Chinese Journal of Chromatography

2022, Vol. 40, No. 8
Online: 08 August 2022

CN 21-1185/O6
ISSN 1000-8713
Editors-in-Chief: Prof. Yukui Zhang
For Selected: Toggle Thumbnails
Special Columnof Separation and Analysis for Food Safety-Functional Adsorbents
Advances in separation and analysis of aromatic amino acids in food
LU Chenhui, ZHANG Yi, SU Yujie, WANG Wenlong, FENG Yongwei
2022, 40 (8):  686-693.  DOI: 10.3724/SP.J.1123.2022.04011
Abstract ( 17 )   HTML ( 6 )   PDF (1358KB) ( 11 )  

Amino acids are important building blocks of proteins in the human body, which are involved in many metabolic pathways. Patients with metabolic diseases such as phenylketonuria, tyrosinemia, and hepatic encephalopathy are genetically defective and cannot metabolize aromatic amino acids (AAA) in food; hence, a regular diet may lead to permanent physiological damage. For this reason, it is necessary to restrict the intake of AAA in their daily diet by limiting natural protein intake, while ensuring normal intake of low protein foods and supplementation with low-AAA protein equivalents. Sources of low-AAA protein equivalents currently rely on free amino acid complex mixtures and low-AAA peptides (also known as high-Fischer-ratio peptides), which have better absorption availability and palatability. AAA separation and analysis techniques are essential for the preparation and detection of low-AAA peptides. Researchers in this field have explored a variety of efficient adsorption materials to selectively remove AAA from complex protein hydrolysates and thus prepare low-AAA peptide foods, or to establish analysis strategies for AAA. Covering more than 70 publications on AAA removal and separation in the last decade from Web of Science Core Collection and China National Knowledge Infrastructure, this review analyzes the structural characteristics and physicochemical properties of AAA, and summarizes the technological progress of AAA removal based on adsorbents such as activated carbon and resin. The applications of two-dimensional nanomaterials, molecular imprinting, cyclodextrins, and metal-organic frameworks in AAA adsorption and analysis from three dimensions, i. e., sample pretreatment, chiral separation and adsorption sensing, are also reviewed. The mainstream adsorbents for AAA removal, such as activated carbon, still suffer from poor specificity and cause environmental pollution during post-use treatment. Existing AAA separating materials show impressive selective adsorption capability in food samples and chiral mixtures as well as high sensitivity in adsorption sensing. The development of an efficient detection technology for AAA may help in detecting trace AAA in food and in evaluating chiral AAA adulteration in food samples. By exploring the advantages and disadvantages of each type of technology, we provide support for the advancement of the removal and analysis techniques for AAA.

Separation and enrichment of trace aflatoxin B1 in grains by magnetic nanomaterials based on SiO2@Fe3O4
LI Xiaohan, LU Yingying, DONG Yongzhen, JIANG Feng, FAN Zhiyong, PAN Hui, LIU Mingjun, CHEN Yiping
2022, 40 (8):  694-703.  DOI: 10.3724/SP.J.1123.2022.03002
Abstract ( 17 )   HTML ( 7 )   PDF (2883KB) ( 13 )  

