Food contaminant analysis at ultra-high mass resolution: application of hybrid linear ion trap - orbitrap mass spectrometry for the determination of the polyether toxins, azaspiracids, in shellfish

Current Research Status of Azaspiracids

The presence and impact of toxins have been detected in various regions worldwide ever since the discovery of azaspiracids (AZAs) in 1995. These toxins have had detrimental effects on marine resource utilization, marine environmental protection, and fishery production. Over the course of more than two decades of research and development, scientists from all over the world have conducted comprehensive studies on the in vivo metabolism, in vitro synthesis methods, pathogenic mechanisms, and toxicology of these toxins. This paper aims to provide a systematic introduction to the discovery, distribution, pathogenic mechanism, in vivo biosynthesis, and in vitro artificial synthesis of AZA toxins. Additionally, it will summarize various detection methods employed over the past 20 years, along with their advantages and disadvantages. This effort will contribute to the future development of rapid detection technologies and the invention of detection devices for AZAs in marine environmental samples.

Foodomics and Food Safety: Where We Are

The power of foodomics as a discipline that is now broadly used for quality assurance of food products and adulteration identification, as well as for determining the safety of food, is presented. Concerning sample preparation and application, maintenance of highly sophisticated instruments for both high-performance and high-throughput techniques, and analysis and data interpretation, special attention has to be paid to the development of skilled analysts. The obtained data shall be integrated under a strong bioinformatics environment. Modern mass spectrometry is an extremely powerful analytical tool since it can provide direct qualitative and quantitative information about a molecule of interest from only a minute amount of sample. Quality of this information is influenced by the sample preparation procedure, the type of mass spectrometer used and the analyst's skills. Technical advances are bringing new instruments of increased sensitivity, resolution and speed to the market. Other methods presented here give additional information and can be used as complementary tools to mass spectrometry or for validation of obtained results. Genomics and transcriptomics, as well as affinity-based methods, still have a broad use in food analysis. Serious drawbacks of some of them, especially the affinity-based methods, are the cross-reactivity between similar molecules and the influence of complex food matrices. However, these techniques can be used for pre-screening in order to reduce the large number of samples. Great progress has been made in the application of bioinformatics in foodomics. These developments enabled processing of large amounts of generated data for both identification and quantification, and for corresponding modeling.

Use of Foodomics for Control of Food Processing and Assessing of Food Safety

Food chain, food safety, and food-processing sectors face new challenges due to globalization of food chain and changes in the modern consumer preferences. In addition, gradually increasing microbial resistance, changes in climate, and human errors in food handling remain a pending barrier for the efficient global food safety management. Consequently, a need for development, validation, and implementation of rapid, sensitive, and accurate methods for assessment of food safety often termed as foodomics methods is required. Even though, the growing role of these high-throughput foodomic methods based on genomic, transcriptomic, proteomic, and metabolomic techniques has yet to be completely acknowledged by the regulatory agencies and bodies. The sensitivity and accuracy of these methods are superior to previously used standard analytical procedures and new methods are suitable to address a number of novel requirements posed by the food production sector and global food market.

Validation of a confirmatory method for lipophilic marine toxins in shellfish using UHPLC-HR-Orbitrap MS

Lipophilic marine toxins are produced by harmful microalgae and can accumulate in edible filter feeders such as shellfish, leading to an introduction of toxins into the human food chain, causing different poisoning effects. During the last years, analytical methods, based on liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS), have been consolidated by interlaboratory validations. However, the main drawback of LC-MS/MS methods remains the limited number of compounds that can be analyzed in a single run. Due to the targeted nature of these methods, only known toxins, previously considered during method optimization, will be detected. Therefore in this study, a method based on ultra-high-performance liquid chromatography coupled to high-resolution Orbitrap mass spectrometry (UHPLC-HR-Orbitrap MS) was developed. Its quantitative performance was evaluated for confirmatory analysis of regulated lipophilic marine toxins in shellfish flesh according to Commission Decision 2002/657/EC. Okadaic acid (OA), dinophysistoxin-1 (DTX-1), pectenotoxin-2 (PTX-2), azaspiracid-1 (AZA-1), yessotoxin (YTX), and 13-desmethyl spirolide C (SPX-1) were quantified using matrix-matched calibration curves (MMS). For all compounds, the reproducibility ranged from 2.9 to 4.9 %, repeatability from 2.9 to 4.9 %, and recoveries from 82.9 to 113 % at the three different spiked levels. In addition, confirmatory identification of the compounds was effectively performed by the presence of a second diagnostic ion ((13)C). In conclusion, UHPLC-HR-Orbitrap MS permitted more accurate and faster detection of the target toxins than previously described LC-MS/MS methods. Furthermore, HRMS allows to retrospectively screen for many analogues and metabolites using its full-scan capabilities but also untargeted screening through the use of metabolomics software.

