Use Of Tetramethylammonium Hydroxide Research Articles

Determination of polyurethanes within microplastics in complex environmental samples by analytical pyrolysis

Polyurethanes (PUR) are a group of polymers synthesized from different diisocyanate and polyol monomers resulting in a countless number of possible structures. However, the large market demand, and the variety of application fields justify the inclusion of PUR in microplastic (MP) investigation. This study aimed at providing comprehensive information on PUR within MP analysis by pyrolysis–gas chromatography-mass spectrometry to clarify whether (i) it is possible to make a reliable statement on the PUR content of environmental samples based on a few pyrolysis products and (ii) which restrictions are required in this context. PUR were managed as subclasses defined by the diisocyanates employed for polymer synthesis. Methylene diphenyl diisocyanate (MDI)- and toluene diisocyanate (TDI)-based PUR were selected as subclasses of greatest relevance. Different PUR were pyrolyzed directly and under thermochemolytic conditions with tetramethylammonium hydroxide (TMAH). Distinct pyrolytic indicators were identified. The study supported that the use of TMAH greatly reduced the interactions of pyrolytic MP analytes with the remaining organic matrix of environmental samples and the associated negative effects on analytical results. Improvements of chromatographic behavior of PUR was evidenced. Regressions (1–20 µg) showed good correlations and parallelism tests underlined that quantitation behavior of different MDI-PUR could be represented by the calibration of just one representative with sufficient accuracy, entailing a good estimation of the entire subclass if thermochemolysis were used. The method was exemplary applied to road dusts and spider webs sampled around a plastic processing plant to evaluate the environmental spread of PUR in an urban context. The environmental occurrence of MDI-PUR as MP was highly influenced by the proximity to a potential source, while TDI markers were not observed.Graphical

Hierarchically porous and highly transparent polymethylsilsesquioxane aerogels with an ultrahigh specific surface area using an organic alkali as a catalyst, surfactant, and template

A hierarchically porous aerogel with an ultrahigh specific surface area, high visible light transmittance, excellent mechanical properties, and cubic shell-shaped pores was obtained using a supercritical drying process. Ethanol and methyltriethoxysilane (MTES) were used as a solvent and silicon source, respectively, whereas tetramethylammonium hydroxide (TMAOH) acted as a basic catalyst, surfactant, and template. The phase separation during gelation was finely adjusted by changing the ethanol-to-water ratio to control the gel skeleton structure, the number of crystallization templates, and the light transmittance of the aerogel. The hierarchical porous aerogels exhibited a uniform three-dimensional network. Notably, the specific surface area of the aerogels was 909 m2/g, the visible light transmittance was 58.1%, the hydrophobic angle was 166.5°, the thermal conductivity was 18.2 mW/(m·K), and the stress was 0.301 MPa at 50% compressive strain. The unique structure and excellent performance of the hierarchical porous aerogels make them promising for thermal and sound insulation applications. Moreover, the innovative use of TMAOH as a surfactant and template can be inspiring for the preparation of polymer-reinforced or highly crosslinked aerogels.

Sample Preparation Using TMAH and Nitric Acid for Multielement Determination in Crustacean Samples by MIP OES

This study proposes a simple sample preparation procedure using tetramethylammonium hydroxide (TMAH) and nitric acid (HNO3) to determine Cr, Cu, Fe, K, Mg, Mn, and Zn concentrations in shrimp (Macrobrachium amazonicum) and crab (Ucides cordatus) samples from the Amazon region by microwave-induced plasma optical emission spectrometry (MIP OES). The sample solubilization was carried out employing TMAH and HNO3 using an ultrasound bath and a thermostatic water bath. The accuracy of the proposed procedure was performed using microwave-assisted digestion as comparative method. Certified fish protein reference material (DORM-4) and also addition recovery experiments were used to assess the accuracy of the proposed procedure and recoveries obtained were adequate, ranging from 91 to 106%. In this study, the use of TMAH and HNO3 simplified sample preparation, maintaining the identity of analytes and ensuring efficiency in determinations.