In this study, a magnetic nanomaterial antibody (Ab)-SiO2@Fe3O4 was synthesized, which was employed to absorb aflatoxin B1 (AFB1) in complicated grain matrices. The Ab-SiO2@Fe3O4 material was then paired with high performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) for subsequent accurate detection. The Ab-SiO2@Fe3O4 material has a specific adsorption capacity for AFB1 because of the stable and specific biological binding between antigen and antibody. This process can achieve the identification between the material and food matrix quickly, thereby completing the separation and enrichment process. Then, high sensitivity and high accuracy HPLC-MS/MS were employed for signal readout and actual quantification, which can significantly increase the detection efficiency and enable high-throughput detection of numerous samples. In the pretreatment process, Fe3O4 was first synthesized by microwave-assisted hydrothermal synthesis within 1 h, and Ab-SiO2@Fe3O4 was then produced using the enhanced Stober’s approach. This material with high adsorption performance was synthesized under relatively mild conditions and short time. To obtain Ab-SiO2@Fe3O4 materials with uniform particle size, magnetic properties, and dispersibility that met the requirements, synthesis conditions of Ab-SiO2@Fe3O4 and conditions for capturing the AFB1 target were analyzed. The findings demonstrated that the best effect was obtained when the dosage of FeCl3·6H2O was 10.0 mmol, the heating time was 40 min, and 100 μL tetraethoxysilane was employed for SiO2 coating. The AFB1 antibody was then combined with the surface of SiO2@Fe3O4 under several conditions. The findings revealed that the best coupling efficiency of Ab could be obtained when the concentration of 2-morpholinoethanesulfonic acid monohydrate (MES) was 10 mmol/L, pH was 6.5, and the molar ratio of 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride (EDC)∶N-hydroxysuccinimide substances (NHS) was 2∶1. The coupling buffer was then selected as phosphate buffer (PBS) with pH=7.4, and 8 mg Ab-SiO2@Fe3O4 was employed to separate and enrich AFB1 at 37 ℃ for 10 min. In the actual detection, acetonitrile-water-formic acid (85∶10∶5, v/v/v) was employed as the extraction solution. After ultrasonic extraction for 10 min, Ab-SiO2@Fe3O4 was employed to separate and enrich AFB1 in the extract. The supernatant was dried with nitrogen and reconstituted with 1-mL acetonitrile. The solution was then filtered through a 0.22 μm filter and detected using HPLC-MS/MS, thereby realizing the quick and quantitative detection of AFB1. AFB1 had an excellent linear relationship in the range of 2-50 μg/L under the optimal analytical conditions, and the correlation coefficient was less than 0.99. The LOD was 0.04 μg/kg, and the LOQ was 0.13 μg/kg. The spiked recoveries of AFB1 in three grain matrices ranged from 76.21% to 92.85% with RSD≤5.29% at four different spiked levels. The approach was applied to the determination and analysis of AFB1 in 30 real grain samples of rice, corn, and wheat. The findings demonstrated that AFB1 was detected in one wheat sample and two corn samples, and its content was 0.38, 0.13, and 0.47 μg/kg, respectively, and no toxins were found in other samples. The approach combined Ab-SiO2@Fe3O4 magnetic nanomaterials with HPLC-MS/MS, which could obtain high-efficiency separation and enrichment of AFB1. Furthermore, the low-cost Ab-SiO2@Fe3O4 could be stored for more than a week and complete the pretreatment process within 30 min. This effective pretreatment process combined with HPLC-MS/MS could realize the analysis of several samples within a short time, and had a promising application prospect in the detection of AFB1 in grains.

Imine-linked porous covalent organic framework used for the solid-phase extraction of estrogens from honey prior to liquid chromatography-tandem mass spectrometry
LI Hui, REN Gengbiao, LI Huijuan, CHEN Xiangfeng, ZHANG Zhiguo, ZHAO Yanfang
2022, 40 (8):  704-711.  DOI: 10.3724/SP.J.1123.2022.03017
Abstract ( 8 )   HTML ( 11 )   PDF (2119KB) ( 9 )  

