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Chinese Journal of Chromatography
2024, Vol. 42, No. 6
Online: 08 June 2024

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PREFACE

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Preface for Special Issues of Celebrating the 40th Anniversary of Chinese Journal of Chromatography ZHANG Lihua 2024, 42 (6):  495-495.  DOI: 10.3724/SP.J.1123.2024.05021 Abstract ( 112 )   HTML ( 39 )   PDF (704KB) ( 67 )

Perspective

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Recent advances in research on sample pretreatment methods based on supramolecular-derived porous organic polymers KANG Jingyan, SHI Yanping 2024, 42 (6):  496-507.  DOI: 10.3724/SP.J.1123.2023.09001 Abstract ( 85 )   HTML ( 19 )   PDF (3108KB) ( 56 )   Porous organic polymers (POPs) are a class of materials composed of organic building blocks usually consisting of the elements C, H, O, N, and B and other light elements connected by covalent bonds. Owing to the diversity of synthesis methods in organic chemistry, POPs can be prepared by Suzuki coupling, Sonogashira-Hagihara cross-coupling, Schiff-base condensation, Knoevenagel condensation, and Friedel-Crafts alkylation. POPs show great application potential in the field of sample pretreatment because of their large specific surface area, adjustable pore size, high tailorability, and easy modification. The design of new functional building blocks is an important factor in advancing the development of POPs and is key to the efficient separation and enrichment of target molecules in complex substrates. In recent years, supramolecular-derived compounds have provided new inspiration and breakthroughs in the construction of POPs on account of their excellent host-guest recognition properties, simple functionalization strategies, and adjustable topological configurations. The “cavitand-to-framework” approach, that is, the knitting of 0D macrocycles into hierarchical 2D or 3D POPs using suitable linkers, and extension of the research scope of supramolecular chemistry from discrete cavities to rigidly layered porous organic frameworks can lead to significant improvements in the porosity and stability of supramolecular-derived compounds. They can also provide an effective means to expand the structural diversity of POPs and generate layered structures with high porosity. This review summarizes the preparation strategies and structural characteristics of supramolecular-derived POPs with different structures, such as crown ether-based POPs, cyclodextrin-based POPs, and calixarene-based POPs. The promising applications of these materials in sample pretreatment focusing on food analysis and environmental monitoring, including epoxides, organic dyes, heavy metals, algatoxins, halogens, and antibiotic drugs, are then summarized. Next, the extraction mechanisms mainly attributed to host-guest recognition, π-π stacking, and hydrogen-bonding and electrostatic interactions between the supramolecular structures and analytes are described. The key role and potential advantages of the different preparation strategies and structural characteristics of these POPs in sample pretreatment are also discussed. Finally, the future prospects and remaining challenges of supramolecular-derived POPs are proposed. Supramolecular-derived POPs can not only achieve the rapid and selective extraction of target analytes during sample pretreatment but also improve the extraction effect of online solid phase extraction technologies. However, although numerous supramolecular-derived POPs have been developed, few have been applied in the field of sample pretreatment. Thus, the expansion of the application potential of more POP materials requires further exploration and research. The design and synthesis of supramolecular-derived POPs with highly selective recognition performance remains an important research direction in the field of sample pretreatment.

