Rapid identification and determination of pyrrolizidine alkaloids in herbal and food samples via direct analysis in real-time mass spectrometry

Paper-immobilized liquid-phase microextraction for direct paper spray mass spectrometry and immuno-detection of atropine in baby food, buckwheat cereals, and edible oils at regulatory levels

BACKGROUND

Atropine is a strictly regulated natural toxin. Monitoring for atropine is thus important, but often expensive and time-consuming. Moreover, the range of relevant matrices, and corresponding differences in required detection limits for atropine vary. Therefore, we developed a more simplified and affordable method, combining immunodetection and mass spectrometry to detect atropine in buckwheat, canola oil, and baby cereals at regulatory levels.

RESULTS

In this method, atropine is selectively enriched on paper using a dual-paper-immobilized liquid-phase microextraction (PI-LPME; enrichment ∼144×). One PI-LPME paper can be directly coupled to a lateral flow immunoassay, for initial screening. In case of a suspect sample, the other PI-LPME paper is transported to a laboratory, where it can be stored at room temperature (recovery >90%, no difference between 1 and 10 days of storage). The PI-LPME paper can then be analyzed with paper spray-(high resolution) mass spectrometry (PS-(HR)MS). Using atropine-d5 as internal standard, the PS-HRMS method could reach detection limits in matrix almost as low as HPLC-HRMS, respectively 1.2-2.7 μg kg-1 and 0.2-1.3 μg kg-1. Furthermore, the accuracy and precision of the PS-HRMS method was comparable to HPLC-HRMS for buckwheat cereals (precision: 8.7%-9.6% vs. 7.6%-10%, accuracy: -4.0%-17% vs. -6.7%-15%) and canola oil (precision: 6.4%-10% vs. 1%-1.8%, accuracy: -12%-7.7% vs. -2.4%-1.9%).

SIGNIFICANCE

Our paper-based workflow has the potential to aid in the fast and affordable monitoring of atropine. Importantly, the method's suitability is demonstrated for diverse matrices, and it is expected that it can be easily adapted to monitor for other food safety hazards - given the wide applicability of liquid-liquid extractions.

Rapid on-site identification of pyrrolizidine alkaloids in herbal medicines using miniature mass spectrometry

Pyrrolizidine alkaloids (PAs) are naturally occurring plant toxins with significant multi-organ toxicity, especially hepatotoxicity. Accidental consumption of PAs-containing herbal medicines can lead to severe health consequences, emphasizing the need for rapid and effective detection methods to ensure medicinal safety. In this study, we developed a novel on-site rapid analytical method using paper capillary spray miniature mass spectrometry (PCS-mini MS), and created a database containing 34 different PAs with a detection limit ranging from 0.5 to 2 ng mL-1. This method is particularly suitable for identifying PAs in herbal medicines, the accuracy of PCS-mini MS was validated through high-performance liquid chromatography-mass spectrometry. Furthermore, the method's environmental impact was assessed using three green evaluation tools, demonstrating its compliance with green analytical chemistry principles, highlighting both efficiency and sustainability. This study provides a convenient and precise approach for regulating the herbal medicine market, enabling quick identification of toxic plants and reducing the risk of adverse health effects from herb misidentification. In the future, this method is expected to be widely adopted for clinical applications and market regulation of herbal products.

Quantitative Analysis of Pyrrolizidine Alkaloids in Food Matrices and Plant-Derived Samples Using UHPLC-MS/MS

Pyrrolizidine alkaloids (PAs) are a class of nitrogen-containing basic organic compounds that are frequently detected in foods and herbal medicines. Owing to their potential hepatotoxic, genotoxic, and carcinogenic properties, PAs have become a significant focus for monitoring global food safety. In this study, an ultra-high-performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS) method was developed for the detection and analysis of three foods (tea, honey, and milk) susceptible to PA contamination. This optimized method effectively separated and detected three types of PAs, namely, three pairs of isomers and two pairs of chiral compounds. The limits of detection (LODs) and limits of quantification (LOQs) were determined to be 0.015-0.75 and 0.05-2.5 µg/kg, respectively, with the relative standard deviations (RSDs) of both the interday and intraday precisions remaining below 15%. The average PA recoveries from the honey, milk, and tea matrices fell within the ranges of 64.5-103.4, 65.2-112.2, and 67.6-107.6%, respectively. This method was also applied to 77 samples collected from 33 prefecture-level cities across 16 provinces and included 40 tea, 6 milk, 8 honey, 14 spice, and 9 herbal medicine samples. At least one PA was detected in twenty-three of the samples, with herbal medicines exhibiting the highest total PA content. The obtained results indicate that the developed method demonstrated good repeatability and stability in the detection and quantitative analyses of PAs in food- and plant-derived samples. This method is therefore expected to provide reliable technical support for food safety risk monitoring.

