Major Thermal Degradation Products Research Articles

Gas chromatography tandem mass spectrometric analysis of alkylphosphonofluoridic acids as verification targets of nerve agents

Alkylphosphonofluoridic Acids (APFA) are the major thermal degradation products of G- and A-series nerve agents and thus play a vital role in the verification analysis of Chemical Weapons Convention. Present study focuses on the development of sample clean-up, derivatization procedures and gas chromatography tandem mass spectrometric analysis of APFA in aqueous samples. APFA were found to be much more delicate than the corresponding alkylphosphonic acids and thus required subtle optimizations. Retention of analytes on silica and polymer-based anion exchangers followed by elution under alkaline conditions yielded best recoveries. Elution under acidic conditions led to partial or complete degradation of the analytes to alkylphosphonic acids. Silylation reactions, particularly with MTBSTFA were found the best in terms of chromatographic responses and resolution of the derivative peaks. Methylations with diazomethane, which requires acidic reaction media, failed to produce desired yields of the derivatives. Under optimized conditions, the analytes produced the recoveries ranging from 76.9 to 94.5% with RSD ≤9.2%. The best LOD's in the tandem mass spectrometric analysis ranged from 13 to 56 ng/ml. The applicability of the method was tested by spiking the analytes in the retained aqueous samples received for the 52nd proficiency test conducted by the Organization for the Prohibition of Chemical Weapons (OPCW).

Monitoring of methylglyoxal/indole interaction by ATR-FTIR spectroscopy and qTOF/MS/MS analysis

Sugar derived reactive 1,2-dicarbonyl intermediates are considered important precursors for the formation of Maillard reaction products. Efficient strategies are needed to modulate their formation in food. Indole a major thermal degradation product of tryptophan, has been shown to scavenge such 1,2-dicarbonyls at high temperatures. In this study, the trapping of methylglyoxal by indole was monitored at various temperatures either by (a) ATR-FTIR spectroscopy or (b) in-solution using qTOF/MS/MS analysis. Information obtained through these studies have indicated that even at room temperature indole can quickly react with methylglyoxal forming an adduct as confirmed by the emergence of a new peak at 1729 cm−1 and by qTOF/MS/MS analysis. On the open surface of the ATR crystal this adduct underwent a fast oxidization into carboxylic acid as evidenced by the disappearance of the band at 1729 cm−1 and the formation of a new band at 1712 cm−1 and its subsequent conversion into a carboxylate band under basic conditions.

Thermal degradation mechanism of a cured acetylene/aldehyde functional benzoxazine with high thermal stability

A cured mono-benzoxazine (PHB-apa) with both acetylene and aldehyde functional groups exhibits excellent heat resistance. The thermal degradation process of this polybenzoxazine was studied in this work. The pyrolysis temperature range and major thermal degradation products were determined by TGA-FTIR analysis. The stepwise-temperature Py-GC/MS was employed to identify the structures and the contents of the pyrolysis products at different temperature stages. Transformation of chemical structures of the polymer bulk during the pyrolysis process was speculated. The results suggest that the concerted reaction of the aldehyde groups and the polymerization of the acetylene groups form special crosslinking structures that can effectively prevent the release of the amines and the phenols.

Identification of a thermal degradation product of CUMYL-PEGACLONE and its detection in biological samples.

The structural diversity of synthetic cannabinoids makes it a challenging task to have a comprehensive screening method for this class of drugs. The difficulty is increased by the fact that some synthetic cannabinoids undergo thermal decomposition during common routes of administration, such as smoking or vaping. CUMYL-PEGACLONE is a relatively new synthetic cannabinoid which has a structural variant from most other synthetic cannabinoids: a γ-carbolinone core. To investigate its thermal stability, CUMYL-PEGACLONE was heated in an oven at temperatures ranging from 200 to 350o C, and a major thermal degradation product, N-pentyl-γ-carbolinone, was subsequently identified. Unlike some other synthetic cannabinoids, the thermal degradation product of CUMYL-PEGACLONE is not one of its known metabolites, nor were any known metabolites detected during the thermal stability experiments. The degradation product was formed in significant amounts at temperatures above 250°C, and has been detected (along with CUMYL-PEGACLONE) in case samples, including post-mortem blood and urine, and residue found at a scene.

