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Chinese Journal of Chromatography
2015, Vol. 33, No. 2
Online: 08 February 2015

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Recent developments of dispersive liquid-liquid microextraction technique ZANG Xiaohuan, ZHANG Guijiang, WANG Chun, WANG Zhi 2015, 33 (2):  103-111.  DOI: 10.3724/SP.J.1123.2014.11015 Abstract ( 789 )   [Full Text(HTML)] () PDF (2961KB) ( 258 )   As a relatively new sample preparation technique, dispersive liquid-liquid microextraction (DLLME) has the advantages of simplicity of operation, high enrichment factor and low consumption of organic solvent. In this review, the recent advances of DLLME and its important applications are briefly reviewed, including (1) the combined use of DLLME with other extraction methods, (2) the expansion of the extraction solvent, (3) the development of extraction devices.

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Isotopic tracing technique in quantitative analysis of metabolic reprogramming in tumor cells LIN Shuhai, CAI Zongwei 2015, 33 (2):  112-115.  DOI: 10.3724/SP.J.1123.2014.11011 Abstract ( 858 )   [Full Text(HTML)] () PDF (1496KB) ( 559 )   It is hard to begin to discuss tumor metabolism without mentioning Warburg effect. Tumor metabolism has been received intensive attention in recent years for understanding Warburg effect which is also known as aerobic glycolysis. Even Warburg did not anticipate, other nutrients, such as glutamine, serine and glycine could serve as alternative source for energy demands and block building in cancer cells. To delineate altered metabolic pathways in cancer cells, isotopic tracing technique provides a novel and holistic insight in metabolic switch under control of oncogenes and tumor suppressor genes. An array of chromatography coupled with mass spectrometry is the powerful tool to detect the isotope-labeled metabolites for unlocking the underlying biochemical reactions in cancer cells. In this review article, we focus on carbon-13 and deuterium-labeling for quantitative analysis of intermediate metabolites including reduced form of nicotinamide adenine dinucleotide phosphate (NADPH). NADPH is mainly derived from pentose phosphate pathway in previous biochemical textbook. However, deuterium-isotope labeling metabolic flux analysis can reveal other important pathways for NADPH production, such as one-carbon metabolism, which is also discussed in this review.

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Preparation of graphene oxide based immobilized lectin and its application to efficient glycoprotein/glycopeptide enrichment SHI Zhaomei, FAN Chao, HUANG Junjie, BAI Haihong, QIN Weijie, CAI Yun, QIAN Xiaohong 2015, 33 (2):  116-122.  DOI: 10.3724/SP.J.1123.2014.09037 Abstract ( 744 )   [Full Text(HTML)] () PDF (5832KB) ( 247 )   Protein glycosylation in eukaryotic cells regulates a variety of physiological processes including cell recognition, cell adhesion, migration, and immune response. It is also closely related with the occurrence and development of many critical diseases. Therefore, large scale identification of protein glycosylation not only provides important information for the study of basic biological mechanisms, but also is crucial for the discovery of new diagnostic biomarkers and therapeutic targets. Due to the low abundance of glycoprotein/glycopeptide in real biological samples, enrichment before mass spectrometry (MS) analysis is an essential step for achieving deep glycosylation site coverage. Lectin enrichment, as an effective method for glycoproteins/glycopeptides enrichment, has been utilized widely in glycoproteomics research. To solve the problems of low lectin loading and limited enrichment efficiency of existing lectin functional materials, we prepared two kinds of new graphene oxide (GO) immobilized lectin. Besides good dispersion in aqueous solution as well as good chemical stability, GO has extremely large specific surface area and also carries high density of functional groups on its surface, which is especially beneficial for achieving high lectin loading amount. As a result, lectin loading as high as 1.90 mg/mg was achieved for GO-lectin (GO-ConA 2.073 mg/mg, RSD=1.0%; GO-WGA 1.908 mg/mg, RSD=0.14%). One milligram GO-lectin can adsorb more than 200 μg glycoprotein each experiment in two weeks. The GO-lectin was successfully applied in glycoproteins/glycopeptides enrichment with high efficiency and selectivity, indicating its good application potential in glycoproteomics research.

