STUDY ON THE GASEOUS PRODUCTS OF HIGH TEMPERATURE PYROLYSIS OF ACRYLONITRILE POLYMERS BY ON-LINE FTIR METHOD

The gaseous products of high temperature pyrolysis (300℃ to 960℃) of aerylonitrile polymers were measured continuously under nitrogen atmosphere by on-line Fourier Transform Infrared Spectroscopic method (FTIR). From the variations of characteristic peaks it was found that the nitrogen of macromolecules evolved were mainly in the form of hydrogen cyanide and ammonia. During the pyrolysis amorphous carbonaceous element was formed, and crosslinked to form network structure. Three kinds of samples were used for comparison. The experimental results show that the gaseous products of volatile small molecules were HCN, NH_3, CH_4, C_2H_6 and cyanide. CO and CO_2 were also formed when copolymers of PAN were thermally pyrolyzed.     

INSERTION REACTION OF CARBOETHOXYLCARBENE TO N-HEXANE IN THE PRESENCE OF BENZOPHENONE AND THE SENSITIZED PHOTO-OXIDATION OF N-HEXANE

In the presence of protosensitizer-benzophenone, ethyl diazoacetate was photolyzedand the resulting carboethoxylcarbene reacted with n-hexane. The result was compared withthat done without the sensitizer. It was revealed that the nature of the insertion products andtheir relative proportions remained the same, whether the sensitizer was presentor not. At the same time, the influence of oxygen on the sensitized and unsensitized inser-tion reaetions was also studied; these showed also no influence on the nature of insertionproducts and their relative proportions no matter whether the sensitizer or oxygen was pres-ent or not. Since oxygen ks a well-known seavenger for the triplet state carbene, the ex-perimental results indicate clearly that the insertion reactions are conducted by the carbenein singlet state. The photo-oxidation products of n-hexane sensitized by air in the presence of benzophe-none were carefully studied, showing that the primary hexyl radical seemed to be rearrang-ed to thermodynamicall     

毛细管气相色谱法测定热不稳定有机磷农药辛硫磷

The thermo-labile organophosphorous pesticide Phoxim was determined by capillary gas chromatographywith flame phototnetric detector. When high linear velocity H_2(>200cm/s) was used as carrier gas,the thermo-decomposition of Phoxim was considerably reduced.The most important gas chromatography conditions,injectortempereture and column head pressure,were studied.The thermo-decomposition preducts were identified by gaschromatography-mass spectrometry.     

端羟基β-氰乙基甲基聚硅氧烷气相色谱毛细管柱的研制

Sol-gel capillary column for gas chromatography was prepared with Hydroxyl-Terminated β-cyan-ethyl methyl-Polysiloxane as stationary phase.On this column alkanes,aromatic compounds,amines,alcohols etc.were separated successfully,although the length of this column was only 2.5m.Experiments showed that the column-inertness was good and the unsymmetrical factor was 1.At high temperatures the stationary phase of the column showed excellent stability.Results showed that the relative standard deviation of the ret...     

Synthesis and characterization of β-cyclodextrin modified hyperbranched carbosilane as stationary phase for GC

A new β-cyclodextrin modified hyperbranched carbosilane stationary phase for gas chromatography was synthesized by substituting the -OH groups ofβ-cyclodextrin with hyperbranched carbosilane and was coated on the inner wall of fused silica capillary column for gas chromatography.The chromatographic behaviors of the stationary phase were studied.The initial testing results showed mat it possessed good separation abilities for several kinds of mixtures,such as benzenes,acrylates,ketones and alkylchlorides.     

Determination of multiple phenolic compounds in infant textile products by derivatization gas chromatography-mass spectrometryEI北大核心CSCD

A method for the simultaneous determination of 17 phenolic compounds in infant textile products， including phenol，o-phenylphenol，alkylphenols and bisphenols，was established using gas chromatography-mass spectrometry（GC-MS）. The samples were extracted by 0.1 mol/L KOH solution，derived with acetic anhydride. The derivatives were extracted with ethyl acetate，separated by HP-5MS column，and determined by gas chromatography-mass spectrometry with ion mode scanning. Under the optimized conditions，the method had a good linear relationship in the range of 0.5-6.25 mg/L（R2>0.9990），the recoveries ranged from 80% to 110%， the relative standard deviations were 1.0%-8.6%，and the limit of quantification was 1.0 mg/kg. The method can achieve the simultaneous detection of 17 phenolic compounds in infant textile products. © 2023, Youke Publishing Co., Ltd. All rights reserved.     