Kinetics of thermal degradation of betamethasone valerate and betamethasone dipropionate in different media

The effect of pH, media, phosphate concentration and ionic strength on the kinetics of thermal degradation of betamethasone valerate and betamethasone dipropionate has been investigated. A validated HPLC method has been used to determine the parent compounds and their major thermal degradation products identified in the reaction. Betamethasone-17-valerate gave rise to two major products, namely, betamethasone-21-valerate and betamethasone alcohol, and betamethasone dipropionate degraded into three major products, namely, betamethasone-17-propionate, betamethasone-21-propionate and betamethasone alcohol, in different media. Betamethasone valerate showed maximum stability at pH 4-5 while betamethasone dipropionate was maximally stable at pH 3.5-4.5. The degradation of betamethasone valerate and betamethasone dipropionate was found to follow first-order kinetics and the apparent first-order rate constants (kobs) for thermal degradation in different media range from 0.399-9.07×10-3 h-1 and 0.239-1.87×10-3 h-1, respectively. The values of the rate constants decrease with increasing solvent polarity, phosphate concentration and ionic strength. The second-order rate constants (k΄) for the phosphate ion inhibited reactions lie in the range of 3.02-1.30×10-6 M-1 s-1.

Fluorescence and NIR spectroscopic study on the water interaction in polycarbonate film

Water interactions in polycarbonate films have been studied using fluorescence and NIR Fourier transform spectroscopy. During water sorption process, the fluorescence emission spectra showed sensitive changes with the peak at 332 nm red shifted by 18 nm with water sorption. This red-shifted peak could be due to phenyl-2-phenoxybezoate, which is one of two major thermal degradation products in polycarbonate. In the spectra of phenyl-2-phenoxybenzoate in dimethyl formamide solution, a progressive red shift was also observed with the water addition. By using the NIR spectra, hydrogen-bonding interactions of the sorbed water with polycarbonate were investigated. It was found that water can be analyzed as free water S0 or single hydrogen bonded water, S1 while double hydrogen bonded water was negligible. During water immersion, most water species which are present as S0 species decrease slightly, with a small increase in S1 species. During desorption, S0 species decrease sharply, while S1 species is reduced gradually. Two examples of S1 structure in water-sorbed polycarbonate are proposed.

HPLC Determination of Acenocoumarol and its Major Thermal Degradation Product

A High performance liquid chromatographic (HPLC) method is presented for the determination of acenocoumarol and its thermal degradation product using a reverse phase C18 column at ambient temperature with the mobile phase consisting of water, and the pH adjusted to 3.0 using phosphoric acid:acetonitrile (50∶50). Quantitation was achieved with UV detection at 280 nm based on peak area. The method was developed and validated for the determination of acenocoumarol in tablets. The proposed method was validated for selectivity, linearity, accuracy, and robustness. The method was found to be suitable for the quality control of acenocoumarol in tablets as well as the stability‐indicating studies.

Intrinsic UV reflection and fluorescence studies for water sorption in polycarbonate, polyurethane and poly(ethylene terephthalate) films

Intrinsic UV reflection and fluorescence behaviors of polycarbonate, polyurethane and poly(ethylene terephthalate) films were investigated in order to characterize the interaction of water in these films. During water sorption process, UV reflection spectra of polycarbonate and polyurethane films showed little peak position changes. Fluorescence emission spectra of polycarbonate films showed red spectral shifts from 332 nm with water immersion time. This red-shifted peak could be due to phenyl-2-phenoxybenzoate, which is one of the major thermal degradation products in polycarbonate. Fluorescence peaks of polyurethane films appeared at two different positions and the ratio of these peak intensities increased with increasing immersion time. In the case of PET films, the UV reflection spectrum showed the peak intensity around 340 nm to change in response to water sorption. The fluorescence near 388 nm probably due to ground state dimer exhibited sensitivity with water sorption, when excited at 340 nm.