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Rapid fabrication of molecularly imprinted polymer fibers for solid phase microextraction of bisphenol A HU Mei, ZHANG Yijun, YANG Jinghua, ZHOU Xiaomao, WEI Zhuqing, DING Xiaoqing, ZHANG Yuping 2015, 33 (2):  123-131.  DOI: 10.3724/SP.J.1123.2014.10008 Abstract ( 595 )   [Full Text(HTML)] () PDF (8519KB) ( 139 )   The rapid preparation of molecularly imprinted polymer (MIP) fibers was reported using bisphenol A (BPA) as the template molecular, acetonitrile (ACN) as the porogenic solvent, α -methacrylic acid (MAA) as the functional monomer, ethylene dimethacrylate (EDMA) as the crosslinker, and azodiisobutyronitrile (AIBN) as the thermal initiator. It was carried out within a capillary of 530 μm inner diameter (I. D.) by microwave irradiation in 7 min. The resulted BPA-MIP fibers were pushed out from the capillary, eluted in a vial and inserted in the capillary again followed by the application of the solid phase microextraction (SPME) procedure. The extraction performance was investigated in detail by varying the molar ratios between the template and the monomer (BPA/MAA), the concentration of NaCl, the extraction and desorption time, the pH value and the desorption solvents. The selectivity of the prepared MIP and non-molecularly imprinted polymer (NIP) fibers was comparatively evaluated by selecting two structurally-related compounds, phenol (P) and 4-phenylphenol (PP), and non-analogue dicyandiamide (DCD). The established method was successfully applied for the pretreatment and determination of BPA from beverage samples coupled to high performance liquid chromatography (HPLC). Under the optimal conditions, the linear range of BPA was 10-400 μg/L; the detection limit (LOD) was 0.45 μg/L and the recoveries spiked in the mineral water were 88.4%-102.8%. The results demonstrated that the developed method can determine BPA in real samples with some advantages of simple pretreatment, rapid analysis, low limit of detection and low consumption of materials.

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Multi-residue determination of veterinary drugs in cheese by QuEChERS and liquid chromatography- tandem mass spectrometry CAO Yafei, KANG Jian, CHANG Qiaoying, HU Xueyan, WANG Zhibin, FAN Chunlin, WANG Minglin 2015, 33 (2):  132-139.  DOI: 10.3724/SP.J.1123.2014.10022 Abstract ( 1067 )   [Full Text(HTML)] () PDF (1044KB) ( 284 )   A rapid and sensitive method has been developed for the simultaneous determination of 50 veterinary drugs (including macrolides, quinolones, sulfonamides, and tetracyclines) in cheese using a modified QuEChERS method coupled with liquid chromatography-tandem mass spectrometry (LC-MS/MS). After adding Na2EDTA buffer solution and ceramic homogenizer, the cheese sample was extracted by 5% (v/v) acetic acid-acetonitrile, sodium chloride and anhydrous sodium sulfate were used for salting-out process. The resulting supernatant solution was purified by C18 sorbent and the re-dissolved solution was analyzed by LC-MS/MS under dynamic multi-reaction monitoring (dynamic MRM) mode via positive electrospray ionization with a ZORBAX-SB-C18 column. The limits of quantification (LOQ, S/N=10) of the target compounds ranged from 0.05 μg/kg to 20 μg/kg in cheese. At spiked levels of 20, 50, 100 μg/kg (n=6), the percentages of drug with a recovery between 70% and 120% were 94%, 92%, and 96%, respectively. The relative standard deviations (RSDs) were between 1% and 14%. This method has been applied to determine seven real samples from markets. Roxithromycin and flumequine have been detected in two samples separately. The results demonstrated that this simple, rapid and accurate method is suitable for the detection of multi-class veterinary drugs in cheese.

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Regression evaluation index intelligent filter method for quick optimization of chromatographic separation conditions GAN Wei, LIU Xuemin, SUN Jing 2015, 33 (2):  140-145.  DOI: 10.3724/SP.J.1123.2014.09040 Abstract ( 612 )   [Full Text(HTML)] () PDF (1520KB) ( 142 )   This paper presents a method of regression evaluation index intelligent filter method (REIFM) for quick optimization of chromatographic separation conditions. The hierarchical chromatography response function was used as the chromatography-optimization index. The regression model was established by orthogonal regression design. The chromatography-optimization index was filtered by the intelligent filter program, and the optimization of the separation conditions was obtained. The experimental results showed that the average relative deviation between the experimental values and the predicted values was 0.18% at the optimum and the optimization results were satisfactory.