This study aimed to establish a method for the rapid determination of trace estrogens in honey samples by high performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) using imine-linked porous covalent organic framework material (IL-COF-1) as the adsorbent for solid-phase extraction (SPE). Estradiol (E1), diethylstilbestrol (DES), estriol (E3), β-estradiol (E2), and ethinylestradiol (EE2) were used as the target analytes. A single factor optimization method was performed to optimize the extraction effect by adding estrogens to honey samples. The optimal conditions were as follows. A total of 30 mg IL-COF-1 was filled in the SPE column. The sample pH was adjusted to 7. The sample was loaded at a flow rate of 3 mL/min and eluted with 5 mL of a 1% (v/v) NH3·H2O-methanol solution. The flow rate of the eluent was 0.4 mL/min. NaCl was not added in the extraction process. HPLC coupled to electrospray ionization and triple quadrupole mass spectrometry was introduced to quantify the estrogens in the extracts. The estrogens were separated on a Thermo Fisher Scientific C18 analytical column (100 mm×2.1 mm, 5 μm). Acetonitrile and 5 mmol/L ammonium acetate solution were used as the mobile phases for gradient elution. The column temperature was set at 40 ℃, and the autosampler temperature was maintained at 10 ℃. The rapid qualitative and quantitative analysis of the five estrogens in the honey samples was operated under multiple reaction monitoring mode in a negative electrospray ion source mode. IL-COF-1 prepared in six batches was used as a filler for the SPE column. The relative standard deviations (RSDs) of the recoveries of the estrogens among different batches were 5.2%-9.1%. The reusability of IL-COF-1 material was assessed. After six SPE cycles on the same solid-phase extraction column, the RSDs of the estrogen recoveries were 2.5%-6.1%, indicating that IL-COF-1 has good reusability. The recoveries of estrogens obtained on an IL-COF-1 solid-phase extraction column within 6 days (tested once a day) were 95.1%-107.4%, and the RSDs were 6.2%-8.9%. These results confirmed that the SPE filler had good stability. The method validation results showed that the linear detection ranges were 1-500 ng/g for E3, E2, and EE2, and 0.1-100 ng/g for E1 and DES withe the correlation coefficients of 0.9934-0.9972. The limits of detection (LODs, S/N=3) were 0.01-0.30 ng/g, and the limits of quantification (LOQs, S/N=10) were 0.05-0.95 ng/g. Five estrogens were added (50 ng/g) for the repeated experiments. The RSDs of the intra-day precision were 3.2%-6.6%. The RSDs of the inter-day precision were 4.2%-7.9%. This method was applied to determine the estrogen levels in four honey samples, and no estrogen was found. The recoveries of the five estrogens in sample spiked at three levels including low, middle, and high levels were investigated, and satisfactory recoveries (80.1%-115.2%) were obtained. The SPE-HPLC-MS/MS method based on IL-COF-1 is rapid, accurate, and sensitive, making it suitable for analyzing and detecting estrogen in honey. Further exploration of the use of IL-COF-1 for the extraction processes is in progress.

Metal-organic framework UiO-67-based enrichment and purification of progesterone residues in milk
SHANG Weiwei, SUO Decheng, LI Tong, DU Qiuling, JIANG Xianhong, WANG Peilong
2022, 40 (8):  712-720.  DOI: 10.3724/SP.J.1123.2022.04002
Abstract ( 15 )   HTML ( 7 )   PDF (2326KB) ( 7 )  

Progesterone functions as an endocrine-disrupting compound. Imitating endogenous hormones disrupt the animals’ hormone levels. The potential hazard of progesterone in milk cannot be neglected. Thus, research has focused on establishing an efficient and convenient pretreatment and analytical approach. In this study, a metal-organic framework (MOF) material UiO-67 was prepared, which possessed a large specific surface area and excellent stability. It was employed to enrich and purify trace progesterones in a complex milk matrix as a filler to integrate the solid phase extraction column. An approach based on MOF was developed using ultra-high performance liquid chromatography-quadrupole/electrostatic field orbitrap high resolution mass spectrometry (UHPLC-Q-Orbitrap HRMS). This approach could simultaneously determine seven kinds of progesterone residues in milk. The element spectra of UiO-67 were first measured and analyzed using X-ray photoelectron spectroscopy. The chemical interaction between UiO-67 and progesterone was proved by comparing the changes in binding energy and relative contents of functional groups, and the adsorption efficiency of 1 mg/L and 5 mg/L progesterones by UiO-67 was studied. The adsorption efficiencies of UiO-67 for 1 mg/L and 5 mg/L progesterones were 99.73%-99.95% and 88.87%-99.23%, respectively, according to the results. It proved the efficient adsorption of UiO-67 to progesterones and ensured that subsequent studies went smoothly. Furthermore, key parameters, such as the amount of sorbent, elution solvent type, and pH value, were examined and optimized to obtain optimal extraction recovery of the progesterones. Spiked concentrations of 50 μg/L were employed for extraction optimization. All experiments were performed three times. It also evaluated the matrix effect on mass spectrum signal of the progesterones. The optimized results showed that the seven progesterones could be satisfactorily recovered when the amount of adsorbent was 40 mg, pH value of the sample solution was 5, and elution solution was 5-mL acetone. Additionally, the matrix effect of progesterone in the milk sample was <20%. The matrix effect could be neglected using the aforementioned approach to extract and purify progesterones in milk. Finally, the seven progesterones showed good linearity between 1 and 100 μg/L under the optimized conditions, with linear correlation coefficients values >0.99. The limits of detection (LODs) ranged from 0.06 to 0.30 μg/L, and limits of quantification (LOQs) ranged from 0.19 to 1.0 μg/L, respectively. At various concentration levels of progesterones in milk, the recoveries were 87.10%-105.58%, with relative standard deviations of 2.66%-9.64%. Most importantly, the approach was successfully employed to determine progesterone levels in milk samples, with results in good agreement with the standard SN/T 1980-2007. The proposed approach had the advantages of high sensitivity and satisfactory accuracy compared with the reported pretreatment and detection approaches of progesterone in milk. Satisfactory experimental results can be obtained without the calibration by isotope inner standard. Meanwhile, considering the excellent performance of MOF materials in reducing matrix interference in complex samples, such the application of materials offers a new approach. It can be employed to enrich and detect hazards in a complex matrix in the future.