Characterization of Thermal Products of Alpha-Tocopherol

Alpha-tocopherol was thermally oxidized and degraded at high temperatures and the resulting products were chromatographically separated and identified by LC-MS. Alpha-tocopherol dissolved in glycerol was heated at 200℃ for 30 min. The thermal products were separated by hexane extraction and analyzed by HPLC using a reversed phase μ-Bondapak C_(18)-column with two kinds of elution solvents: a mixture of acetonitrile and methanol (3:2), and of acetonitrile, methanol, 2-propanol, chloroform and methylene chloride (3:2:5:0.5:0.5) in a gradient mode. The isolated thermal products of alpha-tocopherol were more viscous than alpha-tocopherol, and dark brown in color. Major thermal degradation products of alpha-tocopherol were identified by LC-MS, and the structures of thermal products were proposed. Alpha-tocopherol and its thermal degradation products were degraded into fragments, mainly at the non-aromatic parts. The degradation products of alpha-tocopherol were combined with oxidized product (tocopherylquinone) to make thermal products through dimerization.

A long-range15N-NMR study of the oxazolidinone antibiotic zyvox® and the major thermal degradation products

The structures of the major thermal degradation products of linezolid (Zyvox®, PNU-100766) are reported. Following hydrolytic decarboxylation, the remaining oxazolidinone-derived skeleton of the antibiotic underwent a variety of acetyl migrations prior to deacetylation. Three of the degradation products are structural isomers. Structural characterization of the degradants was accomplished via the concerted analysis of 2D NMR, mass spectrometric, and infrared data. Direct and long-range 1H-15N heteronuclear shift correlation experiments at natural abundance were performed on linezolid as well as each of the isolated products of the degradation cascade. 15N chemical shifts for linezolid and each of the degradants, as well as the observed long-range 1H-15N coupling pathways are reported.

Effect of Sucrose on the Volatile Compounds Produced from Heated Glycine and Soybean Oil.

A mixture of soybean oil and glycine was heated at different temperatures for different periods. The volatile compounds produced were extracted by solid phase microextraction (SPME) and then analyzed by GC and GC-MS. 2-Pentylpyridine was the highest heterocyclic volatile compound found in the mixture. Effect of sucrose on the volatile compounds produced from heated glycine and soybean oil was also studied, furfurals, pyrroles and oxidative thermal degradation products of fatty acids (OTDPFA) were found, but no pyridines. Factors affecting the producing of 2-pentylpyridine were investigated by two sources of chemicals: one was furfural which is one of the major thermal degradation products of sucrose, and the other was OTDPFA which remains from soybean oil after heating. The results indicated that 2, 4-heptadienal induced the production of 2-ethylpyridine, but no 2-pentyl-pyridine; 2, 4-decadienal enhanced the production of 2-pentylpyridine; while all other chemicals tested in this study decreased pyridines. This suggested that oxidation-reduction potential and availability of 2, 4-decadienal affected the production of 2-pentylpyridine.

Degradation Products of Mycophenolate Mofetil in Aqueous Solution

The thermal and peroxide-catalyzed degradation products of mycophenolate mofetil (1) were studied in aqueous solution at pH 2.0, 3.5, 6.0, and 8.2. The major thermal degradation product observed was mycophenolic acid (2). At pH 6.0 and 8.2, 2 was the only product observed in the absence of peroxide, while at pH 2.0 and 3.5, the lactone analogue of mycophenolic acid (5), a hydroxylactone due to oxygenation of the double bond (6), and an unidentified product were formed. Compound 6 degraded to 4-hydroxy-6-methoxy-7-methyl-3-oxo-1,3-dihydro-isobenzofuran-5-carbaldehyde (9) on prolonged storage and was present in the sample stressed at pH 2. Mycophenolic acid (2), the N-oxide of mycophenolate mofetil (3), the hydroxylactone of mycophenolic acid (6), and the erythro form of 4-methoxy-5-methyl- 2-(2-methyl-5-oxo-tetrahydro-furan-2-yl)-3,6-dihydro-2H-1,7-dioxa-as-indacen-8- one (8) were observed in the presence of hydrogen peroxide at pH 3.5, 6.0, and 8.2. In addition, at pH 8.2, 4-hydroxy-4-(4-methoxy-5-methyl-8-oxo-2,3,6,8-tetrahydro-1,7-dioxa-as-indacen-2-yl)-pentanoic acid (7) was seen. Peroxide-stressed samples at pH 2.0 gave no major degradation peaks, but a small amount of the hydroxylactone of mycophenolic acid (6) was formed.

