Software-Assisted Pattern Recognition of Persistent Organic Pollutants in Contaminated Human and Animal Food.

Persistent Organic Pollutants (POPs) are a serious food safety concern due to their persistence and toxic effects. To promote food safety and protect human health, it is important to understand the sources of POPs and how to minimize human exposure to these contaminants. The POPs Program within the U.S. Food and Drug Administration (FDA), manually evaluates congener patterns of POPs-contaminated samples and sometimes compares the finding to other previously analyzed samples with similar patterns. This manual comparison is time consuming and solely depends on human expertise. To improve the efficiency of this evaluation, we developed software to assist in identifying potential sources of POPs contamination by detecting similarities between the congener patterns of a contaminated sample and potential environmental source samples. Similarity scores were computed and used to rank potential source samples. The software has been tested on a diverse set of incurred samples by comparing results from the software with those from human experts. We demonstrated that the software provides results consistent with human expert observation. This software also provided the advantage of reliably evaluating an increased sample lot which increased overall efficiency.

QUICK: Quality and Usability Investigation and Control Kit for Mass Spectrometric Data from Detection of Persistent Organic Pollutants.

Persistent organic pollutants (POPs) cause a significant public and environmental health concern due to their toxicity, long-range transportability, persistence, and bioaccumulation. The US Food and Drug Administration (FDA) has a program to monitor POPs in human and animal foods at ultra-trace levels, using gas chromatography coupled with mass spectrometry (GC-MS). Stringent quality control procedures are practiced within this program, ensuring the reliability and accuracy of these POP results. Due to the complexity of this program's quality control (QC), the decision-making process for data usability was very time-consuming, upward of three analyst hours for a batch of six extracts. We significantly reduced this time by developing a software kit, written in Python, to evaluate instrument and sample QC, along with data usability. A diverse set of 45 samples were tested using our software, QUICK (Quality and Usability Investigation and Control Kit), that resulted in equivalent results provided by a human reviewer. The software improved the efficiency of the analytical process by reducing the need for user intervention, while simultaneously recognizing a 95% decrease in data reduction time, from 3 hours to 10 minutes.

Mycotoxins in infant/toddler foods and breakfast cereals in the US retail market.

The objective of this study was to conduct a mycotoxin survey of commercial infant/toddler foods (cereals and teething biscuits) and breakfast cereals in the United States. A total of 215 retail samples were collected from three geographical locations and analysed for aflatoxins, fumonisins, deoxynivalenol, HT-2 toxin, ochratoxin A, T-2 toxin, and zearalenone using a stable isotope dilution liquid-chromatography tandem mass spectrometry (LC-MS/MS) method. One or more mycotoxins were found in 69% (101/147) of the infant/toddler foods and 50% (34/68) of breakfast cereals. Mycotoxin co-occurrence was observed in 12% of infant/toddler foods and 32% of breakfast cereals. However, the concentrations of detected mycotoxins were lower than the current FDA action and guidance levels. Aflatoxins and HT-2 toxin were not detected in any of the samples, while deoxynivalenol was the most frequently detected mycotoxin. Rice-based cereals appeared to be less susceptible to mycotoxin contamination than other cereal types.

Enumeration of hydroxyl groups of sugars and sugar alcohols by aqueous-based acetylation and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry.

RATIONALE: The properties of carbohydrates are determined in part by the number and stereochemical arrangement of their hydroxyl groups. To facilitate their analysis, rapid methods are needed to identify and enumerate hydroxyl groups in sugars and polyalcohols, especially methods that are water-based. METHODS: The present report details the results of an alternative method for identification and enumeration of hydroxyl groups in aqueous media. It employs vinyl acetate to selectively derivatize hydroxyl groups in analytes, followed by analysis of the reaction mixtures by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS). RESULTS: The method has been applied to several single and multi-component mixtures of monosaccharides and polyalcohols. The O-acetylated products were analyzed without chromatographic separation or purification by MALDI-TOF-MS. The mass spectra revealed consecutive ion peaks that are separated by 42 mass units as a consequence of displacement of one hydroxyl hydrogen by one acetyl group. CONCLUSIONS: A rapid and aqueous-based method is described to enumerate the hydroxyl groups in carbohydrates. The number of ion peaks due to derivatized products is determined by MALDI-TOF-MS, and corresponds to the number of free hydroxyl groups in the analyte. The method is applicable to both single and multi-component mixtures.