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Application of gas chromatography-high resolution quadrupole time of flight mass spectrometry to the analysis of benzaldehyde, benzyl alcohol, acetophenone and phenylacetaldehyde in complex aromatic samples LIU Junyan, CAO Zhe, LI Jiwen, WANG Zheming, WANG Chuan, GU Songyuan 2015, 33 (2):  146-151.  DOI: 10.3724/SP.J.1123.2014.09051 Abstract ( 723 )   [Full Text(HTML)] () PDF (805KB) ( 266 )   The study focuses on the quantitative analytical characterization of benzaldehyde, benzyl alcohol, acetophenone and phenylacetaldehyde in complex aromatic samples by gas chromatography-high resolution quadrupole time of flight mass spectrometry (GC-QTOF MS). The four compounds in real sample were accurately qualified and quantified through a comprehensive analysis of the GC retention times and the accurate masses of the ion fragments obtained by the high resolution MS. The new method therefore effectively avoids the interference of the real sample substrate, which reduces the accuracy of the analysis results. The peak area of the characteristic ion fragment for each compound was used for quantitation calculation. The MS signal responses of the four compounds showed good linear relationships with the corresponding mass concentrations and the linear regression coefficients were greater than 0.99. The method recoveries were 87.97%-103.01%. The limits of detection (LODs) were 0.01, 0.03, 0.02 and 0.01 mg/L for benzaldehyde, benzyl alcohol, acetophenone and phenylacetaldehyde respectively. The contents of the four compounds in three real samples were analyzed. The study provided a new strategy for oxygenate analysis in complex aromatic samples using GC-QTOF MS. By measuring the accurate masses, the new method reduces the reliance on chromatographic separation ability and makes up the shortcomings of the traditional GC-MS methods.

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Determination of gambogic acid in Gamboge by non-aqueous capillary electrophoresis OU Wanlu, LI Yujuan, SHI Dongdong, QU Feng 2015, 33 (2):  152-157.  DOI: 10.3724/SP.J.1123.2014.11006 Abstract ( 457 )   [Full Text(HTML)] () PDF (1047KB) ( 177 )   Gambogic acid (GA), a kind of caged xanthones, has low solubility in water. A non-aqueous capillary electrophoresis (NACE) was established for the determination of GA in Gamboge based on the optimized conditions. The effect of 20%-60% methanol or acetonitrile spiked in running solution was investigated. The effects of compositions, concentration, pH, additives like β-cyclodextrin in running buffer were thoroughly studied. Applied voltage and applied temperature were also observed. Optimal electrophoretic conditions were as follows: 20 mmol/L sodium borohydride solution (pH 9.86) containing 40% (v/v) acetonitrile, 10 mmol/L β-cyclodextrin as running buffer, applied voltage of 10 kV, capillary temperature of 30 ℃ and detection wavelength of 280 nm. The calibration curve had good linearity in the range of 2-2000 mg/L with the correlation coefficient of 0.9996. The limit of quantification (S/N=3) of the method was 2 mg/L. The quantifications of GA in Gamboge from different producing places including Vietnam, Thailand, Burma, India were 1.67-472.40 mg/g with the RSD (n=3) of 1.12%-2.60%. The content of Gamboge from Vietnam is obviously low while the others are high. The recoveries of GA spiked in real samples ranged from 95.2% to 105.6%. The method of NACE is simple, efficient and of good reproducibility, can be served as a novel reference to identify and control the quality of Gamboge.

