Selective ionization of oxidized lipid species using different solvent additives in flow injection mass spectrometry.

Lipid oxidation in food products is a crucial problem that causes undesirable changes in the food's flavor, texture, and nutritional value. It should be carefully monitored as it can lead to the formation of potentially toxic compounds and in that way reduce the shelf life of the product. Liquid chromatography coupled to mass spectrometry is a powerful tool to monitor the formation of oxidized lipids. However, the presence of lipid species in both their non-oxidized and oxidized forms at distinctly different concentrations can hinder the detection and identification of the less abundant oxidized species, due to coelution. In this study, a flow injection mass spectrometry approach was used to selectively ionize oxidized triacylglycerols versus their non-oxidized precursors. Three mobile phase additives were investigated (ammonium formate, sodium acetate, and sodium iodide) at three different concentrations, and ion source settings (i.e., sheath gas temperature, capillary voltage, and nozzle voltage) were optimized. A fractional factorial design was conducted to examine not only the direct effect of the operating parameters on the selectivity of ionization for the oxidized lipid species, but also to assess their combined effect. Overall, selective ionization of oxidized versus non-oxidized lipid species was favored by the use of sodium-containing solvent additives. The application of specific ion source settings resulted in an increased ionization selectivity, with sheath gas temperature and capillary voltage having the most significant influence. A selectivity factor as high as 120 could be reached by combining 0.1 mg/mL sodium-containing additives, with 250 °C sheath gas temperature and 5000 V capillary voltage. These findings will contribute to future studies on fast detection and relative quantification of low abundant oxidized triacylglycerols and their possible impact on human health.

Comprehensive cannabinoid profiling of acid-treated CBD samples and Δ8-THC-infused edibles.

Δ8-Tetrahydrocannabinol (Δ8-THC) is increasingly popular as a controversial substitute for Δ9-tetrahydrocannabinol (Δ9-THC) in cannabinoid-infused edibles. Δ8-THC is prepared from cannabidiol (CBD) by treatment with acids. Side products including Δ9-THC and other isomers that might end up in Δ8-THC edibles are less studied. In this paper, three orthogonal methods, namely reversed-phase (RP)-UHPLC-DAD/HRMS, normal-phase/argentation (silica-Ag(I))-HPLC-DAD/MS, and GC-FID/MS were developed for analysis of cannabinoid isomers, namely Δ8-THC, Δ9-THC, CBD, Δ8-iso-THC, Δ(4)8-iso-THC, and hydrated THC isomers. Eight acid-treated CBD mixtures contained various amounts of Δ8-THC (0-89%, w/w%), high levels of Δ9-THC (up to 49%), Δ8-isoTHC (up to 55%), Δ(4)8-iso-THC (up to 17%), and three hydrated THC isomers. Commercial Δ8-THC gummies were also analyzed, and issues like overclaimed Δ8-THC, excessive Δ9-THC, undeclared Δ8-iso-THC, and Δ(4)8-iso-THC were found. These findings highlight the urgency of improving regulations towards converting CBD to Δ8-THC for use as food ingredients.

Unraveling the Role of Flavor Structure and Physicochemical Properties in the Binding Phenomenon with Commercial Food Protein Isolates.

Food protein-flavor binding influences flavor release and perception. The complexity of the binding phenomenon lies in the flavor and protein properties. Thus, molecular interactions between commercial whey- or plant-based protein isolates (PI) such as pea, soy, and lupin, with carbonyl and alcohol flavor compounds were assessed by static headspace (HS) GC-MS. HS results showed that not only the displacement of the carbonyl group from the inner part of the flavor structure toward the edge promoted binding up to 52.76% ± 4.65 but also the flavor's degree of unsaturation. Similarly, thermal treatment led to a slight increase in hexanal-protein binding because of possible protein conformational changes. Protein's residual fat (<1%) seemed insufficient to promote significant flavor binding to PI. Despite the complexity of commercial food protein isolates, the results displayed that binding is predominantly influenced by the flavor structure and physicochemical properties, with the protein source and residual fat playing a secondary role.

Improved LC-MS identification of short homologous peptides using sequence-specific retention time predictors.