One-step rapid enrichment and detection of malachite green in aquaculture water based on metal-organic framework hydrogel
LIU Na, LI Peiyi, SUN Mengmeng, QIN Haiyang, LI Yuanxin, LI Jincheng, LIU Huan, WU Lidong
2022, 40 (8):  721-729.  DOI: 10.3724/SP.J.1123.2022.04019
Abstract ( 12 )   HTML ( 4 )   PDF (3680KB) ( 3 )  

Malachite green is a triphenylmethane compound, which has a good effect on disease prevention and control in the breeding of aquatic products, but it is a prohibited drug because it is detrimental to human health. Owing to the low content of target malachite green and complex components in the actual sample, simultaneously achieving good enrichment, high sensitivity, convenience, and rapidity detecting is difficult. Metal-organic framework (MOF) has a multidimensional network structure, good stability, and large specific surface area, and has broad application prospects in adsorption. However, the small particle size of MOF materials and the difficulty of recycling hinder their development. The hydrogel has a three-dimensional network structure that can encapsulate the MOF nanomaterials in the network, enhancing adsorption performance and facilitating separation from the adsorbed solution. In this study, MOF materials were prepared, and hydrogel doped with MOF nanomaterials (polyacrylamide-sodium alginate/metal-organic framework, PAAM-SA/MOF) was used to investigate the adsorption of malachite green in aquaculture water. The transmission electron microscopy was used to characterize MOF nanomaterials, scanning electron microscopy was used to examine the morphology and structure of the hydrogels before and after adsorption of malachite green, representing the successful synthesis of adsorbent materials with excellent properties. The mechanical properties of the hydrogels were investigated using a tensile testing machine, with a maximum tensile strain of up to 300%, without breaking and failing to remove when separated from the solution to be tested. The pore size of PAAM-SA/MOF hydrogel is considerably smaller than that of PAAM-SA, which is beneficial to increase the specific surface area of the adsorbent and thus improve the adsorption performance.
A series of optimizations were performed on the adsorption conditions of the hydrogel adsorbent and the optimized conditions were obtained as follows: the amount of adsorbent used was 0.1 g, adsorption time was 5 h, the pH of malachite green solution was 9, the adsorption temperature was 40 ℃, and the initial concentration of malachite green solution was 100 mg/L. Under these conditions the adsorption efficiency could reach up to 97%. Furthermore, the adsorbed malachite green was eluted with organic solvents of various polarities, and the highest desorption efficiency was achieved when acetonitrile with higher polarity was used as the eluent. Simultaneously, the eluent volume was optimized, with 2 mL acetonitrile added to the malachite green-enriched hydrogel adsorbent to achieve the highest desorption efficiency of 99%. The enriched sample was separated using a Dionex Bonded Silica Products C18 column (50 mm×2.1 mm, 3 μm), and eluted with an ammonium acetate-acetonitrile solvent system. The results showed that the limit of detection (LOD, S/N=3) was 0.083 μg/L, the limit of quantification (LOQ, S/N=10) was 0.25 μg/L, and the spiked recoveries of malachite green at high, medium, and low levels were 84.8%-118.1% with the relative standard deviations less than 5.1%. The pretreatment is simplified using this approach and combines the respective advantages of MOF and hydrogel to enable one-step enrichment of malachite green in aquaculture water. The additional MOF material can exert good adsorption in the hydrogel system, which solves the problem of low recovery of traditional MOF materials caused by tiny particle size, facilitating direct extraction after adsorption, and also solves the problem of low adsorption efficiency of pure hydrogel, improving the overall adsorption efficiency and recyclability. The actual sample test shows that the new hydrogel adsorption material can be used to extract and detect trace malachite green in aquaculture water. It is a novel, fast and convenient pretreatment approach with great potential in food detection.

