Towards nutrition with precision: unlocking biomarkers as dietary assessment tools.

Precision nutrition requires precise tools to monitor dietary habits. Yet current dietary assessment instruments are subjective, limiting our understanding of the causal relationships between diet and health. Biomarkers of food intake (BFIs) hold promise to increase the objectivity and accuracy of dietary assessment, enabling adjustment for compliance and misreporting. Here, we update current concepts and provide a comprehensive overview of BFIs measured in urine and blood. We rank BFIs based on a four-level utility scale to guide selection and identify combinations of BFIs that specifically reflect complex food intakes, making them applicable as dietary instruments. We discuss the main challenges in biomarker development and illustrate key solutions for the application of BFIs in human studies, highlighting different strategies for selecting and combining BFIs to support specific study designs. Finally, we present a roadmap for BFI development and implementation to leverage current knowledge and enable precision in nutrition research.

A Comprehensive Database for DNA Adductomics.

The exposure of human DNA to genotoxic compounds induces the formation of covalent DNA adducts, which may contribute to the initiation of carcinogenesis. Liquid chromatography (LC) coupled with high-resolution mass spectrometry (HRMS) is a powerful tool for DNA adductomics, a new research field aiming at screening known and unknown DNA adducts in biological samples. The lack of databases and bioinformatics tool in this field limits the applicability of DNA adductomics. Establishing a comprehensive database will make the identification process faster and more efficient and will provide new insight into the occurrence of DNA modification from a wide range of genotoxicants. In this paper, we present a four-step approach used to compile and curate a database for the annotation of DNA adducts in biological samples. The first step included a literature search, selecting only DNA adducts that were unequivocally identified by either comparison with reference standards or with nuclear magnetic resonance (NMR), and tentatively identified by tandem HRMS/MS. The second step consisted in harmonizing structures, molecular formulas, and names, for building a systematic database of 279 DNA adducts. The source, the study design and the technique used for DNA adduct identification were reported. The third step consisted in implementing the database with 303 new potential DNA adducts coming from different combinations of genotoxicants with nucleobases, and reporting monoisotopic masses, chemical formulas, .cdxml files, .mol files, SMILES, InChI, InChIKey and IUPAC nomenclature. In the fourth step, a preliminary spectral library was built by acquiring experimental MS/MS spectra of 15 reference standards, generating in silico MS/MS fragments for all the adducts, and reporting both experimental and predicted fragments into interactive web datatables. The database, including 582 entries, is publicly available (https://gitlab.com/nexs-metabolomics/projects/dna_adductomics_database). This database is a powerful tool for the annotation of DNA adducts measured in (HR)MS. The inclusion of metadata indicating the source of DNA adducts, the study design and technique used, allows for prioritization of the DNA adducts of interests and/or to enhance the annotation confidence. DNA adducts identification can be further improved by integrating the present database with the generation of authentic MS/MS spectra, and with user-friendly bioinformatics tools.

Discovery of Urinary Biomarkers of Spinach Consumption Using Untargeted LC-MS Metabolomics in a Human Intervention Trial.

SCOPE: Biomarkers for intake of green leafy vegetables such as spinach can help investigate their health effects. However, only few potential intake markers have been reported in the literature so far. METHODS AND RESULTS: Based on a cross-over study on whole leaf and minced spinach, we investigate changes in metabolites before and after spinach intake and differences between the two treatments and health status. Nineteen volunteers (12 healthy subjects and 7 short bowel patients) completed the study within 48 days. Urine samples (24-h intervals before and after spinach intake) and serum samples (baseline, post 8 d, and post 15 d) are collected and analyzed by ultra-high performance liquid chromatography quadrupole time-of-flight mass spectrometry (UHPLC-QTOF-MS). The acquired data is analyzed by multivariate and univariate analyses. Three candidate biomarkers are observed in urine only after the spinach intake, including des-amino arginine pentenol ester, D/L-malic acid ester of cis-p-coumarate, D/L-malic acid ester of trans-p-coumarate, and 69 metabolites are present before spinach intake but showing an altered level after treatment. These metabolites are related to dietary habits or meal structure, and some changes are possibly affected by spinach intake. The candidate biomarkers are independent of spinach pre-processing and healthy status. No markers are discovered in serum samples. CONCLUSION: We propose structures for three candidate spinach intake biomarkers; these markers will need further validation in independent studies.