Reviews

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Recent advances of molecular imprinting technology for the separation and recognition of complex biological sample systems XIE Baoxuan, LYU Yang, LIU Zhen 2024, 42 (6):  508-523.  DOI: 10.3724/SP.J.1123.2024.01011 Abstract ( 112 )   HTML ( 20 )   PDF (3013KB) ( 50 )   Given continuous improvements in industrial production and living standards, the analysis and detection of complex biological sample systems has become increasingly important. Common complex biological samples include blood, serum, saliva, and urine. At present, the main methods used to separate and recognize target analytes in complex biological systems are electrophoresis, spectroscopy, and chromatography. However, because biological samples consist of complex components, they suffer from the matrix effect, which seriously affects the accuracy, sensitivity, and reliability of the selected separation analysis technique. In addition to the matrix effect, the detection of trace components is challenging because the content of the analyte in the sample is usually very low. Moreover, reasonable strategies for sample enrichment and signal amplification for easy analysis are lacking. In response to the various issues described above, researchers have focused their attention on immuno-affinity technology with the aim of achieving efficient sample separation based on the specific recognition effect between antigens and antibodies. Following a long period of development, this technology is now widely used in fields such as disease diagnosis, bioimaging, food testing, and recombinant protein purification. Common immuno-affinity technologies include solid-phase extraction (SPE) magnetic beads, affinity chromatography columns, and enzyme linked immunosorbent assay (ELISA) kits. Immuno-affinity techniques can successfully reduce or eliminate the matrix effect; however, their applications are limited by a number of disadvantages, such as high costs, tedious fabrication procedures, harsh operating conditions, and ligand leakage. Thus, developing an effective and reliable method that can address the matrix effect remains a challenging endeavor. Similar to the interactions between antigens and antibodies as well as enzymes and substrates, biomimetic molecularly imprinted polymers (MIPs) exhibit high specificity and affinity. Furthermore, compared with many other biomacromolecules such as antigens and aptamers, MIPs demonstrate higher stability, lower cost, and easier fabrication strategies, all of which are advantageous to their application. Therefore, molecular imprinting technology (MIT) is frequently used in SPE, chromatographic separation, and many other fields. With the development of MIT, researchers have engineered different types of imprinting strategies that can specifically extract the target analyte in complex biological samples while simultaneously avoiding the matrix effect. Some traditional separation technologies based on MIP technology have also been studied in depth; the most common of these technologies include stationary phases used for chromatography and adsorbents for SPE. Analytical methods that combine MIT with highly sensitive detection technologies have received wide interest in fields such as disease diagnosis and bioimaging. In this review, we highlight the new MIP strategies developed in recent years, and describe the applications of MIT-based separation analysis methods in fields including chromatographic separation, SPE, diagnosis, bioimaging, and proteomics. The drawbacks of these techniques as well as their future development prospects are also discussed.

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Preparation and application of chromatographic stationary phase based on two-dimensional materials ZHENG Desheng, TANG Wenqi, ZHU Jianping, GU Zhiyuan 2024, 42 (6):  524-532.  DOI: 10.3724/SP.J.1123.2024.01022 Abstract ( 90 )   HTML ( 13 )   PDF (1613KB) ( 58 )   The stationary phase is the heart of chromatographic separation technology and a critical contributor to the overall separation performance of a chromatographic separation technique. However, traditional silicon-based materials designed for this purpose usually feature complex preparation processes, suboptimal permeability, pronounced mass-transfer resistance, and limited pH-range compatibility. These limitations have spurred ongoing research efforts aimed at developing new chromatographic stationary phases characterized by higher separation efficiency, adaptable selectivity, and a broader scope of applicability. In this context, the scientific community has made significant strides toward the development of new-generation materials suitable for use as chromatographic stationary phases. These materials include carbon-based nanomaterial arrays, carbon quantum dots, and two-dimensional (2D) materials. 2D-materials are characterized by nanometer-scale thicknesses, extensive specific surface areas, distinctive layered structures, and outstanding mechanical properties under standard conditions. Thus, these materials demonstrate excellent utility in various applications, such as electrical and thermal conductivity enhancements, gas storage and separation solutions, membrane separation technologies, and catalysis. Graphene, which is arguably the most popular 2D-material used for chromatographic separation, consists of a 2D-lattice of carbon atoms arranged in a single layer, with a large specific surface area and efficient adsorption properties. Its widespread adoption in research and various industries is a testament to its versatility and effectiveness. In addition to graphene, the scientific community has developed various 2D-materials that mirror the layered structures of graphene, such as boron nitride, transition-metal sulfides, and 2D porous organic frameworks, all of which offer unique advantages. 2D porous organic frameworks, in particular, have received attention because of their nanosheet morphology, one-dimensional pores, and special interlayer forces; thus, these frameworks are considered promising candidate chromatographic stationary phase materials. Such recognition is especially true for 2D-metal organic frameworks (MOFs) and 2D-covalent organic frameworks (COFs), which exhibit low densities, high porosities, and substantial specific surface areas. The modifiability of these materials, in terms of pore size, shape, functional groups, and layer-stacking arrangements allows for excellent separation selectivity, highlighting their promising potential in chromatographic separation. Compared with their three-dimensional counterparts, 2D-MOFs feature a simple pore structure that offers reduced mass-transfer resistance and enhanced column efficiency. These attributes highlight the advantages of 2D-MOF nanosheets as chromatographic stationary phases. Similarly, 2D-COFs, given their high specific surface area and porosity, not only exhibit great thermal stability and chemical tolerance but also support a wide selection of solvents and operational conditions. Therefore, their role in the preparation of chromatographic stationary phases is considered highly promising. This review discusses the latest research developments in 2D porous organic framework materials in the context of gas- and liquid-chromatographic stationary phases. It introduces the synthesis methods for these novel materials, elucidates their retention mechanisms, and describes the applications of other 2D-materials, such as graphene, its derivatives, graphitic carbon nitride, and boron nitride, in chromatography. This review aims to shed light on the promising development prospects and future directions of 2D-materials in the field of chromatographic separation, offering valuable insights into the rational design and application of new 2D-materials in chromatography.