Preparation of an anion stationary phase modified by quaternary ammoniated allyl glycidyl ether
LI Zongying, CHEN Xin, ZHANG Feifang, YANG Bingcheng
2022, 40 (8):  730-735.  DOI: 10.3724/SP.J.1123.2022.03008
Abstract ( 17 )   HTML ( 4 )   PDF (3757KB) ( 5 )  

A polymer-based strong anion stationary phase modified by quaternary ammoniated allyl glycidyl ether (AGE) for ion chromatography (IC) was developed. It was prepared by surface copolymerization between AGE and the pedant double bonds associated with hydrolyzed poly(glycidylmethacrylate-divinylbenzene) (GMA-DVB) substrate, followed by quaternization with N,N-methyldiethanolamine (a tertiary amine, MDEA). The synthesis conditions were optimized, including the type of organic tertiary amines (MDEA, N,N-dimethylethanolamine, trimethylamine), substrate hydrolysis, the amount of monomer and initiator, reaction temperature and reaction time. The obtained anion stationary phase was characterized by scanning electron microscope and elemental analysis. MDEA was observed to be the best quaternization reagent since the anion exchanger obtained by such reagent showed good separation and suitable retention time towards model inorganic anions. The resulting reason probably lies in higher hydrophilicity of MDEA relative the other two ones. The use of rich epoxy groups of GMA-DVB to introduce the functional groups was commonly used in many previous reports. Here the epoxy groups were firstly hydrolyzed to be diol groups and the pendant double bonds onto the surface of GMA-DVB particles were used to graft AGE. The data achieved indicated that the use of hydrolyzed GMA-DVB substrate would be helpful to reduce anion exchange capacity and unwanted non-ion exchange interaction, in which the rich epoxy groups were converted to hydroxy groups. More important, the obtained anion exchanger after hydrolytic treatment could offer a significantly reduction of retention time (~68%) and a ~1.67-fold higher plate count (take Br- as an example). The apparent capacity of the phase was computed to be 264 μmol/g by content of N data and its effective capacity was measured to be 98.5 μmol/column by the breakthrough curve method. Under the optimal chromatographic conditions, the obtained stationary phase showed baseline separation of seven common inorganic anions in less than 13 min using carbonate-bicarbonate mixed eluent, exhibiting high separation efficiency and peak shape, e. g. 49000 plate/m and 38000 plate/m of the theoretical plate counts respectively for chloride and nitrate, and their asymmetric factor were 1.3 and 1.4. These can be comparable or slightly higher than those of commercial columns. The fitted equation of the eluent concentration and the retention factors of model anions was proved that ion exchange model dominates the retention mechanism of the anion stationary phase. This offers a simple way to prepare anion exchanger and to manipulate anion exchange capacity. The utility of the obtained anion exchanger has been demonstrated to the analysis of tap water.

Plasma metabolomics in a deep vein thrombosis rat model based on ultra-high performance liquid chromatography-electrostatic field orbitrap high resolution mass spectrometry
GU Yan, ZANG Peng, LI Jinxia, YAN Yanyan, WANG Jia
2022, 40 (8):  736-745.  DOI: 10.3724/SP.J.1123.2021.12024
Abstract ( 20 )   HTML ( 3 )   PDF (3931KB) ( 9 )  

