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Chinese Journal of Chromatography
2022, Vol. 40, No. 1
Online: 08 January 2022

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Preparation of molecularly imprinted polymers based on covalent organic frameworks and their application to selective recognition of trace norfloxacin in milk XIE Yang, ZHANG Yi, SHI Haizhu, WU Zhaoju, YU Xuehong, ZHANG Chungu, FENG Shun 2022, 40 (1):  1-9.  DOI: 10.3724/SP.J.1123.2021.03013 Abstract ( 313 )   HTML ( 220 )   PDF (2590KB) ( 177 )   Norfloxacin (NFX) is an antibiotic that is widely used in animal husbandry. However, the presence of NFX even in trace amounts in animal-derived food may harm human health. Therefore, it is of practical significance to establish a method for monitoring NFX residues in food. Molecularly imprinted polymers (MIPs) imitate interactions established by natural receptors to selectively retain a target molecule, like antibodies or antigens do. MIPs have been widely employed in the selective recognition of specific target molecules from complex samples. Covalent organic frameworks (COFs) are a new type of organic polymer with uniform and ordered crystal structures. COFs form crystal structures by constructing organic units for ordered assembly through reversible chemical reactions. Their porous structure, regular morphology, and easy modification make COFs promising for use as excellent adsorbent carriers. Owing to these advantages of COFs, researchers have attempted to coat one MIP layer on COFs; however, the preparation methods are time-consuming and laborious, and the conditions are harsh. Hence, this study proposes a simple and rapid method for the preparation of novel MIPs with COFs as the support (DP-COF@MIPs) for the selective recognition of NFX. First, a Schiff-base COF (DP-COF) was rapidly synthesized using 3,3'-diaminobenzidine and p-phthalaldehyde with a metal trifluorate as a catalyst at room temperature. Subsequently, a two-step sequence was adopted as the synthesis strategy using NFX as the template, methacrylic acid as a functional monomer, and ethylene glycol dimethacrylate as a crosslinking agent. The entire synthesis was completed within 5 h under mild conditions. The material was then characterized by multiple analytical methods, including field-emission scanning electron microscopy, Fourier-transform infrared spectroscopy, X-ray diffraction, and the Brunauer-Emmett-Teller (BET) method (to determine the specific surface area). The experimental results confirmed the successful preparation of DP-COF@MIPs. The DP-COF@MIPs presented a rough and porous surface, with a pore size of approximately 17.79 nm (mesoporous structure). The properties of the material were evaluated by adsorption and regeneration experiments. The kinetic adsorption experiment showed that the DP-COF@MIPs reached adsorption equilibrium in 90 min. Two straight lines were fitted using the pseudo-second-order kinetics model based on the experimental results for thermodynamic adsorption, indicating that the adsorption process was primarily dominated by chemical adsorption. The maximum apparent adsorption capacity was 41.57 mg/g. In the selective and competitive binding test, five drugs, namely ciprofloxacin, dimetridazole, oxytetracycline, sulfadiazine, and chloramphenicol, were selected as the interferents. The experimental results showed that the DP-COF@MIPs possessed good stereoselectivity and competitive recognition ability. The regeneration of DP-COF@MIPs was evaluated by multiple cycles of adsorption-desorption experiments. The loss in the adsorption capacity of the particles was only approximately 4.7% after seven adsorption-desorption cycles. These results from the regeneration experiments show that the DP-COF@MIPs had high stability and reusability in the selective adsorption and separation of NFX. In addition, the employed method could accurately identify trace NFX in milk samples. The average recoveries were in the range of 88.8%-92.9% at three spiked levels (0.03, 0.10, and 0.30 mg/L) with relative standard deviations (RSDs) in the range of 0.6-1.7% (n=3). Notably, the method could successfully determine NFX at contents as low as 0.0020 mg/L in the milk sample with an average recovery of 77.6% and RSD of 6.4% (n=3). This concentration is one-fiftieth of the maximum residue level stipulated by the European Union (EU), and even lower than the limit of detection (LOD) of conventional high performance liquid chromatography (HPLC) methods. The above results confirm that DP-COF@MIPs can be used to determine trace NFX in actual complex samples using HPLC equipment, even when coupled to conventional UV-Vis detectors. This study offers a facile and general method for the preparation of MIPs based on COFs with selective recognition ability.

