Two-dimensional heart-cut LC-LC improves accuracy of exact-matching double isotope dilution mass spectrometry measurements of aflatoxin B1 in cereal-based baby food, maize, and maize-based feed

Two-dimensional liquid chromatography with reversed phase in both dimensions: A review

Two-dimensional liquid chromatography (2D-LC), and in particular comprehensive two-dimensional liquid chromatography (LC×LC), offers increased peak capacity, resolution and selectivity compared to one-dimensional liquid chromatography. It is commonly accepted that the technique produces the best results when the separation mechanisms in the two dimensions are completely orthogonal; however, the use of similar separation mechanisms in both dimensions has been gaining popularity as it helps avoid difficulties related to mobile phase incompatibility and poor column efficiency. The remarkable advantages of using reversed phase in both dimensions (RPLC×RPLC) over other separation mechanisms made it a promising technique in the separation of complex samples. This review discusses some physical and practical considerations in method development for 2D-LC involving the use of RP in both dimensions. In addition, an extensive overview is presented of different applications that relied on RPLC×RPLC and 2D-LC with reversed phase column combinations to separate components of complex samples in different fields including food analysis, natural product analysis, environmental analysis, proteomics, lipidomics and metabolomics.

Advances of stable isotope technology in food safety analysis and nutrient metabolism research

Food quality, safety, and the regulatory metabolism of food nutrients in cells are primary factors in determining human health. However, residues of undesirable or hazardous compounds in food products and dysregulation in the nutrient metabolism inevitably occur occasionally. For years, chromatography-mass spectrometry technology has been recognized as an essential research tool in food analysis and nutrient metabolism research, and it is more accurate and robust when coupled with stable isotopes. In this study, we summarize the applications of stable isotope technology in the quantification of contaminant residues (pesticides, veterinary drugs, mycotoxins, polycyclic aromatic hydrocarbons, and other hazardous compounds) in foods and in the nutrients (glucose, lipids, amino acids and proteins) metabolism research. The aim of this review was to serve as a reference for providing effective analysis techniques for protecting food quality and human health, and to pave the way for the broader application of stable isotope technology.

Comprehensive and heart-cutting multidimensional liquid chromatography-mass spectrometry and its applications in food analysis

In food analysis, conventional one-dimensional liquid chromatography methods sometimes lack sufficient separation power due to the complexity and heterogeneity of the analyzed matrices. Therefore, the use of two-dimensional liquid chromatography (2D-LC) turns out to be a powerful tool to consider, especially when coupled to mass spectrometry (MS). This review presents the most remarkable 2D-LC-MS food applications reported in the last 10 years, including a critical discussion of the multiple approaches, modulation strategies as well as the importance of the optimization of the different analytical aspects that will condition the 2D-LC-MS performance. The presence of contaminants in food (food safety), the food quality, and authenticity or the relationship between the beneficial effects of food and human health are some of the fields in which most of the 2D-LC-MS applications are mainly focused. Both heart-cutting and comprehensive applications are described and discussed in this review, highlighting the potential of 2D-LC-MS for the analysis of such complex samples.

Comprehensive and heart-cutting multidimensional liquid chromatography-mass spectrometry and its applications in food analysis

In food analysis, conventional one-dimensional liquid chromatography methods sometimes lack sufficient separation power due to the complexity and heterogeneity of the analysed matrices. Therefore, the use of two-dimensional liquid chromatography (2D-LC) turns out to be a powerful tool to consider, especially when coupled to mass spectrometry (MS). This review presents the most remarkable 2D-LC-MS food applications reported in the last 10 years, including a critical discussion of the multiple approaches, modulation strategies as well as the importance of the optimisation of the different analytical aspects that will condition the 2D-LC-MS performance. The presence of contaminants in food (food safety), the food quality and authenticity or the relationship between the beneficial effects of food and human health are some of the fields in which most of the 2D-LC-MS applications are mainly focused. Both heart-cutting and comprehensive applications are described and discussed in this review, highlighting the potential of 2D-LC-MS for the analysis of such complex samples.