Combined Urinary Biomarkers to Assess Coffee Intake Using Untargeted Metabolomics: Discovery in Three Pilot Human Intervention Studies and Validation in Cross-Sectional Studies.

Coffee is a widely consumed beverage worldwide and has a high content of chlorogenic acids, polyphenols, methylxanthines, and volatile flavor compounds. Scientific evidence to support the beneficial health effects of coffee is limited, and validated urinary biomarkers of coffee intake are therefore needed. We observed 23 common putative biomarkers of coffee intake in three separate parallel intervention studies by ultra-high-performance liquid chromatography-electrospray ionization-quadrupole time-of-flight-mass spectrometry (UHPLC-ESI-QTOF-MS) and multivariate analyses. Baseline samples from the NU-AGE study were used to confirm and validate 16 of these candidate biomarkers, including their robustness, time response, and dose response. These validated candidate biomarkers are N-methylpyridinium cation, 1-methyl-1H-pyrrole-2-carboxaldehyde, 1H-pyrrole-2-carboxaldehyde sulfate, 3-piperidinemethanol, furfurylidene-furfurylamine, 2-furoylglycine, N-substituted-5-(aminoethyl) furan-2-carbaldehyde derivative, 3',4'-dihydroxyacetophenone sulfate, caffeine, dihydroxystyrene glucuronide, ferulic acid sulfate, 4-ethylcatechol glucuronide, 3-feruloylquinic acid, 3,4-dihydroxystyrene sulfate, one unknown glucuronide, and one unknown sulfate. Combinations of candidate biomarkers gave a better prediction of coffee consumption than individual biomarkers. The robustness of the combined biomarkers requires additional validation in cohort studies covering other populations.

Discovery of Urinary Biomarkers of Seaweed Intake Using Untargeted LC-MS Metabolomics in a Three-Way Cross-Over Human Study.

Seaweeds are a marine source rich in potentially bioactive components, and therefore have attracted attention since the middle of the twentieth century. Accurate and objective assessment of the intake of seaweeds to study their health effects is hampered by a lack of validated intake biomarkers. In this three-armed, randomized, cross-over study, an untargeted metabolomics approach was applied for discovering novel intake biomarkers. Twenty healthy participants (9 men and 11 women) were provided each of three test meals in a randomized order: 5 g of Laminaria digitate (LD), 5 g of Undaria pinnatifida (UP), or a control meal with energy-adjusted pea protein. Four urine samples and a 24 h pooled urine were collected along with blood samples at seven time-points. All samples were profiled by LC-ESI-QTOF-MS and the data were analyzed by univariate analysis and excretion kinetics to select putative intake biomarkers. In total, four intake biomarkers were selected from urine samples. They were identified as hydroxyl-dihydrocoumarin at Level III, loliolid glucuronide at level I, and isololiolid glucuronide at level II, while the last one remains unknown. Further identification and validation of these biomarkers by a cross-sectional study is essential to assess their specificity and robustness.

A new software-assisted analytical workflow based on high-resolution mass spectrometry for the systematic study of phenolic compounds in complex matrices.