Deep vein thrombosis (DVT) is a venous thromboembolic disease characterized by high incidence, mortality, and sequelae. Therefore, the effective prevention of DVT has become a critical public health concern. However, due to its complexity, the pathophysiological mechanism of DVT remains unclear. Metabolomics can be employed to analyze disease characteristics and provide scientific evidence on the underlying mechanisms. In this study, an established left femoral vein ligation rat model of DVT (n=10) was used and compared with sham surgery controls (n=10). In the DVT group, rats were anesthetized using an intraperitoneal injection of 10% chloral hydrate (300 mg/kg), after which the hair was shaved and the groin disinfected. A 2-cm longitudinal incision was made along the midpoint of the left groin area, and then the left femoral vein was separated. The vein was partially ligated at its proximal end to shrink the blood vessel lumen to approximately half. Then, 0.4 mL of 10% hypertonic saline was slowly injected from the distal end of the left femoral vein. At the same time, the femoral vein turned dark red, which indicated the formation of thrombosis. Finally, the incision was sutured after verifying bleeding in the surrounding tissue. Keeping all other procedures the same as the DVT group, the vein in the control group was not ligated or stimulated using hyper-tonic saline. The abdominal aorta plasma from rats in each group was collected seven days later. Untargeted metabolomics analysis based on ultra-high performance liquid chromatography-electrostatic field orbitrap high resolution mass spectrometry (UHPLC-Orbitrap HRMS) was conducted to investigate the plasma metabolic profiles of the sham surgery control and DVT groups. Principal component analysis (PCA) and orthogonal to partial least squares discrimi-nant analysis (OPLS-DA) on metabolome data for multivariate statistical analysis were employed to assess differences in the metabolic profile between the two groups. The results revealed distinct profiles for the DVT and control groups. The selection criteria for the differential metabolites were the variable importance in the projection (VIP) values of OPLS-DA (VIP>1) and fold changes (FC) in the DVT group (FC≤0.5 or FC≥2, P<0.05). The resulting 27 differential metabolites reflecting a metabolic disorder in the DVT group were selected and analyzed. Of these, the levels of 17 metabolites significantly increased in the DVT group, including trimethylamine N-oxide (TMAO), 4-amino-2-methyl-1-naphthol, chenodeoxycholic acid, and 7-ketocholesterol, whereas the levels of 10 metabolites decreased, including 3-dehydroxycarnitine, phosphatidylcholine 22∶6/20∶2 (PC 22∶6/20∶2), diglyceride 18∶3/20∶4 (DG 18∶3/20∶4) and anserine. To identify the changes in the metabolic pathway reflected by these differential metabolites, a differential abundance (DA) analysis based on the Kyoto Encyclopedia of Genes and Genomes metabolic pathway was conducted. The results showed that the differences in the metabolic pathways between the DVT and control groups were mainly manifested in the primary bile acid biosynthesis, bile secretion, histidine metabolism, linoleic acid metabolism, glycerophospholipid metabolism, and β-alanine metabolism pathways. Among them, the primary bile acid biosynthesis and bile secretion pathways were upregulated in the DVT group, whereas the glycerophospholipid metabolism, linoleic acid metabolism, and β-alanine metabolism pathways were downregulated. The histidine metabolism pathway contained upregulated as well as downregulated metabolites, resulting in a DA score of 0. In conclusion, these results indicate that the plasma metabolic profiling of the DVT group was significantly altered, while the disordered metabolites and metabolic pathways could provide a reference to further understand the pathological mechanism of DVT and identify new drug targets.

Determination of three oryzanols in rice by mixed-mode solid-phase extraction coupled with high performance liquid chromatography-tandem mass spectrometry
LI Hongyan, YANG Huan, MA Chenyi, ZHANG Wanyue, XU Qingyu, CHEN Mingxue, MA Youning
2022, 40 (8):  746-752.  DOI: 10.3724/SP.J.1123.2021.12016
Abstract ( 24 )   HTML ( 2 )   PDF (938KB) ( 16 )  