Current Developments of Analytical Methodologies for Aflatoxins' Determination in Food during the Last Decade (2013-2022), with a Particular Focus on Nuts and Nut Products

This review aims to provide a clear overview of the most important analytical development in aflatoxins analysis during the last decade (2013-2022) with a particular focus on nuts and nuts-related products. Aflatoxins (AFs), a group of mycotoxins produced mainly by certain strains of the genus Aspergillus fungi, are known to impose a serious threat to human health. Indeed, AFs are considered carcinogenic to humans, group 1, by the International Agency for Research on Cancer (IARC). Since these toxins can be found in different food commodities, food control organizations worldwide impose maximum levels of AFs for commodities affected by this threat. Thus, they represent a cumbersome issue in terms of quality control, analytical result reliability, and economical losses. It is, therefore, mandatory for food industries to perform analysis on potentially contaminated commodities before the trade. A full perspective of the whole analytical workflow, considering each crucial step during AFs investigation, namely sampling, sample preparation, separation, and detection, will be presented to the reader, focusing on the main challenges related to the topic. A discussion will be primarily held regarding sample preparation methodologies such as partitioning, solid phase extraction (SPE), and immunoaffinity (IA) related methods. This will be followed by an overview of the leading analytical techniques for the detection of aflatoxins, in particular liquid chromatography (LC) coupled to a fluorescence detector (FLD) and/or mass spectrometry (MS). Moreover, the focus on the analytical procedure will not be specific only to traditional methodologies, such as LC, but also to new direct approaches based on imaging and the ability to detect AFs, reducing the need for sample preparation and separative techniques.

Multiple heart-cutting two dimensional liquid chromatography and isotope dilution tandem mass spectrometry for the absolute quantification of proteins in human serum

We evaluate here the combination of two-dimensional liquid chromatography (2D-LC) in the multiple heart cutting mode and isotope dilution tandem mass spectrometry for the direct analysis of tryptic digests of serum samples. As a proof of concept, we attempt the quantification of proteotypic peptides of Apolipoprotein AIV (APOA4), Complement C3 (C3) and Vitronectin (VTN) which have been previously identified as potential candidate biomarkers of glaucoma. Using this 2D-LC strategy, analyte enrichment steps are avoided and the sample preparation involved after enzymatic digestion amounted to a simple centrifugation, evaporation of the supernatant and reconstitution in the 1D mobile phase. A mobile phase not compatible with the ESI source (10 mM KH₂PO₄ at pH 2.7) was used in the first dimension as it provided a satisfactory chromatographic resolution of the peptides and a high buffering capacity avoiding changes in retention times when analyzing complex matrices like human serum. We also demonstrate that using coeluting labelled analogues of the target peptides, protein concentrations were not affected by slight retention time shifts affecting the amount of target peptides transferred to the second dimension. Satisfactory results were obtained when analyzing fortified serum samples (recoveries from 98 to 113%). Precisions in the range of 1-9% RSD were obtained when replicating the analysis of a pooled serum sample. The comparative analysis of serum samples from n = 94 control subjects and n = 91 patients diagnosed with primary open-angle glaucoma did not show significant differences in the APOA4, VTN and C3 concentrations in contrast with previous studies using immunoassays.

Development, validation, and application of a multi-method for the determination of mycotoxins, plant growth regulators, tropane alkaloids, and pesticides in cereals by two-dimensional liquid chromatography tandem mass spectrometry

