosomes as samples for proteomic analysis has proven the application value of exosomes.

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Analysis of metabolite differences in skin between Clapp’s Favorite and its mutant Red Clapp’s Favorite through non-targeted metabolomics MU Hongmei, CI Zhijuan, Aisajan MAMAT, LIANG Yanping, LIU Xiaohong, DU Xiaoyun, YU Qiang, LI Qingyu, LI Yuanjun 2021, 39 (11):  1203-1212.  DOI: 10.3724/SP.J.1123.2021.05002 Abstract ( 137 )   HTML ( 38 )   PDF (3385KB) ( 76 )   Red Clapp’s Favorite is the red mutation cultivar of the pear cultivar Clapp’s Favorite. Fruit color is an important feature of pear fruits, with red skin generally attracting consumers. Anthocyanin, chlorophyll, and carotenoids are the most important pigments in the color formation of fruits. The red color of pear skin is mainly due to the concentration and composition of anthocyanin. Metabolomics is an emerging discipline that focuses on the qualitative and quantitative analysis of small metabolites with low molecular weight in biological cells and tissues. As an important part of systems biology, it is an effective means to solve many complex biological problems. Studies have analyzed pigment content, composition, and differentially expressed genes in the skin of green and red pears from various aspects. Anthocyanins are responsible for physiological activity on regulating pathways. The aim of this study was to discover differential metabolites in the skin of Clapp’s Favorite and its red mutation cultivar Red Clapp’s Favorite. The metabolic components were detected using high-performance liquid chromatography coupled with tandem mass spectrometry (UPLC-MS/MS). Chromatographic experiments were performed on an HSS T3 column (100 mm×2.1 mm, 1.8 μm) by using a mobile phase consisting of 0.1% (v/v) formic acid in acetonitrile and water, and mass spectrometry was conducted in the positive and negative modes by electrospray ionization (ESI). Red Clapp’s Favorite and Clapp’s Favorite were collected from the pear germplasm resource nursery of Yantai Institute of Agricultural Sciences in Shandong. The data were analyzed by principal component analysis (PCA) and orthogonal partial least squares discriminant analysis (OPLS-DA) as well as cluster analysis and heat map. The first two principal components exhibited 62.3% and 8% of the total variance in the positive and negative ion modes, respectively. PCA can generally reflect metabolite differences between the two groups of samples, and there are significant differences in metabolites between the two cultivars. The results showed that PLS-DA clearly distinguishes the two groups of samples, which can be used to analyze the subsequent difference in components. The compounds were identified based on data retrieved from the PMDB databases according to the accurate mass number, secondary fragment, and isotope distribution. The results showed that the metabolite content in the skin of Red Clapp’s Favorite and Clapp’s Favorite were significant. There were 83 different metabolites (P<0.05, variable importance in project (VIP)≥1), including phenols and amino acids, which are involved in flavonoid metabolism, amino acid metabolism, phenyl propanoid biosynthesis, and other metabolic pathways, including 5 polyphenols, 3 flavonoids, 1 amino acid and derivatives, 8 phenylpropanes, 2 anthocyanins, 5 proanthocyanidins, 6 flavanols, 14 flavonols, 2 isoflavones, 13 triterpenoids, 3 organic acids and derivatives, 1 vitamin, 3 organic acids and derivatives, 15 lipids, and 2 other compounds. The chlorogenic acid and crypto-chlorogenic acid in Red Clapp’s Favorite are 2.40 and 3.46 times as much as those in Clapp’s Favorite. The anthocyanins of cornulin 3-glucoside and cornulin 3-galactoside were 10.235 and 9.394 times, respectively. Phenolic epicatechin and catechin increased by 4.689 and 4.635, respectively. The content of phenylpropane 3, 4-dihydroxycinnamic acid in Red Clapp’s Favorite increased by 3.13 times. Among the 83 differential metabolites, 23 metabolites were enriched in the pathway. To display the relationship between the samples and the differences in metabolites among the different samples intuitively, hierarchical clustering and heat map analysis were performed on the metabolite expression levels with significant differences in the enrichment pathways. The Kyoto Encyclopedia of Genes and Genomes database was used to further analyze the pathway enrichment of different metabolites. According to the results, there were 6 metabolic pathways (P<0.05): flavonoid biosynthesis, flavone and flavonol biosynthesis, phenylpropanoid biosynthesis, butanoate metabolism, phenylalanine metabolism, and tyrosine metabolism. Plant secondary metabolism shows a complex diversity. This study would screen out other pathways affecting the biosynthesis of flavonoids, which could provide reference for the further study of biosynthesis and biological function of flavonoids in red fruits. This study provides a useful reference for metabolomics of red pears, which could provide a theoretical reference for the quality analysis and biological function research of pears.