Determination of lipophilic marine toxins in mussels. Quantification and confirmation criteria using high resolution mass spectrometry

A multitoxin method has been developed for quantification and confirmation of lipophilic marine biotoxins in mussels by liquid chromatography coupled to high resolution mass spectrometry (HRMS), using an Orbitrap-Exactive HCD mass spectrometer. Okadaic acid (OA), yessotoxin, azaspiracid-1, gymnodimine, 13-desmethyl spirolide C, pectenotoxin-2 and Brevetoxin B were analyzed as representative compounds of each lipophilic toxin group. HRMS identification and confirmation criteria were established. Fragment and isotope ions and ion ratios were studied and evaluated for confirmation purpose. In depth characterization of full scan and fragmentation spectrum of the main toxins were carried out. Accuracy (trueness and precision), linearity, calibration curve check, limit of quantification (LOQ) and specificity were the parameters established for the method validation. The validation was performed at 0.5 times the current European Union permitted levels. The method performed very well for the parameters investigated. The trueness, expressed as recovery, ranged from 80% to 94%, the precision, expressed as intralaboratory reproducibility, ranged from 5% to 22% and the LOQs range from 0.9 to 4.8pg on column. Uncertainty of the method was also estimated for OA, using a certified reference material. A top-down approach considering two main contributions: those arising from the trueness studies and those coming from the precision's determination, was used. An overall expanded uncertainty of 38% was obtained.

The chromatographic role in high resolution mass spectrometry for non-targeted analysis

Resolution improvements in time-of-flight instrumentation and the emergence of the Orbitrap mass spectrometer have researchers using high resolution mass spectrometry to determine elemental compositions and performing screening methods based on the full-scan data from these instruments. This work is focused on examining instrument performance of both a QTOF and a bench-top Orbitrap. In this study, the impact of chromatographic resolution on mass measurement accuracy, mass measurement precision, and ion suppression is examined at a fundamental level. This work was extended to a mixture of over 200 pesticides to determine how well two different software algorithms componentized and correctly identified these compounds under different sets of chromatographic conditions, where co-elution was expected to vary markedly.

Elucidation of the mass fragmentation pathways of the polyether marine toxins, dinophysistoxins, and identification of isomer discrimination processes

RATIONALE

Most of the liquid chromatography/mass spectrometry (LC/MS) methods that have been developed for the analysis of Diarrhetic Shellfish Poisoning (DSP) toxins in shellfish and algae samples have been unable to differentiate the isomers okadaic acid (OA) and dinophysistoxin-2 (DTX2), unless separated by chromatography. Since there are many bioconversion products of these compounds it is imperative to determine characteristic product ions, which can provide unequivocal identification of OA and DTX2 and their analogs.

METHODS

Using electrospray ionization, the fragmentation processes for two types of precursor ions, [M+Na](+) and [M-H](-), of the polyether marine toxins, dinophysistoxins (DTXs), were studied using a hybrid linear ion trap Orbitrap mass spectrometer which provided high mass accuracy data in combination with multiple tandem mass (MS(n)) spectra. Three structurally related toxins were compared; okadaic acid (OA), dinophysistoxin-2 (DTX2) and dinophysistoxin-1 (DTX1). A quick multiple reaction monitoring (MRM) LC/MS/MS method was developed utilizing the characteristic precursor/product ion mass transitions.

RESULTS

Comparison of the high-resolution product ion, [M-H](-), spectra of these toxins featured dominant signals that resulted from two six-centered rearrangements and previously proposed fragmentation pathways for the ion of m/z 321 and 293 have been corrected and identified. By contrast, the [M+Na](+) product ion spectra only revealed distinctive ions for the isomers, OA (m/z 595, 443 and 151) and DTX2 (m/z 581, 429 and 165). To illustrate the benefits of this study, a mass selective LC/MS/MS method was developed in which the isomers OA and DTX2 co-eluted but were distinguished using the mass transitions, m/z 827/595, 827/443 (OA) and m/z 827/581, 827/429 (DTX2).

CONCLUSIONS

Comparison of OA, DTX2 and DTX1 led to the correction of proposed negative ion mode fragmentation pathways. Through extensive study and comparison of the [M+Na](+) product ion spectra, distinctive product ions were identified which allowed for these compounds to be identified and distinguished without separation for the first time.