Mycotoxins and pesticides regularly co-occur in agricultural products worldwide. Thus, humans can be exposed to both toxic contaminants and pesticides simultaneously, and multi-methods assessing the occurrence of various food contaminants and residues in a single method are necessary. A two-dimensional high performance liquid chromatography tandem mass spectrometry method for the analysis of 40 (modified) mycotoxins, two plant growth regulators, two tropane alkaloids, and 334 pesticides in cereals was developed. After an acetonitrile/water/formic acid (79:20:1, v/v/v) multi-analyte extraction procedure, extracts were injected into the two-dimensional setup, and an online clean-up was performed. The method was validated according to Commission Decision (EC) no. 657/2002 and document N° SANTE/12682/2019. Good linearity (R2 > 0.96), recovery data between 70-120%, repeatability and reproducibility values < 20%, and expanded measurement uncertainties < 50% were obtained for a wide range of analytes, including very polar substances like deoxynivalenol-3-glucoside and methamidophos. However, results for fumonisins, zearalenone-14,16-disulfate, acid-labile pesticides, and carbamates were unsatisfying. Limits of quantification meeting maximum (residue) limits were achieved for most analytes. Matrix effects varied highly (-85 to +1574%) and were mainly observed for analytes eluting in the first dimension and early-eluting analytes in the second dimension. The application of the method demonstrated the co-occurrence of different types of cereals with 28 toxins and pesticides. Overall, 86% of the samples showed positive findings with at least one mycotoxin, plant growth regulator, or pesticide.

A Review: Sample Preparation and Chromatographic Technologies for Detection of Aflatoxins in Foods

As a class of mycotoxins with regulatory and public health significance, aflatoxins (e.g., aflatoxin B1, B2, G1 and G2) have attracted unparalleled attention from government, academia and industry due to their chronic and acute toxicity. Aflatoxins are secondary metabolites of various Aspergillus species, which are ubiquitous in the environment and can grow on a variety of crops whereby accumulation is impacted by climate influences. Consumption of foods and feeds contaminated by aflatoxins are hazardous to human and animal health, hence the detection and quantification of aflatoxins in foods and feeds is a priority from the viewpoint of food safety. Since the first purification and identification of aflatoxins from feeds in the 1960s, there have been continuous efforts to develop sensitive and rapid methods for the determination of aflatoxins. This review aims to provide a comprehensive overview on advances in aflatoxins analysis and highlights the importance of sample pretreatments, homogenization and various cleanup strategies used in the determination of aflatoxins. The use of liquid-liquid extraction (LLE), supercritical fluid extraction (SFE), solid phase extraction (SPE) and immunoaffinity column clean-up (IAC) and dilute and shoot for enhancing extraction efficiency and clean-up are discussed. Furthermore, the analytical techniques such as gas chromatography (GC), liquid chromatography (LC), mass spectrometry (MS), capillary electrophoresis (CE) and thin-layer chromatography (TLC) are compared in terms of identification, quantitation and throughput. Lastly, with the emergence of new techniques, the review culminates with prospects of promising technologies for aflatoxin analysis in the foreseeable future.

Bias reduction in the quantitative analysis of a target analyte present in a limited quantity in human plasma using dual-mode heart-cutting two-dimensional liquid chromatography coupled with isotope dilution mass spectrometry

Dual-mode heart-cutting two-dimensional liquid chromatography (DMHC 2D-LC) was applied to isotope dilution mass spectrometry (IDMS) to reduce the bias in the quantitative analysis of a target analyte present in a limited quantity in human plasma. Based on a Waters I-Class LC system, the DMHC 2D-LC system was operated in one- and two-dimensional modes to facilitate the determination of heart-cutting time and the efficient trapping of the target LC eluate. Experiments to determine the feasibility of coupling with IDMS were performed with triple quadrupole mass spectrometry using folic acid standards and/or ¹³ C₅ -folic acid. To validate the performance of the DMHC 2D-LC/IDMS system on a complex sample, human plasma was analyzed for folic acid and the result was compared with that obtained using conventional single-column LC. The total run time of the DMHC 2D-LC system was 20 min, the same as that of the single-column LC system. The peak profile of the spiked ¹³ C₅ -folic acid obtained with single-column LC/MS was affected by matrix effects, but resolved with DMHC 2D-LC/MS, thus improving the accuracy of the analysis. The DMHC 2D-LC/IDMS system showed reliable performance in analyzing the target analyte in human plasma, eliminating matrix effects and saving analysis time.