Peptides are an important group of compounds contributing to the desired, as well as the undesired taste of a food product. Their taste impressions can include aspects of sweetness, bitterness, savoury, umami and many other impressions depending on the amino acids present as well as their sequence. Identification of short peptides in foods is challenging. We developed a method to assign identities to short peptides including homologous structures, i.e. peptides containing the same amino acids with a different sequence order, by accurate prediction of the retention times during reversed phase separation. To train the method, a large set of well-defined short peptides with systematic variations in the amino acid sequence was prepared by a novel synthesis strategy called 'swapped-sequence synthesis'. Additionally, several proteins were enzymatically digested to yield short peptides. Experimental retention times were determined after reversed phase separation and peptide MS2 data was acquired using a high-resolution mass spectrometer operated in data-dependent acquisition mode (DDA). A support vector regression model was trained using a combination of existing sequence-independent peptide descriptors and a newly derived set of selected amino acid index derived sequence-specific peptide (ASP) descriptors. The model was trained and validated using the experimental retention times of the 713 small food-relevant peptides prepared. Whilst selecting the most useful ASP descriptors for our model, special attention was given to predict the retention time differences between homologous peptide structures. Inclusion of ASP descriptors greatly improved the ability to accurately predict retention times, including retention time differences between 157 homologous peptide pairs. The final prediction model had a goodness-of-fit (Q2) of 0.94; moreover for 93% of the short peptides, the elution order was correctly predicted.

Rapid Single Particle Atmospheric Solids Analysis Probe-Mass Spectrometry for Multimodal Analysis of Microplastics.

Despite mass spectrometry (MS) being proven powerful for the characterization of synthetic polymers, its potential for the analysis of single particle microplastics (MPs) is yet to be fully disclosed. To date, MPs are regarded as ubiquitous contaminants, but the limited availability of techniques that enable full characterizations of MPs results in a lack of systematic data regarding their occurrence. In this study, an atmospheric solid analysis probe (ASAP) coupled to a compact quadrupole MS is proposed for the chemical analysis of single particle microplastics, while maintaining full compatibility with complementary staining and image analysis approaches. A two-stage ASAP probe temperature program was optimized for the removal of additives and surface contaminants followed by the actual polymer characterization. The method showed specific mass spectra for a wide range of single particle MPs, including polyolefins, polyaromatics, polyacrylates, (bio)polyesters, polyamides, polycarbonates, and polyacrylonitriles. The single particle size detection limits for polystyrene MPs were found to be 30 and 5 µm in full scan and selected ion recording mode, respectively. Moreover, results are presented of a multimodal microplastic analysis approach in which filtered particles are first characterized by staining and fluorescence microscopy, followed by simple probe picking of individual particles for subsequent analysis by ASAP-MS. The method provides a full characterization of MP contamination, including particle number, particle size, particle shape, and chemical identity. The applicability of the developed multimodal method was successfully demonstrated by the analysis of MPs in bioplastic bottled water.

Identification of plant polysaccharides by MALDI-TOF MS fingerprinting after periodate oxidation and thermal hydrolysis.

An autoclave treatment at 121 °C on periodate-oxidized plant polysaccharides and mixes thereof was investigated for the release of oligosaccharides to obtain a generic polysaccharide depolymerization method for polysaccharides fingerprinting. Matrix-Assisted Laser Desorption Ionization Time-Of-Flight Mass Spectrometry (MALDI-TOF MS) analysis of the oligosaccharides released showed that each polysaccharide had a unique oligosaccharides profile, even the same type of polysaccharide derived from different sources and/or having different fine structures (e.g. class of (arabino)xylans, galactomannans, glucans, or pectic materials). Various polysaccharide classes present in a polysaccharide mix could be identified based on significantly different (p < 0.05) marker m/z values present in the mass spectrum. Principal component analysis and hierarchical cluster analysis of the obtained MALDI-TOF MS data highlighted the structural heterogeneity of the polysaccharides studied, and clustered polysaccharide samples with resembling oligosaccharide profiles. Our approach represents a step further towards a generic and accessible identification of plant polysaccharides individually or in a mixture.

Periodate oxidation of plant polysaccharides provides polysaccharide-specific oligosaccharides.