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Determination of organophosphorus pesticides based on graphene oxide aerogel solid phase extraction column HOU Xiudan, YU Hui, ZHU Feng, LI Zhaojie, YANG Qingli 2022, 40 (1):  10-16.  DOI: 10.3724/SP.J.1123.2021.03032 Abstract ( 228 )   HTML ( 36 )   PDF (4999KB) ( 168 )   A graphene oxide aerogel was prepared and directly filled in a solid phase extraction (SPE) column without the aid of silica or other substrates. The aerogel was used to extract and detect residual organophosphorus pesticides (phoxim, temephos, fenthion, and fenitrothion) in food, and exhibited good elasticity and high mechanical strength. The graphene oxide aerogel was prepared by freeze-drying. Its morphology and physical properties were characterized by scanning electron microscopy, infrared spectroscopy, and BET surface adsorption. Results proved the successful synthesis of the graphene oxide aerogel. Scanning electron micrographs of the aerogel exhibited a layered and fold structure, with a surface area of 740.51 m2/g. The effect of experimental conditions on the extraction recovery of organophosphorus pesticides was systematically studied through a series of single-factor experiments. Due to limited adsorption sites, sample volumes of 5-60 mL were investigated, and 15 mL was determined was the optimum sample volume. The rate of sample loading was investigated in the range of 0.8-3.0 mL/min. When the rate of sample loading was higher than 3.0 mL/min, the insufficient contact between the analytes and sorbent appeared to cause a decrease in the extraction recovery. A lower rate of sample loading would prolong the operation time due to the re-elution of organophosphorus pesticides. The sample pH was optimized from a pH range of 2-11. An acidic solution was found to be good for inducing electrostatic interactions between the graphene oxide aerogel and organophosphorus pesticides. The maximum extraction recoveries were obtained at pH 4. Three eluents (acetonitrile, methanol, and acetone) were explored for optimization, and results showed that acetonitrile was the most appropriate eluent. The eluent volume (0.6-1.2 mL) was also investigated, and the optimal value was found to be 1.0 mL. Compared with commercial extraction materials including C18 silica, the anion exchange column (SAX), amino (-NH2), and Florisil, the extraction recovery of this new material showed distinct improvement. The lifetime of the extraction column directly filled with the graphene oxide aerogel was investigated. The column could be repeatedly used for 15 times, which overcame the issue of blocking of the sieve plates of fragmented graphene nanosheets dispersed without any matrix support. The linearities of the four organophosphorus pesticides were 1-200 μg/L for phoxim, temephos, and fenthion, and 2-200 μg/L for fenitrothion. The linear correlation coefficients were all ≥0.9949, and limits of detection were in the range of 0.2-0.5 μg/L. An extraction column was used to extract the analytes continuously for five times, and the RSDs of the extraction recoveries were ≤6.5%. Subsequently, five extraction columns were used to extract the analytes under the same conditions, and the RSDs of the extraction recoveries were ≤11.3%. Finally, the established method was applied for the extraction and detection of a real sample (apple peel); no organophosphorus pesticide was detected in the apple peel. The recoveries for spiked standard solutions were between 70.5% and 93.6%, and RSDs were ≤10.4%.

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Optimization and evaluation of protein C-terminal peptide enrichment strategy based on arginine cleavage ZHAO Xiaoxiao, HU Hao, ZHAO Wensi, LIU Ping, TAN Minjia 2022, 40 (1):  17-27.  DOI: 10.3724/SP.J.1123.2021.03030 Abstract ( 375 )   HTML ( 26 )   PDF (3307KB) ( 168 )   As unique biomarkers, protein C-termini are involved in various biological processes such as protein trafficking, subcellular relocation, and signal transduction. Dysregulation of protein C-terminal status is critical during the development of various diseases, including cardiovascular, neurodegenerative, and metabolic diseases and cancer. Thus, global profiling of protein C-termini is of great value in providing mechanistic insight into biological or pathological processes, as well as for identifying potential new targets for therapeutic treatment. Polymer-based negative enrichment is a prominent C-terminomics strategy with advantages of universal applicability and parallel sample preparation. Compared with other methods of such a strategy, the profiling depth of the approaches based on enzymatic cleavage of Arg residues still needs to be improved. This greatly limits our understanding of the physiological functions and molecular mechanisms of C-termini. To add a more powerful tool for C-terminomics, Arg cleavage-based negative enrichment C-terminomics was optimized and evaluated. First, the sample preparation process was optimized. A one-pot enrichment platform based on a V-shaped filter was established, which reduced sample loss, avoided cross-contamination between reactions, and shortened sample preparation time. In addition, the protein-level acetylation conditions were investigated with the optimal labeling conditions as follows: triple coupling using 5 mmol/L Ac-NHS at pH 7.0 and 500 mmol/L ammonium for 15 min provided minimized acetylation rates (acetylation labeling efficiencies of Ser, Thr, and Tyr were lower than 4%, 2%, and 1%, respectively), along with the highest peptide-spectrum match number and satisfactory Lys labeling efficiency (up to 98%). These optimized conditions would not only minimize acetylation, but also facilitate the identification of C-terminal peptides. Second, it was speculated that the unexpected low identification rate was primarily caused by the interference of the large number of organic compounds accumulated during the peptide-level reactions, including reagents, organic buffering agents, and their complex side-reaction products. Therefore, the conditions for StageTip-based fractionation, including pH, the amount of Empore C18 beads, and the number of fractions, were optimized. As a result, by separating the sample enriched from 300 μg proteome into seven fractions, sample complexity was largely decreased and a total of 696 C-termini were identified in duplicates from strict data filtration, that is, percolator false discovery rate (FDR)<0.01, ion score≥20, and C-terminal amidation by ethanolamine. If only peptide FDR<0.01 was considered, the identified C-termini further increased to 933, which was among the largest C-terminome datasets obtained from the polymer-based strategy. Furthermore, compared with the results of a previous study, the optimized method would be a practical strategy for broader C-terminome coverage. Finally, to further broaden the coverage of the sub-C-terminome generated by Arg-specific cleavage, this study explored a new method in which ArgN-specific cleavage (cleavage at the N-terminal of Arg by LysargiNase) was combined with different N-terminal protections (dimethylation and acetylation). Among all the combinations, the additional use of the “LysargiNase+N-terminal acetylation” method increased 47% more identifications of unique C-termini on the basis of “trypsin+N-terminal demethylation” and the two covered 87% of the total C-termini. Therefore, the parallel use of the two methods would further expand the coverage of Arg-cleaved C-terminal peptides. With the analysis of the physicochemical properties of the peptides identified by the two methods, the reason why the C-terminal peptides identified by different strategies are complementary was explained. In conclusion, in this study, the optimized C-terminomics platform can deeply profile Arg cleavage-generated C-terminal peptides using a polymer-based approach. This method provides a powerful tool for the global characterization of protein C-termini.