Properties of injection moulded starch/synthetic polymer blends—I. Effect of processing parameters on physical properties

Corn starch was melt-blended in a twin screw extruder with ethylene vinyl acetate (EVAMA) and polyethylene (EMA) each having a maleic anhydride functional group that could interact with the hydroxyl groups in the starch. The percentage of starch in the blend was 70% by weight. These blends were injection moulded at different melt temperatures, screw speeds, injection pressures and back pressures. The effect of these processing parameters on the tensile strength, percentage elongation, break energy, flexural strength and flexural modulus are reported. Results from statistical analysis indicate that temperature and weldline affected some of the properties. Samples with weldline had lower tensile strength, break energy, and percentage elongation for starch/EVAMA blends. Similarly, samples with weldline had lower tensile strength and flexural modulus for starch/EMA blends. Starch/EVAMA blends absorbed between 22% and 37% by weight of water over a three month period, while starch/EMA blends absorbed between 20% and 27% over the same period. The diffusion mechanism varied from Fickian to anomalous, depending on the process conditions. For both blends, the process parameters had similar effects on the equilibrium water up-take and relaxation time. The major thermal degradation products were ethanoic acid and methanoic acid as identified by head-space-gas chromatography. Starch/EVAMA formed four times more ethanoic acid than the starch/EMA blend did during ageing, probably due to the cleavage of the acetate group in the vinyl acetate part of the EVAMA.

Chemical structural investigation of asphaltenes and kerogens by pyrolysis-methylation

Molecular characterization of kerogen and asphaltene fractions isolated from three oil shales taken from the Puertollano deposit has been carried out by pyrolysis-methylation. Long-chain n-alkanes, n-alk-l-enes, long-chain carboxylic acid methyl esters and aromatic compounds were the major thermal degradation products obtained for both kerogen and asphaltene fractions. Different monomeric and dimeric lignin-derived compounds were also released. The use of pyrolysis-methylation provides additional information about the chemical structural composition of the macromolecular organic matter comprising kerogens and asphaltenes at a molecular level, to that gained from conventional pyrolysis. The chemical structures of the released products indicate that considerable amounts of functionalized compounds are bound to the macromolecular structure of asphaltenes and kerogens via ester and ether linkages.

Do flame retardants affect the reliability of molded plastic packages?

Epoxy based thermoset materials are widely used for molding of microelectronic devices. Accelerated aging of molded devices has led to increased failure rates when the molding compound contained a brominated flame retardant (FR). In this paper, we investigate the effect of a brominated FR on the failure rate of a device aged at elevated temperatures under bias. We also ask whether aging characteristics in the 200°C range can be extrapolated through the glass transition (Tg) to service temperatures. We chose an electrical/electronic, rather than semiconductor, grade novolac epoxy which previously exhibited the poorest bias aging results of a group of FR and non-FR molding compounds. Half FR and non-FR versions of the epoxy in question were also obtained for the present experiments. The test vehicle was a molded DIP with a TTL device and Tape Automated Bonding (TAB) technology. Devices were prepared with and without a silicone rubber junction coating. Devices were aged for times up to 10,000 h at 125, 150, and 200°C, with and without bias. The results from time to failure and failure mode analyses were complemented by X-ray fluorescence, and aqueous extraction performed on the cured molding compounds. Failure rate at elevated temperature was found to be independent of the presence of FR. This result is consistent with our finding of four times as much extractable Cl − as Br −, and with the identification of CH 3Cl as a major thermal degradation product below 200°C, in a companion study by Lum and Feinstein. The silicone rubber junction coating retarded failures by a factor of 5–10. Both electrolytic (operating bias) and chemical (no bias) corrosion mechanisms were operative. However, the failure rate was a factor of 5–10 lower for unbiased devices. Direct attack of the Cu beams did not appear to be a problem in this study, although leads may act as fuses after shorting of the chip metallization. Although a linear extrapolation of failure rates from 200°C to lower temperatures is not valid, the result will be conservative.

Identification of the major thermal degradation products of the insecticide mirex.

Identification of the major thermal degradation products of the insecticide mirex.