Rice is a major dietary staple in many communities owing to its high nutritional value and characteristic aroma. Oryzanol, a mixture of ferulic acid esters of triterpene alcohols and phytosterols, is a major group of phytochemicals found in rice. 24-Methylenecycloartanyl ferulate (24MCA-FA), cycloartenyl ferulate (CA-FA), and campestanyl ferulate (Camp-FA) have been identified as the primary components of oryzanol. At present, for the quantification of oryzanol in rice and rice products, UV spectroscopy or high performance liquid chromatography (HPLC) is widely employed. However, these methods cannot differentiate individual oryzanols, resulting in higher measured values. To extract oryzanol, methods including liquid-liquid extraction, acidulation extraction, and direct solvent extraction have been typically employed, as they do not require specific extraction instrumentation. However, there has been no systematic study on the direct solvent extraction and purification conditions of oryzanol in rice. In this study, a rapid and accurate analytical method based on HPLC-MS/MS and mixed-mode anion exchange (MAX) solid-phase extraction was established to determine the content of three oryzanols (24MCA-FA, CA-FA, and Camp-FA) in rice. The MS parameters, such as the collision energy of three ion pairs of each oryzanol, were optimized. Further, the chromatographic separation conditions and response intensities of the oryzanols in different mobile phases were compared. The effects of different pretreatment conditions on the extraction efficiency of the three oryzanols in rice samples and different purification conditions on their recovery were investigated. Combined with the external standard method, the three oryzanols in rice were successfully quantified. The results showed that the baseline separation and highest response for the three oryzanols were achieved using the Agilent Eclipse XDB-C8 chromatographic column (150 mm×2.1 mm, 3.5 μm) when methanol∶ acetonitrile in a 1∶1 ratio (v/v) and an aqueous solution of 5 mmol/L ammonium acetate were used as the mobile phases for gradient elution. The extraction rate of the three oryzanols was highest when using 2.5 g of the sample, adding 20 mL of methanol, soaking for 12 h, ultrasonicating at a temperature of 40 ℃ for 20 min, and centrifuging the extracted solutions at 4500 r/min for 10 min. The samples were purified by MAX, and the sample matrix effect was found to be lesser than 1.6%-10.8%. Under the optimum conditions, the calibration curves of the three oryzanols showed good linearity (correlation coefficients r2≥0.9983) within their respective linear ranges. The limits of detection were in the range of 0.5-1.0 μg/L, and limits of quantification were in the range of 2.0-3.5 μg/L. Accuracy and precision experiments were performed on rice samples spiked at three levels (2, 5, and 10 times the background concentration), with three replicates. The average recoveries of the three oryzanols ranged from 86.1% to 110.6%, and the relative standard deviations (RSDs) were between 0.9% and 3.2%. The method showed good performance when applied to the analysis of real samples. In conclusion, the developed method can determine the content of the three oryzanols in rice quickly and accurately, and can be used for the subsequent measurement of oryzanol compounds in rice.

Identification of polysaccharide binding materials used in cultural relics by pyrolysis-gas chromatography/mass spectrometry
WANG Na, GU An, QU Yajie, LEI Yong
2022, 40 (8):  753-762.  DOI: 10.3724/SP.J.1123.2022.03005
Abstract ( 3 )   HTML ( 2 )   PDF (1332KB) ( 2 )  

Pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) is suitable for the qualitative analysis of natural organic materials in cultural relics owing to its ability of accurately and rapidly identifying trace quantities of organic components in samples. In the present study, pyrolytic components of starch and peach gum, which are commonly used in ancient Chinese cultural relics such as calligraphic works, paintings, architecture, and objects, as well as gum Arabic, which is commonly used in western cultural relics, were systematically characterized using Py-GC/MS. As polysaccharide materials are often found mixed with other organic materials in cultural relics, an online methylation Py-GC/MS procedure previously established by the authors’ research group, which is suitable for the qualitative analysis of drying oils, proteins, and waxes, was performed to analyze the starch, peach gum, and gum Arabic reference samples. The established experimental procedure can be used to comprehensively analyze the polysaccharides and other organic materials in cultural relics owing to its slow heating rate, long running time, wide mass spectrometry detection range, and high chromatographic separation efficiency.

The experimental results were examined by dividing the pyrolytic products into three sections depending on the retention time. In the first section (2.5-10 min), pyrolytic products from the three sample types were similar and mostly included small molecule furans and ketones. However, the peach gum and gum Arabic contain a wider variety of pyrolytic products than starch, possibly because starch contains only glucose, whereas peach gum and gum Arabic contain a variety of monosaccharides. In the middle section (10-19 min), the pyrolytic products of starch, peach gum, and gum Arabic mostly consisted of furanones and other components. However, a unique profile was produced for each material type. Nevertheless, it should be noted that 2-methoxy-phenol and maltol were detected in all three materials with high chromatographic peak intensities. Therefore, these components are suitable markers for the identification of polysaccharides. In the last section (19-60 min), a variety of monosaccharide derivatives and monosaccharide oligomer derivatives were detected in the reference samples. The pyrolytic products of peach gum and gum Arabic were similar but completely different from those of starch. Therefore, starch, peach gum, and gum Arabic could be distinguished according to their pyrolytic products. In particular, 1,6-anhydro-β-D-glucopyranose was detected in starch with an extremely high intensity and was undetected in either of the other reference materials. Thus, this compound could act as a characteristic pyrolytic component for the identification of starch. Peach gum and gum Arabic could be rapidly distinguished according to the extracted ion chromatograms for m/z 60 and m/z 101, which represented major fragments of the pyrolytic products of peach gum and gum Arabic in the last section of the chromatogram.

