Microwave-assisted Silylation Research Articles

Aminopropyl bentonites obtained by microwave-assisted silylation for copper removal

In this work, sodium bentonite was silylated with 3-aminopropyltrimethoxysilane (APTMS) under microwave irradiation at 50 °C at different times (5, 10 and 15 min). Silylation was performed in presence and absence of ethylene glycol. Infrared and 29Si NMR spectroscopies were used to monitor the grafting process, while the degree of functionalization was calculated by using CHN elemental analysis and thermogravimetry. X-ray diffraction and transmission electron microscopy (TEM) were carried out to evaluate alterations in the basal spacing. The silylation degree of bentonite was higher at short reaction time. The modified solids were used to remove Cu(II) from aqueous solutions. Parameters such as contact time and initial cation concentration for the Cu(II) were investigated. Fast copper retention occurred in the pristine and silylated solids with saturation time of 40 min and maximum adsorption capacity of 1.54 mmol g−1 for organofunctionalized sample. The adsorption equilibrium data were fitted using the Langmuir and Freundlich isotherms. Zeta potential measurements, UV–vis spectra and X-ray spectroscopy were used to understand the adsorption mechanism. The silylated solids obtained by microwave irradiation behaved as good sorbents for rapid Cu(II) removal from aqueous solution.

Improved conventional and microwave-assisted silylation protocols for simultaneous gas chromatographic determination of tocopherols and sterols: Method development and multi-response optimization

This paper reports on improved conventional thermal silylation (CTS) and microwave-assisted silylation (MAS) methods for simultaneous determination of tocopherols and sterols by gas chromatography. Reaction parameters in each of the methods developed were systematically optimized using a full factorial design followed by a central composite design. Initially, experimental conditions for CTS were optimized using a block heater. Further, a rapid MAS was developed and optimized. To understand microwave heating mechanisms, MAS was optimized by two distinct modes of microwave heating: temperature-controlled MAS and power-controlled MAS, using dedicated instruments where reaction temperature and microwave power level were controlled and monitored online. Developed methods: were compared with routine overnight derivatization. On a comprehensive level, while both CTS and MAS were found to be efficient derivatization techniques, MAS significantly reduced the reaction time. The optimal derivatization temperature and time for CTS found to be 55°C and 54min, while it was 87°C and 1.2min for temperature-controlled MAS. Further, a microwave power of 300W and a derivatization time 0.5min found to be optimal for power-controlled MAS. The use of an appropriate derivatization solvent, such as pyridine, was found to be critical for the successful determination. Catalysts, like potassium acetate and 4-dimethylaminopyridine, enhanced the efficiency slightly. The developed methods showed excellent analytical performance in terms of linearity, accuracy and precision.

Dispersive liquid–liquid microextraction followed by microwave-assisted silylation and gas chromatography-mass spectrometry analysis for simultaneous trace quantification of bisphenol A and 13 ultraviolet filters in wastewaters

A novel multi-residue gas chromatography-mass spectrometry (GC-MS) method was validated for the simultaneous determination of trace levels (ng/L) of 13 UV-filters and bisphenol A (BPA) in wastewater samples. It was based on dispersive liquid–liquid microextraction (DLMME) followed by rapid microwave-assisted silylation of the analytes. Several parameters of both extraction and derivatization steps such as type of extractive and dispersive solvents, solvent volumes, pH, salt addition, time and power of microwave were evaluated to achieve the highest yield and to attain the lowest detection limits. Optimized DLLME consisted in the formation of a cloudy solution promoted by the fast addition to the sample (10mL) of a mixture of tetrachloroethylene (50μL, extraction solvent) in acetone (1mL, dispersive solvent). The sedimented phase obtained was evaporated and further silylated under the irradiation of 600W microwave for 5min, being the derivatization yields similar to those obtained after a conventional heating process for 30min at 75°C. Limits of detection and quantification of the method using real samples were 2ng/L and 10ng/L, respectively. Mean extraction efficiency of 82% for three concentrations were achieved, supporting the accuracy of the method. Intra-day and inter-day repeatability of measurements (expressed as relative standard deviation) were lower than 22%. The method was successfully applied to the determination of UV-filters and BPA in samples collected from 15 wastewater treatment plants (WWTPs) in Portugal. Eight analytes were detected, among which 2-hydroxy-4-methoxybenzophenone, 2-ethylhexyl-4-(dimethylamino)benzoate, octocrylene, and BPA were consistently found in the three seasons of collection.