Growth and Characterization of Vertical and Lateral p‐n Junctions Formed by Selective‐Area p‐GaN MOVPE on Patterned Templates

In this work, vertical and lateral GaN p‐n junctions are investigated. In particular, there is a strong demand of lateral p‐n junctions for the realization of numerous types of power devices. The comparison of I‐V characteristics of regrown and continuously‐grown p‐n diodes, formed by metal‐organic vapor phase epitaxy (MOVPE), reveals the impact of different surface treatments before regrowth. The use of tetramethylammonium hydroxide (TMAH) prove vital for growth on etch‐damaged GaN and to smoothen vertical sidewalls for selective‐area regrowth (SAR). Initial growth on patterned templates is identified to occur both vertically on the horizontal c‐plane and laterally on the vertical m‐planes allowing for an integration of the developed process in power device fabrication routes. The formation of local superelevations (LSE) near edges of masked areas is analyzed and explained.

Separation of superparamagnetic magnetite nanoparticles by capillary zone electrophoresis using non-complexing and complexing electrolyte anions and tetramethylammonium as dispersing additive.

Separations of bare superparamagnetic magnetite nanoparticles (BSPMNPs, approx. 11 nm diameter) was performed using non-complexing (nitrate) and complexing (chloride, citrate and phosphate) electrolyte ions with additions of tetramethylammonium hydroxide (TMAOH), which is commonly applied to control the synthesis of stable iron oxides. The use of TMAOH as a background electrolyte (BGE) additive for capillary electrophoresis (CE) separations provided for the first time electropherograms of BSPMNPs exhibiting symmetrical and highly reproducible peaks, free of spurious spikes characteristic of nanoparticle clusters. Consequently, accurate determination of the electrophoretic effective mobility of BSPMNPs was possible, yielding a value of -3.345E-08 m2 V-1 s-1 (relative standard deviation (RSD) of 0.500%). The obtained mobilities of BSPMNPs in the presence of various electrolyte ions show that the degree of complexation with the surface of BSPMNPs follows the order chloride < citrate < phosphate, correlating with the stabilities of Fe(III) complexes with the respective anions. Finally, bare and carboxylated iron oxide nanoparticles were successfully separated in only 10 min using 10 mM Tris-nitrate containing 20mM of TMAOH as electrolyte. Our findings show that simple and rapid CE experiments are an excellent tool to characterise and monitor properties and interactions of iron oxide nanoparticles with other molecules for surface modification purposes.

Homogenization of food samples for gamma spectrometry using tetramethylammonium hydroxide and enzymatic digestion

We have developed a method of food sample preparation for gamma spectrometry involving the use of tetramethylammonium hydroxide (TMAH) and/or enzymes such as α-amylase or cellulase for sample homogenization. We demonstrated the effectiveness of this method using food matrices spiked with 60Co, 131I, 134,137Cs, and 241Am radionuclides, homogenized with TMAH (mixed salad, parmesan cheese, and ground beef); enzymes (α-amylase for bread, and cellulase for baked beans); or α-amylase followed by TMAH (cheeseburgers). Procedures were developed which are best compromises between the degree of homogenization, accuracy, speed, and minimizing laboratory equipment contamination. Based on calculated sample biases and z-scores, our results suggest that homogenization using TMAH and enzymes would be a useful method of sample preparation for gamma spectrometry samples during radiological emergencies.

