Cytotoxic Evaluation and Determination of Organic and Inorganic Eluates from Restorative Materials

Over the last years, diverse commercial resin-based composites have dominated as dental filling materials. The purpose of the present study was to determine organic and inorganic eluates from five restorative materials using GC/MS and ICP–OES and to compare the effect on cell survival of human gingival fibroblasts of a conventional and a bioactive resin. Five commercially available restorative materials were employed for this study: Activa^TM Bioactive Restorative, ENA HRi, Enamel plus HRi Biofunction, Fuji II LC Capsule, and Fuji IX Capsule. Disks that were polymerized with a curing LED light or left to set were immersed in: 1 mL methanol or artificial saliva for GC/MS analysis, 5mL deionized water for ICP–OES, and 5mL of culture medium for cell viability. Cell viability was investigated with a modified staining sulforhodamine B assay.The following organic substances were detected: ACP, BHT, BPA, 1,4-BDDMA, CQ, DBP, DMABEE, HEMA, MCE, MeHQ, MOPA, MS, TMPTMA, and TPSb and the ions silicon, aluminum, calcium, sodium, and barium. Activa Bioactive Restorative was found to be biocompatible. Elution of organic substances depended on material’s composition, the nature of the solvent and the storage time. Ions’ release depended on material’s composition and storage time. The newly introduced bioactive restorative was found to be more biocompatible.

Principal component analysis of molecularly based signals from infant formula contaminations using LC-MS and NMR in foodomics

BACKGROUND

The challenge in developing analytical assessment of unexpected excess contaminations in infant formula has been the most significant project to address the widespread issue of food safety and security. Foodomics based on metabolomics techniques provides powerful tools for the detection of tampering cases with intentional contaminations. However, the safety and risk assessments of infant formula to reveal not only the targeted presence of toxic chemicals, but also molecular changes involving unexpected contaminations, have not been reported. In this study, a huge amount of raw molecularly based signals from infant formula was analysed using reversed phase and hydrophilic interaction chromatography with time-of-flight MS (LC-MS) and (1) H nuclear magnetic resonance (NMR) and then processed by a principal component analysis (PCA).

RESULTS

PCA plots visualised signature trends in the complex signal-data batches from each excess contamination of detectable chemicals by LC-MS and NMR. These trends in the different batches from a portion of excess chemical contaminations such as pesticides, melamine and heavy metals and out-of-date products can be visualised from spectrally discriminated infant formula samples.

CONCLUSION

PCA plots provide possible attempts to maximise the covariance between the stable lot-to-lot uniformity and excess exogenous contaminations and/or degradation to discriminate against the molecularly based signals from infant formulas. © 2015 Society of Chemical Industry.

Highly Sensitive Detection of Melamine Using a One-Step Sample Treatment Combined with a Portable Ag Nanostructure Array SERS Sensor

There is an urgent need for rapid and reliable methods able to detect melamine in animal feed. In this study, a quick, simple, and sensitive method for the determination of melamine content in animal feed was developed using surface-enhanced Raman spectroscopy on fabricated Ag nanorod (AgNR) array substrates with a one-step sample extraction procedure. The AgNR array substrates washed by HNO₃ solvent (10⁻⁷ M) and methanol and showed the good stability within 6 months. The Raman shift at △ν = 682 cm⁻¹ was used as the characteristic melamine peak in the calculations. Sufficient linearity was obtained in the 2–200 μg·g⁻¹ range (R² = 0.926). The limits of detection and quantification were 0.9 and 2 μg·g⁻¹, respectively. The recovery rates were 89.7–93.3%, with coefficients of variation below 2.02%. The method showed good accuracy compared with the tradition GC-MS analysis. This new protocol only need 2 min to fininsh the detection which could be developed for rapid onsite screening of melamine contamination in quality control and market surveillance applications.

Effect of resin content and substrate on the emission of BTEX and carbonyls from low-VOC water-based wall paint

The primary aim of this work is to explore the effect of resin content and the effect of substrate on the emission of benzene, toluene, ethylbenzene, and xylene (BTEX) and carbonyls from low-VOC water-based wall paint. Four low-volatile organic compound (VOC) paints include paints A (20% acrylic), B (30% acrylic), C (20% polyvinyl acetate), and D (30% polyvinyl acetate) were painted on stainless steel specimen for the study of resin effect. Green calcium silicate, green cement, and stainless steel were painted with paints A and C for the study of substrate effect. Concentrations of the VOCs in the chamber decreased with the elapsed time. Both resin type and resin quantity in paint had effects on VOC emissions. Paints with acrylic resin emitted less BTEX and carbonyls than paints with polyvinyl acetate resin. However, the effects of resin quantity varied with VOCs. Porous substrates were observed to interact more strongly with paints than inert substrates. Both green calcium silicate and green cement substrates have strong power of adsorption of VOCs from wall paints, namely toluene, formaldehyde, acetaldehyde, 2-butanone, methacrolein, butyraldehyde, and benzaldehyde. Some compounds like toluene, formaldehyde, and butyaldehyde were desorbed very slowly from green calcium silicate and green cement substrates.