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Determination of plant growth regulators in animal-derived foods using QuEChERS-isotope-labeled internal standards with high performance liquid chromatography-tandem mass spectrometry DAI Wei, LI Qiao, ZHU Ming, LIANG Yixin, CAI Qiu, WANG Mian, LI Jie, LIU Kangshu, WANG Xingning 2021, 39 (11):  1213-1221.  DOI: 10.3724/SP.J.1123.2021.01029 Abstract ( 156 )   HTML ( 37 )   PDF (1448KB) ( 121 )   As among the most widely used pesticides in agriculture, plant growth regulators (PGRs) have a positive influence on plants. However, the overuse of PGRs may induce toxicity in food and even be hazardous to human health. Numerous studies have investigated the presence and residues of PGRs on vegetables and fruits. Animal-derived foods are one of the most dominant food sources providing nutrients to fulfil the daily dietary intake, and could also be potentially contaminated by PGRs. However, there is little information on PGR residues in animal-derived foods. Standardization also lacks among the techniques for PGR determination in animal-derived foods, thereby restricting the further establishment of pesticide usage and food safety regulations. Therefore, in this study, a rapid and effective method for analyzing chlormequat chloride, thidiazuron, and paclobutrazol in animal-derived food samples was established. The method primarily involves high performance liquid chromatography-tandem mass spectrometry combined with the use of isotope-labeled internal standards. The extraction and clean-up procedures were based on the QuEChERS method. The analytes were extracted from pork, beef, chicken, pork liver, egg, and milk samples using acetonitrile, followed by 4 g anhydrous magnesium sulfate (MgSO4), and 1 g sodium chloride (NaCl). The supernatant was removed using a mixture of 50 mg N-propyl ethylenediamine (PSA), 50 mg octadecyl silane (C18), and 150 mg MgSO4, and then passed through a 0.22 μm membrane filter before determination. The Agilent ZORBAX Eclipse Plus C18 column (150 mm×3.0 mm, 1.8 μm) was used to separate the analytes under a gradient elution program, with acetonitrile and 5 mmol/L ammonium acetate solution as mobile phases. The analytes were detected by mass spectrometry using the positive and negative electrospray ionization modes under the multiple reaction monitoring mode. Matrix-matched calibration combined with internal standards was used to quantify the PGRs. The linear regression correlation coefficients (r2) for the PGRs were all greater than 0.990 in the corresponding linear concentration ranges. Chlormequat chloride, thidiazuron, and paclobutrazol showed good linearities in the range of 0.1-100 μg/L for the egg and pork liver samples and 0.1-50 μg/L for the pork, beef, and chicken samples. For the milk samples, thidiazuron and paclobutrazol showed good linearities in the range of 0.05-10 μg/L, while chlormequat chloride showed linearity in the range of 0.05-5 μg/L. The limit of detection (LOD) and limit of quantification (LOQ) for each PGR were based on the signal-to-noise (S/N) ratios. Under optimal conditions, the LODs ranged from 0.01 μg/kg to 0.1 μg/kg, where the LOD was defined as the amount of the tested compound that generated an S/N ratio higher than 3. In addition, the LOQs were in the range of 0.5-5 μg/kg, with an S/N ratio higher than 10. The precision and accuracy were evaluated by recovery experiments. At the LOQ, twice the LOQ, and 10 times the LOQ, the mean recoveries were in the range of 70.0%-117.4%, and the relative standard deviations (RSDs) ranged from 0.8% to 16.1%. The results indicated that the proposed method is accurate and reliable. This method is a modification of the QuEChERS method, and is advantageous owing to its simplicity and high sensitivity. The use of matrix-matching calibration curves and internal standards can eliminate matrix interference, thereby increasing the accuracy of the method. This method satisfies the testing requirements for chlormequat chloride, thidiazuron, and paclobutrazol residues in animal-derived foods, and is promising for the determination of other PGRs or other types of pesticides in animal-derived foods.