Polyphenols are a broad class of plant secondary metabolites which carry out several biological functions for plant growth and protection and are of great interest as nutraceuticals for their antioxidant properties. However, due to their structural variability and complexity, the mass-spectrometric analysis of polyphenol content in plant matrices is still an issue. In this work, a novel approach for the identification of several classes of polyphenol derivatives based on ultra-high performance liquid chromatography coupled to high-resolution mass spectrometry was developed. First, mass-spectrometric parameters were optimized in order to obtain a large set of diagnostic product ions for their high-confidence identification. The software Compound Discoverer 3.0 was then implemented with a comprehensive database of 45,567 polyphenol derivatives and with mass-spectrometric data for their building blocks, resulting in a specific tool for the semi-automatic identification of flavonoids, anthocyanins, ellagitannins, proanthocyanidins and phenolic acids. The method was then applied to the identification of polyphenols in industrial hemp (Cannabis sativa), a matrix whose use is recently spreading for pharmaceutical and nutraceutical purposes, resulting in the identification of 147 compounds belonging to the classes of flavonoids, proanthocyanidins and phenolic acids. The proposed method is applicable to the polyphenol profiling of any plant matrix and it is not dependent on data in the literature for their identification, allowing the discovery of compounds which have been never identified before.

A comprehensive analysis of liposomal biomolecular corona upon human plasma incubation: The evolution towards the lipid corona.

When drug nanocarriers enter a physiological environment, their surface gets coated by a dynamic biomolecular corona (BMC) mainly constituted by proteins. Although a deep investigation has been performed on the composition of BMC in terms of proteins, scarce attention has been posed to low molecular weight metabolites present in human plasma. In this work, for the first time, the investigation of the BMC of liposomal nanoparticles (NPs) constituted by 1,2-dioleoyl-3-trimethylammonium-propane polar lipid has been carried out by an ultra-high performance liquid chromatography coupled to high-resolution mass spectrometry based untargeted metabolomics approach. Compounds were tentatively identified based on matches with online databases and comparison of MS/MS spectra with available spectral libraries. Moreover, a comparison of three metabolite extraction strategies, including an ultrafiltration membrane based protocol, a methanol extraction based protocol, and Wessel & Flügge protocol, was performed. Methanol extraction procedure resulted in the widest metabolic coverage of liposomal NP BMC. A total of 193 metabolites has been tentatively identified, 166 of which belonged to the class of lipids including phospholipids, steroids, carnitines, fatty alcohols, diglycerides and fatty acids. The high abundance of lipids in the BMC can be explained by the adsorption of plasma lipoproteins onto liposome surface, confirming previous works on other kinds of NPs. Lipids are important bioactive molecules, which could impact NP circulation and uptake by cells. Extending the investigation of BMC beyond the protein corona and towards the "lipid corona" may be the keystone of a better understanding and control of NP fate in human body.

Enrichment procedure based on graphitized carbon black and liquid chromatography-high resolution mass spectrometry for elucidating sulfolipids composition of microalgae.

Microalgae have recently become a popular functional food due to their health benefits. Sulfolipids, a class of substances abundant in this matrix, have been reported to have interesting bioactivities, such as anti-carcinogenic activity. However, despite the potential interest in sulfolipids, a dedicated analytical method for their characterization is currently lacking but would significantly increase the coverage of sulfolipids with respect to the direct lipidomic analysis. To achieve this goal, in this work a procedure, based on graphitized carbon black solid phase extraction, was developed for clean-up and enrichment of sulfolipids (sulfoquinovosyldiacylglycerols and sulfoquinovosylmonoacylglycerols) and it was applied to spirulina (Arthrospira platensis) microalgae. A careful study of the solid phase extraction conditions was performed, first to maximize the recovery of reference standards, then to increase the total number of identified sulfolipids from the spirulina lipid extract. All samples were analysed by ultra-high performance liquid chromatography coupled to high resolution mass spectrometry and lipids were tentatively identified by Lipostar, for a reliable lipid structure assignment. The developed method was compared to the direct lipidomic analysis without enrichment, to establish the enrichment efficiency in terms of number of identifications. From the comparison, the enrichment procedure proved better and allowed the tentative identification of 199 sulfolipids, which is the largest number reported so far for the Arthrospira platensis species. The described method was validated in terms of precision, accuracy, recovery, limit of quantitation and detection for two sulfolipids. Finally, a relative lipid quantitation based on peak area was carried out on the microalgae sample, which indicated nine abundant sulfolipids as representing ca. 60% of sulfolipids in spirulina microalgae.