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Determination of fluorescent whitening agents in disposable sanitary products by high performance liquid chromatography WEI Feng, WU Song, YU Xi, YIN Xianggang, GE Mingqiao 2015, 33 (2):  158-163.  DOI: 10.3724/SP.J.1123.2014.10003 Abstract ( 571 )   [Full Text(HTML)] () PDF (844KB) ( 226 )   A method for the determination of four fluorescent whitening agents (FWAs) (FWA 357, FWA 220, FWA 204 and FWA 113) in disposable sanitary products by high performance liquid chromatography with diode array detection (HPLC-DAD) was developed. The sample was extracted with a 20 mL ultrapure water by sonication for 30 min at 80 ℃. The HPLC method was performed on an SB Phenyl column (250 mm×4.6 mm, 5 μm) by gradient elution using 5 mmol/L ammonium acetate and acetonitrile as mobile phases, which can separate the target analytes successfully. The target analytes showed good linearity in the range of 0.025-400 mg/L with the correlation coefficients (r2) greater than 0.9999. The limits of detection (LODs, S/N=3) were 0.02-0.1 mg/L, and the method limits of quantification (MLOQs) were 1.0-5.0 mg/kg for the target analytes. The feasibility of this method was demonstrated by the determination of FWAs in samples with spiked recoveries. The recoveries were in the range between 83.7% and 101.0%, and the relative standard deviations (RSDs) (n=6) ranged from 2.4% to 7.0%. This method is simple, and has high recoveries for the determination of FWAs in disposable sanitary products.

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Simultaneous determination of three inorganic anions in food-grade lubricating oils by ion chromatography with suppressed conductivity detection ZHANG Liyuan, FEI Xudong, QIU Feng, LIN Miao 2015, 33 (2):  164-168.  DOI: 10.3724/SP.J.1123.2014.10009 Abstract ( 550 )   [Full Text(HTML)] () PDF (779KB) ( 108 )   An ion chromatographic (IC) method with suppressed conductivity detection was developed for the simultaneous determination of Cl-, NO3-, SO42- in food-grade lubricating oils. After ultrasonic extraction with 50% (v/v) methanol aqueous solution and centrifugation, the sample in aqueous phase was purified with 0.22 μm hybrid fiber membranes, then analyzed by IC using 15 mmol/L KOH solution as eluent, and detected by a suppressed conductivity detector. Effects of the concentration and flow rate of the eluent, and the concentration of the methanol aqueous solution on the detection of the three anions were investigated. Under the optimized separation conditions, the three anions were separated completely and the system peaks didn't interfere with the determination. The calibration curves showed good linearity (R2>0.999) in the range of 0.10-20.00 mg/L. The limits of detection (LODs, S/N=3) were 0.01-0.03 mg/kg. The average recoveries of Cl-, NO3-, SO42- anions were 90.0%-103.6% with the relative standard deviations (RSDs) of 2.8%-5.7%. This method avoids the time-consuming pretreatment process to burn or ash the oil phase matrix, and can determine the amounts of three inorganic anions (Cl-, NO3-, SO42-) in food-grade lubricating oils fast and accurately. It is suitable for simultaneously separating and detecting trace inorganic anions in lubricating oils or other oil products.

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Simultaneous determination of five active components of compound α -ketoacid tablet in human urine by ion-pair reversed-phase high performance liquid chromatography HUANG Xiaoya, ZHONG Yuan, HUANG Zhongping, JIN Chen, WANG Lili, PAN Zaifa 2015, 33 (2):  169-173.  DOI: 10.3724/SP.J.1123.2014.10024 Abstract ( 720 )   [Full Text(HTML)] () PDF (792KB) ( 211 )   A simple and sensitive method for the simultaneous determination of five active components, D,L-α-hydroxymethionine calcium (HMACa), α -ketovaline calcium (KVCa), D, L-α-ketoisoleucine calcium (KILCa), α -ketoleucine calcium (KLCa) and α-ketophenylalanine calcium (KPACa) of compound α -ketoacid tablet in human urine by ion-pair reversed-phase high performance liquid chromatography (RP-HPLC) was developed and validated. The separation conditions, such as the concentration of ion-pair reagent, the pH value of the mobile phase and the concentration of the buffer were optimized. All the five analytes were separated well on a C18 column (250 mm×4.6 mm, 5 μm) with diode array detection at 210 nm and the column temperature of 35 ℃. The mobile phases were acetonitrile and 20 mmol/L phosphate buffer (containing 15 mmol/L tetrabutylammonium hydroxide; pH 7) at the flow rate of 1.0 mL/min with gradient elution. The calibration curves for the five components were linear in the range from 20 to 200 mg/L (r≥0.9990). The limits of detection (LODs, S/N=3) were 3.0, 5.0, 3.6, 5.7 and 2.5 mg/L, and the limits of quantification (LOQs, S/N=10) were 9.6, 16.7, 12.0, 19.0 and 8.3 mg/L for HMACa, KVCa, KILCa, KLCa and KPACa, respectively. The intra-day and inter-day precisions were less than 7%, and the average recoveries were between 86.79% and 112.00% in the human urine with RSDs lower than 9% (n=5). The method proved precise, specific and reproducible, and can be used for the determination of the five components in urine.