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Determination of 40 dyes in oxidative hair dye products by high performance liquid chromatography ZUO Xue, DI Zheng, DU Yong, YANG Ling, ZHANG Rong, WU Guoqing 2021, 39 (11):  1222-1229.  DOI: 10.3724/SP.J.1123.2020.11020 Abstract ( 218 )   HTML ( 36 )   PDF (915KB) ( 141 )   Oxidative hair dye products have always been one of the key concerns in cosmetic supervision. The various aromatic amine and phenol dyes used in such products have different degrees of sensitization and toxicities. Therefore, it is necessary to establish a rapid and accurate method for the determination of various dyes. A high performance liquid chromatography (HPLC) method was developed for the determination of 40 dyes in oxidative hair dye products, and the method was optimized in terms of mobile phase type, column temperature, detection wavelength, and extraction solvent concentration. The sample pretreatment method was as follows: weighed 0.5 g sample accurately, added to 10 mL of sodium bisulfite solution containing 70% ethanol, extracted by ultrasonication for 15 min, added to 25 mL of the sodium bisulfite solution. Chromatographic separation was carried out on a Waters Atlantis® T3 MV Kit column (250 mm×4.6 mm, 5 μm) by gradient elution. To protect the column, the sample solution was filtered using a syringe filter with a 0.45-μm membrane before injection. The mobile phase was 0.02 mol/L ammonium acetate aqueous solution (containing 4% acetonitrile) and acetonitrile. The column temperature was varied between 30 ℃ and 35 ℃ during the separation. The dyes were detected using a photodiode array detector. The detection wavelength of 31 dyes was 235 nm, and that of the other nine dyes was 280 nm. The external standard method was used for quantitative analysis. The results showed that the 40 dyes could be separated well. All the dyes had good linearities in their own concentration ranges, with correlation coefficients (r) exceeding 0.999. The limits of detection (LODs) of the 40 dyes ranged from 5 to 168 μg/g, and the limits of quantification (LOQs) ranged from 16 to 504 μg/g. The average spiked recoveries at three levels (2.5, 5.0, and 10 mg/g) of the 40 dyes ranged from 81.4% to 109.6%, with relative standard deviations (RSDs) less than 5%. The stability of each dye in the standard solutions was good within 24 h, with RSDs ranging from 0.2% to 2.2%. To demonstrate the applicability of the method, 12 batches of commercial oxidative hair dye products from different manufacturers were analyzed. In total, 24 kinds of dyes were detected in the 12 batches of samples, and the contents of these dyes ranged from 0.01% to 2.83%. The method greatly increased the types of dyes detected by a single chromatography step, especially the permitted dyes (36 types). Compared with the standard method of Safety and Technical Standards for Cosmetics (2015 edition), this method replenished 13 permitted dyes: 1-hydroxyethyl 4,5-diaminopyrazole sulfate, hydroxyethyl-p-phenylenediaminesulfate, tetraaminopyrimidine sulfate, 2,6-dihydroxyethylaminotoluene, 2-amino-6-chloro-4-nitrophenol, 2-methyl-5-hydroxyethylaminophenol, 3-nitro-p-hydroxyethylaminophenol, 4-hydroxypropylamino-3-nitrophenol, 5-amino-4-chloro-o-cresol, 5-amino-6-chloro-o-cresol, HC yellow No. 2, hydroxybenzomorpholine, and hydroxyethyl-2-nitro-p-toluidine. The sensitivity and accuracy of the results could ensure and the detection efficiency could be improved through validation of the method. The developed method is suitable for the determination of various dyes in oxidative hair dye products and can provide an effective technical means for the supervision of such products.