STATISTICAL STUDIES ON THE RELATIONSHIP BETWEEN WIDTHS AND RETENTION TIMES OF GAS CHROMATOGRAPHIC PEAKS

The k' (capacity ratio)and w_(1/2) (width at half peak height) values of chromatographic peaks were measured for the members of three homologous series, i.e. n-alkanes, n-alkyl alcohols and n-alkyl benzencs on three packed columns with OV 22,5, EGS or PEG 4000 as liquid phase respectively under suitable chromatographic conditions. It was found that the k'-w_(1/2) points of any homologous series on any column did not fall into a straight line, while they were best fitted by a curve.When the method of linear regression was applied to the k'-w_(1/2) data in order to make a comparison with the results of other chromatographers, it was proven that the linear regression lines obtained on the same column for samples of different homologous series always differed significantly.Whether β, a column parameter proposed by Lu, the author who advanced the theory of multi-component chromatography, may hold constant was also experimentally tested, and it was concluded that the constancy of β found little experimental     

气相色谱法测定三环氧丙基异氰尿酸酯中环氧氯丙烷残留量

A simple,rapid and reliable method for the determination of trace epichlorohydrin residue in tris (2 ,3-epoxy propyl) isocyanurate for industrial use by gas chromatography is described. The gas chromatographic separation was achieved on a glass colunin packed with 4% SE-30/Chromosorb W HP at a column temperature of 80℃.The detector was FID and the carrier gas was N2.Three preducts from various manufacturers were analyzed by this methed with the coefficient of variation of 2. 2%-5. 2%。     

Analysis of Ginsenosides by SPE-HPLC and Its Application to Quality Control

<正>A rapid and effective method,solid phase extraction coupled with high performance liquid chromatography (SPE-HPLC),was applied to the separation and analysis of ginsenosides.Waters OASIS HLB was used for concentrating and purifying samples and Alltima C_(18)(53 mm×7 mm,3μm) chromatography column was used for separating ginsenoside Rg_1,Re,Rb_1,Rc,Rb_2 and Rd.These ginsenosides were analyzed within 20 min in our gradient elution process and the equilibrium time of the chromatography column cost only 5 min.Moreover,there was no obvious baseline drift in our experiment.This method was used to analyze the contents of ginsenosides in different ginseng products for quality control.Four ginseng products were studied,including two kinds of capsules,one kind of tablet and one kind of injection.The results show that the method developed in this paper had good accuracy,linearity and precision.Therefore,this method could be applied in quality control of ginseng products.     

Fabrication and thermal decomposition of glycidyl azide polymer modified nitrocellulose double base propellants

Glycidyl azide polymer(GAP) with the advantages of non-volatility and excellent thermal stability is a candidate as a replacement for nitroglycerine(NG) in a double base propellant. The GAP-NC double base propellants were formulated with GAP and nitrocellulose(NC) fibers. Tensile test and SEM characterization indicated that GAP-NC propellants had a homogeneous structure. Thermogravimetric analysis of GAP-NC propellants revealed that the onset decomposition temperature reached a high level ranging from 192.9 to 194.6 °C, which indicated that the substitution of NG with GAP contributed to the safe storage and process operations for double base propellant. The result analysis of decomposition products of GAP-NC propellants showed that the main gas decomposition products of the propellants were NO, NO_2, CO, CO_2, NH_3, CH_4, HCN, N_2, CH_2O and C_2H_4O. The thermal decomposition process of the specimens was proposed.     

CARBONIZED FIBROUS RESIN AS A NEW SORBENT FOR SAMPLING POLYCYCLIC AROMATIC HYDROCARBONS （PAHS）IN AMBIENT AIR

A new sampling method of ambient air analysis using carbonized fibrous resin as a sorbent for polycyclic aromatic hydrocarbons(PAHs) was reported.The physical and chemical properties of the carbonized fibrous resins were measured.The sample pretreatment with ultrasonic extraction and subsequent clean-up elution through a silica gel column was optimized.The suitable ultrasonic extraction conditions were selected as follows:resin weight was 1.5g,ultrasonic extraction time 20min,volume of extraction solvent 100 ml and extraction operation times 2-3.The concentrated extractable organic matter was submitted to next step of clean-up procedure of adsorption chromatography on silica gel column/n-hexane and a mixture of dichloromethene:n-hexane solution 2:3(v/v).The PAHs fractions in the real samples from Changzhou,China were particularly analyzed using GC-MS data system and the data of mass spectra,retention times and scan numbers of the real samples were compared with that of the standards of 16 PAHs listed by the US EPA as “priority pollutants” of the environment. The pretreatment of samples of ambient air with carbonized fibrous resin as a sorbent for PAHs is proved to be reliable and might be used for the procedure of the determination of PAHs in atmospheric environment.     