Absolute silicon molar mass measurements, the Avogadro constant and the redefinition of the kilogram

The results of an absolute silicon molar mass determination of two independent sets of samples from the highly 28Si-enriched crystal (AVO28) produced by the International Avogadro Coordination are presented and compared with results published by the Physikalisch-Technische Bundesanstalt (PTB, Germany), the National Research Council (NRC, Canada) and the National Metrology Institute of Japan (NMIJ, Japan). This study developed and describes significant changes to the published protocols for producing absolute silicon isotope ratios. The measurements were made at very high resolution on a multi-collector inductively coupled plasma mass spectrometer using tetramethylammonium hydroxide (TMAH) to dissolve and dilute all samples. The various changes in the measurement protocol and the use of TMAH resulted in significant improvements to the silicon isotope ratio precision over previously reported measurements and in particular, the robustness of the 29Si/30Si ratio of the AVO28 material. These new results suggest that a limited isotopic variability is present in the AVO28 material. The presence of this variability is at present singular and therefore its significance is not well understood. Fortunately, its magnitude is small enough so as to have an insignificant effect on the overall uncertainty of an Avogadro constant derived from the average molar mass of all four AVO28 silicon samples measured in this study. The NIST results confirm the AVO28 molar mass values reported by PTB and NMIJ and confirm that the virtual element–isotope dilution mass spectrometry approach to calibrated absolute isotope ratio measurements developed by PTB is capable of very high precision as well as accuracy. The Avogadro constant NA and derived Planck constant h based on these measurements, together with their associated standard uncertainties, are 6.02214076(19) × 1023 mol−1 and 6.62607017(21) × 10−34 Js, respectively.

Detection and characterization of silver nanoparticles and dissolved species of silver in culture medium and cells by AsFlFFF-UV-Vis-ICPMS: application to nanotoxicity tests

A methodology based on Asymmetric Flow Field-Flow Fractionation (AsFlFFF) coupled with UV-Vis absorption spectrometry and ICP mass spectrometry (ICPMS) has been developed and applied to the study of silver nanoparticles (AgNPs) and dissolved species of silver in culture media and cells used in cytotoxicity tests. The effect of a nano-silver based product (protein stabilized silver nanoparticles ca. 15 nm average diameter) on human hepatoma (HepG2) cell viability has been studied. UV-Vis absorption spectrometry provided information about the nature (organic vs. nanoparticle) of the eluted species, whereas the silver was monitored by ICPMS. A shift towards larger hydrodynamic diameters was observed in the AgNPs after a 24 hour incubation period in the culture medium, which suggests a "protein corona" effect. Silver(I) associated with proteins present in the culture medium has also been detected, as a consequence of the oxidation process experimented by the AgNPs. However, the Ag(I) released into the culture medium did not justify the toxicity levels observed. AgNPs associated with the cultured HepG2 cells were also identified by AsFlFFF, after applying a solubilisation process based on the use of tetramethylammonium hydroxide (TMAH) and Triton X-100. These results have been confirmed by transmission electronic microscopy (TEM) analysis of the fractions collected from the AsFlFFF. The effect of AgNPs on HepG2 cells has been compared to that caused by silver(I) as AgNO3 under the same conditions. The determination of the total content of silver in the cells confirms that a much larger mass of silver as AgNPs with respect to AgNO3 (16 to 1) is needed to observe a similar toxicity.

Combining electrothermal vaporization inductively coupled plasma mass spectrometry with in situ TMAH thermochemolysis for the direct determination of trace impurities in a polymer-based photoresist

Trace impurities in photoresists are difficult to determine when using electrothermal vaporization inductively coupled plasma mass spectrometry (ETV-ICP-MS) because of the presence of excessive amounts of polymeric matrix. In this study, we evaluated the use of tetramethylammonium hydroxide (TMAH) for the removal of the polymeric matrix through the formation of gaseous degradation products. We also investigated the influence that the temperature program had on the separation efficiency. To remove the polymeric matrix to a moderate degree, we performed a pre-reaction step, which was necessary to improve the removal efficiency in order to enhance the thermochemolysis reaction between the photoresist and TMAH. Under the optimized conditions, the signal resulting from the carbon matrix can be suppressed significantly and satisfactory analytical signals can be obtained. The precision of this method was ca. 10% when we used TMAH as a matrix modifier and performed the pre-reaction step during the ETV heating cycle; we confirmed this accuracy by noting the good agreement between the data obtained when using our proposed method and those obtained when using a wet chemical technique. Our method permits the determination of Mn, Zn, Cu, and Pb in photoresists at detection limits within the range from 0.76 to 7.1 ng mL−1.