In situ identification of gastroprotective components from Dendrobium huoshanense using magnetic nanoparticles combined with biomaterials assisted EFISI-MS

The identification of natural active compounds is typically a cumbersome and time-intensive process due to the necessity for elaborate sample pretreatment, leading to inefficiencies. Although recent advancements have introduced methods for targeted screening of these active compounds, they still demand intricate sample handling, and in severe cases, critical active compounds may be lost or degraded beyond detection. This study capitalizes on the novel discovery that Fe3O4 magnetic nanoparticles (MNPs) can be stably immobilized onto a magnetized steel probe of the electrostatic field induced spray ionization mass spectrometry (EFISI-MS) platform. By employing a method that targets the isolation of active compounds using MNPs paired with biomaterials (such as enzymes and cell membranes), we fixed complexes of cell membranes bound to Fe3O4 MNPs onto the magnetized probe through magnetic adsorption. This modified probe enables direct sampling from fresh plants, followed by EFISI-MS analysis. Employing this method, we successfully identified three gastroprotective compounds (schaftoside, isoschaftoside and 4-allyl-2,6-dimethoxyphenyl glucoside) directly from fresh Dendrobium huoshanense in situ, eliminating the need for preliminary sample treatment. The structures of these compounds were confirmed through total synthesis and comparative analysis with standards. Further biological experiments demonstrated that these compounds not only enhanced the survival rate of MNNG induced GES-1 cells in vitro in a dose-dependent manner but also significantly ameliorated gastric mucosal injury in a mouse model. Furthermore, the conventional approach using Fe3O4 MNPs combined with cell membranes to extract components from D. huoshanense failed to detect active compound 4-allyl-2,6-dimethoxyphenyl glucoside. This demonstrates that our newly developed methodology not only facilitates the direct in situ identification of plant derived active compounds but also significantly improves the detection rate of these bioactive substances.

Recent application of direct analysis in real time mass spectrometry in plant materials analysis with emphasis on traditional Chinese herbal medicine

Direct analysis in real time (DART) represents a new generation of ionization techniques that are used to rapidly ionize small molecules under ambient environments. The combination of DART with various mass spectrometry (MS) instruments allows analyzing multiple plant materials, including traditional Chinese herbal medicines (TCHMs), under simple or no sample treatment conditions. This review discussed the DART principles, including devices, ionization mechanisms, and operation parameters. Typical spectra detected by DART-MS were exhibited and discussed. Numerous applications of DART-MS in the fields of plant material and TCHM analysis were reviewed, including compound identification, biomarker discovery, fingerprinting analysis, and quantification analysis. Besides, modifications and improvements of DART-MS, such as hyphenated application with other separation methods, laser-based desorption techniques, and online sampling configuration, were summarized as well.

Novel litchi-like Au-Ag nanospheres driven dual-readout lateral flow immunoassay for sensitive detection of pyrimethanil

Pyrimethanil (PYR) is a fungicide that is harmful to consumers when present in foods at concentrations greater than maximum permitted residue levels. High-performance immunoprobes and dual-readout strategy may be useful for constructing sensitive lateral flow immunoassay (LFIA). Herein, the prepared litchi-like Au-Ag bimetallic nanospheres (LBNPs) exhibited high mass extinction coefficients and fluorescence quenching constants. Benefiting from LBNPs and dual-readout mode, the limits of detection of LBNPs-CM-LFIA and LBNPs-FQ-LFIA for PYR were 0.957 and 0.713 ng mL-1, which were 2.54- and 3.41-fold lower than that of gold nanoparticles-based LFIA, respectively. The limits of quantitation of LBNPs-CM-LFIA and LBNPs-FQ-LFIA were 3.740 and 1.672 ng mL-1, respectively. LBNPs-LFIA was applied to detect PYR in cucumber and grape samples with satisfactory recovery (90%-111%). LBNPs-LFIA showed good agreement with LC-MS/MS for the detection of PYR in the samples. Accordingly, this sensitive and accurate dual-readout LFIA based on LBNPs can be effectively applied for food safety.