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Prediction of n-octanol/water partition coefficient of strongly ionized compounds by ion-pair reversed-phase liquid chromatography with silica-based stationary phase LIU Xiaolan, GAO Wei, LIANG Chao, QIAO Junqin, WANG Kang, LIAN Hongzhen 2021, 39 (11):  1230-1238.  DOI: 10.3724/SP.J.1123.2021.02005 Abstract ( 102 )   HTML ( 20 )   PDF (940KB) ( 60 )   The n-octanol/water partition coefficient (log P) is an important parameter to characterize the overall hydrophobicity of organic compounds. Reversed-phase liquid chromatography (RPLC) has been recommended as an effective method for the indirect determination of log P by the Organization for Economic Cooperation and Development (OECD). Using RPLC, most studies focus on the determination of log P or the apparent n-octanol/water partition coefficient (log D) of neutral compounds and weakly ionized compounds. However, the experimental log P or log D values of strongly ionized compounds have rarely been reported. In our previous work, the experimental log D of strongly ionized compounds could be determined well by ion-pair reversed-phase liquid chromatography (IP-RPLC) on an octadecyl-poly(vinyl alcohol) column using the log D-log kw-IP model established by different types of model compounds. However, the universality of this strategy for different chromatographic columns has yet to be verified. In this study, the retention behavior of neutral compounds, phenolic acids, carboxylic acids, sulfonic acids, and some amphoteric compounds was systematically investigated on a silica-based C18 column (150 mm×4.6 mm, 5 μm) via ion-suppressed RPLC (IS-RPLC) and IP-RPLC, respectively. In the IS-RPLC mode, methanol and 20 mmol/L ammonium dihydrogen phosphate buffer (pH 7.0) were used as the mobile phase to perform isocratic elution at different methanol ratios. The log kw values of the test compounds were obtained using the linear solvent strength (LSS) model. Neutral compounds, weakly ionized phenolic acids and benzene carboxylic acids were then used as model compounds to establish the log D-log kw-IS model. The quantitative structure-retention relationship (QSRR) model, including structure-related descriptors like the charge (ne) and Abraham solvation parameters (A and B), exhibited much better correlation than the unary linear regression model between log D and log kw-IS. The log D7.0 (log D under pH 7.0) values of 19 ionized compounds were then determined by the model; the determined compounds were used as model compounds and validation compounds in IP-RPLC. In the IP-RPLC mode, besides methanol and ammonium dihydrogen phosphate buffer, the mobile phase also contained tetrabutylammonium bromide, as an ion-pair reagent. The retention behaviors of all tested compounds conformed well with the LSS model even under IP-RPLC, with a log k-φ linear correlation coefficient (R 2) greater than 0.99. The log D-log kw-IP model was then established using 62 compounds as a mixed model set, including neutral, weakly ionized, and strongly ionized compounds. Similarly, by introducing ne, A, and B, the log D-log kw-IP model showed good linearity, with R 2 greater than 0.94. Comparing the log D-log kw-IP model established on the silica-based C18 column in this work with that established on a poly(vinyl alcohol)-based C18 column in our previous work, ne, A, and B contributed more to the model in this work, indicating there was a greater secondary effect on the silica-based column. To confirm the reliability of the log D-log kw-IP model, three different types of acidic compounds were used as validation compounds. The predicted log D of the three ionic compounds was very similar to that determined by the shake-flask method (SFM)/slow stirring method (SSM) or IS-RPLC method in this work, confirming the reliability of the model. Based on the above results, the log D7.0 values of eight strongly ionized compounds were predicted by IP-RPLC. The findings suggested that IP-RPLC is a promising method to predict the experimental log D of strongly ionized compounds, and that the conventional silica-based C18 column offers more flexible options in log D determination.