Development of a new screening method for the detection of antibiotic residues in muscle tissues using liquid chromatography and high resolution mass spectrometry with a LC-LTQ-Orbitrap instrument

A liquid chromatography-high resolution mass spectrometry (LC-HRMS) method was developed for screening meat for a wide range of antibiotics used in veterinary medicine. Full-scan mode under high resolution mass spectral conditions using an LTQ-Orbitrap mass spectrometer with resolving power 60,000 full width at half maximum (FWHM) was applied for analysis of the samples. Samples were prepared using two extraction protocols prior to LC-HRMS analysis. The scope of the method focuses on screening the following main families of antibacterial veterinary drugs: penicillins, cephalosporins, sulfonamides, macrolides, tetracyclines, aminoglucosides and quinolones. Compounds were successfully identified in spiked samples from their accurate mass and LC retention times from the acquired full-scan chromatogram. Automated data processing using ToxId software allowed rapid treatment of the data. Analyses of muscle tissues from real samples collected from antibiotic-treated animals was carried out using the above methodology and antibiotic residues were identified unambiguously. Further analysis of the data for real samples allowed the identification of the targeted antibiotic residues but also non-targeted compounds, such as some of their metabolites.

The current role of high-resolution mass spectrometry in food analysis

High-resolution mass spectrometry (HRMS), which is used for residue analysis in food, has gained wider acceptance in the last few years. This development is due to the availability of more rugged, sensitive, and selective instrumentation. The benefits provided by HRMS over classical unit-mass-resolution tandem mass spectrometry are considerable. These benefits include the collection of full-scan spectra, which provides greater insight into the composition of a sample. Consequently, the analyst has the freedom to measure compounds without previous compound-specific tuning, the possibility of retrospective data analysis, and the capability of performing structural elucidations of unknown or suspected compounds. HRMS strongly competes with classical tandem mass spectrometry in the field of quantitative multiresidue methods (e.g., pesticides and veterinary drugs). It is one of the most promising tools when moving towards nontargeted approaches. Certain hardware and software issues still have to be addressed by the instrument manufacturers for it to dislodge tandem mass spectrometry from its position as the standard trace analysis tool.

High-resolution mass spectrometry method for the detection, characterization and quantitation of pharmaceuticals in water

The presence of pharmaceuticals in drinking water is an emerging environmental concern. In most environmental testing laboratories, LC-MS/MS assays based on selected reaction monitoring are used as part of a battery of tests used to assure water quality. Although LC-MS/MS continues to be the best tool for detecting pharmaceuticals in water, the combined use of hybrid high-resolution mass spectrometry (HRMS) and ultrahigh pressure liquid chromatography (UHPLC) is starting to become a practical tool to study emerging environmental contaminants. The hybrid LTQ-orbitrap mass spectrometer is suitable for integrated quantitative and qualitative bioanalysis because of the following reasons: (1) the ability to collect full-scan HRMS spectra with scan speeds suitable for UHPLC separations, (2) routine measurement of mass with less than 5 ppm mass accuracy, (3) high mass resolving power, and (4) ability to perform on-the-fly polarity switching in the linear ion trap (LTQ). In the present work, we provide data demonstrating the application of UHPLC-LTQ-orbitrap for the detection, characterization and quantification of pharmaceuticals and their metabolites in drinking water.

Mussels increase xenobiotic (azaspiracid) toxicity using a unique bioconversion mechanism

Azaspiracid Poisoning (AZP) is a human toxic syndrome which is associated with the consumption of bivalve shellfish. Unlike other shellfish, mussels contain a large array of azaspiracid analogs, many of which are suspected bioconversion products. These studies were conducted to elucidate the metabolic pathways of azaspiracid (AZA1) in the blue mussel (Mytilus edulis) and revealed that the main biotransformation product was the more toxic demethyl analog, AZA3. To elucidate the mechanism of this C-demethylation, an unprecedented xenobiotic bioconversion step in shellfish, AZA1 was fed to mussels that contained no detectable azaspiracids. Triple quadrupole mass spectrometry (MS) and high resolution Orbitrap MS were used to determine the uptake of AZA1 and the toxin profiles in three tissue compartments of mussels. The second most abundant bioconversion product was identified as AZA17, a carboxyl analog of AZA3, which is a key intermediate in the formation of AZA3. Also, two pairs of isomeric hydroxyl analogs, AZA4/AZA5 and AZA7/AZA8, have been confirmed as bioconversion products for the first time. Ultra high resolution (100 k) MS studies showed that the most probable structural assignment for AZA17 is 22-carboxy-AZA3 and a mechanism for its facile decarboxylation to form AZA3 has been proposed.