Although polysaccharides are frequently used in foods, detailed characterization and/or identification of their structures using a single method remains a challenge. We investigated the suitability of periodate oxidation as an approach to depolymerize polysaccharides, allowing characterization and/or identification of the original polysaccharides based on ESI-MS analyses of the released oligosaccharides. Various periodate oxidation conditions were tested on (arabino)xylan, galactomannan, xyloglucan and homogalacturonan. Each polysaccharide required a different oxidation condition to release a substantial level of oligosaccharides. These oligosaccharides had highly complex structures due to the presence of e.g., dialdehyde sugars, hemialdals, and remnants of (oxidized) sugars, as verified by ESI-MS/MS. Despite these oligosaccharides were highly complex and lost some polysaccharide structural features, each periodate-oxidized sample comprised polysaccharide structure-dependent MS oxidized oligosaccharide profiles. Our findings are a good starting point to find a more generic chemical polysaccharide depolymerization approach based on periodate oxidation to identify polysaccharides by oligosaccharides fingerprinting using MS.

Partial acid-hydrolysis of TEMPO-oxidized arabinoxylans generates arabinoxylan-structure resembling oligosaccharides.

Arabinoxylans (AXs) display biological activities that depend on their chemical structures. To structurally characterize and distinguish AXs using a non-enzymatic approach, various TEMPO-oxidized AXs were partially acid-hydrolysed to obtain diagnostic oligosaccharides (OS). Arabinurono-xylo-oligomer alditols (AUXOS-A) with degree of polymerization 2-5, comprising one and two arabinuronic acid (AraA) substituents were identified in the UHPLC-PGC-MS profiles of three TEMPO-oxidized AXs, namely wheat (ox-WAX), partially-debranched WAX (ox-pD-WAX), and rye (ox-RAX). Characterization of these AUXOS-A highlighted that single-substitution of the Xyl unit preferably occurs at position O-3 for these samples, and that ox-WAX has both more single substituted and more double-substituted xylose residues in its backbone than the other AXs. Characteristic UHPLC-PGC-MS OS profiles, differing in OS abundance and composition, were obtained for each AX. Thus, partial acid-hydrolysis of TEMPO-oxidized AXs with analysis of the released OS by UHPLC-PGC-MS is a promising novel non-enzymatic approach to distinguish AXs and obtain insights into their structures.

A Fast GC-MS-Based Method for Efficacy Assessment of Natural Anti-Oxidants for Inhibiting Lipid Oxidation.

BACKGROUND: For health reasons it is preferred to prepare food products with edible fats and oils that are high in unsaturated fatty acids. Unfortunately, these unsaturated acids are susceptible to lipid oxidation and the addition of natural antioxidants, e.g., rosemary extracts, etc. is needed. OBJECTIVE: To assess the efficacy of natural oxidation inhibition strategies, fast, yet realistic, and objective methods are needed to study oxidation inhibition. METHODS: A model system consisting of salt and sunflower oil is proposed as a model for dry soups and sauces. Hexanal formation is studied using fast GC-MS as a quantitative indicator for lipid oxidation. RESULTS: A fast GC-MS method using a short, 6-m 150 µm inner-diameter column was developed that allowed elution of hexanal within approximately 20 s, with a total run time of 2 min. The GC method has quantification limits below 1 ppm and is hence much more sensitive than the human nose. CONCLUSIONS: The new accelerated method with hexanal read-out was successfully applied in a study to identify spices and herbs mixtures that can act as natural inhibitors of lipid oxidation. The fast GC-MS method is extremely stable and allowed the analysis of thousands of samples with very little maintenance. HIGHLIGHTS: With the right mixture of spices and herbs, lipid oxidation can be delayed more than 100 times as compared to non-stabilized systems.

A comprehensive two-dimensional liquid chromatography method for the simultaneous separation of lipid species and their oxidation products.