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Analysis of 29 fentanyl analogs and their fragmentation mechanism by liquid chromatography-quadrupole time-of-flight mass spectrometry DONG Zhenlin, YANG Chunguang, XU Tian, DAI Di, GAO Lu, YANG Lu, WANG Qiuyan 2022, 40 (1):  28-40.  DOI: 10.3724/SP.J.1123.2021.01036 Abstract ( 503 )   HTML ( 38 )   PDF (1900KB) ( 103 )   Given the wide variety of fentanyl analogs, the test for this entire group tends to be crucial and particularly difficult since all fentanyl-like substances are listed as controlled substances in China. This study meticulously analyzed the fragmentation pathways and mechanisms of 29 fentanyl analogs and summarized the fragmentation pathways and features for the entire group of fentanyl analogs, thus providing a reference for related screening tests. Fentanyl, thiofentanyl, and sufentanil were selected as the representative compounds in this study, and the fragmentation mechanism of their fragment ions was interpreted. The general fragmentation rules for fentanyl analogs were summarized as well. The fragment ions of the three compounds formed by induced cleavage (i) came with high abundance ratios, such as fragment ions of m/z 188, 105, 194, 111, and 238, while the induced cleavage was due to the amide and piperidinyl groups. Moreover, the induction ability of amide group was significantly stronger than that of the piperidinyl group, and induced cleavage was the main fragmentation pathway for most of the fentanyl analogs. Furthermore, the fragment ions with m/z 281 and 287 for fentanyl and thiofentanyl were formed by loss of the propionyl group after single H rearrangement (rH). The fragment ions with m/z 216, 146, and 132 for fentanyl and thiofentanyl were formed by double H rearrangement (r2H). Although their abundance ratios were not high, they still had specificity and regularity. Elimination reaction (re) was also a very common fragmentation pathway for these compounds, leading to fragment ions with m/z 134 and 140. Phenylethyl substituents were more prone to the elimination reaction with a higher abundance ratio than thiophenethyl substituents. Compounds such as sufentanil with methoxy substituents at the piperidinyl para-position could produce a large number of fragment ions, which were more susceptible to the rH pathway and loss of methanol neutral molecules, leading to the formation of ions with m/z 355. Similarly, compounds such as remifentanil bearing a methyl formate substituent at the piperidine para-position also produced numerous fragment ions, which were more prone to the rH pathway to lose methyl formate or methanol neutral molecules and furnish fragment ions with m/z 317 or 345. Compounds containing hydroxyl substituents, such as β-hydroxyfentanyl and β-hydroxythiofentanyl, produce significant dehydration ions and formed fragment ions with m/z 335 (β-hydroxyfentanyl) and m/z 341 (β-hydroxythiofentanyl). A method based on liquid chromatography-quadrupole time-of-flight mass spectrometry (LC-QTOF-MS) for the qualitative and quantitative determination of the 29 fentanyl analogs was developed. Drugs and white powder samples were extracted by acetonitrile, as well as protein and milk beverage samples. Sugar-containing solids or powders, drinking water, fruit and vegetable drinks, health drinks, tea drinks, and alcohol samples were extracted by 10% acetonitrile aqueous solution. Following vortexing, centrifugation, and membrane separation, the target compounds were separated on a Kinetex C18 column (100 mm×2.1 mm, 2.6 μm) with gradient elution at a flow rate of 0.4 mL/min. The mobile phases were composed of acetonitrile and 0.08% formic acid aqueous solution. The target compounds were quantified by LC-QTOF-MS using an external standard method in positive ion mode. The 29 fentanyl analogs showed good linear relationships in the range of 1-20 μg/L, and the correlation coefficients were greater than 0.995. The limits of detection (LODs) and limits of quantification (LOQs) were 0.01 mg/kg and 0.05, respectively. The average recoveries were 85.2%-112.9% for hypoglycemic drugs, Lulu drinks, glucose powder, Zhenlu health drink and chocolate, with RSDs of 1.9%-19.8% (n=6). This method is rapid, simple, time-saving, highly sensitivity and stable, and it is applicable to a wide variety of samples. Hence, it is suitable for the identification, confirmation, and quantitative detection of the 29 fentanyl analogs in drugs, solids or powders containing sugar, beverages, drinking water, wine samples, etc.