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Simultaneous determination of 11 volatile perfluorinated compound precursors in textiles using gas chromatography-triple quadrupole mass spectrometry WANG Chunlan, ZHANG Haixuan, ZHU Li, HU Wangxia, LIN Ziwei 2021, 39 (11):  1239-1246.  DOI: 10.3724/SP.J.1123.2021.01043 Abstract ( 171 )   HTML ( 26 )   PDF (1341KB) ( 100 )   Perfluorinated compounds (PFCs) are persistent organic compounds. PFCs are artificially prepared hydrocarbons in which hydrogen atoms are completely replaced by fluorine. PFCs have excellent thermal stability and chemical stability, high surface activity, and hydrophobic and/or oleophobic properties owing to their exceptionally strong C-F bonds, low polarizability, and weak intermolecular van der Waals interactions. Currently, PFCs and their precursors are widely used in textile production as finishing agents and surfactants. In recent years, increasing attention has been devoted to PFCs and their precursors. In many countries and regions, such as the European Union, Canada, Denmark, and the United States, directives and regulations have been issued to restrict the use of PFCs and their precursors; the number of these compounds in such lists is increasing continuously. Studies have shown that PFCs are hepatotoxic, embryotoxic, reproductive-toxic, neurotoxic, and carcinogenic, and can interfere with the endocrine system, change animal instinct behavior, and potentially induce developmental neurotoxicity in humans, especially in young children. However, there are few established methods for the simultaneous detection of multiple PFC precursors, necessitating the same particularly for textiles. In this study, a method was developed for the simultaneous determination of 11 volatile PFC precursors in textiles using gas chromatography-triple quadrupole tandem mass spectrometry (GC-MS/MS). The target compounds included four fluorotelomer alcohols (FTOHs), three fluorotelomer acrylates (FTAs), two fluorooctane sulfonamides (FOSAs), and two fluorooctane sulfonamide-ethanols (FOSEs). Studies have shown that FTOHs and FTAs are precursors of perfluorocarboxylic acid, and FOSAs are precursors of perfluorooctanesulfonic acid. Some PFC precursors are converted into perfluorocarboxylic acid and perfluoroalkyl sulfonic acid, which threaten human health and ecological security. In this study, an effective ultrasonic-assisted extraction method for the 11 target compounds was established. The effects of the extraction solvent, extraction temperature, and extraction time on the extraction efficiency were investigated. The optimum extraction conditions for the developed method were carrying out ultrasonic extraction at 70 ℃ for 60 min with methanol as the extraction solvent. Separation was performed on a VF-WAXms capillary column (30 m×0.25 mm×0.25 μm) with temperature programming, following which the target compounds were detected by GC-MS/MS in the multiple reaction monitoring (MRM) mode and quantified using the external standard method. The matrix effects of three textile matrices were also investigated. The calibration curves of the 11 volatile PFC precursors showed good linearity in the concentration range of 10-500 μg/L with correlation coefficients not less than 0.9984. The limits of detection were 0.002-0.04 mg/kg (S/N=3), and limits of quantification were 0.006-0.1 mg/kg (S/N=10). The recoveries for the 11 analytes in different textile matrix samples at three spiked levels ranged from 73.2% to 117.2% with relative standard deviations (RSDs) of 0.1%-9.4% (n=6). Through actual sample analysis, four PFC precursors were detected in the textile product samples. The method has the advantages of simple pretreatment, accurate qualitative and quantitative analysis, high sensitivity, and good reproducibility. It can be effectively used for the simultaneous determination of 11 volatile PFC precursors in textiles. The establishment of this method has theoretical and practical significance for controlling PFC precursor levels in textiles. This study offers a new testing method for mitigating risk to safety and controlling textile products. It also provides a reference for establishing testing standards for PFC precursors in textiles and other similar consumer goods.