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Recent progress of chromatographic techniques for antibody purification LIU Jiawei, TANG Changwei, XIA Yiran, BAI Quan 2024, 42 (6):  533-543.  DOI: 10.3724/SP.J.1123.2023.12010 Abstract ( 161 )   HTML ( 21 )   PDF (1184KB) ( 109 )   Antibody drugs are becoming increasingly popular in disease diagnosis, targeted therapy, and immunoprevention owing to their characteristics of high targeting ability, strong specificity, low toxicity, and mild side effects. The demand for antibody drugs is steadily increasing, and their production scale is expanding. Upstream cell culture technology has been greatly improved by the high-capacity production of monoclonal antibodies. However, the downstream purification of antibodies presents a bottleneck in the production process. Moreover, the purification cost of antibodies is extremely high, accounting for approximately 50%-80% of the total cost of antibody production. Chromatographic technology, given its selectivity and high separation efficiency, is the main method for antibody purification. This process usually involves three stages: antibody capture, intermediate purification, and polishing. Different chromatographic techniques, such as affinity chromatography, ion-exchange chromatography, hydrophobic interaction chromatography, mixed-mode chromatography, and temperature-responsive chromatography, are used in each stage. Affinity chromatography, mainly protein A affinity chromatography, is applied for the selective capture and purification of antibodies from raw biofluids or harvested cell culture supernatants. Other chromatographic techniques, such as ion-exchange chromatography, hydrophobic interaction chromatography, and mixed-mode chromatography, are used for intermediate purification and antibody polishing. Affinity biomimetic chromatography and hydrophobic charge-induction chromatography can produce antibodies with purities comparable with those obtained through protein A chromatography, by employing artificial chemical/short peptide ligands with good selectivity, high stability, and low cost. Temperature-responsive chromatography is a promising technique for the separation and purification of antibodies. In this technique, antibody capture and elution is controlled by simply adjusting the column temperature, which greatly eliminates the risk of antibody aggregation and inactivation under acidic elution conditions. The combination of different chromatographic methods to improve separation selectivity and achieve effective elution under mild conditions is another useful strategy to enhance the yield and quality of antibodies. This review provides an overview of recent advances in the field of antibody purification using chromatography and discusses future developments in this technology.