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Determination of chlorpropham residues in animal-derived foods by solid phase extraction and ultra-high performance liquid chromatography-tandem mass spectrometry YANG Lixia, HUANG Xiaobei, ZENG Xike, YI Zi 2022, 40 (1):  41-47.  DOI: 10.3724/SP.J.1123.2021.02009 Abstract ( 233 )   HTML ( 32 )   PDF (1292KB) ( 138 )   Chlorpropham is a plant growth regulator and a herbicide. It is commonly used in the post-harvest treatment of potato to inhibit germination. It can also be used for flower thinning and fruit thinning of fruit trees, and for controlling annual gramineous weeds and a few broad-leaved weeds. Improper or excessive use of chlorpropham in crop cultivation will affect the safety of animal-derived food and impair human health through the food chain and water cycle. Therefore, accurate quantification of chlorpropham is imperative for risk assessment and mitigating risks to food safety. A method based on solid phase extraction and ultra-high performance liquid chromatography-tandem mass spectrometry (SPE-UHPLC-MS/MS) was established for the determination of chlorpropham in animal-derived food. First, the pretreatment conditions were optimized. To purify the samples and remove impurities, SPE column cartridges with different packing materials such as PXC, PXA, Florisil, and PLS were investigated. Based on the retention of chlorpropham, the ProElut PLS SPE column was selected as the pretreatment purification column. The washing solution and eluents were then optimized. When water was used as the washing solution, chlorpropham remained adsorbed on the SPE column and was not eluted along with other water-soluble substances. When the proportion of acetonitrile exceeded 40%, chlorpropham adsorbed on the filler of the SPE column could be gradually washed down. Acetonitrile-water solution(30∶70, v/v) was used for washing the SPE column. The elution ability of seven eluents for chlorpropham on the SPE column was then investigated. Among them, pure methanol, pure acetonitrile, and 1% (v/v) formic acid-methanol showed better elution effect. Considering that acetonitrile was used in the sample extraction, it was chosen as the mobile phase eluent. Subsequently, the chromatographic conditions and MS parameters were optimized. By examining the ionization cracking of chlorpropham, the quasimolecular ions and corresponding fragmentations in the chlorpropham primary MS were determined. The separation effect of three C18 columns was investigated. Based on the retention ability and peak effect of chlorpropham on the column, the Agilent ZORBAX SB-C18 (150 mm×2.1 mm, 5 μm) column was used for chlorpropham separation. The response of chlorpropham in the positive and negative ionization modes was investigated and optimized. The results showed that the response was better in the positive ion mode than that in the negative ion mode. After optimizing the chromatographic conditions and MS parameters, the sensitivity of the method was improved. Finally, the analytes were separated on the Agilent ZORBAX SB-C18 (150 mm×2.1 mm, 5 μm) under a gradient elution program using acetonitrile and 0.2% (v/v) formic acid aqueous solution as the mobile phases. The analytes were detected in the multiple reaction monitoring (MRM) mode under positive electrospray ionization (ESI+) conditions. The standard curve solutions were prepared using the matrix solution and quantified by the external standard method. The results showed a good linear relationship in the range of 0.5-100.0 μg/L, with correlation coefficients (r2) greater than 0.9929. The limit of quantification (LOQ) of this method was 3 μg/kg (S/N ≥ 10). At three spiked levels (0.003, 0.006, and 0.060 mg/kg) in 13 animal-derived foods (pork, milk, beef, chicken, duck, egg, chicken gizzard, duck egg, pork kidney, pork liver, beef liver, mutton, duck gizzard), the average recoveries were in the range of 74.9% to 97.6%, and the RSDs were in the range of 2.9% to 9.5% (n=6). Sixty batches of animal-derived food available on the market were analyzed by the developed method, and chlorpropham was not detected in any of these foods. The developed method is rapid, sensitive, and accurate, and it is suitable for the qualitative and quantitative detection of chlorpropham in a variety of animal-derived foods.

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Rapid screening and identification of 62 kinds of illegally added traditional Chinese medicine in food by high performance liquid chromatography coupled with quadrupole-time of flight mass spectrometry WU Wanqin, JIANG Feng, FAN Xiaolong, CHEN Ran, ZHU Xiaoling, CAO Qi, ZHU Zhengwei, ZHU Songsong, WANG Huixia 2022, 40 (1):  48-56.  DOI: 10.3724/SP.J.1123.2021.02031 Abstract ( 278 )   HTML ( 44 )   PDF (1801KB) ( 128 )   Supporting Information An analytical method based on high performance liquid chromatography coupled with quadrupole time-of-flight mass spectrometry (HPLC-Q-TOF/MS) was established for the rapid screening and identification of 62 kinds of illegally added traditional Chinese medicine (TCM) in food. According to the notice of the Ministry of Health of the People’s Republic of China on further regulating the management of raw materials of health food (Weifa Jianfa (2002) No. 51), the characteristic components of the 62 kinds of TCM were screened, and the corresponding characteristic component lists of different TCM were obtained. Methanolic extracts of the 62 kinds of standard medicinal materials were subjected to HPLC-Q-TOF-MS analysis. The filtrate was separated on a Thermo Accucore aQ column (150 mm×2.1 mm, 2.6 μm) using 0.1%(v/v) formic acid aqueous solution or water and acetonitrile as the mobile phases for gradient elution in the electrospray positive and negative ion scanning mode. All the data were determined on the full scan of primary mass spectrometry and secondary mass spectrometry, with mass acquisition ranges of 100-1000 Da and 50-1000 Da, respectively. A 10 mmol/L sodium formate solution was used as the mass correction solution in both the positive and negative ion modes. Library View software was used to establish the precursor ion accurate quality database and the product ion fragment mass spectrometry database of the corresponding characteristic components of the different kinds of TCM. In the Library View database software, the name of each characteristic component of the 62 kinds of TCM was input (serial number) in order to classify the screened characteristic components. The samples were processed using the same method and analyzed. Peak View software was used to rapidly analyze and screen the target components of the TCM. The high-resolution data collected from the samples to be tested were imported into the Peak View software, followed by the compound list of the established MS database of standard medicinal materials. After setting the identification method parameters and library retrieval parameters, a matching analysis was performed, and the candidate substances for each peak were automatically identified by comparing the mass spectrum, accurate molecular ion mass number, fragment ion mass number, retention time, and other related parameters. The determination conditions of compound detection were as follows: the comprehensive score was more than 70 points. The molecular formula, retention time, mass spectrum as well as the primary isotope mass spectrometry, primary mass spectrometry, and secondary mass spectrometry data were matched with the library compounds. The corresponding list of “TCM-characteristic components” was established, and a high-resolution MS library of 388 characteristic components from the 62 types of TCM was constructed. Each TCM contains 5-10 characteristic components. According to the screening analysis of the actual food samples of the prepared wine, substitute tea, and beverage, one batch of the prepared wine sample matched with seven characteristic components of epimedium, and it was inferred that epimedium was added to the prepared wine samples. This method can allow for the qualitative screening of TCM without standards and has the characteristics of high throughput, accuracy, simplicity, and rapidity. It solves the difficulty in identifying and confirming illegally added TCM in food; provides technical methods and a basis for cracking down on the illegal addition of TCM in food; and facilitates the rapid screening and identification of illegally added TCM in food.