[Endodontic filling with gutta-percha- requirements, formation and characteristics]

Gutta-percha is a tough plastic substance from the latex of several Malaysian trees of the sapodilla family that resembles rubber but contains more resin. It is especially used as insulation and in dentistry. Gutta-percha endodontic filling points were found to contain approximately 20% gutta-percha (matrix), 66% zinc oxide (filler), 11% heavy metal sulphates (radiopacifier), and 3% waxes and/or resins (plasticiser). The mechanical properties were indicative of a partially crystalline viscoelastic polymeric material.

Microplastic resin pellets on an urban tropical beach in Colombia

Microplastics are a problem in oceans worldwide. The current situation in Latin America is not well known. This paper reports, for the first time, the presence of microplastics on an urban Caribbean beach in Cartagena, Colombia. Pellet samples were collected from a tourist beach over a 5-month period covering both dry and rainy seasons. Pellets were classified by color and their surface analyzed by stereomicroscopy, and some were characterized by infrared spectroscopy. The most abundant pellets were white, presenting virgin surfaces, with few signs of oxidation. This is congruent with a short residence time in the marine environment and primary sources possibly located nearby. The frequency of white pellets did not change with sampling period. Surface features identified in the pellets included cracks, material loss, erosion, adhesion, granulation, color change, and glazed surfaces. Reticulated granular pellets exhibited the greatest degradation, easily generating submicroplastics. Sample composition was mostly polyethylene, followed by polypropylene. This pollution problem must be addressed by responsible authorities to avoid pellet deposition in oceans and on beaches around the world.

Determination of polyoxymethylene (POM)--water partition coefficients for oxy-PAHs and PAHs

Oxygenated polycyclic aromatic hydrocarbons (oxy-PAHs) are a class of ubiquitously occurring pollutants of which little is known. They can be co-emitted with PAHs or formed from PAHs in the environment. The environmental fate and risk of oxy-PAHs are difficult to assess due to a lack of methods to quantify their pore water concentrations. One sampler that can be used to determine freely dissolved concentrations of organic contaminants is polyoxymethylene (POM). In this study, POM - water partition coefficients (KPOM) were determined for 11 oxy-PAHs. KPOM values of 8 PAHs with similar hydrophobicities as the oxy-PAHs were determined for comparison. Results showed that logKPOM values ranged from 2.64 to 4.82 for the PAHs (2-4 rings), similar to previously determined values. LogKPOM values for investigated oxy-PAHs ranged from 0.96 to 5.36. The addition of carbonylic oxygen on a parent PAH generally lowered KPOM by 0.5 to 1.0 log units, which is attributable to the presence of carbonylic oxygens increasing water solubility. The KPOM values presented here will facilitate simultaneous assessments of freely dissolved water concentrations of oxy-PAHs and PAHs in environmental media.

Volatile organic compound and formaldehyde emissions from Populus davidiana wood treated with low molecular weight urea-formaldehyde resin

Populus davidiana wood was usually impregnated with low molecular weight thermosetting resins to improve its physical and mechanical properties. However, volatile organic compounds (VOCs) and formaldehyde emitted from treated wood have lead to poor indoor air quality (IAQ). The trends of VOC and formaldehyde emissions as a function of the weight percent gain (WPG) factor were mainly investigated in this work. Aldehydes and alkanes were the predominant compositions indentified in the VOC emissions, although low amount of ketones, terpenes and alcohols were also found. With the increase in WPG, VOC and formaldehyde concentrations improved. However, their concentration began to decrease when WPG was over 44.06% (VOC) and 36.35% (formaldehyde), respectively. The modulus of elasticity (MOE) of untreated and treated wood at different WPG levels was detected. It showed that treatment of wood with UF resin significantly improved the mechanical properties. Therefore, it is probably helpful to comprehensively analyze correlations among environmental performance, mechanical performance and processing costs.

Assessing potential nanoparticle release during nanocomposite shredding using direct-reading instruments

This study was conducted to determine if engineered nanoparticles are released into the air when nanocomposite parts are shredded for recycling. Test plaques made from polypropylene resin reinforced with either montmorillonite nanoclay or talc and from the same resin with no reinforcing material were shredded by a granulator inside a test apparatus. As the plaques were shredded, an ultrafine condensation particle counter; a diffusion charger; a photometer; an electrical mobility analyzer; and an optical particle counter measured number, lung-deposited surface area, and mass concentrations and size distributions by number in real-time. Overall, the particle levels produced were both stable and lower than found in some occupational environments. Although the lowest particle concentrations were observed when the talc-filled plaques were shredded, fewer nanoparticles were generated from the nanocomposite plaques than when the plain resin plaques were shredded. For example, the average particle number concentrations measured using the ultrafine condensation particle counter were 1300 particles/cm(3) for the talc-reinforced resin, 4280 particles/cm(3) for the nanoclay-reinforced resin, and 12,600 particles/cm(3) for the plain resin. Similarly, the average alveolar-deposited particle surface area concentrations measured using the diffusion charger were 4.0 μm(2)/cm(3) for the talc-reinforced resin, 8.5 μm(2)/cm(3) for the nanoclay-reinforced resin, and 26 μm(2)/cm(3) for the plain resin. For all three materials, count median diameters were near 10 nm during tests, which is smaller than should be found from the reinforcing materials. These findings suggest that recycling of nanoclay-reinforced plastics does not have a strong potential to generate more airborne nanoparticles than recycling of conventional plastics.