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Progress of highly reproducible capillary electrophoresis GUO Zhenpeng, CHEN Yi 2024, 42 (6):  544-554.  DOI: 10.3724/SP.J.1123.2023.12004 Abstract ( 75 )   HTML ( 17 )   PDF (1907KB) ( 32 )   Following rapid developments in capillary electrophoresis (CE), this technology has become an established analytical technique owing to its microscale characteristics, high speed, high efficiency, and versatility. However, the challenges of poor peak stability and/or reproducibility have consistently hindered its wider applications. CE has long been used as a measurement tool for plotting signal intensities versus the migration time; however, the migration time is not an independent variable in CE, but is affected by many direct and indirect parameters, including capillary (length, diameter, and inner surface properties), electric field (or voltage, current, and/or power), temperature, and running buffer (electrolytes, additives, solvents, and their concentration, buffering pH, etc.). These intricacies render the acquisition of reproducible electropherograms difficult. Various studies ranging from those on the early stages of CE development to those on the exploration of three important strategies have been conducted to address this issue. In the first strategy, the CE conditions, especially those parameters that can maintain a stable electro-osmotic flow, are strictly controlled and stabilized to significantly improve peak repeatability. In the second strategy, either the peak position is corrected using internal standards or the peak time is converted into other variables, such as electrophoretic mobility, to offset or eliminate some unstable factors, thereby improving the repeatability and even reproducibility of the peaks; this strategy is useful when plotting signals versus the migration time ratio, correlated migration time, effective mobility, or temperature-correlated mobility. In the third strategy, a new methodology called highly reproducible CE (HRCE) is established using theoretical studies to explore better principles for real-time CE with the aim of the complete removal of the challenge from the root. This strategy includes the development of novel methods that plot electropherograms based on weighted mobility, migrated charge, charge density, or partial differential molar charge density. Similar to ordinary CE approaches, this strategy can also draw electropherograms based on the ratios of these properties. As theoretically predicted, these novel methods can offset or resist changes in critical CE conditions (mainly electric field strength, capillary length and diameter, and/or some buffer parameters such as concentration). Our experimental results demonstrate that given certain prerequisites, a new set of methods can produce highly reproducible electropherograms. This review focuses on the theoretical basis and advancements of HRCE, and elucidates the link between electrophoretic migration/peak expression theories and their impact on reproducibility. Studies on the transformation of time-scale electropherograms in the CE literature are summarized and analyzed in general. However, this review does not directly discuss research on and progress in improving CE repeatability or reproducibility through instrument upgrades, parameter optimization, or practical method refinements.

Articles

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Preparation of peptide-functionalized affinity materials for the highly specific capture and analysis of mitochondria CHEN Jian, XU Kun, GAO Han, ZHAO Rui, HUANG Yanyan 2024, 42 (6):  555-563.  DOI: 10.3724/SP.J.1123.2024.01013 Abstract ( 82 )   HTML ( 25 )   PDF (1761KB) ( 36 )   Mitochondria perform various metabolic processes that significantly affect cell differentiation, proliferation, signal transduction, and programmed cell death. The disruption of mitochondrial bioenergetic and metabolic functions is closely related to many disorders. The specific isolation and purification of intact, high-purity, and functional mitochondria are central to the understanding of their mechanism of action but remain challenging tasks. In this study, a mitochondrial penetrating peptide (MPP) with the sequence FrFKFrFK(Ac) was used as a mitochondrial recognition motif to construct a peptide-guided affinity separation material. The multiple aromatic phenylalanine (F) residues in this amphiphilic peptide can confer lipophilicity to the mitochondrial membrane, whereas the basic residues (D-arginine and lysine) render the MPP surface positively charged, thereby promoting the binding of negatively charged mitochondria. After the derivatization of the N terminal of MPP with an oligoglycine spacer, the peptide ligands were conjugated to matrix beads (MB) with surface aldehyde functional groups. Peptide functionalization was performed via a condensation reaction between the amino group in the peptide ligand and the aldehyde group on the beads. The generated Schiff bases were reduced, affording stable covalent bonds. The dense and stable functionalization of the beads with the mitochondria-targeting peptides was demonstrated using high performance liquid chromatography (HPLC), zeta potential assay, and scanning electron microscopy (SEM). The immobilization efficiency of the peptide ligands was 1.47 μmol/g, and the surface potential of MB@MPP was 11 mV. MB@MPP was used for the direct isolation of mitochondria after cell homogenization. As observed by SEM, mitochondria with a cross-sectional diameter of 500 nm were efficiently captured on the MB@MPP surface. Because the mitochondrial membrane potential is an important marker of mitochondrial function and the driving force behind the staining of mitochondria with Mito Tracker dyes, the specific binding and separation of fluorescent mitochondria from the cell samples revealed that the proposed MB@MPP-based isolation approach can keep mitochondria intact and retain their functions. Western blot assays were employed to characterize the protein markers of the mitochondria (citrate synthase (CS) and voltage-dependent anion channel protein (VDAC)) and cytoplasmic protein (vinculin), and examine the integrity and purity of the captured mitochondria. The results showed that the lysates released from MB@MPP had high CS and VDAC contents. By contrast, vinculin, which is highly abundant in whole-cell lysates, was barely detected in the lysates from MB@MPP. These results suggest that MB@MPP isolates mitochondria with high affinity, specificity, and antifouling ability by using the targeting peptide as the capture handle. A comparison with a commercial mitochondrial isolation kit demonstrated that MB@MPP can separate mitochondria with higher CS and VDAC abundance and purity. Given the superior separation performance of MB@MPP, the molecular profiles of the isolated mitochondria under stress were subjected to further analysis of their molecular profiles under stress. A liquid chromatography-tandem mass spectrometry (LC-MS/MS) method was established to detect tryptophan (Trp) and riboflavin in the mitochondria. Quantification was performed in multiple-reaction monitoring (MRM) mode. Owing to the high purity of the mitochondria, the Trp and riboflavin contents were determined to be 265 and 0.67 nmol/mg, respectively. The metabolic response of mitochondria to external stimuli was further examined using acadesine, an adenosine 5'-monophosphate (AMP)-activated protein kinase activator with a wide range of metabolic effects, to treat cells. After cell homogenization, MB@MPP was used to separate the mitochondria from the cell samples with and without acadesine treatment, followed by LC-MS/MS analysis. The quantification results demonstrated that acadesine induced a 14% upregulation of Trp content in the mitochondria. By contrast, the riboflavin content decreased to 0.48 nmol/mg, which is 72% of that in untreated mitochondria. The changes in Trp and riboflavin contents could influence their metabolic pathways and, thus, the levels of their metabolites, such as nicotinamide adenine dinucleotide, flavin mononucleotide, and flavin adenine dinucleotide, which are essential coenzymes in mitochondria. Peptide-functionalized affinity microbeads with high affinity and specificity for mitochondria are promising for the efficient isolation of high-quality mitochondria, and offer a useful tool for understanding the complicated functions and dynamics of this unique organelle.