Pyrrolizidine Alkaloids as Hazardous Toxins in Natural Products: Current Analytical Methods and Latest Legal Regulations

Pyrrolizidine alkaloids (PAs) are toxic compounds that occur naturally in certain plants, however, there are many secondary pathways causing PA contamination of other plants, including medicinal herbs and plant-based food products, which pose a risk of human intoxication. It is proven that chronic exposure to PAs causes serious adverse health consequences resulting from their cytotoxicity and genotoxicity. This review briefly presents PA occurrence, structures, chemistry, and toxicity, as well as a set of analytical methods. Recently developed sensitive electrochemical and chromatographic methods for the determination of PAs in honey, teas, herbs, and spices were summarized. The main strategies for improving the analytical efficiency of PA determination are related to the use of mass spectrometric (MS) detection; therefore, this review focuses on advances in MS-based methods. Raising awareness of the potential health risks associated with the presence of PAs in food and herbal medicines requires ongoing research in this area, including the development of sensitive methods for PA determination and rigorous legal regulations of PA intake from herbal products. The maximum levels of PAs in certain products are regulated by the European Commission; however, the precise knowledge about which products contain trace but significant amounts of these alkaloids is still insufficient.

Rapid analysis of bioactive compounds from citrus samples by direct analysis in real-time mass spectrometry combined with chemometrics

Renowned for their nutritional benefits, citrus fruits are harvested at various stages in China for functional food production. This study introduces an innovative analytical method, DART-MS, enabling direct qualitative analysis of citrus samples without the need for preprocessing. Simultaneously, the combination of chemometrics can be applied to distinguish between three different citrus samples: Citri Reticulatae Pericarpium, Citri Reticulatae Pericarpium Viride, and Citri Reticulatae "Chachi". Notably, given the international regulatory concerns surrounding synephrine, a precise quantitative analysis method for synephrine was developed. The limit of detection (LOD) and the limit of quantification (LOQ) were 39 ng mL-1 and 156 ng mL-1, respectively. The recovery rates obtained varied from 98.46% to 100.71%. Furthermore, the intra-day and inter-day precision demonstrated robust consistency, with values spanning 5.0-6.1% and 5.03-6.08%, respectively, offering quicker results compared to those from HPLC-MS, promising a safer assessment of herbal and food products.

Mass spectrometric analysis strategies for pyrrolizidine alkaloids

Pyrrolizidine alkaloids (PAs) in food and natural preparations have received widespread attention due to their hepatotoxicity, genotoxicity, and embryotoxicity. Mass spectrometry (MS), as a high resolution, high sensitive, and high throughput detection tool, has been the most commonly used technique for the determination of PAs. The continuous advancement of new technologies, methods, and strategies in the field of MS has contributed to the improvement of the analytical efficiency and methodological enhancement of PAs. This paper provides an overview of the structure, toxicity properties and commonly employed analytical methods, focusing on the concepts, advances, and novel techniques and applications of MS-based methods for the analysis of PAs. Additionally, the remaining challenges, future perspectives, and trends for PA detection are discussed. This review provides a reference for toxicological studies of PAs, content monitoring, and the establishment of quality control and safety standards for herbal and food products.

Levels, Toxic Effects, and Risk Assessment of Pyrrolizidine Alkaloids in Foods: A Review

Pyrrolizidine alkaloids (PAs) are naturally occurring secondary metabolites of plants. To date, more than 660 types of PAs have been identified from an estimated 6000 plants, and approximately 120 of these PAs are hepatotoxic. As a result of PAs being found in spices, herbal teas, honey, and milk, PAs are considered contaminants in foods, posing a potential risk to human health. Here, we summarize the chemical structure, toxic effects, levels, and regulation of PAs in different countries to provide a better understanding of their toxicity and risk assessment. With recent research on the risk assessment of PAs, this review also discusses the challenges facing this field, aiming to provide a scientific basis for PA toxicity research and safety assessment.