Bisphenol A and related compounds in dental materials

CONTEXT

Dental sealants and composite filling materials containing bisphenol A (BPA) derivatives are increasingly used in childhood dentistry. Evidence is accumulating that BPA and some BPA derivatives can pose health risks attributable to their endocrine-disrupting, estrogenic properties.

OBJECTIVES

To systematically compile and critically evaluate the literature characterizing BPA content of dental materials; to assess BPA exposures from dental materials and potential health risks; and to develop evidence-based guidance for reducing BPA exposures while promoting oral health.

METHODS

The extant toxicological literature and material safety data sheets were used as data sources.

RESULTS

BPA is released from dental resins through salivary enzymatic hydrolysis of BPA derivatives, and BPA is detectable in saliva for up to 3 hours after resin placement. The quantity and duration of systemic BPA absorption is not clear from the available data. Dental products containing the bisphenol A derivative glycidyl dimethacrylate (bis-GMA) are less likely to be hydrolyzed to BPA and have less estrogenicity than those containing bisphenol A dimethacrylate (bis-DMA). Most other BPA derivatives used in dental materials have not been evaluated for estrogenicity. BPA exposure can be reduced by cleaning and rinsing surfaces of sealants and composites immediately after placement.

CONCLUSIONS

On the basis of the proven benefits of resin-based dental materials and the brevity of BPA exposure, we recommend continued use with strict adherence to precautionary application techniques. Use of these materials should be minimized during pregnancy whenever possible. Manufacturers should be required to report complete information on the chemical composition of dental products and encouraged to develop materials with less estrogenic potential.

[Contamination of solid-cast rubber tires by microscopic fungi]

The main peculiarities of fungal resistance of two types of unit cast rubber tires of domestic manufacture have been investigated. Rubber tires which contained synthetic plasticizer were non-resistant to fungal contamination in contrast to ones with natural plasticizer. Using the method of confocal laser-scanning microscopy, it was shown that inner layers of two types of rubber tires were contaminated with fungal mycelium. Our findings indicate that the investigation of microscopic fungi resistance of new materials is necessary for general mechanical rubber goods, especially exported to tropical climate countries.

The risk of melamine-induced nephrolithiasis in young children starts at a lower intake level than recommended by the WHO

We investigated 683 children with nephrolithiasis and 6,498 children without nephrolithiasis aged <3 years. Nephrolithiasis was diagnosed by renal ultrasonography in hospitals in Beijing in September/October 2008. In addition, data was collected on current and past formula feeding and on other possible risk factors for nephrolithiasis. Daily intake of melamine per kilogram of body weight was calculated for each individual. In general, the adjusted odds ratios between melamine dose and nephrolithiasis increased with an increasing daily level of melamine intake per kilogram of body weight. The risk of nephrolithiasis also increased with the increasing duration of exposure. Preterm infants, urinary malformation, and parents with a history of urinary stones were independent risk factors. In children exposed to melamine levels <0.2 mg/kg per day, the adjusted odds ratio expressing the risk for nephrolithiasis was still 1.7 times higher than in those without melamine exposure. These findings suggest that the risk of melamine-induced nephrolithiasis in young children starts at a lower intake level than the levels recommended by the World Health Organization.

Kinetic study of free radicals trapped in dental resins stored in different environments

In this work, we used electron paramagnetic resonance to follow the decrease kinetics of free radicals trapped in an experimental resin (ER) and in a commercial composite (Charisma (Ch)) stored under different conditions (in air at 25 and 37 degrees C; in argon, oxygen and water at 25 degrees C). During the first day, the decay was fast (0-24h-rate of decay of allylic radical: 1700-1000a.u. for Ch, 1700-1500a.u. for ER) and the storage conditions had no influence on the kinetics. This phase was ascribed to a post-polymerization phenomenon. From 1day to 1month, the rate of decay depended on the storage environment. In argon, free radicals were quite stable (1day to 1month-rate of decay of allylic radical: 1200-1000a.u. for Ch, 1400-1200a.u. for ER). For the other storage environments, in ER, the rate of decay was higher in water than in oxygen and in air (1day to 1month-rate of decay of allyl radical: 1400a.u. to 100, 500 and 800a.u., respectively). In Ch, free radicals faded quicker than in ER, as undetectable levels were reached before 1month, which attests to the influence of fillers on radical decrease kinetics. Heating experiments were also performed, and free radical concentrations decreased faster at higher temperatures, especially above the glass transition temperature. In conclusion, ambient oxygen is mainly involved in the termination process of free radicals. Therefore, conditions influencing oxygen diffusion have an impact on radical kinetics as well.