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Preparation of magnetic carbon nitride composite toward phosphopeptide enrichment JIANG Liyan, ZHANG Weilu, ZHAO Lu, HU Lianghai 2024, 42 (6):  564-571.  DOI: 10.3724/SP.J.1123.2023.11007 Abstract ( 57 )   HTML ( 12 )   PDF (1060KB) ( 28 )   Protein phosphorylation plays an important role in cellular signaling and disease development. Advances in mass spectrometry-based proteomics have enabled qualitative and quantitative phosphorylation studies as well as in-depth biological explorations for biomarker discovery and signaling pathway analysis. However, the dynamic changes that occur during phosphorylation and the low abundance of target analytes render direct analysis difficult because mass spectral detection offers no selectivity, unlike immunoassays such as Western blot and enzyme-linked immunosorbent assay (ELISA). The present study aimed to solve one of the key problems in the specific and efficient isolation of phosphorylated peptides. A method based on a magnetic carbon nitride composite coupled with matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) was developed for the enrichment and analysis of phosphopeptides with low abundance in complex samples. Magnetic carbon nitride composite was synthesized and characterized by electron microscopy, infrared spectroscopy, and X-ray diffractometry. The composite showed a well-distributed two-dimensional layered structure and functional groups with excellent paramagnetic performance. Two classical phosphoproteins, namely, α- and β-caseins, were selected as model phosphorylated samples to assess the performance of the proposed enrichment technique. The magnetic carbon nitride composite exhibited high selectivity and sensitivity for phosphopeptide enrichment. The limit of detection was determined by MALDI-TOF-MS analysis to be 0.1 fmol. The selectivity of the method was investigated using the digest mixtures of α-casein, β-casein, and bovine serum albumin (BSA) with different mass ratios (1∶1∶1000, 1∶1∶2000, and 1∶1∶5000). Direct analysis of the samples revealed the dominance of spectral signals from the abundant peptides in BSA. After enrichment with the magnetic carbon nitride composite, the high concentration of background proteins was washed away and only the signals of the phosphopeptides were captured. The signals from the casein proteins were clearly observed with little background noise, indicating the high selectivity of the composite material. The robustness of the method was tested by assessing the reusability of the same batch of magnetic carbon nitride materials over 20 cycles of enrichment. The composite showed nearly the same enrichment ability even after several cycles of reuse, demonstrating its potential applicability for a large number of clinical samples. Finally, the method was applied to the analysis of phosphopeptides from several commonly used phosphoprotein-containing samples, including skimmed milk digest, human serum, and human saliva; these samples are significant in the analysis of food quality, disease biomarkers, and liquid biopsies for cancer. Without enrichment, no phosphopeptide was detected because of the high abundance of nonphosphopeptide materials dominating the spectral signals obtained. After pretreatment with the developed magnetic carbon nitride composite, most of the phosphosites were identified with high selectivity and sensitivity via MALDI-TOF-MS. These results revealed the practicality of the developed approach for clinical applications. In addition, our method may potentially be employed for phosphoproteomics with real complex biological samples.