The established Py-GC/MS method was successfully applied to the identification of starch in binding materials from the rim of a globular carved red lacquer vase with dragon and cloud motifs, as well as in paper collected from a Tieluo with Bingdihanfang written by Min-ning. Both objects are part of the Palace Museum collection and originate from the Qing Dynasty. Research results of the present work are easy to be popularized. This study provides a method suitable for the accurate and rapid identification of polysaccharide materials in cultural relics, as well as a scientific basis for the research, conservation, and restoration of similar cultural relics. However, it should be noted that aging and the presence of other organic or inorganic materials in cultural relics may interfere with the detection of polysaccharide materials. Therefore, a further investigation on the aging behavior of polysaccharides and the effects of other materials on the identification of polysaccharides is required.

Technical Notes
Monitoring of atmospheric CH4, CO, CO2, N2O and SF6 using three-channel gas chromatography
HONG Haixiang, ZANG Kunpeng, CHEN Yuanyuan, LIN Yi, LI Jiaxin, QING Xuemei, QIU Shanshan, XIONG Haoyu, JIANG Kai, FANG Shuangxi
2022, 40 (8):  763-771.  DOI: 10.3724/SP.J.1123.2022.02011
Abstract ( 5 )   HTML ( 2 )   PDF (1549KB) ( 9 )  

China is approaching a critical period of carbon peak and carbon neutrality. To assess the impact of carbon peak and carbon neutrality measures, an accurate understanding of the variations of the spatial and temporal distribution of greenhouse gases is crucial. Gas chromatography, a classical approach for greenhouse gas observation, can be employed for the high-precision analysis of partial greenhouse gases. In this research, a new greenhouse gas analytical system capable of measuring five gases (CH4, CO, CO2, N2O and SF6) on a single instrument was developed based on the traditional gas chromatography approach. The following are the chromatographic operation conditions. The carrier gases were high purity N2(99.999%) and argon-methane (5% methane in argon, 99.9999%), and a stainless steel switching valve triggered the injection. Compressed CH4, CO, CO2, N2O and SF6 mixed standard gases were stored in a 0.029 m3 aluminum alloy steel cylinder for this experiment. After numerous rounds of calibration by Greenhouse Gas Laboratory of Atmospheric Sounding Center of China Meteorological Administration, the gas scale met the primary standard of World Meteorological Organization (WMO). The main performance of the system, including the measurement precision, accuracy and linear response, was tested. The results showed that the detection performance of the system met the quality standards of WMO/Global Atmospheric Watch (GAW). Precision test results indicated that the relative standard deviations (RSDs) of the mole fractions of CH4, CO, CO2, N2O and SF6 were 0.08%, 1.90%, 0.05%, 0.08%, and 0.66%, respectively. For the linear and accuracy test, the C1-C5 tested standard gases were employed and the deviations of five gases (CH4, CO, CO2, N2O and SF6) between the calculated mole fractions of the regression equation and calibrated mole fractions were 0.15×10-9, 0.20×10-9, 0.37×10-6, 0.35×10-9 and 0.02×10-12, respectively. For CH4, CO, CO2, N2O and SF6, the linear regression coefficients (R2) between the peak areas or heights and calibrated mole fractions were 0.9999. The linear regression residual and accuracy could roughly meet the expanded target of WMO/GAW quality control. The atmospheric greenhouse gases in the Hangzhou urban area were continuously measured from May 2021 to July 2021 using the developed system. The results revealed that atmospheric CH4, CO, CO2 and N2O have visible diurnal variation characteristics that were primarily affected by anthropogenic emissions. The target standard gases were measured every 2 h to monitor the stability of the system operation, and the gas mole fractions of the system response were routinely computed and compared with the assigned calibrated values. The results demonstrated that the system had good stability during the observation period and could meet the requirements of high-precision monitoring. The comprehensive test and trial operation results showed that the developed system had good precision, accuracy, linearity and stability.