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Rapid determination of bisphenols in surface water by modified QuEChERS-ultra performance liquid chromatography-tandem mass spectrometry TAN Xuerong, ZHAO Bin, LU Jianwei, LIU Shaoying, GOU Weini, YANG Rong, ZUO Peng 2022, 40 (1):  57-65.  DOI: 10.3724/SP.J.1123.2021.03010 Abstract ( 261 )   HTML ( 40 )   PDF (4053KB) ( 192 )   Chromatography combined with mass spectrometry is the most commonly used detection technology, and it offers the advantages of high sensitivity and high selectivity. However, the contents of bisphenols (BPs) in water samples are at the ng/L level. Even if the BPs contents are determined by mass spectrometry, the samples must be pretreated and enriched. A quick, easy, inexpensive, effective, rugged, and safe technique (QuEChERS) can offer advantages such as cost effectiveness and time efficiency. The application of QuEChERS is currently extended to the analysis of contaminants in food and water samples. In this work, QuEChERS coupled with ultra performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) was proposed for the determination of eight BPs in surface water. Method optimization was carried out in terms of process efficiency (PE), which included the matrix effect (ME) and extraction recovery (RE). First, the water samples were extracted with 10 mL ethyl acetate and cleaned with 50 mg primary secondary amine (PSA) and 50 mg graphitized carbon black (GCB). Then, the organic layer was collected and evaporated to dryness under nitrogen flow (40 ℃). Finally, the extracts were redissolved in 0.5 mL of a methanol-water (1∶1, v/v) mixture and subjected to UPLC-MS/MS analysis. Chromatographic separation was accomplished on a Waters ACQUITY UPLC BEH C18 column (100 mm×2.1 mm, 1.7 μm) with gradient elution. Methanol and 0.1 mmol/L ammonium bicarbonate aqueous solution were used as the mobile phases. The eight BPs were analyzed by MS/MS with negative electrospray ionization (ESI-) and in the multiple reaction monitoring (MRM) mode. The matrix matching external standard method was used for quantitative determination. The eight compounds could be analyzed within 8 min. Under the optimized conditions, the calibration curves showed good linearities for the eight BPs, and the coefficients of determination (R2) were greater than 0.9990. The limits of detection (LODs, S/N=3) and limits of quantification (LOQs, S/N=10) were in the ranges of 0.1-2.3 ng/L and 0.3-6.1 ng/L, respectively. The average recoveries of the eight BPs in river water samples were 78.8%-116.6%, and the corresponding relative standard deviations (RSDs) were 1.8%-9.0% (n=6). This method was applied to the analysis of BPs pollution in Guangyuan section of Jialing river and its tributaries, and widespread pollution was confirmed. The detection rate of BPA was 100% with a content of 6.15-90.03 ng/L, and the detection rate of BPS was 91%, with the contents being in the range not detected (nd) to 4.63 ng/L. The method established in this study allowed for the rapid enrichment and purification of the eight BPs in water. With its advantages of simplicity, rapidness, high sensitivity, and low cost, the method can be used for the rapid determination of trace BPs in surface water such as lake water and river water.