Graphitized Carbon Black Enrichment and UHPLC-MS/MS Allow to Meet the Challenge of Small Chain Peptidomics in Urine.

Short peptide sequences represent emerging analytes in a variety of fields, including biomarker discovery, but also a well-known analytical challenge in complex matrices, due to the low abundance, extensive suppression during MS analysis, and lack of workflows, as they cannot be identified by ordinary peptidomics strategies and coverage is extremely limited by metabolomics as well. In this context, in this work, a solid phase extraction method was developed for the cleanup and enrichment of dipeptides, tripeptides, and tetrapeptides in urine using graphitized carbon black Carbograph 4 as the sorbent. The method was first developed on analytical standards spiked in urine, with recoveries in the range of 60-100%. Then the method was applied to urine samples from healthy volunteers. The enriched urine samples were analyzed by ultrahigh performance liquid chromatography (UHPLC) using an orthogonal strategy in which both a reversed phase (RP) C18 column and a zwitterionic hydrophilic interaction liquid chromatography (HILIC) column were used, for better coverage of peptide polarity and improved detection of peptides. High-resolution mass spectra were acquired in data-dependent mode using a suspect screening strategy with inclusion list; peptides were identified by a semiautomated workflow for feature extraction, candidate mass filtering, and MS/MS spectra comparison with in silico mass spectra. The complementarity of the orthogonal separation strategy was confirmed by peptide identification, resulting in 101 peptides identified from the RP runs and 111 peptides from the HILIC runs, with 60 common identifications. The method is applicable to both hydrophobic and hydrophilic peptides. Peptides were stable over 2 h after collection and protease inhibitors were not necessary, as no formation of artifacts was observed.

A Novel Magnetic Molecular Imprinted Polymer for Selective Extraction of Zearalenone from Cereal Flours before Liquid Chromatography-Tandem Mass Spectrometry Determination.

Zearalenone (ZEN) is a nonsteroidal estrogenic mycotoxin produced by various Fusarium species and commonly occurring in corn and other cereals. Even though its acute toxicity is low, still the estrogenic activity of ZEN and metabolites is a matter of concern. In this work, a new magnetic molecularly imprinted polymer (mMIP) for the selective extraction of ZEN from cereal flours is presented. The mMIP was synthesized previously using quercetin as dummy template, and here we wanted to test its applicability to complex food samples. Analyte determination was carried out by high-performance liquid chromatography coupled to tandem mass spectrometry. The selectivity of the mMIP and the main validation method parameters were assessed. In particular, even in samples as complex as cereals, matrix effect was negligible. Although the mMIP showed cross-selectivity towards both ZEN-related and quercetin-related compounds, nonetheless ZEN recovery was > 95% for the two lower spiking levels, and the quantification limit was 0.14 ng g-1, i.e., ca. 500 times lower than the maximum limit fixed for most cereals by European law. Therefore, the material, also in comparison with a commercial sorbent, appears suitable for the application in food analysis, also to isolate ZEN at trace levels.

Development of an Analytical Method for the Metaproteomic Investigation of Bioaerosol from Work Environments.

The metaproteomic analysis of air particulate matter provides valuable information about the properties of bioaerosols in the atmosphere and their influence on climate and public health. In this work, a new method for the extraction and analysis of proteins in airborne particulate matter from quartz microfiber filters is developed. Different protein extraction procedures are tested to select the best extraction protocol based on protein recovery. The optimized method is tested for the extraction of proteins from spores of ubiquitous bacteria species and used for the metaproteomic characterization of filters from three work environments. In particular, ambient aerosol samples are collected in a composting plant, in a wastewater treatment plant, and in an agricultural holding. A total of 179, 15, 205, and 444 proteins are identified in composting plant, wastewater treatment plant, and agricultural holding, (cow stable and blending plant), respectively. In agreement with the major categories of primary biological aerosol particles, all identified proteins originated primarily from fungi, bacteria, and plants. The paper is the first metaproteomic study applied to bioaerosol samples collected in occupationally relevant environmental sites and, even though not aimed at monitoring the risk exposure of workers, it provides information on the possible exposure in the working environmental sites.