Lipid oxidation is one of the major causes of food spoilage for lipid-rich foods. In particular, oil-in-water emulsions, like mayonnaises and spreads, are prone to oxidation due to the increased interfacial area that facilitates contact between the lipids and hydrophilic pro-oxidants present in the water phase. Polar, amphiphilic lipid species present at the oil/water interface, like the mono- (MAGs) and di-acylglycerols (DAGs), act as oxidation starters that initiate subsequent oxidation reactions of the non-polar lipids in the oil droplets. A comprehensive two-dimensional liquid chromatography (LC×LC) method with evaporative light-scattering detection (ELSD) was set up to study the composition of the complex mixture of oxidized polar and non-polar lipids. The LC×LC-ELSD method employs size exclusion chromatography (SEC) in the 1D (1st dimension) to separate the various lipid species according to size. In the 2D (2nd dimension), normal-phase liquid chromatography (NPLC) is used to separate the fractions according to their degree of oxidation. The coupling of SEC with NPLC yields a good separation of the oxidized triacylglycerols (TAGs) from the large excess of non-oxidized TAGs. In addition, it allows the isolation of non-oxidized DAGs and MAGs that usually interfere with the detection of a variety of oxidized products that have similar polarities. This method facilitates elucidating how lipid composition affects oxidation kinetics in emulsified foods and will aid in the development of more oxidation-stable products.

TEMPO/NaClO2/NaOCl oxidation of arabinoxylans.

TEMPO-oxidation of neutral polysaccharides has been used to obtain polyuronides displaying improved functional properties. Although arabinoxylans (AX) from different sources may yield polyuronides with diverse properties due to their variable arabinose (Araf) substitution patterns, information of the TEMPO-oxidation of AX on its structure remains scarce. We oxidized AX using various TEMPO:NaClO2:NaOCl ratios. A TEMPO:NaClO2:NaOCl ratio of 1.0:2.6:0.4 per mol of Ara gave an oxidized-AX with high molecular weight, minimal effect on xylose appearance, and comprising charged side chains. Although NMR analyses unveiled arabinuronic acid (AraAf) as the only oxidation product in the oxidized-AX, accurate AraA quantification is still challenging. Linkage analysis showed that > 75 % of the ß-(1→4)-xylan backbone remained single-substituted at position O-3 of Xyl similarly to native AX. TEMPO-oxidation of AX can be considered a promising approach to obtain arabinuronoxylans with a substitution pattern resembling its parental AX.

Supercritical fluid chromatography as a rapid single-step method for the determination of mineral oil saturated and aromatic hydrocarbons in purified mineral oils for food and cosmetics applications.

Mineral oil hydrocarbons are used in the consumer goods sector for the elaboration of a wide range of foods and cosmetics. Traditional methods for determining their levels and composition are time consuming and laborious, besides requiring complex instrumentation. Here a simple and fast method was developed that uses columns packed with silver-modified silica in supercritical fluid chromatography with flame ionization and UV detection (SFC-FID/UV) for the determination of mineral oil saturated hydrocarbons (MOSH) and mineral oil aromatic hydrocarbons (MOAH) in purified mineral oil samples. The method requires no sample preparation apart from dilution. Direct quantification of MOSH and MOAH was possible for samples with MOSH/MOAH ratios around one. For other samples deconvolution of the MOSH and MOAH humps in the FID chromatogram using the UV signal was needed since baseline separation of the two fractions could not be obtained. Validation of the method performance showed an excellent linearity (R2 > 0.9995) in the range of concentrations tested (2.5-100 mgmL-1) and a better repeatability than the standard methods (<5%). MOAH detection limits were better than 0.36% MOAH, which makes the method sufficiently sensitive for analysis of all but the highest purity mineral oils. The proposed SFC-FID/UV method was suitable for the analysis of mineral oils with viscosities and molecular weights below approximately 56 mm2s-1 and 450 gmol-1. The quantitative results of the new method were not statistically significantly different from those obtained with the standard SPE-GC-FID method where the new method has the advantages of a better repeatability, simpler operation and a significantly shortened analysis time. This new method could potentially also be used for the analysis of mineral oil contaminations in consumer products such as foods. However, in this case additional sample clean-up and preconcentration steps are needed for reducing matrix interferences from e.g. triglycerides and olefins and for improving the detection limits.

Distinguishing drug isomers in the forensic laboratory: GC-VUV in addition to GC-MS for orthogonal selectivity and the use of library match scores as a new source of information.