Molecular Characterization of Biodegradable Dissolved Organic Matter Using Bioreactors and [12C/13C] Tetramethylammonium Hydroxide Thermochemolysis GC−MS

Little is known about the molecular composition of the biodegradable fraction of dissolved organic matter (BDOM) in stream ecosystems. We combined plug-flow biofilm reactors, tetramethylammonium hydroxide (TMAH) thermochemolysis GC-MS, and 13C-labeled TMAH thermochemolysis GC-MS to study the molecular composition of BDOM from two stream ecosystems. TMAH products derived from fatty acids, lignin, and other aromatic molecules were quantified using an internal standard approach. We applied the 13C-TMAH thermochemolysis procedure to differentiate between compounds in dissolved organic matter (DOM) that had natural methoxyl groups from those that acquired methoxyl groups during the TMAH reaction. In Rio Tempisquito, a stream draining a tropical evergreen forest, and White Clay Creek, a stream draining a temperate deciduous woodlands, carbohydrates, fatty acids, and lignin contributed to the DOM and BDOM molecular composition. We observed 97 different peaks in the chromatograms of streamwater, with 57% of the peaks common to both streams. The DOM and BDOM pools from each site also contained a unique suite of compounds. Our combined use of TMAH and 13C-TMAH thermochemolysis revealed that heterotrophic bacteria can selectively degrade and demethylate different types of compounds in the lignin residues of DOM. This demonstration of bacterial demethylation of lignin, an abundant and refractory plant molecule, has potential implications for global carbon cycling.

Improvement of metal dispersion in Pd/SiO2 cogelled xerogel catalysts for 1,2-dichloroethane hydrodechlorination

The study of the influence of synthesis operating variables (nature and concentration of complexing silane, palladium percentage, temperatures of gelling, aging and vacuum drying of xerogels, molar ratio between the complexing silane and palladium, molar concentration of ammonia solution, and use of tetramethylammonium hydroxide as base instead of NH3) allows improving metal dispersion in Pd/SiO2 cogelled xerogel catalysts. The use of 3-(2-aminoethylamino)propyltrimethoxysilane (EDAS) or 3-(2-aminoethylamino)propyltriethoxysilane (EDAES) to complex palladium in an ethanolic solution containing tetraethoxysilane (TEOS) and an ammonia solution of 0.54mol/l allows obtaining a Pd/SiO2 xerogel catalyst with a mean metal particle diameter of 2.4nm located inside silica particles. Indeed, complexes Pd(EDA(E)S)xn+ induce a nucleation mechanism because of their higher reactivity compared to the network-reagent (TEOS). Although metal particles are located inside the silica particles, their complete accessibility, via the micropore network, has been shown. 1,2-dichloroethane hydrodechlorination over Pd/SiO2 catalysts mainly produces ethane and the specific hydrodechlorination rate per gram of palladium increases proportionally with palladium dispersion. Hydrodechlorination over Pd/SiO2 cogelled xerogel catalysts is a structure insensitive reaction with regard to the ensemble size concept.