A Triple Quadrupole and a Hybrid Quadrupole Orbitrap Mass Spectrometer in Comparison for Polyphenol Quantitation.

Liquid chromatography coupled to low-resolution mass spectrometry (LRMS) has historically been a popular approach for compound quantitation. Recently, high-resolution mass spectrometry (HRMS) technical developments led to the introduction of new approaches for quantitative analysis. Whereas the performances of HRMS have been largely assessed for qualitative purposes, there are still questions about its suitability for quantitative analysis. Several papers on LRMS and HRMS comparison have been published; however, none of them was applied to polyphenol quantitation. In this work, a comparison between HRMS, operated in data-dependent acquisition mode, and LRMS, operated in selected-reaction-monitoring mode, was performed for polyphenol quantitation in wine. The two techniques were evaluated in terms of sensitivity, linearity range, matrix effect, and precision, showing the better performances of HRMS. The suitability of HRMS for quantitation purposes as well as qualitative screening makes HRMS the new technique of choice for both targeted and untargeted analysis.

Identification of bioactive short peptides in cow milk by high-performance liquid chromatography on C18 and porous graphitic carbon coupled to high-resolution mass spectrometry.

Short peptides are important compounds in a variety of fields, including food and nutraceutical applications, but also biomarker discovery, bioactive peptide discovery and peptide drug separation. Despite the importance of short peptides, they are currently less studied than other peptides because of the lack of dedicated methods for their characterization. The method described in this paper comprises a combination of strategies to tackle the main limitations in short peptide analysis. In particular, in this work an untargeted peptidomic approach based on ultrahigh-performance liquid chromatography coupled to high-resolution mass spectrometry was developed for the identification of short peptides in cow milk samples. After milk defatting and precipitation, the sample was purified by cotton-hydrophilic interaction liquid chromatography (HILIC) micro tip in order to avoid suppression phenomena due to contaminants present in milk, such as carbohydrates. The sample was then separated by means of two chromatographic columns, with a complementary selectivity mechanism, namely reversed-phase C18 column and porous graphitic carbon (PGC). By this approach, the method allowed the separation and characterization of di-, tri- and tetrapeptides. A total of 57 and 41 peptides were identified by using a C18 and a PGC column, respectively; in particular, 31 were exclusively identified by using the C18 column, 15 unique peptides were identified by using the PGC column, while 26 were in common between the two data sets, demonstrating that the two columns have a different selectivity mechanism. The results indicated that an integrated approach may be appropriate to improve the separation of different peptides and increase the number of identifications because of the wide range of polarity of short peptides. The method allowed the untargeted identification of short peptides in milk, a complex matrix chosen as a representative real sample for method application, and provides complementary information to that accessible by ordinary peptidomics. Graphical abstract.

Investigation of free and conjugated seleno-amino acids in wheat bran by hydrophilic interaction liquid chromatography with tandem mass spectrometry.

An analytical method for determining seleno-methionine, methyl-seleno-cysteine, and seleno-cystine in wheat bran was developed and validated. Four different extraction procedures were evaluated to simultaneously extract endogenous free and conjugated seleno-amino acids in wheat bran in order to select the best extraction protocol in terms of seleno amino acid quantitation. The extracted samples were subjected to a clean-up by a reversed phase/strong cation exchange solid-phase extraction and analyzed by chiral hydrophilic interaction liquid chromatography-tandem mass spectrometry. The optimized extraction protocol was employed to validate the methodology. Process efficiency ranged from 58 to 112% and trueness from 73 to 98%. Limit of detection and limit of quantification were lower than 1 ng/g. Four wheat bran samples were analyzed for both total Se and single seleno-amino acids determination. The results showed that Se- seleno-methyl-lselenocysteine was the major seleno-amino acid in wheat bran while seleno-methionine and seleno-cysteine were both minor species.