The use of FT-IR as a screening technique for organic residue analysis of archaeological samples

A range of archaeological samples have been examined using FT-IR spectroscopy. These include suspected coprolite samples from the Neolithic site of Catalhöyük in Turkey, pottery samples from the Roman site of Silchester, UK and the Bronze Age site of Gatas, Spain and unidentified black residues on pottery sherds from the Roman sites of Springhead and Cambourne, UK. For coprolite samples the aim of FT-IR analysis is identification. Identification of coprolites in the field is based on their distinct orange colour; however, such visual identifications can often be misleading due to their similarity with deposits such as ochre and clay. For pottery the aim is to screen those samples that might contain high levels of organic residues which would be suitable for GC-MS analysis. The experiments have shown coprolites to have distinctive spectra, containing strong peaks from calcite, phosphate and quartz; the presence of phosphorus may be confirmed by SEM-EDX analysis. Pottery containing organic residues of plant and animal origin has also been shown to generally display strong phosphate peaks. FT-IR has distinguished between organic resin and non-organic compositions for the black residues, with differences also being seen between organic samples that have the same physical appearance. Further analysis by GC-MS has confirmed the identification of the coprolites through the presence of coprostanol and bile acids, and shows that the majority of organic pottery residues are either fatty acids or mono- or di-acylglycerols from foodstuffs, or triterpenoid resin compounds exposed to high temperatures. One suspected resin sample was shown to contain no organic residues, and it is seen that resin samples with similar physical appearances have different chemical compositions. FT-IR is proposed as a quick and cheap method of screening archaeological samples before subjecting them to the more expensive and time-consuming method of GC-MS. This will eliminate inorganic samples such as clays and ochre from GC-MS analysis, and will screen those samples which are most likely to have a high concentration of preserved organic residues.

Diagnostic determination of melamine and related compounds in kidney tissue by liquid chromatography/tandem mass spectrometry

In 2007, it was determined that melamine, ammeline, ammelide, and cyanuric acid (abbreviated as MARC for melamine and related contaminants) had been added to wheat gluten and rice protein that were subsequently incorporated into pet food. The consumption of food tainted by MARC compounds was implicated in numerous instances of renal failure in cats and dogs. A method for the analysis of MARC compounds in kidney tissue using high-performance liquid chromatography/tandem mass spectrometry (HPLC/MS/MS) has been developed. MARC analytes were extracted by homogenization of kidney tissue in 50/40/10 acetonitrile/water/diethylamine. The homogenate was centrifuged, and an aliquot of supernatant was diluted with acetonitrile, concentrated, and fortified with a stable isotope-labeled analogue of melamine. Analytes were detected using atmospheric pressure chemical ionization and multiple reaction monitoring. Quantitation of positive samples was performed using the internal standard method and five-point calibration curves ranging between 50 and 1000 ng/mL of each analyte. The method was validated by analysis of replicate kidney tissue samples fortified with the individual analytes and by analysis of kidney samples fortified with melamine cyanurate powder at two different concentrations. This method was successfully used for routine postmortem diagnosis of melamine toxicosis in animals. Melamine was also detected by this method in paraffin-embedded tissue from animals suspected to have died of melamine toxicosis.

Determination of dose rates from natural radionuclides in dental materials

Different types of materials used for dental prosthetics restoration, including feldspathic ceramics, glass ceramics, zirconia-based ceramics, alumina-based ceramics, and resin-based materials, were investigated with regard to content of natural radionuclides by means of thermoluminescence beta dosimetry and gamma spectrometry. The gross beta dose rate from feldspathic and glass ceramics was about ten times higher than the background measurement, whereas resin-based materials generated negligible beta dose rate, similarly to natural tooth samples. The specific activity of uranium and thorium was significantly below the levels found in the period when addition of uranium to dental porcelain materials was still permitted. The high-beta dose levels observed in feldspathic porcelains and glass ceramics are thus mainly ascribable to (40)K, naturally present in these specimens. Although the measured values are below the recommended limits, results indicate that patients with prostheses are subject to higher dose levels than other members of the population. Alumina- and zirconia-based ceramics might be a promising alternative, as they have generally lower beta dose rates than the conventional porcelain materials. However, the dosimetry results, which imply the presence of inhomogeneously distributed clusters of radionuclides in the sample matrix, and the still unsuitable structural properties call for further optimization of these materials.

Synthesis and Application of Amberlite XAD-2 Functionalized with Dithizone for Field Preconcentration and Separation of Trace Cadmium in Seawater

A chelating resin coupling Amberlite XAD-2 functionalized with dithizone is synthesized and characterized. Dissolved cadmium is field-preconcentrated using a minicolumn packed with the synthesized resin and determined by flame atomic absorption spectrometry. Five experimental variables are evaluated. The enrichment factor of 416 is obtained for 50 mL of sampling volume, and the detection limit (3 sigma) of the procedure is 6.7 ng L(-1). The precision (RSD) for 11 independent determinations is 1.97%. This method has been successfully applied to the determination of cadmium in natural seawater samples.

Forensic analysis of architectural finishes using fourier transform infrared and Raman spectroscopy, part II: white paint

White household paints are commonly encountered as evidence in the forensic laboratory but they often cannot be readily distinguished by color alone so Fourier transform infrared (FT-IR) microscopy is used since it can sometimes discriminate between paints prepared with different organic resins. Here we report the first comparative study of FT-IR and Raman spectroscopy for forensic analysis of white paint. Both techniques allowed the 51 white paint samples in the study to be classified by inspection as either belonging to distinct groups or as unique samples. FT-IR gave five groups and four unique samples; Raman gave seven groups and six unique samples. The basis for this discrimination was the type of resin and/or inorganic pigments/extenders present. Although this allowed approximately half of the white paints to be distinguished by inspection, the other half were all based on a similar resin and did not contain the distinctive modifiers/pigments and extenders that allowed the other samples to be identified. The experimental uncertainty in the relative band intensities measured using FT-IR was similar to the variation within this large group, so no further discrimination was possible. However, the variation in the Raman spectra was larger than the uncertainty, which allowed the large group to be divided into three subgroups and four distinct spectra, based on relative band intensities. The combination of increased discrimination and higher sample throughput means that the Raman method is superior to FT-IR for samples of this type.