Profiling of pyrrolizidine alkaloids using a retronecine-based untargeted metabolomics approach coupled to the quantitation of the retronecine-core in medicinal plants using UHPLC-QTOF

Pyrrolizidine alkaloids (PA) are secondary metabolites of high toxicological relevance. Several PA quantitative methodologies were developed based on a limited number of certified standards, including time consuming solid phase extraction (SPE) purification steps. Herein, we shed light on the variability of PA in herbal extracts and propose a quantification methodology based on ultra-high-performance liquid chromatography high-resolution mass spectrometry (UHPLC-HRMS) for the evaluation of the total PA content as retronecine-equivalents (RE) directly from crude matrices. Particularly in the focus of the investigation were Alkanna spp. (Boraginaceae), which possess a wide range of pharmaceutical properties. In addition, a comparative PA screening of crude and SPE enriched extracts was performed and PA-containing plants from Fabaceae and Compositae families were included to demonstrate universal applicability. In total, 105 PA were identified using HRMS^e experiments, specific MS/MS fragmentation PA patterns, a customized in-house library and literature data. Among them, 18 glycosidic PA derivatives were reported for the first time in literature. Using a hierarchical clustering approach, PA distribution in herbal extracts was shown to be family-dependent and significantly different among species. This was further supported by the results of the total PA concentrations, obtained using a retronecine/heliotridine/internal standard-based targeted UHPLC-HRMS quantification method, which varied from 8.64 ± 0.08-3096.28 ± 273.72 μg RE/g extract dry weight in shoots extracts of Alkanna spp. and leaves extracts of Crotalaria retusa L. respectively. Worth mentioning is that the procedure allowed to quantify PA in Alkanna spp. If the procedure based on 35 specific PA recommended by European regulations had been used, results would have been equal to zero for the four species since none were observed in Alkanna spp. Finally, by combining the RE results with the corresponding dereplication results, a customized correction factor for each extract (ranging from 2.12 to 2.48) was assessed leading to a more accurate estimate of the PA content regardless of the molecular weight of each PA. The present methodology will facilitate PA quantification directly from crude extracts and avoid the underestimation the real PA content due to limited availabilty of authentic reference compounds in botanical extracts used in phytomedicines or food supplements/cosmetics.

Plasma-based ambient mass spectrometry: Recent progress and applications

Ambient mass spectrometry (AMS) has grown as a group of advanced analytical techniques that allow for the direct sampling and ionization of the analytes in different statuses from their native environment without or with minimum sample pretreatments. As a significant category of AMS, plasma-based AMS has gained a lot of attention due to its features that allow rapid, real-time, high-throughput, in vivo, and in situ analysis in various fields, including bioanalysis, pharmaceuticals, forensics, food safety, and mass spectrometry imaging. Tens of new methods have been developed since the introduction of the first plasma-based AMS technique direct analysis in real-time. This review first provides a comprehensive overview of the established plasma-based AMS techniques from their ion source configurations, mechanisms, and developments. Then, the progress of the representative applications in various scientific fields in the past 4 years (January 2017 to January 2021) has been summarized. Finally, we discuss the current challenges and propose the future directions of plasma-based AMS from our perspective.

Pyrrolizidine Alkaloid Extraction and Analysis: Recent Updates

Pyrrolizidine alkaloids are natural secondary metabolites that are mainly produced in plants, bacteria, and fungi as a part of an organism's defense machinery. These compounds constitute the largest class of alkaloids and are produced in nearly 3% of flowering plants, most of which belong to the Asteraceae and Boraginaceae families. Chemically, pyrrolizidine alkaloids are esters of the amino alcohol necine (which consists of two fused five-membered rings including a nitrogen atom) and one or more units of necic acids. Pyrrolizidine alkaloids are toxic to humans and mammals; thus, the ability to detect these alkaloids in food and nutrients is a matter of food security. The latest advances in the extraction and analysis of this class of alkaloids are summarized in this review, with special emphasis on chromatographic-based analysis and determinations in food.