Sensitive untargeted identification of short hydrophilic peptides by high performance liquid chromatography on porous graphitic carbon coupled to high resolution mass spectrometry.

The combination of an efficient chromatographic separation with post-column addition of a supercharging agent was evaluated for the determination of small peptides. The procedure takes advantage of porous graphitic carbon (PGC) ability in retaining very polar and ionic molecules to overstep the poor retention of small peptides on conventional reversed phase (RP) columns. The method was developed specifically for the most hydrophilic di-, tri- and tetrapeptides, which are not identified in ordinary peptidomics experiments. In addition to retention mechanisms acting on conventional RP, the method exploited the charge induced interactions generated by the charges on the peptides with the polarizable surface of PGC. This results in efficient retention of very short and highly polar peptides using classical RP mobile phases. The effects of varying mobile phase composition (organic solvent and ion-pairing additives) as well as column temperature have been thoroughly investigated using short peptide standards. Under optimized conditions (water and acetonitrile/tetrahydrofuran 99:1 (v/v), both with 0.15% trifluoroacetic acid, as phase A and B, respectively, 0.5 mL min-1 flowrate at 50 °C) the effect of post-column addition of 3-nitrobenzylic alcohol was also investigated allowing effective coupling of the chromatographic system with high resolution mass spectrometry. Finally, an untargeted approach for peptide identification was pursued, based on precursor identification in database with all possible combinations of the 20 natural amino acids and fragmentation spectra matching to in silico generated spectra. The method was then applied to investigation of the short endogenous peptides in human serum from healthy individuals resulting in the identification of 30 short peptides.

Investigation of free seleno-amino acids in extra-virgin olive oil by mixed mode solid phase extraction cleanup and enantioselective hydrophilic interaction liquid chromatography-tandem mass spectrometry.

An analytical method for determining seleno-methionine (SeMet), methyl-seleno-cysteine and seleno-cystine in extra-virgin olive oil (EVOO) was developed and validated. EVOO sample (15 g) was diluted with hexane, extracted with methanol/water 80:20 (v/v), and cleaned up by a reversed phase/strong cation exchange solid phase extraction. Analysis was performed by chiral hydrophilic interaction liquid chromatography-tandem mass spectrometry. Process efficiency ranged between 49 and 97% and trueness between 87 and 126%, with intermediate precision, expressed as standard deviation, lower than 10%. Method detection limits (MDLs) and method quantification limits (MQLs) were lower than 1 µg kg-1. Thirty-two EVOO samples from different Italian regions were analyzed for both total Se and single seleno-amino acids determination. Only l-SeMet was found at level MQL (0.2 µg kg-1)-1.42 µg kg-1 in ten samples, while total Se was in the range of MDL-9.1 µg kg-1. Concentration of l-SeMet (5-6% of total Se) and total Se correlated very well to each other (R2 = 0.995).

Liquid Chromatographic Strategies for Separation of Bioactive Compounds in Food Matrices.

Nowadays, there is an increasing attention for nutraceuticals and, in general, bioactive compounds naturally present in food. Indeed, the possibility of preserving human health and preventing disease (e.g., cardiovascular diseases, cancer etc.) by the intake of healthy food is attractive for both consumers and food industries. In turn, research in this field was also prompted significantly, with the aim of characterizing these bioactive compounds and ascribe to them a specific activity. The bioactive compounds can belong to several chemical classes. However, their chemical diversity and presence in complex matrices, such as food, make it challenging both their isolation and characterization. To tackle this issue, efficient separation systems are needed, which are mainly based on chromatography. In this context, this mini-review aims to provide the reader with an overview of the most relevant and recent approaches for the separation of the most common bioactive compounds in food, in particular polyphenols, phenols, carotenoids, and peptides, by liquid chromatography approaches.