Forensic analysis of architectural finishes using fourier transform infrared and Raman spectroscopy, part I: the resin bases

The ability of Raman spectroscopy and Fourier transform infrared (FT-IR) microscopy to discriminate between resins used for the manufacture of architectural finishes was examined in a study of 39 samples taken from a commercial resin library. Both Raman and FT-IR were able to discriminate between different types of resin and both split the samples into several groups (six for FT-IR, six for Raman), each of which gave similar, but not identical, spectra. In addition, three resins gave unique Raman spectra (four in FT-IR). However, approximately half the library comprised samples that were sufficiently similar that they fell into a single large group, whether classified using FT-IR or Raman, although the remaining samples fell into much smaller groups. Further sub-division of the FT-IR groups was not possible because the experimental uncertainty was of similar magnitude to the within-group variation. In contrast, Raman spectroscopy was able to further discriminate between resins that fell within the same groups because the differences in the relative band intensities of the resins, although small, were larger than the experimental uncertainty.

Determination of the percentage of homopolymer component in Ziegler/Natta catalyst linear low-density polyethylene resins using high-temperature cell Fourier transform infrared and partial least squares quantitative analysis technique

A new method for the determination of the percentage of homopolymer component, using high-temperature cell Fourier transform infrared (FT-IR) by partial least squares (PLS) quantitative analysis technique, was developed and applied to Ziegler Natta linear low-density polyethylene (LLDPE). The method is based on the IR spectrum changes between the 730 cm(-1) band and 720 cm(-1) band at the temperature of 110 degrees C, which is near the melting point of the polyethylene. The HD % (the percentage of high-density component, i.e., the percentage of homopolymer component) results obtained by CTREF (CRYSTAF in TREF mode) technique are used as the input data together with the respective FT-IR spectra for PLS analyses to establish a calibration curve. The PLS quality is characterized by a correlation coefficient of 0.997 (cross-validation) using four factors and a root mean square error of calibration (RMSEC) of 0.772. The HD% of the unknown can then be predicted by the PLS software from the unknown FT-IR spectrum. A control resin was tested seven times by CTREF and FT-IR. The HD% of the control resin was 28.59+/-0.88% by CTREF and 29.05+/-2.37% by FT-IR. It was found that the method was applicable for the same comonomer type of LLDPE within a melt index range and density.

1H high-resolution magic-angle spinning (HR-MAS) NMR analysis of ligand density on resins using a resin internal standard

We recently attempted to generate an affinity chromatography adsorbent to purify cytochrome P450 4A1 by coupling 11-(1'-imidazolyl)-3,6,9-trioxaundecanoic acid to Toyopearl AF-Amino 650 M resin. Variations in ligand density for several resin batches were quantified by high-resolution magic-angle spinning (HR-MAS) NMR spectroscopy using a novel resin internal standard. The uniquely designed ImQ internal resin standard yields its signature resonance in a transparent region of the analyte spectrum making suppression of the polymer background unnecessary. This method enabled us to target a reasonable ligand density for enzyme purification and provides an advantageous alternative to quantitation against soluble standards or protonated solvent.

On-Resin Assembly of a Linkerless Lanthanide(III)-Based Luminescence Label and Its Application to the Total Synthesis of Site-Specifically Labeled Mechanosensitive Channels

A synthesis strategy for the on-resin assembly of luminescent lanthanide chelates from commercially available compounds was developed. Advantages of the approach include the absence of spacers between the metal ion and the attachment site, and the compatibility with typical chemical protein synthesis protection schemes. Methoxycoumarin-labeled lysine and tris(tert-butyl)-DOTA were consecutively coupled with high efficiency to a free amino group in otherwise fully protected peptide segments using standard peptide synthesis methods. Addition of stoichiometric amounts of Tb(3+) to the modified, cleaved, and purified peptides yielded the desired lanthanide chelate. Incorporation of this label into a chemically synthesized, full-length mechanosensitive channel of large conductance (MscL) of E. coli and subsequent reconstitution into vesicles resulted in a functional mechanosensitive channel of comparable conductance to the wild-type channel. However, this channel required increased suction to gate. Excitation of the antenna molecule methoxycoumarin at 336 nm resulted in an emission spectrum typical for Tb(3+) and a luminescence lifetime of 0.67 ms. The location of the probe close to the backbone of this protein may provide precise information about conformational changes during channel opening from LRET studies.

Solid-phase synthesis and 1H and 13C high-resolution magic angle spinning NMR of 13C-labeled resin-bound saccharides

We show how high-resolution magic angle-spinning NMR spectroscopy can be used to characterize 13C-labeled saccharides that have been prepared using solid-phase synthesis techniques while they are still bound to a solid-support resin. With the use of 13C-labeled glucose as the starting material, we have successfully synthesized mono-, di- and trisaccharides with uniform 13C labeling of the saccharide rings. Using these materials, we have been able to assign the 13C and 1H spectra and to characterize various impurities on the resin beads.