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Development of an asymmetrical flow field-flow fractionation system for the size characterization of starch granules GUO Yuxi, SONG Tiange, SUN Yushan, YU Qian, DOU Haiyang 2021, 39 (11):  1247-1254.  DOI: 10.3724/SP.J.1123.2021.05001 Abstract ( 136 )   HTML ( 19 )   PDF (3889KB) ( 46 )   Starch occurs naturally in the form of semicrystalline granules, and is composed of two types of carbohydrate molecules, amylose (AM) and amylopectin (AP). Starch granules and starch molecules have sizes in the range of 1-100 μm and 20-250 nm, respectively; these size ranges are among the key factors affecting the functional properties of starch. Asymmetrical flow field-flow fractionation (AF4) is a size-based separation technique. The major difference between AF4 and dynamic light scattering or microscopy techniques is that AF4 enables the separation of particles based on their size; consequently, the elution profile can be converted to the size distribution of the samples. In the last two decades, AF4 systems, when coupled online with multiangle light scattering (MALS) and differential refractive index (dRI) detectors (AF4-MALS-dRI), have demonstrated to be applicable for the size characterization of starch at the molecular level. Unlike size exclusion chromatography (SEC), AF4 systems use an open channel that does not require a stationary phase or packing materials. Thus, the shear scission of AP molecules during AF4 separation is minimized. The size detection range of a commercial AF4 system ranges from 1 nm to 10 μm, which is smaller than the size range of starch granules. In this study, a home-made AF4 system was developed, and its capability for the size characterization of starch granules extracted from sweet potato, lotus seed, and rice was investigated. The performance of the developed AF4 system was evaluated by running a mixture of polystyrene (PS) with diameter of 2, 6, 12, and 20 μm, respectively. Baseline separation of four PS samples was achieved, and the resolution for 6 μm PS and 12 μm PS was 1.40. The detection limit of the developed AF4 system was higher than that of commercial AF4 systems. Thus, the developed AF4 system is promising for the separation and characterization of starch granules. The effect of the composition of the carrier liquid on the AF4 separation of starch granules was also studied. Moreover, the accuracy of AF4 in terms of size characterization of the starch granules was evaluated by optical microscopy (OM). The results revealed that the type of dispersant and viscosity of the carrier liquid affect the accuracy of size characterization of the starch granules. The size distribution of rice starch granules obtained using a carrier liquid containing 0.01% (w/v) sodium dodecyl sulfate (used as a dispersant), 0.02% (w/v) NaN3 (used as a bactericide), and 0.001% (w/v) hydroxypropylmethylcellulose (used to adjust the viscosity of the carrier liquid) was in agreement with that obtained from OM. Furthermore, a commercial AF4 system coupled with MALS and dRI detectors was employed for the separation and characterization of starch molecules. A molecularly dispersed solution is necessary for the reliable molecular characterization of starch. The effect of the starch dissolution temperature on the AF4 characterization of starch was also investigated. The optimal dissolution temperature for lotus seed and rice starch granules was 75 ℃, while that for sweet potato starch granules was 78 ℃; this difference is mainly attributed to the different botanical origins of the granules. The results showed that the ratio of the radius of gyration (Rg) to the hydrodynamic radius (Rh) of rice starch and sweet potato starch is in the range of 0.9-1.1 over the molar mass range of 10 6-108 g/mol. For rice starch, the Rg/Rh ratio is between 1.2 and 1.4. Rice starch has the highest apparent density among the three starches, indicating that rice starch molecules have a dense structure. The results demonstrated that the AF4 system developed in this study is rapid and accurate for the size characterization of starch granules. The developed AF4 system, when combined with commercial AF4 systems coupled online with MALS and dRI detectors, can provide technical support to study the relationship between the size from the nanoscale to the microscale and functional properties of starch.

Technical Notes

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Determination of donkey skin ingredients in Asini Corii Colla by ultra-high performance liquid chromatography-tandem mass spectrometry GONG Liping, SHI Feng, SU Shufang, XIE Qiangsheng, XIAN Ruiqing, HANG Baojian, ZHAO Yanxia 2021, 39 (11):  1255-1260.  DOI: 10.3724/SP.J.1123.2021.02003 Abstract ( 199 )   HTML ( 23 )   PDF (869KB) ( 93 )   In recent years, due to the shortage of donkey skin resources, the price of Asini Corii Colla has seen a rapid increase. Consequently, fake gelatin prepared from horse, mules, pig, and cow skin has appeared in the market, resulting in unreliable quality of Asini Corii Colla. Therefore, there is an urgent need to develop an efficient and accurate method for improving the quality of Asini Corii Colla. Ultra-high performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS) was used to determine the donkey skin components in Asini Corii Colla. Accordingly, 0. l g of the evenly mixed sample was weighed and placed in a 50 mL volumetric flask; then, 1% ammonium bicarbonate solution was added to dissolve the sample, and the solution was diluted to the scale. Precisely 1.00 mL of the solution was extracted