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Analysis of the volatile components in Minnan oolong tea by headspace solid phase microextraction coupled with comprehensive two-dimensional gas chromatography- time of flight mass spectrometry and the application in its variety identification CHENG Quan, YANG Fang, LI Jie, LU Shengyu, LAN Jinchang, JIANG Jinbin 2015, 33 (2):  174-181.  DOI: 10.3724/SP.J.1123.2014.09042 Abstract ( 879 )   [Full Text(HTML)] () PDF (1993KB) ( 458 )   A method to analyze the volatile components in Minnan oolong tea was developed based on headspace solid phase microextraction (HS-SPME) coupled with comprehensive two-dimensional gas chromatography-time of flight mass spectrometry (GC×GC-TOF MS). Volatile compounds of 48 oolong tea samples with different qualities and production seasons from five varieties (Tieguanyin, Huangjingui, Benshan, Maoxie and Meizhan) were extracted by HS-SPME and analyzed by GC×GC-TOF MS. More than 2000 peaks were obtained from each sample, and 51 common compounds were tentatively identified by comparison with the standard mass spectrum databases, retention indices and structure spectra. The projection score of the common compounds obtained from principal component analysis (PCA) had presented a straightforward classification trend for different oolong tea varieties. In addition, 9 compounds which had significant impact on the classification were selected by stepwise discriminate analysis, and used as variables to establish four discriminated functions by Fisher's discriminate analysis (FDA). The accuracy for the recognition of 48 samples was 97.9%. The results had demonstrated the feasibility of the method to be used to discriminate the oolong tea varieties.

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Determination of short chain chlorinated paraffins in polyvinyl chloride plastics by gas chromatography- negative chemical ion/mass spectrometry XING Yuanna, LIN Zhihui, FENG Anhong, WANG Xin, GONG Yemeng, CHEN Zeyong 2015, 33 (2):  182-187.  DOI: 10.3724/SP.J.1123.2014.10004 Abstract ( 764 )   [Full Text(HTML)] () PDF (1170KB) ( 259 )   A novel method was established to determine short chain chlorinated paraffins (SCCPs) in polyvinyl chloride (PVC) plastics by gas chromatography-negative chemical ion/mass spectrometry (GC-NCI/MS). Ultrasonic extraction was used to extract SCCPs from PVC plastics. The optimal extraction time was 1.5 h, and concentrated sulfuric acid was adopted to purify the extracted solution. Finally, SCCPs in a sample were detected by GC-NCI/MS at 160 ℃ and with methane reagent gas at 1.5 mL/min. This method was not influenced by medium chain chlorinated paraffins (MCCPs) in the sample, and accurate quantitation was made for SCCPs. Twelve batches of samples were analyzed and SCCPs were detected in each batch with the contents from 0.3×102 mg/kg to 3.5×104 mg/kg. With respect to European limitation of SCCPs (1%), four batches of samples did not comply with the European regulation, and they accounted for 33.3%. Obviously, high SCCPs risk was presented in PVC plastics.