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Synthesis of fluorinated nitrogen-rich porous organic polymers and removal of perfluorooctanoic acid from water CHEN Xin, QIAN Wenping, CHEN Tianqi, SHAO Lingyun, ZHANG Wenfen, ZHANG Shusheng 2024, 42 (6):  572-580.  DOI: 10.3724/SP.J.1123.2024.04006 Abstract ( 73 )   HTML ( 13 )   PDF (4914KB) ( 40 )   Perfluorooctanoic acid (PFOA) is a persistent contaminant with detrimental effects on the natural environment. This persistence leads to potential enrichment and osmotic transfer, which can affect normal circulation in the environment. PFOA poses significant threats to both the natural environment and human health. Therefore, the development of cost-effective, highly efficient, and environment-friendly PFOA adsorbents is a crucial endeavor. This paper presents the catalyst-free one-pot synthesis of fluorinated nitrogen-rich porous organic polymers (POP-3F) via a Schiff-base condensation reaction. The reaction between the nitrogen-rich compound 1,4-bis(2,4-diamino-1,3,5-triazine)benzene and p-trifluoromethylbenzaldehyde yielded POP-3F. The introduction of fluorine atoms into the nitrogen-rich porous organic polymer enhanced its hydrophobicity, thereby facilitating favorable fluoro-fluorine interactions with PFOA and, thus, improving the efficacy of the adsorbent. Scanning electron microscopy (SEM), Fourier transform infrared (FT-IR) spectroscopy, X-ray diffraction (XRD), solid-state nuclear magnetic resonance (ssNMR) spectroscopy, X-ray photoelectron spectroscopy (XPS), nitrogen adsorption-desorption analysis, and thermogravimetric analysis (TGA) were used to confirm the successful synthesis and characterization of POP-3F. Liquid chromatography-tandem mass spectrometry (LC-MS/MS) was conducted in negative electrospray ionization (ESI) mode coupled with multi-reaction monitoring mode (MRM). The instrument was equipped with an Atlantis T3 column (100 mm×2.1 mm, 3 μm), and analysis was conducted using an external standard method. The influences of various factors on PFOA adsorption by POP-3F, including pH, salt concentration, and humic acid presence, were investigated. The highest PFOA removal rate (98.6%) was achieved at a pH of 2, indicating the applicability of POP-3F for the effective removal of PFOA from acidic industrial wastewater. The removal rate of PFOA was unaffected by increases in NaCl concentration. This phenomenon can be attributed to electrostatic interactions between the protonated secondary amines in POP-3F and deprotonated PFOA. Upon the addition of NaCl, a double electric layer is formed on the POP-3F surface, with Cl- ions in the outer layer and Na+ ions in the inner layer, which weakened these interactions. Humic acid is competitively adsorbed with PFOA. However, POP-3F demonstrated good removal rates even in the presence of high humic acid concentrations in water. Adsorption isotherm and kinetics experiments were conducted at the optimal pH to explore the relevant adsorption mechanism. The results showed a rapid initial adsorption rate, with 95.4% PFOA removal within 5 min. Optimal adsorption equilibrium was achieved within 6 h, and the removal rate decreased by only 0.3% after 24 h. This finding indicates that POP-3F exhibits sustained efficacy for PFOA removal. Langmuir fitting analysis revealed a theoretical maximum adsorption capacity of 191 mg/g for POP-3F; this value surpasses those of activated carbon materials and most other adsorbents, highlighting the superior PFOA-adsorption performance of POP-3F. Additionally, matrix effects minimally affected the removal of PFOA by POP-3F, with only a slight reduction (0.1%) observed in simulated natural water. The recyclability of POP-3F was assessed over five adsorption-desorption cycles. The removal efficenecy exhibited a minor decrease of only 0.67% after five cycles. These results demonstrate the recyclability of the proposed adsorbent, which translates into cost reduction through reusability. This characteristic renders POP-3F a promising candidate for the economical and efficient removal of PFOA from wastewater in practical applications.