into a 5 mL volumetric flask, followed by the addition of 1.0 mL trypsin solution and 100 μL mixed internal standard working solution. This mixture was diluted to the scale using 1% ammonium bicarbonate solution, shaken, and placed in an incubator for 16 h to induce enzymolysis at a constant temperature of 37 ℃. The mixture was subsequently removed from the incubator, cooled to ambient temperature, filtered through a 0.22 μm membrane, and analyzed by LC-MS. Separation was performed on an UPLC system with a BEH C18 column (100 mm×2.1 mm, 2.5 μm) under gradient elution using acetonitrile containing 0.1% (v/v) formic acid (B) and water containing 0.1% (v/v) formic acid (A) as the mobile phases at a flow rate of 0.3 mL/min. The column temperature was 30 ℃, and the sample size was 2 μL. The gradient elution conditions are: 0-1 min, 10%B; 1-5 min, 10%B-30%B; 5-5.1 min, 30%B-70%B; 5.1-7 min, 70%B; 7-7.1 min, 70%B-10%B; 7.1-10 min, 10%B. The marker peptides were determined in positive electrospray ionization (ESI +) and multiple reaction monitoring (MRM) modes using the isotopic internal standard method. The optimized enzymolysis conditions were as follows: enzymolysis temperature, 37 ℃; enzymolysis time, 16 h; and amount of enzyme, 1 mL. The two marker peptides showed good linearities in the range of 50 to 1250 mg/L; the correlation coefficients (r) were greater than 0.996, and the limits of quantitation (S/N=10) were 20 mg/kg. At spiked levels of 300 mg/kg, 600 mg/kg, and 900 mg/kg, the average recovery ratios of the two marker peptides were 103.2% to 108.3%, while the relative standard deviations (RSDs) of 1.0%-3.0%. This method was favorable for testing actual samples. Asini Corii Colla from 29 production companies was detected by this method, and the sum contents of the two marker peptides was different because the production process and raw materials were different. The sum contents of the samples were 0.096% to 0.180% with an average of 0.151%. The developed method is simple, reliable, and reproducible, and it is suitable for detecting the donkey hide components Asini Corii Colla.

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Determination of 197 pesticide residues in edible vegetable oil by gas chromatography-time-of-flight mass spectrometry HOU Jing, CHEN Dan, TU Fengqin, YANG Ming, WANG Mengying, LIU Mengting 2021, 39 (11):  1261-1272.  DOI: 10.3724/SP.J.1123.2020.12008 Abstract ( 159 )   HTML ( 44 )   PDF (4500KB) ( 114 )   An analysis method based on gas chromatography-time-of-flight mass spectrometry (GC-TOF-MS) with single acquisition was established for the simultaneous rapid screening and accurate confirmation of 197 pesticide residues in edible vegetable oil. First, a standard library of the 197 pesticides was established. The library contained GC-TOF-MS information such as retention time, accurate mass measurements of quantitative and quantitative ions, and ratio of the qualitative ion. According to the European Union regulation (SANTE/11945/2015), the standard for qualitative determination by HRMS was determined; that is, each compound was confirmed by at least two ions. Second, the instrument conditions and sample pretreatment conditions for the determination of different pesticides were optimized. The following observations were made: the extraction efficiency of acetonitrile was better than that of acetonitrile containing 0.1% formic acid because pesticide recovery in the former case was in the range of 70%-120%; C18 and PSA adsorbents exerted a better purification effect than did the other two purification materials (C18 and Z-Sep adsorbent or PRiME HLB column), thus ensuring good recovery of the target compounds; most pesticides showed a matrix enhancement effect, necessitating the use of a matrix-matched external calibration method for quantitation. Finally, based on the above findings, the experimental procedure was established. The edible vegetable oil samples were ultrasonically extracted with acetonitrile, and the resultant solution was subjected ot fat removal by freezing at -20 ℃ for 2 h. The supernatant (1.0 mL) was cleaned-up by dispersive solid phase extraction using 50 mg C18 and 50 mg PSA powder. The compounds were separated on an HP-5MS UI capillary column (30 m×0.25 mm×0.25 μm) and ionized using an electron impact ion source. Qualitative and quantitative detection of the pesticides was completed in full scan mode. The retention time, mass accuracy, and qualitative ion matching ratio were used for qualitative screening, while the peak areas of the quantitative ion were used for quantification. The limits of quantification (LOQs) of 174 pesticides were 0.01 mg/kg, and the LOQs of the other 23 pesticides ranged from 0.025 to 0.1 mg/kg. The linear ranges were LOQs to 200 μg/L for 196 pesticides, and from 2 to 100 μg/L for biphenyl, with the correlation coefficients being greater than 0.99. The recoveries of 156 pesticides were in the range of 70% to 120% at three spiked levels (0.1, 0.25, and 0.5 mg/kg), accounting for 79% of the total pesticides. The proposed method was successfully applied to the determination of pesticide residues in 23 edible vegetable oil samples. Chlorpyrifos was detected in all six peanut oil samples. Bromopropylate, fenpropathrin, oxadiazon, permethrin, tebufenpyrad, cyproconazole and pirimiphos-methyl were detected in a fourth-grade rapeseed oil sample. The results demonstrate that the developed method is accurate, reliable, and time-saving. It can be used for the high-throughput screening and quantitative determination of pesticide residues in edible vegetable oil.