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Coupling of gas chromatography with single photon ionization time-of-flight mass spectrometry and its application to characterization of compounds in diesel XIE Yuanyuan, HUA Lei, CHEN Ping, HOU Keyong, JIANG Jichun, WANG Yan, LI Haiyang 2015, 33 (2):  188-194.  DOI: 10.3724/SP.J.1123.2014.10028 Abstract ( 516 )   [Full Text(HTML)] () PDF (3320KB) ( 205 )   A novel analytical method coupling gas chromatography (GC) with single photon ionization time-of-flight mass spectrometry (SPI-TOF MS) has been developed. First of all, a double-wall-tube transfer line was built to combine GC with SPI-TOF MS, which realized seamless connection between GC and SPI ion source. Based on this, standard n-pentadecane and benzene/toluene/xylene standard gas mixtures were used to study important voltage parameters of the ion source. After the optimization of the ion source voltages, pure molecular ion peaks of the analytes were obtained in the mass spectra and qualitative analysis of different kinds of organic compounds were eventually realized rapidly and accurately. At last, GC/SPI-TOF MS was applied to the characterization of volatile and semi-volatile organic compounds in diesel and two-dimensional spectra of GC×SPI-TOF MS were obtained. Without complicated spectra interpretation and data processing, volatile and semi-volatile organic compounds in diesel have been classified qualitatively by ion mass-to-charge ratio (m/z) in SPI mass spectra, including aliphatic compounds, aromatic compounds and nitrogen-containing compounds with low concentration such as benzopyrroles. Isomeric compounds in diesel were separated and identified by retention times of chromatographic peaks. The results indicate that the proposed analytical method of GC/SPI-TOF MS is suitable for the characterization of complicated samples such as diesel and environmental pollutants with easy operation and high efficiency.

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Determination of the four generic fractions of aged bitumen by thin-layer chromatography with flame ionization detection FENG Zhengang, ZHANG Jianbin, LI Xinjun, YU Jianying 2015, 33 (2):  195-200.  DOI: 10.3724/SP.J.1123.2014.09052 Abstract ( 674 )   [Full Text(HTML)] () PDF (798KB) ( 249 )   The aging process of bitumen has been paid more and more attention by the researchers. The four generic fractions (saturates, aromatics, resins and asphaltenes) of bitumen change significantly during the aging process. The analysis of the changes of the four generic fractions of bitumen is very helpful to reveal the bitumen aging mechanisms and guide its engineering applications. In this study, the bitumen was aged by thin film oven test (TFOT), pressurized aging vessel (PAV) test and ultraviolet (UV) aging test, respectively. Then the four generic fractions of bitumen before and after aging were analyzed by thin-layer chromatography with flame ionization detection (TLC-FID), which was further compared with the solubility procedures and chromatographic technique (named as Corbett method). The compositions of the expanded solvents were also investigated. Finally, the correlation between the TLC-FID and Corbett method was further studied, which revealed a proper TLC-FID method for detection of aged bitumen. The bitumen solution dissolved by dichloromethane was successively expanded by n-heptane, toluene/n-heptane (80:20, v/v) and toluene/ethanol (55:45, v/v), followed by TLC-FID. This method is of great significance for the analysis of the four generic fractions of bitumen and for the exploration of bitumen aging mechanisms.

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Analysis of difference of serum proteins between patients with cirrhosis and normal people by capillary electrophoresis with light-emitting diode induced fluorescence detection BAO Rihuang, FAN Qingjie, SONG Long, YAO Yuan, GAO Weiping 2015, 33 (2):  201-206.  DOI: 10.3724/SP.J.1123.2014.11010 Abstract ( 695 )   [Full Text(HTML)] () PDF (1224KB) ( 206 )   An experimental method of protein separation by capillary electrophoresis coupled with light-emitting diode induced fluorescence detection (CE-LED-IF) was established. The fluorescein isothiocyanate (FITC) was used as fluorescent dye in this method. An optical fiber was inserted into the separation capillary and was suited right at the detection window which was used to transmit the excitation light of LED. The efficiency of the light of LED and the detection limits of FITC was improved. The difference of serum proteins between the patients with cirrhosis and normal people was detected by this method. A series of effects on CE were studied, such as the wavelength of the light source and filter, the concentration and pH of the running buffer and the separation voltage. Then the optimized method was established for the determination of the serum proteins. The repeatability of CE-LED-IF was tested and the RSDs of migration time and peak area were 1.14% and 3.23%, respectively. The results showed that there were two specific peaks in cirrhosis serum. The differences between the patients with cirrhosis and normal people having statistical significance indicated that these proteins might be the potential biomarkers for cirrhosis diagnosis. The developed CE-LED-IF method proved suitable for the separation of serum proteins with good repeatability and supportable for the clinical diagnosis of cirrhosis.