[Studies on analysis of terpene resin in imported chewing gums]

We have developed an analytical method for terpene resins in chewing gum. The fraction including terpene resins was prepared by means of hexane extraction and two silica gel column chromatography treatments (hexane and ethyl acetate) from chewing gum. The terpene resin fraction was analyzed with LC/MS and IR. The terpene resins are mixtures of polymeric pinene and/or limonene, which have a monomer molecular weight of 136. The MS spectrum of the terpene resin peak on the LC/MS total ion chromatogram showed protonated molecular ion (M + H)+ peaks at intervals of m/z 136, characteristic of a complex mixture of polyterpenes. IR spectroscopy is a suitable technique to identify the terpene resin type, ie., pinene or limonene. When the method was applied to imported chewing gum sold in Japan, terpene resins were clearly detected.

Migration from can coatings: Part 1. A size-exclusion chromatographic method for the simultaneous determination of overall migration and migrating substances below 1000 Da

The Council of Europe Resolution on coatings suggests a limit of 10 mg dm-2 for the sum of substances migrating into food simulants from an internal can coating. The Scientific Committee on Food differentiates the migrants into the substances with a molecular weight below 1000 Da, potentially being of toxicological concern, and the less toxicologically relevant species above 1000 Da. Hitherto, the determination of overall migration was based on a gravimetric method. A new method is described for the simultaneous determination of both overall migration and the migration of substances below 1000 Da based on separation by size exclusion chromatography (SEC) followed by ultraviolet detection (UVD) and evaporative light scattering detection (ELSD). The method is suitable for all volatile extraction media and simulants recommended by the European Union. For statistical comparison of both methods, the slightly modified reference method was validated in-house and extended to an additional gravimetric measurement of the migrants below 1000 Da. For the determination of the overall migration, both methods provided similar reproducibility (validated gravimetry: standard deviation (SD) = 0.16 mg dm-2; SEC-ELSD/UVD: SD = 0.12 mg dm-2) but significantly better results were obtained by the SEC-ELSD/UVD method. For migrating substances below 1000 Da, the gravimetric determination provides a poor sensitivity (limit of detection = 0.35 mg dm-2) compared with the SEC-ELSD/UVD method (limit of detection = 0.04 mg dm-2). The new method offers a lower limit of detection and higher precision as well as being less time consuming and easier to use.

Colorimetric Monitoring of Solid-Phase Aldehydes Using 2,4-Dinitrophenylhydrazine

A simple and rapid method to achieve colorimetric monitoring of resin-bound aldehydes, based on ambient temperature reaction with 2,4-dinitrophenylhydrazine (DNPH) in the presence of dilute acid, has been developed as an adjunct to solid-phase organic synthesis and combinatorial chemistry. By this test, the presence of aldehydes is indicated by a red to dark-orange appearance, within a minute. Alternatively, resins that are free of aldehydes or in which aldehyde functions have reacted completely retain their original color. The DNPH test was demonstrated for poly(ethylene glycol)-polystyrene (PEG-PS), aminomethyl polystyrene (AMP), cross-linked ethoxylate acrylate resin (CLEAR), and acryloylated O,O'-bis(2-aminopropyl)poly(ethylene glycol) (PEGA) supports and gave results visible to the naked eye at levels as low as 18 micromol of aldehyde per gram of resin.

Evaluation of CZ-resin vials for packaging protein-based parenteral formulations

Due to the fact that some proteins have a tendency to bind to glass surfaces, plastic CZ-resin vials were evaluated as an alternative material to glass vials for packaging protein-based parenteral formulations. Physico-chemical tests including protein binding, extractable evaluation, oxygen permeation, light transmission and moisture loss were performed. Data show that two proteins (A and B) were found to bind to USP type I glass but not to CZ-resin. The CZ-resin vials passed all USP test specifications for extractables (organic extractable, non-volatile residue and residue on ignition). The oxygen permeation rate (79.06 cm(3)mm/m(2)24 h atm) was consistent with that reported by the vendor (67 cm(3)mm/m(2)24 h atm). The value obtained for light transmission, which was also found to be consistent with that reported by the vendor, shows that these vials offer no protection from light. The average moisture loss from 2 cm(3) vials filled with water was gravimetrically determined to be 0.04 mg/day/vial when the vials were stored at 40 degrees C/75% relative humidity (RH). Assuming a 1cm(3) product fill, this corresponds to approximately a 3% loss over a 2-year period. However, moisture loss was found to be negligible at the typical storage condition of 5 degrees C for protein formulations. The physico-chemical tests indicate that CZ-resin vial is a suitable candidate for packaging parenteral formulations since it shows low moisture loss at typical storage condition of 5 degrees C, and does not leach out extractables. However, it should not be used for light-sensitive and oxygen-sensitive parenteral formulations. For proteins A and B, the CZ-resin vial is a viable alternate to the use of glass vials since it offered significantly less protein binding. Protein binding in general, should be evaluated on a case by case basis, since it may vary for different proteins and under different formulation conditions.