Multi-template imprinted solid-phase microextraction coupled with UPLC-Q-TOF-MS for simultaneous monitoring of ten hepatotoxic pyrrolizidine alkaloids in scented tea

Pyrrolizidine alkaloids (PAs) are a series of ubiquitous natural toxins in flowering plants, which are associated with serious hepatic disease in humans. However, the simultaneously fast and sensitive monitoring of different PAs are still challenge because of the diversity of PAs and huge amount of interference in complex samples, such as scented tea samples. In this study, molecularly imprinted solid phase microextraction (MIP-SPME) fibers were fabricated by using multi-template imprinting technique for selective recognition and efficient enrichment of different PAs from scented teas. MIP-SPME could be used for selective adsorption of ten types of PAs through specific recognition cavity and strong ionic interaction, including senecionine, lycopsamine, retrorsine, heliotrine, lasiocarpine, monocrotaline, echimidine, erucifoline, europine and seneciphylline. The extraction parameters were also optimized including extraction time, elution solvent and elution time. Then, ultra performance liquid chromatography- quadrupole-time of flight mass spectrometry (UPLC-Q-TOF-MS) coupled with MIP-SPME method was developed for fast, simple, sensitive and accurate determination of ten PAs in scented teas. The established method was validated and presented satisfactory accuracy and high precision. It was also successfully applied for simultaneous determination of ten PAs in different scented tea samples. PAs were found in most of these scented tea samples, which suggest the cautious use of scented tea for consumers.

Mass spectrometry-based profiling and imaging strategy, a fit-for-purpose tool for unveiling the transformations of ginsenosides in Panax notoginseng during processing

BACKGROUND

Panax notoginseng, a valuable medicinal plant, is traditionally used to treat trauma, body pain, and cardiovascular diseases in two clinical forms including raw (crude) and processed form. Processing-triggered compound transformation is responsible for the distinct bioactivity between raw and processed Panax notoginseng. Nevertheless, investigating the chemical diversity and dynamic transformation pattern of processed Panax notoginseng is challenging.

METHODS

A new approach, which integrates multi-components characterization, processing trajectory depiction, discovery of differential markers, transformation mechanism of metabolites, in situ spatial distribution and transformation of metabolites, was established to elucidate the role of processing on the holistic chemical transformations of Panax notoginseng (PN).

RESULTS

In this study, 136 ginsenosides (mainly rare ginsenosides) were identified or tentatively characterized and the temperature-dependent chemical variation trajectory was depicted via principal component analysis (PCA). Nineteen processing-associated markers were confirmed by orthogonal partial least squares-discriminant analysis (OPLS-DA). For the first time, the transformation pathway of ginsenosides during processing were elucidated by integrating the precursor ion scan (PIS) and mimic processing strategy that involves with deglycosylation, dehydration, hydration, acetylation, and isomerization. Results of mass spectrometry imaging (MSI) revealed the major ginsenosides M-Rb1, R1, Rg1, Rb1, Rd, and Re exhibited distinct spatial distribution pattern that are highly abundant in the xylem and showed a downward trend during processing. We firstly depicted the spatial distribution of processing-triggered rare ginsenosides (Rg3, Rk1, Rg5, etc.), and in situ transformation of ginsenosides was discovered in the process of steaming. Additionally, this variation trend was consistent with untargeted metabolomics results.

CONCLUSION

This study comprehensively revealed chemical diversity and dynamic transformation pattern and depicted the spatial distribution of ginsenosides of PN during processing. It could provide a clue for the distinct bioactivities between raw and processed PN and elucidate the role of processing on the holistic chemical transformations of natural products, more importantly, the proposed strategy is valuable for the quality evaluation and control of the processing of natural product.

Sulfonated halloysite nanotubes as a novel cation exchange material for solid phase extraction of toxic pyrrolizidine alkaloids