Currently, forensic drug experts are facing chemical identification challenges with the increasing number of new isomeric forms of psychoactive substances occurring in case samples. Very similar mass spectra for these substances could easily result in misidentification using the regular GC-MS screening methods in combination with colorimetric testing in forensic laboratories. Building on recent work from other groups, this study demonstrates that GC-VUV is a powerful technique for drug isomer differentiation, showing reproducible and discriminating spectra for aromatic ring-isomers. MS and VUV show complementary selectivity as VUV spectra are ring-position specific whereas MS spectra are characteristic for the amine moieties of the molecule. VUV spectra are very reproducible showing less than 0.1‰ deviation in library match scores and therefore small spectral differences suffice to confidently distinguish isomers. In comparison, MS match scores gave over 10‰ deviation and showed significant overlap in match score ranges for several isomers. This poses a risk for false positive identifications when assigning compounds based on retention time and GC-MS mass spectrum. A strategy was developed, based on Kernel Density Estimations of match scores, to construct Receiver Operating Characteristic (ROC) curves and estimate likelihood ratios (LR values) with respect to the chemical differentiation of drug related isomers. This approach, and the added value of GC-VUV is demonstrated with the chemical analysis of several samples from drug case work from the Amsterdam area involving both compounds listed in Dutch drug legislation (3,4-MDMA; 3,4-MDA; 4-MMC; 4-MEC and 4-FA) as well as their unlisted and thus uncontrolled isomers (2,3-MDMA; 2,3-MDA; 2- and 3-MMC; 2- and 3-MEC and 2- and 3-FA).

Comprehensive off-line silver phase liquid chromatography × gas chromatography with flame ionization and vacuum ultraviolet detection for the detailed characterization of mineral oil aromatic hydrocarbons.

Highly purified mineral oils used for the elaboration of pharmaceutical, food and cosmetic products can contain residual mineral oil aromatic hydrocarbons (MOAH). Quantification of the MOAH level as well as detailed characterization of the aromatic species present is important for safety evaluations and for optimization of the purification process. Two comprehensive off-line silver phase liquid chromatography × gas chromatography (AgLC × GC) methods, one with flame ionization detection (FID) and another with vacuum ultraviolet detection (VUV), were developed for MOAH analysis. The methods showed a better resolution between the MOSH and MOAH groups compared to the traditional online LC-GC methods due to the different retention mechanisms employed in the two dimensions, albeit that the gain was less than seen e.g. in edible oil analysis. An important advantage of the new comprehensive AgLC × GC methods is that the use of markers to determine the MOSH/MOAH cut-point is no longer needed, because all the eluent coming from the LC separation is transferred as narrow fractions to the GC. Due to the use of silver based stationary phases in the first separation dimension, a group-type separation of the mineral oil according to the degree of aromaticity (aliphatics, mono-aromatics and poly-aromatics) was obtained. Moreover, thanks to the use of VUV detection, the new method also delivered additional structural information on the different groups of compounds present.

Methods for one- and two-dimensional gas chromatography with flame ionization detection for identification of Mycobacterium tuberculosis in sputum.

Two simplified methods based on manual thermally-assisted hydrolysis and methylation (THM) GC and GC × GC with flame ionization detection (FID) were developed for the detection of mycobacteria and Mycobacterium tuberculosis (MTB) in sputum. A central composite design was employed to optimize the THM derivatization conditions. For the detection of MTB the known mycobacterial markers tuberculostearic acid (TBSA) and hexacosanoic acid (C26), as well as three MTB specific markers, the mycocerosates, were evaluated. We found that the optimum conditions for THM release of TBSA and C26 differ from those for maximum release of the mycocerosates. Higher reagent volumes, higher temperatures and longer incubation increase the mycocerosates yield. Application of these conditions unfortunately resulted in unacceptable safety hazards. A GC × GC-FID method was developed that allowed accurate detection of mycocerosates even at poor conversion yields of the derivatization reaction. Using spiked sputum samples from non-TB patients, the detection limit of the method based on TBSA and C26 was found to be comparable to that of microscopy, i.e. 104-105 bacteria/mL sputum. To validate the new test, we compared the results we found for fifteen sputum samples from patients from South Africa suspected of having tuberculosis with those of culture, the gold standard method. Based on the presence of TBSA and C26, all eight microscopy and culture positive samples, and even two microscopy negative but culture positive samples were positive by THM-GC-FID. All five microscopy and culture negative sputum samples were also negative for THM-GC-FID, giving a specificity of 100%. Using GC × GC-FID we could detect mycocerosates, the specific markers for MTB in seven out of ten MTB culture positive sputum samples. The five culture negative cases were also negative for mycocerosates in manual THM-GC × GC-FID giving again 100% specificity. The results obtained indicate that the new methods hold great potential for the early diagnosis of TB in developing countries.