Synthesis, characterization and catalytic activity of MCM-41-type mesoporous silicas functionalized with sulfonic acid

This paper reports the results obtained in the synthesis, characterization and catalytic activity of thiol-MCM-41 materials synthesized using an improved method of preparation. This novel method of synthesis includes the partial replacement of the surfactant used previously — hexadecyltrimethylammonium bromide, for a shorter chain surfactant such as dodecyltrimethylammonium bromide. It also includes the use of tetramethylammonium hydroxide (TMAOH) as co-structuring agent instead of NaOH. The materials obtained from this modified gels present a higher order in the channels arrangement confirmed by X-ray diffraction (XRD) and transmission electron microscopy (TEM) measurements. These materials incorporates an important amount of thiol groups which can be oxidized with H 2O 2 in order to obtain the corresponding sulfonic groups, with a very strong acidity. The catalysts so obtained have been tested in the esterification of glycerol with fatty acids — oleic and lauric. The results obtained indicate that the catalysts prepared with mixtures of surfactants are more selective to the monoglycerides than the ones synthesized only with hexadecyltrimethylammonium bromide, probably due to the higher order in the channels packing.

Colloidal filtration of silicon nitride aqueous slips. Part I: optimization of the slip parameters

The slip parameters for the manufacture of dense, pressureless sintered silicon nitride by colloidal forming methods, such as slip or pressure casting, are studied. This work focuses the optimization of the rheological behaviour of the slip considering different kinds and concentrations of dispersants and it has been stated that the electrostatic stabilizing mechanism is essential. The best rheological conditions are achieved with tetramethylammonium hydroxide (TMAH) or any strong base (as NaOH), but the use of TMAH limits the progressive oxidation of the particles suspended in water by action of a partially oxidized protective screen. The study has been made with Al 2O 3 and Y 2O 3 as sintering aids, in concentrations of 3 and 6 wt% each. An optimum pH for dispersing has been located at 11·3±0·2, where neither yield point nor thixotropy are found for 65 wt% slips. Different homogenizing techniques are used and compared, such as strong mechanical agitation, centrifugal milling or mixing in a rotatory bottle with nylon balls. Since the starting silicon nitride powder is submicronic, no milling is required, but a long homogenization time is convenient to assure an equilibrium state at the particles surface.

Determination of twelve elements in botanical samples with inductively coupled plasma atomic emission spectrometry after leaching with tetramethylammonium hydroxide and ethylenediaminetetraacetic acid

The combined use of tetramethylammonium hydroxide (TMAH) and ethylenediaminetetraacetic acid (EDTA) was effective for leaching inorganic constituents from botanical samples for their determination by inductively coupled plasma atomic emission spectrometry (ICP-AES). A powdered sample of 50 mg and 1 ml each of 25% TMAH and 200 mM EDTA were heated for 4 h in a drying oven of 120°C using a doubly sealed PTFE vessel with a metal jacket. To the suspended solution in a small vessel 2 ml of water were added, the pH was adjusted to 8 and the suspension was centrifuged. The supernatant was used for sequential measurements of major and minor constituents by ICP-AES. The results obtained for some standard reference samples of botanical origin agreed well with the certified or reported values, except for slightly low recoveries of aluminium and iron.

Characterisation of chlorogenic acids by simultaneous isomerisation and transesterification with tetramethylammonium hydroxide

The use of tetramethylammonium hydroxide at room temperature is reported for the simple characterisation of trace amounts of chlorogenic acids belonging to the caffeoyl, p-coumaroyl, feruloyl and dicaffeoylquinic acid subgroups. The assignments proposed have been confirmed by conventional proton NMR.

The use of tetramethylammonium hydroxide in the Zimmermann reaction.

The use of tetramethylammonium hydroxide (T.M.A.H.) in place of potassium hydroxide in the Zimmermann reaction has been investigated. Although various pure steroids have different colour equivalents, a comparison of the results of 17-ketosteroid and 17-hydroxycorticosteroid estimations on a series of urines showed that the differences for the two reagents were only small and may be ignored. Tetramethylammonium hydroxide has the considerable advantage over potassium hydroxide of stability and need not be prepared freshly. The correction procedures available are discussed.

Some Observations on Steroid Estimations: The Use of Tetramethylammonium Hydroxide in the Zimmermann Reaction

Some Observations on Steroid Estimations: The Use of Tetramethylammonium Hydroxide in the Zimmermann Reaction