Pyrrolizidine alkaloids are phytochemicals, which present a highly toxic class of compounds in multiple food resources and are therefore a late-breaking topic in food safety. This study describes the first use of modified halloysite nanotubes as a novel solid material for solid phase extraction. As a result of a fast one-pot sulfonation of the cheap and non-toxic halloysite nanotubes, an efficient cation exchange phase has been prepared. After optimization of the solid phase extraction protocol, high extraction efficiencies and overall recoveries were obtained for a mixture of four pyrrolizidine alkaloid structures through UHPLC-MS/MS analysis with caffeine as the internal standard. Furthermore, the novel solid phase was used for the selective binding of the toxic pyrrolizidine alkaloids in a real-life honey sample, which itself is often contaminated with these compounds. In-house validation showed great extraction efficiencies up to 99.9% for senecionine with a lower limit for lycopsamine with 59.3%, which indicated high selectivity even in the presence of potential interfering compounds. Subsequently, overall recoveries up to 91.5% could be obtained for senecionine while the lowest value was reached for lycopsamine with 55.1%. Comparison with a commercial strong cation exchange tube procedure showed the high competitiveness of the novel solid phase with respect to overall performance. Only slight disadvantages regarding precision and repeatability with values under 5.7% and 11.6% could be observed. Therefore, sulfonated halloysite nanotubes present themselves as an easy to prepare, cheap and highly efficient novel cation exchange material for the selective solid phase extraction of toxic pyrrolizidine alkaloids in frequently contaminated real-life samples like honey.

Applications of ambient ionization mass spectrometry in 2021: An annual review

Ambient ionization mass spectrometry (AIMS) has revolutionized the field of analytical chemistry, enabling the rapid, direct analysis of samples in their native state. Since the inception of AIMS almost 20 years ago, the analytical community has driven the further development of this suite of techniques, motivated by the plentiful advantages offered in addition to traditional mass spectrometry. Workflows can be simplified through the elimination of sample preparation, analysis times can be significantly reduced and analysis remote from the traditional laboratory space has become a real possibility. As such, the interest in AIMS has rapidly spread through analytical communities worldwide, and AIMS techniques are increasingly being integrated with standard laboratory operations. This annual review covers applications of AIMS techniques throughout 2021, with a specific focus on AIMS applications in a number of key fields of research including disease diagnostics, forensics and security, food safety testing and environmental sciences. While some new techniques are introduced, the focus in AIMS research is increasingly shifting from the development of novel techniques toward efforts to improve existing AIMS techniques, particularly in terms of reproducibility, quantification and ease-of-use.

Rapid analysis of differential chemical compositions of Poria cocos using thin-layer chromatography spray ionization-mass spectrometry

A simple analytical strategy for determining the chemical composition of Poria cocos using thin-layer chromatography spray ionization-mass spectrometry (TLCSI-MS).

Characterization of natural herbal medicines by thin-layer chromatography combined with laser ablation-assisted direct analysis in real-time mass spectrometry

The characterization and quality control of natural herbal medicines, such as traditional Chinese medicines (TCMs), is of great significance to ensure their potential efficacy and avoid severe side effects. Thin-layer chromatography (TLC) is a simple and classic approach for examining quality marker of natural products. Nevertheless, it is more difficult to further characterize the compounds adsorbed on the TLC plate. Herein, we reported a simple setup of laser ablation-assisted direct analysis in real-time mass spectrometry (LA-DART-MS), in which the coupling of mass spectrometry information to provide a predominant dimension in the identification of unknown chemical compositions separated on standard TLC plates, and it was applied for rapid characterization of various kinds of natural herbal medicines. The results showed that the introduction of low-cost small laser pointer had significantly improved the desorption process. The system was successfully applied in the analysis of alkaloids, flavonoids, anthraquinones, volatile oils, glycosides, organic acids, and eight different TCMs including Sophorae Flavescentis Radix, Angelicae Sinensis Radix, Acori Tatarinowii Rhizoma, Phellodendri Chinensis Cortex, Picrasmae Ramulus et Folium, Gynura Japonica, Rhei Radix et Rhizoma and Dendrobii Caulis. The obtained limits of detection (LODs) of this method for various types of reference substances were in the range of 4.6-162.2 ng/band on TLC plates. Furthermore, the quality control and identification of different species of Dendrobii Caulis herb was achieved. This study combines the advantages of TLC and ambient mass spectrometry to provide a good choice for the screening and identification of active ingredients and the quality evaluation of botanical samples.

Current Knowledge and Perspectives of Pyrrolizidine Alkaloids in Pharmacological Applications: A Mini-Review

Pyrrolizidine alkaloids (PAs) are a widespread group of secondary metabolites in plants. PAs are notorious for their acute hepatotoxicity, genotoxicity and neurological damage to humans and animals. In recent decades, the application of PAs for beneficial biological activities to cure disease has drawn greater attention. Here, we review the current knowledge regarding the pharmacological properties of PAs and discuss PAs as promising prototypes for the development of new drugs.