Influence of hydrogen bonding on hydrogen-atom abstraction reactions of dehydropyridinium cations in the gas phase.

The reactions of several substituted, positively charged dehydropyridinium cations with cyclohexane, methanol, and tetrahydrofuran have been examined in a Fourier-transform ion cyclotron resonance mass spectrometer. All of the charged monoradicals react with the neutral reagents exclusively via hydrogen atom abstraction. For cyclohexane, there is a good correlation between the reaction efficiencies and the calculated electron affinities at the radical sites; that is, the greater the electron affinity of the charged monoradical at the radical site, the faster the reaction. The reaction efficiencies with methanol and tetrahydrofuran, however, do not correlate with the calculated electron affinities. Density functional theory (DFT) calculations indicate that for these reagents a stabilizing hydrogen bonding interaction exists in the hydrogen atom abstraction transition states for some of the charged monoradicals but not for others. At both the MPW1K and G3MP2B3 levels of theory, there is a good correlation between the calculated activation enthalpies and the observed reaction efficiencies, although the G3MP2B3 method provides a slightly better correlation than the MPW1K method. The extent of enhancement in the reaction efficiencies caused by the hydrogen bonding interactions parallels the calculated hydrogen bond lengths in the transition states.

Gas-phase reactivity of protonated 2-, 3-, and 4-dehydropyridine radicals toward organic reagents.

To explore the effects of the electronic nature of charged phenyl radicals on their reactivity, reactions of the three distonic isomers of n-dehydropyridinium cation (n = 2, 3, or 4) have been investigated in the gas phase by using Fourier-transform ion cyclotron resonance mass spectrometry. All three isomers react with cyclohexane, methanol, ethanol, and 1-pentanol exclusively via hydrogen atom abstraction and with allyl iodide mainly via iodine atom abstraction, with a reaction efficiency ordering of 2 > 3 > 4. The observed reactivity ordering correlates well with the calculated vertical electron affinities of the charged radicals (i.e., the higher the vertical electron affinity, the faster the reaction). Charged radicals 2 and 3 also react with tetrahydrofuran exclusively via hydrogen atom abstraction, but the reaction of 4 with tetrahydrofuran yields products arising from nonradical reactivity. The unusual reactivity of 4 is likely to result from the contribution of an ionized carbene-type resonance structure that facilitates nucleophilic addition to the most electrophilic carbon atom (C-4) in this charged radical. The influence of such a resonance structure on the reactivity of 2 is not obvious, and this may be due to stabilizing hydrogen-bonding interactions in the transition states for this molecule. Charged radicals 2 and 3 abstract a hydrogen atom from the substituent in both phenol and toluene, but 4 abstracts a hydrogen atom from the phenyl ring, a reaction that is unprecedented for phenyl radicals. Charged radical 4 reacts with tert-butyl isocyanide mainly by hydrogen cyanide (HCN) abstraction, whereas CN abstraction is the principal reaction for 2 and 3. The different reactivity observed for 4 (as compared to 2 and 3) is likely to result from different charge and spin distributions of the reaction intermediates for these charged radicals.

Electron impact ion fragmentation pathways of peracetylated C-glycoside ketones derived from cyclic 1,3-diketones.

Monosaccharide C-glycoside ketones have been synthesized by aqueous-based Knoevenagel condensation of isotopically labeled and unlabeled aldoses with cyclic diketones, 5,5-dimethyl-1,3-cyclohexanedione (dimedone) and 1,3-cyclohexanedione (1,3-CHD). The reaction products and their corresponding acetylated analogs produce characteristic molecular adduct ions by matrix-assisted laser desorption/ionization mass spectrometry (MALDI-TOF MS). Analysis of the peracetylated C-glycosides by electron ionization (EI) gas chromatography/mass spectrometry (GC/MS) revealed diagnostic fragment ions that have been used to deduce the EI fragmentation pathways and the structure of each C-glycoside ketone. Characteristic gluco- and ribo-specific ions were observed at m/z 350 and 278, respectively. Ions common to both carbohydrate fragmentation pathways were observed at m/z 193 and 169 for the dimedone-C-glycosides, and m/z 165 and 141 for the 1,3-CHD-C-glycosides. Ions with m/z 169 and 141 retain the anomeric carbon (carbon-1) of the original sugar, while m/z 193 and 165 are shown to retain carbons-1, 2, and 3.

Differential EI fragmentation pathways for peracetylated C-glycoside ketones as a consequence of bicyclic ketal ring structures.