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Adsorption, separation, and purification of cyclosporine A using reversed-phase liquid chromatography LI Zhidong, FU Qing, DAI Zhuoshun, JIN Yu, LIANG Xinmiao 2022, 40 (1):  66-73.  DOI: 10.3724/SP.J.1123.2021.01045 Abstract ( 308 )   HTML ( 34 )   PDF (1089KB) ( 129 )   High performance liquid chromatography (HPLC) is widely used in the separation and analysis of cyclosporine A (CsA). Analyzing the chromatographic behavior of CsA is key to the purification of CsA by preparative HPLC. In this study, the retention behavior of CsA on the C18 column using mobile phases of methanol-water and acetonitrile-water was compared. The retention time of CsA was sensitive to the change in the ratio of the organic solvent. When 84%-88% methanol or 75%-85% acetonitrile was used, the retention factor (k) was in the range of 3-7. The change in the peak shape of CsA was investigated with loading amounts of 5, 25, 50, 100, and 500 mg. With an increase in sample loading, the peak shape of CsA in both mobile phases changed from symmetric to tailing, and the retention time reduced. Therefore, it is necessary to focus on the removal of impurities that were eluted before CsA during the purification. In addition, the peak shapes of CsA in methanol-water and acetonitrile-water were similar in the tested concentration range. This indicates that it was not possible to tune the peak shape of CsA by changing the organic solvent. Adsorption isotherms were obtained to describe the retention behavior of CsA. When the mass concentration of CsA in the mobile phase was low, the effect of the organic solvent ratio on the adsorption capacity of CsA on the C18 stationary phase was not distinct. With an increase in the solute mass concentration above 0.5 g/L, the reduced proportion of organic solvent helped improve the adsorption capacity of CsA. When the mass concentration of CsA in the mobile phase reached 5 g/L, the adsorption capacities were 24.9 g/L in 88% methanol and 40.8 g/L in 84% methanol. The adsorption capacity of CsA in acetonitrile-water was higher than that in methanol-water. When the mass concentration of CsA was 5 g/L, the adsorption capacity increased to 46.4 g/L in 75% acetonitrile. Scatchard analysis showed that the slope of the adsorption isotherm decreased gradually, which was consistent with trend observed in the Langmuir adsorption isotherm for the shape of the Langmuir peak (i.e. trailing peak). When the mass concentration of CsA in the mobile phase was between 0.01 g/L and 0.03 g/L, the slope of the curve decreased significantly, and the peak shape of CsA rapidly tailed with increasing loading amount. However, when using a mobile phase with a lower proportion of organic solvent (84% methanol or 75% acetonitrile), this trend was weakened. The adsorption data of CsA were fitted to models. The Langmuir model was found to be suitable for the methanol-water mobile phase, and the Moreau model for the acetonitrile-water mobile phase. The model parameters indicated that the monolayer adsorption of CsA occurred on the C18 stationary phase in both mobile phases, the difference being that more intermolecular interactions between CsA occurred in the acetonitrile-water mobile phase, resulting in a higher adsorption capacity. In methanol-water, the intermolecular interactions between CsA were inhibited by methanol due to its role as a proton donor. As an aprotic solvent, acetonitrile could only weakly inhibit these interactions; hence, the interactions could be improved by increasing the acetonitrile proportion. As the proportion of acetonitrile changed from 85% to 75%, the saturated adsorption capacity increased from 123 g/L to 197 g/L, while the interaction constant decreased from 0.618 to 0.588. Finally, CsA was purified using the conditions of 0-60 min 65%-75% acetonitrile, 60-80 min 75% acetonitrile, by which the impurity could be controlled to below 0.2%. The results of this study will aid in the purification of CsA by preparative HPLC.

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Determination of adsorbable organic halogens in textiles by ultrasonic extraction-high temperature combustion absorption-ion chromatography DING Youchao, CAO Lihua, ZHOU Liping, QIAN Kai, TANG Juan, ZHOU Jia, DONG Shaowei 2022, 40 (1):  74-81.  DOI: 10.3724/SP.J.1123.2021.03018 Abstract ( 290 )   HTML ( 26 )   PDF (1606KB) ( 96 )   Adsorbable organic halogens (AOX) are often introduced or produced in textile and dyeing processes, such as the chlorination shrink proof process of wool, the bleaching process by sodium hypochlorite and chlorite, the dry-cleaning process by chlorinated solvent, etc. However, part of AOX is difficult to biodegrade and is a persistent bioaccumulative toxic substance with high fat solubility. To promote clean production of textiles and to protect the health of consumers, a conventional method for the detection of AOX in textiles must be established urgently. In this study, a new method was developed for the determination of AOX in textiles by ultrasonic extraction-high temperature combustion absorption-ion chromatography (IC). In this method, AOX in textiles were extracted by ultrasonic extraction at room temperature with ultra-pure water as solvent. Activated carbon was added to the extraction solution for oscillatory adsorption and removal of inorganic halides with acidic sodium nitrate solution. The AOX adsorbed on activated carbon were cracked, burned, and gasified by the oxidative combustion method with a programmed heating mode. The product hydrogen halide gas entered the absorption solution with the carrier gas, followed by separation and determination by IC with external standard method of quantification. During the experiment, the pretreatment conditions were optimized, including the extraction time of AOX, the amount of activated carbon, the combustion gas and its flow rate, the temperature program for high-temperature oxidation combustion, the absorption method, and the absorption solution. The instrument conditions of ion chromatography, including the chromatographic column, column temperature, eluent, and its flow rate, were also optimized. The results showed that the method was linear in the range of 0.02-10 mg/L for the standard solutions of fluorine, chlorine, bromine, and iodine ions, and the correlation coefficients (R2) were greater than 0.999. The limits of quantification of the method for AOX were 0.10-0.50 mg/kg. The negative textile samples of cotton, wool, and polyester were used as the sample matrix, and typical organic halogens were selected for standard addition and recovery. At low, medium, and high spiked levels, the average recoveries of AOX in cotton, wool, and polyester fiber were 82.3%-98.7%. The corresponding relative standard deviations (RSDs, n=7) were 2.0%-5.7%, indicating that the method had good recovery and precision. This method was used to determine actual textile samples, and AOX at different contents were detected in blue coated polyester fabric and black modal fabric with good repeatability. The established method improved the recoveries of AOX converted into inorganic halogens via oscillating adsorption of activated carbon, high-temperature oxidation combustion with a programmed heating mode, and secondary absorption using a porous absorption bottle. Meanwhile, the separation and detection of halogen ions was successfully conducted using the ion chromatography instrument with good selectivity and high sensitivity, without any interference of impurity ions. The method is simple, accurate, and reliable, and fully meets the limit requirements of domestic and foreign regulations and textile standards; the method is also suitable for the detection and analysis of AOX in textiles.