Determination of mycotoxins in beer by multi heart-cutting two-dimensional liquid chromatography tandem mass spectrometry method

Beer is one the most consumed alcoholic beverage in the world and its contamination with mycotoxins is of public health concern. This study reports a fast and automated analytical procedure based on a multi-heart-cutting two-dimensional liquid chromatography tandem mass spectrometry method using electrospray ionization for the determination of seven mycotoxins (aflatoxins B1, B2, G2 and G1, ochratoxin A, fumonisins B1 and B2) in beers. The developed method was based on the heart-cutting 2D- HPLC technique in which only the specific portions of the first dimension, in the retention time of analytes, were transferred into the second dimension for the further separation and successive determination. The method uses two different chromatographic columns; in the first dimension, 50 μL of sample was injected on first column, and mycotoxins elution regions were collected in a loop and transferred into the second column for the separation of analytes. Each column operated in gradient elution mode in order to eliminate interfering compounds and improve separation and peak shape. After the optimization, the method has been validated according to EU regulation and finally applied for the analysis of forty beer samples collected from Italian supermarkets. Among all mycotoxins studied, fumonisins B1 was the most widely distributed in analysed beers (>21%) in the range from 0.6 to 12.3 ng mL^-1. The automated methodology developed was able to determine accurately and simultaneously seven mycotoxins in beer. This provided a significant reduction of sample handle and, consequently of analysis time.

Integrating comprehensive two-dimensional gas chromatography mass spectrometry and parallel two-dimensional liquid chromatography mass spectrometry for untargeted metabolomics

The diverse characteristics and large number of entities make metabolite separation challenging in metabolomics. To date, there is not a singular instrument capable of analyzing all types of metabolites. In order to achieve a better separation for higher peak capacity and accurate metabolite identification and quantification, we integrated GC × GC-MS and parallel 2DLC-MS for analysis of polar metabolites. To test the performance of the developed system, 13 rats were fed different diets to form two animal groups. Polar metabolites extracted from rat livers were analyzed by GC × GC-MS, parallel 2DLC-MS (-) and parallel 2DLC-MS (+), respectively. By integrating all data together, 58 metabolites were detected with significant change in their abundance levels between groups (p≤ 0.05). Of the 58 metabolites, three metabolites were detected in two platforms and two in all three platforms. Manual examination showed that discrepancy of metabolite regulation measured by different platforms was mainly caused by the poor shape of chromatographic peaks resulting from low instrument response. Pathway analysis demonstrated that integrating the results from multiple platforms increased the confidence of metabolic pathway assignment.

Simultaneous determination of pesticides, mycotoxins, tropane alkaloids, growth regulators, and pyrrolizidine alkaloids in oats and whole wheat grains after online clean-up via two-dimensional liquid chromatography tandem mass spectrometry

In this study, a two-dimensional liquid chromatography tandem mass spectrometry method was developed and validated for the determination of pesticide residues and contaminants in whole wheat grains and oats. The samples were extracted with a mixture of acetonitrile and water and were injected into the two-dimensional LC-MS/MS system without any further clean-up or sample preparation. Samples were analyzed with four different matrix matched calibrations. Matrix effects were evaluated by comparing analyte signals in the respective matrix matched standard with the neat solvent standards. The final method was validated according to the current Eurachem validation guide and SANTE document. The number of successfully validated analytes throughout all three validation levels in oats and wheat, respectively, were as follows: 330 and 316 out of 370 pesticides, 6 and 13 out of 18 pyrrolizidine alkaloids and 7 out of 9 regulated mycotoxins. Moreover, both plant growth regulators mepiquat and chlormequat as well as the tropane alkaloids atropine and scopolamine met the validation criteria. The majority of pesticides showed limits of detection below 1 µg kg^-1, pyrrolizidine alkaloids below 0.7 µg kg^-1, tropane alkaloids below 0.2 µg kg^-1, growth regulators below 0.7 µg kg^-1 and mycotoxins below 8 µg kg^-1 in both matrices.