Several C-glycoside ketones and peracetylated C-glycoside ketones have been synthesized from 13 structurally-diverse aldoses sugars (including isotope labeled [1-(13)C]Glc, [U-(13)C]Glc, and [6, 6'-(2)H(2)]Glc) via an aqueous-based Knoevanagel condensation with aliphatic 1,3-diketones. Sodium adduct molecular ions observed by MALDI-TOF MS confirmed that the reactions are essentially quantitative, and that the acetylation products are the expected peracetylated C-glycoside ketones, rather than cyclized ketofurans. Analysis of the peracetylated C-glycoside ketones by gas chromatography-EI-MS show characteristic fragment ions that have been assigned to four distinct fragmentation pathways. Peracetylated aldohexose-, aldopentose-, and 6-deoxyaldohexose-C-glycoside ketones fragment via gas phase furanoid intermediates. These data, and DFT calculations, indicate that the furanoid intermediates arise because the peracetylated C-glycoside ketones adopt a bicyclic structure containing a 5-member ketal ring. This ketal ring is the precursor of the furanoid rings in the gas phase. The 2-deoxyhexose-C-glycoside ketones are unable to form an intramolecular 2-ketal bond, and therefore undergo ion fragmentations via nonfuranoid pathways.

Rapid characterization of polyalcohols by silylation and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry.

A matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry method for rapidly enumerating hydroxyl groups in analytes is described, and applied to some common polyalcohols (erythritol, mannitol and xylitol). Polyalcohols were derivatized with trimethylsilylimidazole (TMSI) either separately or as mixtures, and were analyzed, without chromatographic separation or purification. The mass spectra revealed consecutive peaks that are separated by 72 m/z units as a consequence of displacement of one hydroxyl hydrogen atom by one TMS group. The number of observed peaks was used to confirm the number of hydroxyl groups in each analyte.

Enumeration of carbohydrate hydroxyl groups by silylation and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry.

A method for enumerating hydroxyl groups in analytes is described and applied to various carbohydrates. The analytes were derivatized in solution by using trimethylsilylimidazole (TMSI) and the products were analyzed without chromatography by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS). The mass spectra revealed consecutive product ion peaks that are separated by 72 m/z units. This 72 m/z unit separation is a result of displacement of a hydroxyl hydrogen atom by a trimethylsilyl group. The number of the observed ions was used to confirm the number of hydroxyl groups in each analyte. This method was utilized in the analysis of single and multi-component analytes.

Reactivity of aromatic sigma, sigma-biradicals toward riboses.

The gas-phase reactions of sugars with aromatic, carbon-centered sigma,sigma-biradicals with varying polarities [as reflected by their calculated electron affinities (EA)] and extent of spin-spin coupling [as reflected by their calculated singlet-triplet (S-T) gaps] have been studied. The biradicals are positively charged, which allows them to be manipulated and their reactions to be studied in a Fourier-transform ion cyclotron resonance mass spectrometer. Hydrogen atom abstraction from sugars was found to be the dominant reaction for the biradicals with large EA values, while the biradicals with large S-T gaps tend to form addition/elimination products instead. Hence, not all sigma, sigma-biradicals may be able to damage DNA by hydrogen atom abstraction. The overall reaction efficiencies of the biradicals towards a given substrate were found to be directly related to the magnitude of their EA values, and inversely related to their S-T gaps. The EA of a biradical appears to be a very important rate-controlling factor, and it may even counterbalance the reduced radical reactivity characteristic of singlet biradicals that have large S-T gaps.

Erratum to: Reactivity of aromatic σ,σ-biradicals toward riboses.

After publication of the paper, the authors realized that the affiliation of the fourth author (Tiberiu Esanu) was given incorrectly. Its correct version appears above. Moreover, a second funding grant was missed in the acknowledgements. We give their complete correct version below.

Demonstration of tunable reactivity for meta-benzynes.

A combined computational and experimental study on the gas-phase structures and reactivities of charged 1,3-didehydroarenes (meta-benzynes) demonstrates that the reactivity of such biradicals can be "tuned" by using appropriate substituents. Substituents that destabilize a specific zwitterionic resonance structure can change the reactivity of the biradical from mildly carbocationic to radical-like. These substituent effects are not the result of changes in the singlet-triplet gaps of the biradicals, but rather reflect changes in the potential energy surfaces for the dehydrocarbon separation.