Fate of resin acids in pulp mill secondary treatment systems

Profiles of resin and fatty acids (RFAs), COD, and aquatic toxicity were measured across the secondary treatment systems of three pulp mills. The RFAs sorb to suspended solids, principally fiber, and are partially removed through settling. An activated sludge system is more efficient in removing RFAs than an aerated stabilization basin (ASB) because of its higher solids level. Dehydroabietic acid accounts for a significant fraction of the effluent toxicity in the two ASBs studied. The microorganisms in an ASB are unable to respond rapidly to an RFA spill, and effluent toxicity can be elevated for a prolonged period because of hydraulic backmix. The applicability of several laboratory studies to field situations is assessed.

Assessment of total exposure to phenol-formaldehyde resin glue in plywood manufacturing

OBJECTIVE

Respiratory and dermal exposure to phenol-formaldehyde resin-glue components used in plywood manufacturing were assessed.

METHODS

Formaldehyde and phenol were monitored in the workplace air. Formaldehyde was measured both in the breathing zones of the workers and at stationary sampling sites. Phenol was used as a marker agent for dermal exposure due to its near-nonvolatility at the temperatures occurring during the present study and to its ready absorption through the skin, causing systemic exposure in addition to local skin rashes. Sampling and analytical methods were developed to measure the dermal exposure to phenol. Sampling was accomplished with whole-body dosimetry using Tyvek coveralls and cotton gloves. In addition, a liquid chromatography method was developed for the analysis of phenol from dermal exposure samples.

RESULTS

As expected, formaldehyde was noted to be the major compound causing respiratory exposure. When exposure assessment was done on the basis of air samples collected both at stationary sampling sites and in the breathing zones of the workers the agreement between the results obtained was good. The dermal sampling revealed that the workers were exposed to phenol, but the risk for toxic effects was slight due to the low concentrations of urinary phenol.

CONCLUSIONS

We conclude that it is possible to use the stationary sampling method for the assessment of respiratory exposure in a plywood factory instead of the usually more complicated breathing-zone sampling. This study also demonstrates the importance of taking dermal exposure into account, at least due to the ability of the resins to cause skin rashes, in assessment of the exposure to chemicals in plywood manufacturing.

The effect of curing regime on the release of hydroxyethyl methacrylate (HEMA) from resin-modified glass-ionomer cements

This study investigated the effects of degree of cure and specimen maturation on the release of HEMA from four resin-modified glass-ionomer cements. Disc specimens were light-cured for either the manufacturers' recommended time (MRT) for that material, or were under-cured (irradiated for 0.5 MRT), over-cured (1.5 MRT) or allowed to dark-cure (0 MRT). Specimens were matured in the mould at 37 degrees C until set or for 10 min, 40 min or 24 h prior to immersion in distilled water (at 37 degrees C) for 4 h. The HEMA release was determined by measuring the HEMA concentration in the storage water by HPLC. Vitremer, Fuji II LC and Fuji Lining LC set without light-curing (0 MRT) in less than 6 min and these specimens released low levels of HEMA (approximately 1, 7 and 4% of the included HEMA, respectively). Dark-cured Vitrebond took 15 min to set and the HEMA release was high (approximately 50% of the included HEMA) indicating that the material had only set by the acid-base reaction. HEMA release from light-cured Vitremer or Vitrebond was not affected by under- or over-curing but release from Fuji II LC was reduced by over-curing (1.5 MRT). Under-curing Fuji Lining LC caused a significant increase in HEMA release. Specimen maturation times of 10 min, or longer, had little effect on the measured HEMA release. All the materials released HEMA into their storage solutions. In order to minimise HEMA release, resin-modified glass-ionomers should always be cured for at least the manufacturers' recommended time at thicknesses no greater than the maximum recommended.

Carbonaceous matter in cometary dust and coma

The analysis of carbonaceous matter in p/Halley's dust and coma via mass spectrometry of positive ions is reviewed. Dust impact generated ions were analyzed by the PUMA instrument aboard VEGA I, and coma plasma ions by the PICCA instrument aboard GIOTTO. For the organic molecules results an overall C:H:O:N ratio of 1.:1.4:0.6:0.1. Most of this polymer material can formally be understood as an aggregation of monomers C2H2, CH2O, and HCN. Special emphasis is given to possible aromatic, especially heterocyclic, and other unsaturated ions, and their importance for abiotic chemical and prebiotic evolution. Aspects of the potential heterogeneous catalysis in liquid water at the inorganic grain backbone structure found by this analysis, too, are also treated.

Leaching of additives and degradation products from cold-cured orthodontic resins

Unstimulated saliva was collected from orthodontic patients and subjected to combined gas-chromatography and gas-chromatography/mass-spectrometry analyses. Saliva was collected before insertion of removable orthodontic appliances made of cold-cured resins. Saliva was then collected 1-2 months after insertion of the appliances and 1 week after they had been removed. Phenyl benzoate (PB) and phenyl salicylate (PS) were identified in pooled saliva samples from patients wearing the appliances. Biphenyl and 2-methoxy-4-hydroxy-benzophenone in addition to PB and PS were identified in a study with in vitro specimens made of orthodontic resin. The leaching of compounds from these test specimens processed by a powdering technique and a pre-mix technique was compared.