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Determination of fatty acid composition after saponification of common oil pharmaceutical excipients by supercritical fluid-evaporative light scattering method and its application in oil identification WANG Ziying, SHI Haiwei, MA Congyu, LIU Wenyuan, CHEN Lei, LIU Zhen, YUAN Yaozuo, ZHANG Mei, TANG Sheng 2024, 42 (6):  581-589.  DOI: 10.3724/SP.J.1123.2024.01003 Abstract ( 40 )   HTML ( 9 )   PDF (1324KB) ( 21 )   Supporting Information Oils and fats are commonly used in the pharmaceutical industry as solvents, emulsifiers, wetting agents, and dispersants, and are an important category of pharmaceutical excipients. Fatty acids with unique compositions are important components of oil pharmaceutical excipients. The Chinese Pharmacopoeia provides clear descriptions of the fatty acid types and limits suitable for individual oil pharmaceutical excipient. An unqualified fatty acid composition or content may indicate adulteration or deterioration. The fatty acid composition, as a key indicator for the identification and adulteration evaluation of oil pharmaceutical excipients, can directly affect the quality and safety of oil pharmaceutical excipients and preparations. Gas chromatography is the most widely used technique for fatty acid analysis, but it generally requires derivatization, which affects quantitative accuracy. Supercritical fluid chromatography (SFC), an environmentally friendly technique with excellent separation capability, offers an efficient method for detecting fatty acids without derivatization. Unlike other chromatographic methods, SFC does not use nonvolatile solvents (e. g., water) as the mobile phase, rendering it compatible with an evaporative light-scattering detector (ELSD) for enhanced detection sensitivity. However, the fatty acids in oil pharmaceutical excipients exist in the free and bound forms, and the low content of free fatty acids in these oil pharmaceutical excipients not only poses challenges for their detection but also complicates the determination of characteristic fatty acid compositions and contents. Moreover, the compositions and ratios of fatty acids are influenced by environmental factors, leading to interconversion between their two forms. In this context, saponification provides a simpler and faster alternative to derivatization. Saponification degrades oils and fats by utilizing the reaction between esters and an alkaline solution, ultimately releasing the corresponding fatty acids. Because this method is more cost effective than derivatization, it is a suitable pretreatment method for the detection of fatty acids in oil pharmaceutical excipients using the SFC-ELSD approach. In this study, we employed SFC-ELSD to simultaneously determine six fatty acids, namely, myristic acid, palmitic acid, stearic acid, arachidic acid, docosanoic acid, and lignoceric acid, in oil pharmaceutical excipients. Saponification of the oil pharmaceutical excipients using sodium hydroxide methanol solution effectively avoided the bias in the determination of fatty acid species and contents caused by the interconversion of fatty acids and esters. The separation of the six fatty acids was achieved within 12 min, with good linearity within their respective mass concentration ranges. The limits of detection and quantification were 5-10 mg/L and 10-25 mg/L, respectively, and the spiked recoveries were 80.93%-111.66%. The method proved to be sensitive, reproducible, and stable, adequately meeting requirements for the analysis of fatty acids in oil pharmaceutical excipients. Finally, the analytical method was successfully applied to the determination of six fatty acids in five types of oil pharmaceutical excipients, namely, corn oil, soybean oil, coconut oil, olive oil, and peanut oil. It can be combined with principal component analysis to accurately differentiate different types of oil pharmaceutical excipients, providing technical support for the rapid identification and quality control of oil pharmaceutical excipients. Thus, the proposed method may potentially be applied to the analysis of complex systems adulterated with oil pharmaceutical excipients.