Microwave-assisted silylation of graphite oxide and iron(III) porphyrin intercalation

The hybrid material graphite oxide (GO) intercalated with an iron(III) porphyrin was obtained upon a silylation reaction of GO with 3-bromotrimethoxypropylsilane (BrTMS) followed by metalloporphyrin immobilization. Diverse reaction conditions and microwave versus conventional heating were tested. The materials were characterized using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Fourier-transform infrared spectroscopy (FTIR), thermogravimetry (TGA) and temperature programmed desorption (TPD). Microwave-assisted synthesis allowed functionalization reactions of 1h instead of 24h (conventional heating) with equivalent or improved yields on both silylation and metalloporphyrin immobilization reactions. The immobilizations performed in anhydrous solvent and absence of other exfoliation agents led to an increase on the GO interlayer distance of 0.14nm, in a total space of 7Å that match the metalloporphyrin thickness.

Microwave-assisted derivatization: application to steroid profiling by gas chromatography/mass spectrometry.

Gas chromatography-mass spectrometry (GC-MS) remains as the gold-standard technique for the study of the steroid metabolome. A main limitation is the need of performing a derivatization step since incubation with strong silylations agents for long periods of time (usually 16 h) is required for the derivatization of hindered hydroxyls present in some steroids of interest. In the present work, a rapid, simple and reproducible microwave-assisted derivatization method was developed. In the method, 36 steroids already treated with methoxyamine (2% in pyridine) were silylated with 50 μl of N-trimethylsilylimidazole by using microwave irradiation, and the formed methyloxime-trimethylsilyl derivatives were analyzed by GC-MS. Microwave power and derivatization time silylation conditions were optimized being the optimum conditions 600 W and 3 min respectively. In order to evaluate the usefulness of this technique, the urine steroid profiles for 20 healthy individuals were analyzed. The results of a comparison of microwave irradiation with the classical heating protocol showed similar derivatization yields, thus suggesting that microwave-assisted silylation is a valid tool for the rapid steroid metabolome study.

Microwave-assisted silylation followed by gas chromatography/mass spectrometry for simultaneous quantification of nicotine and its four metabolites in urine

In this work, for the first time, microwave-assisted silylation (MAS) followed by gas chromatography-mass spectrometry (GC-MS) was developed for the fast analysis of nicotine and its four metabolites in human urine. MAS conditions and the method's validation were studied. It was found that the derivatization time of 10 min with 200 W microwave power are the best conditions to derive nicotine's metabolites in urine samples. The calibration curve shows good linearity in 0.02–20.00 mg L−1 for nicotine (R2 = 0.9987), cotinine (R2 = 0.9959), and 3-hydroxycotinine (R2 = 0.9974) and 0.02–0.80 mg L−1 for nornicotine (R2 = 0.9998) and norcotinine (R2 = 0.9986), respectively. The RSD values for them are 7.39%, 1.94%, 4.62%, 6.37% and 2.4%, respectively, indicating good reproducibility. The proposed method was successfully applied to the determination of nicotine and its four metabolites in urine from active smokers as well as non-smokers susceptible to passive smoking.

Simultaneous Determination of Resibufogenin and Cinobufagin in Chinese Medicine Ch’an Su by GC–MS Following Microwave-Assisted Silylation

Resibufogenin and cinobufagin are the major bioactive constituents in the Chinese medicine Ch’an Su. In this paper, a novel, simple and rapid method was developed for the qualitative analysis of the two main compounds, which was based on microwave-assisted silylation followed by gas chromatography–mass spectrometry. The components of resibufogenin and cinobufagin were derivatized with N,O-bis(trimethylsilyl)trifluoroacetamide under microwave irradiation, and the trimethylsilyl derivatives formed were analyzed by GC–MS. The derivatization conditions including microwave power and irradiation time were investigated, and the method validations (linear range, detection limit, precision and recovery) were also studied. The experimental results indicate that microwave-assisted silylation followed by GC–MS analysis is a new method for the determination of resibufogenin and cinobufagin in the Ch’an Su samples.

Microwave‐assisted silylation followed by gas chromatography/mass spectrometry for rapid determination of ergosterol in cigarettes

Ergosterol is one of the important precursors of tumorigenic polynuclear aromatic hydrocarbons. To the best of our knowledge, a large amount of ergosterol is present in moldy cigarettes, which derives from fungal contaminations. Thus, the development of a simple, fast, and efficient method for the analysis of ergosterol is in great demand. In this paper, GC/MS following microwave-assisted silylation (MAS) was developed for the rapid quantitative analysis of ergosterol in cigarettes for the first time. In our work, total ergosterol in cigarettes after NaOH saponification was extracted with hexane, and then was fast derivatized with bis(trimethylsilyl)trifluoroacetamide (BSTFA) under microwave irradiation. Finally, the ergosterol trimethylsilyl derivative was analyzed by GC/MS. Derivatization conditions including microwave reaction solvent, irradiation time, and power were investigated. Method validations (linear range, LOD, precision, and recovery) were also studied. The results showed that the proposed method provided a fast, simple, and sensitive approach for the determination of ergosterol in cigarettes. Finally it was successfully applied to the analysis of ergosterol in normal and mildewy cigarettes.