Development of Multiple Heart-Cutting Two-Dimensional Liquid Chromatography Coupled to Quadrupole-Orbitrap High Resolution Mass Spectrometry for Simultaneous Determination of Aflatoxin B1, B2, G1, G2, and Ochratoxin A in Snus, a Smokeless Tobacco Product

The combination of multiple heart-cutting two-dimensional liquid chromatography (MHC-LC/LC) and quadrupole-orbitrap high-resolution mass spectrometry (HRMS) for simultaneous determination of the aflatoxins and ochratoxin A in snus is presented in this work. A C18 capillary column was used as the first dimension (1D) to isolate the aflatoxins and ochratoxin A from the complex matrices; then, a 2-position/10-port high-pressure valve equipped with two 60 μL loops was employed to transfer the heart-cuts of 1D-LC into a pentafluorophenyl (PFP) column for the second dimension (2D) separation. With the better separation of the MHC-LC/LC system, the sensitivity of the method was improved, which is essential for the trace mycotoxins analysis. Furthermore, HRMS performed in parallel reaction monitoring mode was employed to eliminate the interferences, and the sample pretreatment procedure was simplified. A new approach utilizing ethyl acetate with 1% formic acid/water solution was adopted to extract aflatoxins and ochratoxin A in snus, which provided parallel recoveries for aflatoxins and ochratoxin A with higher responses in comparison with the QuEChERS method. A dynamic range between 0.2 and 20 μg/kg was achieved with LOQs of 0.05 μg/kg for aflatoxin B₁, 0.1 μg/kg for aflatoxin B₂, G₁, G₂, and 1.0 μg/kg for ochratoxin A in dry mass of product. The results revealed that the established method exhibited good repeatability and recovery and could be used as a rapid and reliable approach for routine analysis of aflatoxins and ochratoxin A in snus.

A Greener, Quick and Comprehensive Extraction Approach for LC-MS of Multiple Mycotoxins

In food/feed control, mycotoxin analysis is often still performed “one analyte at a time”. Here a method is presented which aims at making mycotoxin analysis environmentally friendlier through replacing acetonitrile by ethyl acetate and reducing chemical waste production by analyzing four mycotoxins together, forgoing sample extract clean-up, and minimizing solvent consumption. For this, 2 g of test material were suspended in 8 mL water and 16 mL ethyl acetate were added. Extraction was accelerated through sonication for 30 min and subsequent addition of 8 g sodium sulfate. After centrifugation, 500 µL supernatant were spiked with isotopologues, dried down, reconstituted in mobile phase, and measured with LC-MS. The method was validated in-house and through a collaborative study and the performance was fit-for-purpose. Repeatability relative standard deviation (RSDs) between 16% at low and 4% at higher contaminations were obtained. The reproducibility RSDs were mostly between 12% and 32%. The trueness of results for T-2 toxin and Zearalenone were not different from 100%, for Deoxynivalenol and HT-2 toxin they were larger than 89%. The extraction was also adapted to a quick screening of Aflatoxin B1 in maize by flow-injection–mass spectrometry. Semi-quantitative results were obtained through standard addition and scan-based ion ratio calculations. The method proved to be a viable greener and quicker alternative to existing methods.

Developments in mycotoxin analysis: an update for 2014-2015

This review summarises developments in the determination of mycotoxins over a period between mid-2014 and mid-2015. In tradition with previous articles of this series, analytical methods to determine aflatoxins, Alternaria toxins, ergot alkaloids, fumonisins, ochratoxins, patulin, trichothecenes and zearalenone are covered in individual sections. Advances in proper sampling strategies are discussed in a dedicated section, as are new methods used to analyse botanicals and spices and newly developed LC-MS based multi-mycotoxin methods. The critical review aims to briefly discuss the most important developments and trends in mycotoxin determination as well as to address shortcomings of current methodologies.