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Determination of five water-soluble anions in solid and liquid aerosols by ion chromatography with a filter membrane and condensation collection YU Zuosi, LIU Yu, ZHU Yan 2022, 40 (1):  82-87.  DOI: 10.3724/SP.J.1123.2021.01007 Abstract ( 218 )   HTML ( 25 )   PDF (1359KB) ( 59 )   Water-soluble ions are important components of solid and liquid aerosols. The ions have a significant impact on the physical and chemical properties of the aerosols and air quality. Thus, determining the concentrations of water-soluble ions in solid and liquid aerosols has far-reaching significance for mitigating pollution and protecting the atmospheric environment. In this study, a technology combining membrane filtration, condensation, and ion chromatography has been established to collect solid aerosols and liquid aerosols and to measure the amount of five water-soluble anions (Cl-, F-, NO3-, NO2-, and SO42-) in these aerosols. First, a solid particle filter was used to collect the solid aerosol, and the condensation collection method was used to collect the liquid aerosol. The solid aerosol was collected in the solid particle filter in the form of solid particles, and the liquid aerosol was collected in the cold trap in the form of a condensate. Next, the amount of water-soluble anions in the solid aerosols and liquid aerosols was detected by ion chromatography using Dionex IonPac AS11-HC-4 μm as the analytical column. The chromatographic separation conditions were as follows: flow rate, 1 mL/min; column temperature, 30 ℃; potassium hydroxide (KOH) concentration of the eluent, 1 to 25 mol/L (linear increase) within 0-40 min; and injection volume, 100 μL. The ions were separated effectively within 40 min. The five anions showed good linear relationships in the range of 0.1-10 mg/L (correlation coefficients ranged from 0.9992 to 0.9997) and the detection limits were 0.02-0.04 mg/L. Finally, the sample collection conditions (sampling time, sampling temperature, and sampling flow rate) for the five water-soluble anions in the solid aerosols and liquid aerosols were optimized, and 2 h, -13 ℃, 1.0 L/min were chosen.Under the optimized conditions, the amounts of the five anions in the solid and liquid aerosols of the actual samples were detected. The mass concentrations of F-, Cl-, NO2-, NO3-, and SO42- ions in the liquid aerosol of the actual sample were 5.7402 μg/m3, 1.1599 μg/m3, 3.3233 μg/m3, 2.4861 μg/m3, and 0.9745 μg/m3, respectively. The mass concentrations of F-, Cl-, NO2-, NO3-, and SO42- ions in the solid aerosol of the actual sample were 14.1037 μg/m3, 5.0398 μg/m3, 9.3052 μg/m3, 8.4528 μg/m3, and 5.6314 μg/m3, respectively. The method can be applied to the detection of actual atmospheric ions detection. In addition, the collection and analysis methods are suitable for exploring the collection and analysis conditions of other ions.

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Novel submicron nonporous silica material modification with high carbon content and its application in reversed-phase pressurized capillary electrochromatography XIA Zihang, Soumia CHEDDAH, WANG Weiwei, WANG Yan, YAN Chao 2022, 40 (1):  88-99.  DOI: 10.3724/SP.J.1123.2021.03042 Abstract ( 220 )   HTML ( 24 )   PDF (6401KB) ( 130 )   Submicron nonporous silica (NPS) materials feature small particle sizes, smooth surfaces, and regular shapes. They also exhibit excellent performance as a stationary phase; however, their use is limited by their low specific surface area and low phase ratio. Therefore, a novel surface modification strategy tailored for NPS microspheres was designed, involving a multi-step reaction. 3-Glycidyloxypropyltrimethoxysilane (GPTS) was first grafted onto NPS particles as a silane coupling agent. Polyethyleneimine (PEI), a high-molecular-weight polymer, was then coated onto the particles, providing numerous amino reaction sites. In the final step, an acylation reaction was initiated between stearoyl chloride and the amino groups to obtain the final product, designated as C18-NH2-GPTS-SiO2. Elemental analysis, FT-IR spectroscopy, Zeta potential analysis, thermogravimetric analysis (TGA), and scanning electron microscopy (SEM) were employed to investigate the success of the chemical modifications at each step. The carbon content increased from 0.55% to higher than 8.29%. Thus, it solved the low carbon loading capacity problem when modifying NPS microspheres with traditional C18 reversed phase (e. g., octadecyl chlorosilane modification). Meanwhile, the reasons for the considerable differences between NPS and porous silica (PS) microspheres in terms of the reactivity to surface modification were investigated in detail. The BET method was employed to compare the pore structures. FT-IR and 29Si solid-state NMR spectroscopy were employed to analyze the differences in the structure and quantity of silanol groups on the surfaces of the NPS and PS microspheres. Differences were observed not only in the pore size and surface area, but also in the types of silanol groups. FT-IR analysis indicated that the NPS and PS microspheres had different υSi-OH band positions, which shifted from 955 to 975 cm-1, respectively. 