Volatile organic compound profiles in outlet air from extracorporeal life-support devices differ from breath profiles in critically ill patients.

INTRODUCTION: It is highly uncertain whether volatile organic compounds (VOCs) in exhaled breath of critically ill intensive care unit patients are formed in the lung locally, in the air compartment or lung tissue, or elsewhere in the body and transported to the lung via the bloodstream. We compared VOC mixtures in exhaled breath and in air coming from extracorporeal support devices in critically ill patients to address this issue. METHODS: First, we investigated whether it was safe to connect an electronic nose (eNose) or a gas sampling pump to extracorporeal support membranes. Then, breath and air from extracorporeal support devices were collected simultaneously for continuous monitoring of VOC mixtures using an eNose. In addition, samples for gas chromatography/mass spectrometry (GC-MS) analysis were taken daily at the two measurement sites. RESULTS: 10 critically ill patients were monitored for a median (interquartile range) duration of 73 (72-113) h; in total, we had 887 h of air sampling. The eNose signals of breath correlated moderately with signals of air from the extracorporeal support devices (R2=0.25-0.44). After GC-MS analysis, 96 VOCs were found both in breath and air from the extracorporeal support devices; of these, 29 (30%) showed a significant correlation (p<0.05) between the two measurement sites, of which 17 were identified. VOCs that did not correlate were found in a higher concentration in breath than in air from the extracorporeal support devices. CONCLUSION: This study suggests VOC analysis in the extracorporeal circulation is safe, and that VOCs of nonpulmonary origin can be measured in the breath and in the extracorporeal circulation of critically ill patients. For VOCs that did not correlate between the two measurement sites, the breath concentration was higher, suggesting pulmonary production of these molecules in a highly selected population of patients that received extracorporeal support.

First international descriptive and interventional survey for cholesterol and non-cholesterol sterol determination by gas- and liquid-chromatography-Urgent need for harmonisation of analytical methods.

Serum concentrations of lathosterol, the plant sterols campesterol and sitosterol and the cholesterol metabolite 5α-cholestanol are widely used as surrogate markers of cholesterol synthesis and absorption, respectively. Increasing numbers of laboratories utilize a broad spectrum of well-established and recently developed methods for the determination of cholesterol and non-cholesterol sterols (NCS). In order to evaluate the quality of these measurements and to identify possible sources of analytical errors our group initiated the first international survey for cholesterol and NCS. The cholesterol and NCS survey was structured as a two-part survey which took place in the years 2013 and 2014. The first survey part was designed as descriptive, providing information about the variation of reported results from different laboratories. A set of two lyophilized pooled sera (A and B) was sent to twenty laboratories specialized in chromatographic lipid analysis. The different sterols were quantified either by gas chromatography-flame ionization detection, gas chromatography- or liquid chromatography-mass selective detection. The participants were requested to determine cholesterol and NCS concentrations in the provided samples as part of their normal laboratory routine. The second part was designed as interventional survey. Twenty-two laboratories agreed to participate and received again two different lyophilized pooled sera (C and D). In contrast to the first international survey, each participant received standard stock solutions with defined concentrations of cholesterol and NCS. The participants were requested to use diluted calibration solutions from the provided standard stock solutions for quantification of cholesterol and NCS. In both surveys, each laboratory used its own internal standard (5α-cholestane, epicoprostanol or deuterium labelled sterols). Main outcome of the survey was, that unacceptably high interlaboratory variations for cholesterol and NCS concentrations are reported, even when the individual laboratories used the same calibration material. We discuss different sources of errors and recommend all laboratories analysing cholesterol and NCS to participate in regular quality control programs.

Direct analysis of aromatic hydrocarbons in purified mineral oils for foods and cosmetics applications using gas chromatography with vacuum ultraviolet detection.