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Speculation of hemoglobin A3 peak position in clinical cation exchange high performance liquid chromatogram of the diabetic blood sample with microarray isoelectric focusing GUO Zehua, LUO Fang, LI Si, FAN Liuyin, WU Yixin, CAO Chengxi 2021, 39 (11):  1273-1278.  DOI: 10.3724/SP.J.1123.2020.12033 Abstract ( 97 )   HTML ( 27 )   PDF (1356KB) ( 57 )   Hemoglobin A1c (HbA1c) is a major component of glycated hemoglobin in human red blood cells. It has been proven to be a significant biomarker for the diagnosis of diabetes; its content in fresh red cells in diabetes blood reflects the average level of blood glucose over the previous three months. Thus, HbA1c level has been used for the assessment of long-term glycemic control in diabetes; the level of 6.5% HbA1c has been certified as a critical cut-off for the diabetes diagnosis. The current commonly used method for HbA1c quantification is based on cation-exchange high performance liquid chromatography (CX-HPLC). The method has advantages such as high stability, rapidity, and automation, but there are still some unidentified peaks of Hb species in CX-HPLC (VARIANT Ⅱ system); in particular, the presence of HbA3 (a glutathiolated Hb) affects the accurate determination of HbA1c. HbA3 is usually present in healthy adult blood samples at 2%-4%, but the concentration of HbA3 increases due to the protection of erythrocytes from oxidation, resulting in decreased HbA1c. However, the relative location of the HbA3 peak in the CX-HPLC clinical chromatogram has not been established. To address this issue, we extracted Hb species from fresh blood samples obtained from a hospital in an anaerobic environment to avoid possible redox reactions of Hb and glutathione. After the extraction, the Hb samples were analyzed using two methods: a low-resolution CX-HPLC (5/50 mm column) currently used for diabetes diagnosis and a high-resolution cationic exchange HPLC (Mono-S 5/50 mm column), to identify the peak corresponding to HbA3. The CX-HPLC analysis of fresh blood samples indicated that the unknown peak P3 located between HbA1c and HbA0 peaks corresponded to the HbA3 peak between HbA1c and HbA0 in the Mono-S-HPLC. Microarray isoelectric focusing (IEF) was used for the micro-preparation of HbA3, HbA1c, and HbA0 in healthy blood samples; then, the micro-prepared species of HbA3, HbA1c, and HbA0 were individually identified via Mono-S-HPLC. The results of the CX-HPLC, Mono-S-HPLC, and microarray IEF experiments indicated that the P3 peak might correspond to HbA3. To confirm this, glutathiolated Hb samples were synthesized via acetylphenylhydrazine and analyzed using both the Mono-S- and CX-HPLC systems. The results showed that the content of both glutaminated hemoglobin of HbA3 in Mono-S-HPLC and P3 in CX-HPLC increased, implying the peak of P3 with the retention time of 1.50 min in CX-HPLC was the peak corresponding to HbA3 in Mono-S-HPLC and microarray IEF. Based on the above experiments and our previous results, the influence of HbA3 on both the analysis of HbA1c in blood samples and the diabetes diagnosis needs to be considered and discussed. The study results are significant for the tentative assignment of peak P3 and for offering more information on diabetes diagnosis using CX-HPLC in the clinical setting.