Delving into the Polar Lipidome by Optimized Chromatographic Separation, High-Resolution Mass Spectrometry, and Comprehensive Identification with Lipostar: Microalgae as Case Study.

The work describes the chromatographic separation optimization of polar lipids on Kinetex-EVO, particularly focusing on sulfolipids in spirulina microalgae ( Arthrospira platensis). Gradient shape and mobile-phase modifiers (pH and buffer) were tested on lipid standards. Different conditions were evaluated, and resolution, peak capacity, and peak shape were calculated both in negative mode, for sulfolipids and phospholipids, and in positive mode, for glycolipids. A high-confidence lipid identification strategy was also applied. In collaboration with software creators and developers, Lipostar was implemented to improve the identification of phosphoglycerolipids and to allow the identification of glycosylmonoradyl- and glycosyldiradyl-glycerols classes, the last being the main focus of this work. By this approach, an untargeted screening also for searching lipids not yet reported in the literature could be accomplished. The optimized chromatographic conditions and database search were tested for lipid identification first on the standard mixture, then on the polar lipid extract of spirulina microalgae, for which 205 lipids were identified.

Extraction of polycyclic aromatic hydrocarbons from polyhydroxyalkanoates before gas chromatography/mass spectrometry analysis.

Among the organic contaminants that could pass from waste to polyhydroxyalkanoates (PHAs), there are the polycyclic aromatic hydrocarbons (PAHs). For this reason, we have developed a rapid analytical method for the determination of sixteen PAHs in PHAs. PAHs were extracted by n-hexane, after matrix dispersion and crumbling into sand; the extract was purified by solid phase extraction using florisil as adsorbent. Recoveries in the range of 89-101% were obtained for the deuterated analytes, except for the two with the lowest molecular weight. Trueness between 92% and 108% and within-laboratory precision (expressed as relative standard deviation) ≤ 18% were estimated for all the analytes. Gas chromatography/mass spectrometry was used for analyte determination. Method limits of quantification were suitable to assure that PAH presence in PHA biolpolymers is much below the limits set by European law for plastic materials. Indeed, analysis of two different PHA samples showed that contamination is limited to few compounds at non-concerning levels.

Simultaneous Preconcentration, Identification, and Quantitation of Selenoamino Acids in Oils by Enantioselective High Performance Liquid Chromatography and Mass Spectrometry.

Selenium is an essential micronutrient for humans. In food, selenium can be present in both inorganic and organic forms, the latter mainly being selenomethionine, Se-methyl-selenocysteine, and selenocystine. Selenoamino acid speciation rarely involves the chirality of selenoamino acids. In this work, a 5 cm long CHIROBIOTIC TAG chromatographic column was used for enantioresolution of selenoamino acids (d- and l-selenomethionine, Se-methyl-l-selenocysteine, d-, l- and meso-selenocystine); in the optimized conditions, the complete resolution of the analytes was achieved within 15 min by using a very polar aqueous mobile phase (gradient elution by methanol/acetonitrile/H2O, 45:45:10 ( v/ v/ v) with 10 mmol L-1 of ammonium formate and 0.5% formic acid as the mobile phase A and acetonitrile/H2O, 20:80 ( v/ v) with 20 mmol L-1 of ammonium formate at apparent pH 4 as the mobile phase B). The affinity of the teicoplanin aglycone was further exploited to devise a preconcentration method for selenoamino acids in oils. In particular, the CHIROBIOTIC TAG precolumn was used to directly concentrate the selenoamino acids after simple dilution of oil samples with dichloromethane. An optimized procedure for selenoamino acid trapping and preconcentration under normal phase conditions was developed. The enrichment procedure also ensured band focusing during the subsequent separation. The target analytes were finally identified and quantified by triple quadrupole selected reaction monitoring. The method allowed obtainment of recovery values up to 73%, with limits of detection between 280 and 750 ng and limits of quantification between 375 and 960 ng for the different selenoamino acids. The method was applied to commercial oil samples, and only l-selenomethionine was detected.