Highly purified mineral oils are used in several pharmaceutical, foods and cosmetics applications. A fast and simple method was developed for the analysis of the total level of residual mineral oil aromatic hydrocarbons (MOAH) in these oils and in the intermediate oils that were sampled during the purification process. The method is based on gas chromatography with vacuum ultraviolet detection (GC-VUV) and relies on the spectral differences between the aliphatic and aromatic compounds in the sample. Because the detector provides a good selectivity for aromatics, direct quantification of the MOAH content is possible without the need for a laborious preseparation of the mineral oil. The method was successfully applied for the direct analysis of the MOAH levels of 18 different mineral oil samples. The aromatics contents obtained by GC-VUV were similar to those obtained using two conventional methods (NPLC-GC-FID and SPE-GC-FID), with no statistically significant difference. The detector response was linear over the concentration range tested (0.5-20 mg/mL) and the repeatability (RSD value) was less than 8%, which is better than the typical values for the conventional methods (up to 15% RSD). The minimum MOAH level that can be determined with this method is approximately 0.13%, making the GC-VUV method sufficiently sensitive for the analysis of all but the highest purity mineral oils.

Synchronous fluorescence spectroscopy combined with chemometrics for rapid assessment of cold-pressed grape seed oil adulteration: Qualitative and quantitative study.

This paper describes the feasibility of synchronous fluorescence (SyF) spectroscopy combined with multivariate data analysis for qualitative and quantitative determination of adulteration of cold pressed grape seed oil (GSO) with refined soybean oil (SBO). SyF spectroscopy data of oil samples were collected in the region of 250-800 nm at excitation-emission wavelength differences (∆λ) of 10, 20, 30, 40, 50, 60, 70 and 80 nm. Three different multivariate methods, namely principal component analysis (PCA), soft independent modeling of class analogies (SIMCA) and partial least square regression (PLSR) analysis were used for data analysis. To simulate the adulteration of cold pressed GSO with refined SBO, ninety-six adulterated samples were prepared at adulterant levels from 5% to 50%. HPLC-FLD method was used as reference in order to authenticate pure oils and binary oil mixtures. The SIMCA models provided an excellent classification for pure cold pressed GSO versus other vegetable oil samples, with a 95% significance level. The classification error rate of SyF spectroscopy for detecting SBO added to GSO was also better than 5%. PLSR calibration models constructed for the evaluation of GSO purity and for the adulterants SBOs were internally validated by the leave-one-out procedure (cross-validation) and their predictive ability was assessed by independent external validation sets. Under the optimum conditions, the plots of observed versus predicted values exhibited a good linearity (R2 > 0.99). The root mean square errors of calibration (RMSEC) and cross-validation (RMSECV) were in the range 0.55-4.46% and 2.14-5.35%, respectively. Excellent predicting capabilities were also obtained using an external validation set consisting of GSO adulterated with SBOs from different brands.

Selective labeling for the identification and semi-quantification of lipid aldehydes in food products.

Lipid oxidation reactions in foods rich in healthy unsaturated fatty acids result in the formation of a wide range of oxidation products that can have adverse effects on food quality and safety. To improve the understanding of oxidation reactions and methods for their inhibition, detailed information on the type and levels of the oxidation products formed is required. Accurate measurement of lipid oxidation products, especially of the non-volatile aldehyde products, has so far been a challenge due to the low sensitivity and limited specificity of most analytical methods. Here, a novel normal-phase LC method that uses selective labeling of aldehydes and epoxides with 7-(diethylamino)coumarin-3-carbohydrazide (CHH) is described. Labeling of alkanals is quantitative within 10 h. For alkenals, conversion is only around 50% at 24 h reaction time. Detailed MS identification of all aldehydes and epoxides is possible by using high-resolution MS and data-dependent MS2 acquisition. Fluorescence detection was successfully used to quantify groups of oxidation products. Sensitivity was high enough to allow accurate quantification even in fresh mayonnaises, where levels of around only 0.3 g total aldehydes/kg oil were found. Individual species can be quantified by MS if suitable reference standards are available. If no standards can be used, semi-quantification using an average response factor is an option. Clearly, the novel derivatization method is suitable for monitoring secondary lipid oxidation products in the early stages of shelf life. This makes it an important tool for developing improved food products. Graphical abstract Selective labeling of low and high molecular weight lipid oxidation products with 7-(diethylamino) coumarin-3-carbohydrazide for identification and semi-quantification.