Fast Diagnosis of Neonatal Phenylketonuria by Gas Chromatography-Mass Spectrometry Following Microwave-Assisted Silylation

Phenylketonuria (PKU) is a fairly common autosomal recessive disease. Phenylalanine (Phe) and tyrosine (Tyr) are the biomarkers of PKU, and it can be diagnosed by the measurement of Phe and Tyr in neonatal blood samples. A fast diagnostic procedure for neonatal PKU has been developed using microwave-assisted silylation followed by gas chromatography-mass spectrometry. Amino acids extracted from neonatal blood samples are rapidly derivatized with N, O-bis(trimethylsilyl)-trifluoroacetamide under microwave irradiation; the derivatives are then analyzed by GC-MS. The silylation conditions have been optimized, and the method validated for linear range, detection limit, precision and recovery. The proposed method is linear from 20 to 800 µM, detection limit is less than 0.35 µM, relative standard deviation (RSD) is less than 9.0%, and recoveries of 87% and 83% were obtained for Phe and Tyr. The proposed method was tested by the determination of Phe and Tyr in blood spots from eight PKU-positive neonates and twelve control neonates. Microwave irradiation considerably accelerates the derivatization reaction of amino acid with BSFTA, and shortens the whole analysis time. Microwave-assisted silylation coupled to GC-MS is a powerful tool for fast screening of neonatal PKU.

Diagnosis of congenital adrenal hyperplasia by rapid determination of 17α‐hydroxyprogesterone in dried blood spots by gas chromatography/mass spectrometry following microwave‐assisted silylation

17alpha-Hydroxyprogesterone (17OHP) is considered to be the biomarker of congential adrenal hyperplasia (CAH). Screening for CAH in newborns by measuring levels of the biomarker of 17OHP has become routine. In the work, a rapid, simple and sensitive technique was developed for the diagnosis of neonatal CAH by the quantitative analysis of 17OHP in neonatal blood spots. The technique was based on microwave-assisted silylation (MAS) followed by gas chromatography/mass spectrometry (GC/MS). In the method, fast derivatization of 17OHP with N,O-bis(trimethylsilyl)trifluoroacetamide was performed by using microwave irradiation, and the trimethylsilyl derivative thus formed was analyzed by GC/MS. The results of the experiment indicate that MAS followed by GC/MS analysis is a rapid, simple and sensitive method for the determination of 17OHP in blood samples. The proposed technique has been shown to have potential as a powerful tool for the rapid diagnosis of neonatal CAH.

Development of microwave‐assisted derivatization followed by gas chromatography/mass spectrometry for fast determination of amino acids in neonatal blood samples

Analysis of amino acids in blood samples is an important tool for the diagnosis of neonatal amino acid metabolism disorders. In the work, a novel, rapid and sensitive method was developed for the determination of amino acids in neonatal blood samples, which was based on microwave-assisted silylation followed by gas chromatography/mass spectrometry (GC/MS). The amino acids were derivatized with N,O-bis(trimethylsilyl)trifluoroacetamide (BSTFA) under microwave irradiation. The controlled reaction was carried out employing BSTFA under conventional heating at 120 degrees C for 30 min. Experimental results show that microwave irradiation can accelerate the derivatization reaction of amino acids with BSFTA, and much shorten analysis time. The method validations (linear range, detection limit, precision and recovery) were studied. Finally, the method was tested by determination of amino acids in neonatal blood by the measurement of their trimethylsilyl derivatives by GC/MS in electron impact (EI) mode. Two biomarkers of L-phenylalanine and L-tyrosine in phenylketonuria (PKU)-positive blood and control blood were quantitatively analyzed by the proposed method. The results demonstrated that microwave-assisted silylation followed by GC/MS is a rapid, simple and sensitive method for amino acid analysis and is also a potential tool for fast screening of neonatal aminoacidurias.

Microwave-accelerated derivatization processes for the determination of phenolic acids by gas chromatography–mass spectrometry

A rapid method for the derivatization of phenolic antioxidants using microwave irradiation has been developed. Six antioxidatively active phenolic components of wines and fruits, namely gallic acid, gentisic acid, vanillic acid, caffeic acid, ferulic acid and p-coumaric acid were used in the model study. The solution of phenolic acids was evaporated to dryness on a rotary evaporator followed by further drying under microwave irradiation (600 W, 30 s). The resultant residue was dissolved in pyridene and treated with bis(trimethylsilyl)acetamide while irradiated by microwave using high power for 30 s. Controlled reaction was carried out employing bis(trimethylsilyl)trifluoroacetamide under conventional heating for 30 min. The trimethylsilyl derivatives were identified and quantified on a gas chromatography/mass selective detector. The mass spectral fragmentation patterns of the derivatives obtained by microwave irradiation were identical to those prepared by heating. The yields of microwave-assisted silylation were comparable to those from conventional heating. The rsd were less than 8% for six replicates. The linearity in wine matrix was nearly perfect. This method is a useful protocol to examine the phenolic constituents in wines and agricultural products.