29Si solid-state NMR analysis further highlighted the differences in structural information for Si atom environments. Results revealed that 16% of silicon atoms in the PS microspheres had one hydroxyl group (isolated silanols, Q3, δ 100), while 19% had two hydroxyl groups (geminal silanols, Q2, δ 90). On the other hand, the NPS microspheres possessed no geminal silanols, and only 30% of the Si atoms were in the Q3 state. Therefore, the NPS microspheres had a lower density of silanol groups and lacked geminal silanol groups, compared to the PS microspheres. Geminal silanol groups have already been confirmed in previous studies to offer far higher reactivity than isolated silanols. These factors together explained the low reactivity of NPS microspheres toward surface modification. Further, the low specific surface area of the microspheres arising from their nonporous nature made it challenging to obtain a high carbon content through a simple one-step reaction. Hydrophobic substances such as hydrocarbons from the benzene series and polycyclic aromatic hydrocarbons (PAHs) were selected to study the chromatographic performance. The hydrophobic mechanism was revealed by the separation of PAHs using different ratios of acetonitrile. Separation was achieved with a C18-NH2-GPTS-SiO2 column, following which a hydrophobic phenomenon occurred. The presence of the amino coating led to the inversion of the electroosmotic flow (EOF) of the silica microspheres on the pressurized capillary electrochromatography (pCEC) platform. It also enhanced the linear velocity in the pCEC platform when the pH was selected to be low. The effects of the applied voltage on the separation ability of the 720 nm C18-NH2-GPTS-SiO2 column were examined to determine optimal conditions. Rapid and effective separation was achieved in a relatively short time. Therefore, the C18-NH2-GPTS-SiO2 stationary phase is promising for practical use with a higher phase ratio, demonstrating superiority for use in reversed-phase pCEC separation, and thus, providing a new strategy and valuable reference for the future application of submicron NPS microspheres.

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Design and application of online derivatization device for polar organics on atmospheric particulate filter ZHANG Han, LIAO Xu, WEI Lai, ZHANG Zixing, REN Hongyun, ZHANG Xian 2022, 40 (1):  100-106.  DOI: 10.3724/SP.J.1123.2021.03009 Abstract ( 167 )   HTML ( 17 )   PDF (1727KB) ( 93 )   An online derivatization device for the analysis of polar organic compounds by gas chromatography-mass spectrometry (GC-MS) is designed. The derivatization reaction occurs in the hot GC injection port, and this is also known as injection port derivatization (IPD). IPD is usually performed in two ways: 1) direct IPD and 2) ion-pair extraction, followed by IPD. In both cases, the derivatization reagent reacts in liquid form. However, a method for online derivatization using gaseous derivatization reagents is provided. A special needle is designed and placed on the carrier gas transfer line to the injection port. The carrier gas is introduced into a glass bottle containing the derivative reagent (N-methyl-N-(trimethylsilyl)trifluoroacetamide, MSTFA), and then, the gaseous derivative reagent in the headspace is pressed out and introduced into the injection port of the GC instrument at a constant speed. The filter to be analyzed is placed directly in the liner, and the polar organic compounds on the filter react with gaseous MSTFA at 310 ℃ for 10 min in the injection port. During derivatization, the column oven is maintained at room temperature, and all the derivatives stay on the column head. When the reaction is complete, the MSTFA supply is ceased. The oven temperature is programmed, and the solvent delay is set until the excessive MSTFA is removed. The derivatives are allowed to pass through the column and analyzed by the MS detector. To prevent a large number of derivative reagents from entering the column, the injection port is set in split mode with a split ratio of 5∶1. Variables such as the injection-port temperature and derivatization time are investigated. The GC-MS responses of the ten silylated derivatives increase with increasing injection-port temperature (290-310 ℃), indicating that high temperatures can enhance the silylation efficiency. The derivatization times were also investigated. The GC-MS responses increased with an increase in the reaction time from 0 to 10 min, while higher temperatures or longer reaction times lead to the loss of some derivatives. The reproducibility of the derivatization reaction was 0.27% to 7.28%, and the linear correlation coefficient was 0.976-0.996. This device can be used for the online silylation of most polar organic compounds such as organic acids, alcohols, and phenols. The advantage of this device over offline derivatization is that the derivatization reagent and derivatives are protected by helium, which eliminates the risk of decomposition caused by moisture in the air, and the high temperature assists the reaction. The analytes were directly desorbed on the filter and derived online, and the sample quantity required was only 1/200 of that in the traditional solvent extraction method. Meanwhile, only the gaseous part of the headspace in the derivative reagent bottle was used, and the amount of derivative reagent was greatly reduced. Additionally, the operation is simple and solvent free, the entire analytical procedure was executed in a “green” manner. A PM2.5 filter was analyzed, and 26 different polar compounds were successfully derived, including monoacids, binary acids, aromatic acids, and alcohols, covering most of the common target polar compounds in atmospheric chemical analysis. Polyols such as glucose and sorbose that bear 5-6 hydroxyl groups and have large steric hindrance were also successfully derived. This device is expected to be an efficient and convenient analytical tool for tracing the sources of organic matter in atmospheric particles such as soil dust, biomass combustion, cooking oil smoke, and automobile exhaust, or for investigating atmospheric photochemical reactions. This gas-phase derivatization provides new insights for the development of chromatographic analysis methods for polar compounds. This device is simple and modular, and it has a wide range of applications; it is suitable for different brands of gas chromatographs and has great prospects for commercialization.