Identification of causative chemicals of allergic contact dermatitis using a combination of patch testing in patients and chemical analysis. Application to cases from rubber footwear

5 cases of allergic contact dermatitis from rubber footwear were investigated by a combination of patch testing in patients and chemical analysis of causative rubber products. Our studies revealed 2-mercaptobenzothiazole (MBT) and benzothiazyl disulfide (MBTS) (typical allergenic accelerators) as causative chemicals in 3 cases from children's rubber shoes, ladies' rubber boots and ladies' canvas shoes. These 3 patients reacted to mercaptobenzothiazole-type accelerators including MBT and MBTS. MBT and MBTS were determined in each item of causative footwear by chemical analysis, including extraction by shaking with acetone-chloroform (1:1) mixture at room temperature and determination using reversed-phase high-performance liquid chromatography (RP-HPLC). Subsequently, we identified styrenated phenol (SP), a newly found allergenic antioxidant, as a causative chemical in a case from ladies' canvas shoes. The patient reacted to SP but not to MBT and MBTS, though SP, MBT and MBTS were determined in the causative shoes by gas chromatography (GC), GC-mass spectrometry (GC-MS) and HPLC. We also identified p-tert-butylphenol-formaldehyde resin (PTBP-F-R), (a known allergenic adhesive ingredient) as a causative chemical in a case from ladies' sneakers. The patient reacted to PTBP-F-R but not to p-tert-butylphenol (PTBP), MBT and MBTS. These 4 compounds were determined in the causative sneakers by GC, GC-MS and HPLC. Thus, our studies revealed that not only known allergens, such as MBT, MBTS and PTBP-F-R, but also a newly found one, such as SP, were important causes of allergic contact dermatitis from rubber footwear.

A rare fatal case of silicone resin precursor (SH792) poisoning

A 39-year-old man committed suicide by ingesting a large quantity of SH792. SH792 is a silicone resin precursor used as a hardener for waterproof paints. It is polymerized in water; this process is then followed by the formation of silicone resin and the release of N,N-diethylhydroxylamine. In this decedent, analysis by infrared spectroscopy showed that polymerized silicone resin was present in the stomach contents. The amount of silica in his tissues was within levels seen in control subjects. N,N-diethylhydroxylamine was detected in the urine (0.7 microliters/ml) but not in the stomach contents. The data suggest that SH792 was polymerized in the stomach and the released N,N-diethylhydroxylamine (DEHA) was absorbed into the body. The mechanism of SH792 poisoning is also discussed.

Release of formaldehyde and melamine from tableware made of melamine-formaldehyde resin

The relationship between the concentrations of formaldehyde and melamine released into 4% acetic acid from dishes and bowls made of melamine-formaldehyde resin was determined. The average concentrations in the migration solution after the sample had been treated at 60, 80, and 95 degrees C for 30 min with 4% acetic acid were 0.0 +/- 0.1, 0.5 +/- 0.4 and 3.0 +/- 2.2 ppm, respectively for formaldehyde and 0.04 +/- 0.07, 0.21 +/- 0.20 and 1.19 +/- 1.18 ppm, respectively for melamine. The correlation between the concentrations of formaldehyde and melamine released at 95 degrees C was y=0.4858x-0.2728 (r=0.8860), where y is melamine concentration (ppm), x is formaldehyde concentration (ppm) and r is the correlation coefficient. The molar concentration ratios of formaldehyde to melamine (F/M ratio) were 15.4 +/- 11.6 at 80 degrees C and 14.9 +/- 10.1 at 95 degrees C. Hence the release of both migrants was affected by temperature but the F/M ratio was not affected. The release of both compounds was was increased on repetition of the migration test at 95 degrees C but their concentrations remained constant after the tenth and seventeenth repetitions of the treatment. During this period, the F/M ratio decreased according to the equation 1n y=-1.4344 1n x+3.7814 (r=-0.9984) for a sample before the tenth repetition of the treatment and remained between 1.7 and 1.9 after the twelfth repetition, where y is the F/M ratio and x is the number of repetitions of the treatment.

Dynamic mechanical thermal analysis of dental polymers. II. Bis-phenol A-related resins

Dynamic mechanical analysis of bis-phenol A-related resins for dental usage provided loss tangent maxima at their transitions and an Arrhenius-type dependence of transition temperature and frequency. A constant maximum in the loss tangent curves, over the frequency range for the unfilled resins below their glass transition temperature, was thought to be caused by their high degree of unsaturation. The calculated activation energies showed the polycarbonate denture base resin required considerably greater energy for segmental motion than the other tested materials. In contrast, the ethylene imine-based temporary crown and bridge material exhibited the lowest activation energy.

[Determination of dibutyltin compounds in polyvinyl chloride resin by capillary gas chromatography]

Dibutyltin compounds (DBTC) in polyvinyl chloride resin (PVC) were examined by capillary gas chromatography using a flame photometric detector (FPD). DBTC was extracted with a carbon tetrachloride-methanol (2:1) mixture under reflux. The extract was mixed with a hydrobromic acid solution. Dibutyltin dibromide was converted to dibutyldipentyltin (DBDPeT) by the Grignard reaction with pentylmagnessium bromide and then subjected to gas chromatography. A linear correlation between the amount of tin and peak height was observed in the range of 7.8 to 250 pg of tin on log-log paper. Recoveries of DBTC added to PVC were 92.6-108.1%. The results show that this procedure is more useful and sensitive (the detection limit is 3-4 pg, as tin) than previous methods reported.