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Highly sensitive detection of fluorescent whitening agents in flour using sheathless capillary electrophoresis-electrospray ionization-tandem mass spectrometry WANG Anping, CHEN Chushi, YANG Jinlan, YANG Li 2024, 42 (6):  590-598.  DOI: 10.3724/SP.J.1123.2023.11023 Abstract ( 63 )   HTML ( 11 )   PDF (1753KB) ( 32 )   Fluorescent whitening agents (FWAs) are dyes that emit visible blue or blue-purple fluorescence upon ultraviolet-light absorption. Taking advantage of light complementarity, FWAs can compensate for the yellow color of many substances to achieve a whitening effect; thus, they are used extensively in various applications. FWAs are generally stable, but their presence in the environment can lead to pollution and accumulation in the body through the food chain. Recent studies have revealed that some types of FWAs, such as coumarin-based FWAs, may exhibit photo-induced mutagenic effects that can trigger allergic reactions in humans and even pose carcinogenic risks. Hence, the development of an accurate and highly sensitive method for detecting FWAs in food-related samples is a crucial endeavor. Owing to the high polarity and structural similarity of FWAs, the accurate determination of these substances in complex food samples requires an analytical method that offers both efficient separation and sensitive detection. Capillary electrophoresis (CE) exhibits essential features such as high separation efficiency, short analysis times, very small sample injection requirements, minimal use of organic solvents, and simple operation. Thus, it is often used as an effective alternative to liquid chromatographic techniques. Over the past few decades, electrospray ionization mass spectrometry (ESI-MS) has been utilized as a highly sensitive and accurate detection method in numerous chemical analytical fields because it enables the analysis of molecular structures. By combining the high separation efficiency of CE with the high sensitivity of ESI-MS, a powerful tool for identifying and quantifying trace amounts of FWAs in food samples may be obtained. In this study, we present a method based on sheathless CE coupled with electrospray ionization tandem mass spectrometry (ESI-MS/MS) for the simultaneous detection of six trace FWAs in flour. In the proposed method, the CE separation device is directly coupled to the mass spectrometer through a sheathless interface without the need for a sheath liquid for electric contact, thereby avoiding the dilution of the analytes and improving detection sensitivity. Various conditions that could affect extraction recovery, separation efficiency, and detection sensitivity were evaluated and optimized. The FWAs were effectively extracted from the sample matrix with reduced matrix effects by ultrasonic-assisted extraction at a temperature of 30 ℃ for 20 min using CHCl3-MeOH (3∶2, v/v) as the extraction solvent. The extract was centrifuged, dried under N2, and reconstituted in CHCl3-MeOH (1∶4, v/v) for subsequent analysis. During the detection process, the CE device was coupled to the ESI-MS/MS instrument via a highly sensitive porous spray needle, which served as the sheathless electrospray interface. The target FWAs were scanned in positive-ion mode (ESI+) to ensure the stability and intensity of the obtained signals. Additionally, multiple-reaction monitoring (MRM) mode and MS/MS analysis were used to simultaneously quantify the six targets with high selectivity. The developed sheathless CE-ESI-MS/MS method detected the FWAs with high sensitivity over wide linear ranges with low method limits of detection (0.04-0.67 ng/g). The recoveries of the six target FWAs at three spiked levels were between 77.5% and 97.2%, with good interday (RSD≤11.5%) and intraday (RSD≤10.2%) precision. Analyses of the six target FWAs in eight commercial flour samples were performed using this method, and four positive samples were identified. These results demonstrate that the proposed CE-ESI-MS/MS method is a promising strategy for the determination of trace FWAs in complex food sample matrices with efficient separation and high sensitivity.