CHROMATOGRAPHIC SEPARATION OF THE ENANTIOMERS OF 3-PHENYL-1,2-EPOXYETHANE AND 1-PHENYL-1-PROPANOL ON A FUSED SILICA CAPILLARY COLUMN COATED WITH PERBENZYL-β-CYCLODEXTRIN

A β-cyclodextrin derivative, perbenzyl-β-cyclodextrin, was prepared and used as a chiral stationary phase for capillary gas chromatography. Using FID detector and the column temperature between 70 and 80℃, the chiral separations of racemic 3-phenyl-1, 2-epoxyethane and 1-phenyl-1-propanol on a 14m×0.23mm I. D. fused silica column with the β-cyclodextrin derivative were carried out and the optical purities of optically active 1-phenyl-1-propanol samples prepared by asymmetric synthesis were determined.     

Analysis of nitrobenzene compounds in water and soil samples by graphene composite-based solid-phase microextraction coupled with gas chromatography–mass spectrometry

In this work, solid-phase microextraction coupled with gas chromatography–mass spectrometry was developed to determine trace levels of nitrobenzene compounds in water and soil samples. Graphene was chosen as the extraction material and its composite was coated on a stainless steel wire through sol–gel technique for the solid phase microextraction. The key parameters influencing the extraction efficiency were optimized. Under the optimal conditions, the linearity for the compounds was observed in the range of 0.02–15.0 mg/L for water samples, and 0.2–60.0 mg/kg for soil samples, with the correlation coefficients（r） of 0.9966–0.9987. The limits of detection of the method were 0.0025–0.005 mg/L for water samples, and 0.02–0.04 mg/kg for soil samples. The recoveries for the spiked samples were in the range of 72.0%–113.2%, and the precision, expressed as the relative standard deviations, was less than 12.1%.     

CO_2 residual concentration of potassium-promoted hydrotalcite for deep CO/CO_2 purification in H_2-rich gas

Elevated-temperature pressure swing adsorption is a promising technique for producing high purity hydrogen and controlling greenhouse gas emissions. Thermodynamic analysis indicated that the CO in H_2-rich gas could be controlled to trace levels of below 10 ppm by in situ reduction of the CO_2 concentration to less than 100 ppm via the aforementioned process. The CO_2 adsorption capacity of potassiumpromoted hydrotalcite at elevated temperatures under different adsorption(mole fraction, working pressure) and desorption(flow rate, desorption time, steam effects) conditions was systematically investigated using a fixed bed reactor. It was found that the CO_2 residual concentration before the breakthrough of CO_2 mainly depended on the total amount of purge gas and the CO_2 mole fraction in the inlet syngas.The residual CO_2 concentration and uptake achieved for the inlet gas comprising CO_2(9.7 mL/min) and He(277.6 mL/min) at a working pressure of 3 MPa after 1 h of Ar purging at 300 mL/min were 12.3 ppm and0.341 mmol/g, respectively. Steam purge could greatly improve the cyclic adsorption working capacity, but had no obvious benefit for the recovery of the residual CO_2 concentration compared to purging with an inert gas. The residual CO_2 concentration obtained with the adsorbent could be reduced to 3.2 ppm after 12 h of temperature swing at 450 °C. A new concept based on an adsorption/desorption process, comprising adsorption, steam rinse, depressurization, steam purge, pressurization, and high-temperature steam purge, was proposed for reducing the steam consumption during CO/CO_2 purification.     

Thermal stability and thermal aging of poly(vinyl chloride)/MgAl layered double hydroxides composites

MgAl-LDH(layered double hydroxides) were prepared with CO(NH_2)_2, NH_4 Cl and NH_3·H_2O by the coprecipitation method, respectively. Corresponding composite membranes were prepared by the coating method. LDHs were characterized by WAXS, CO_2-TPD and SEM. The morphology of the PVC/LDHs composite membranes were characterized by means of SEM. The thermal stability of the membranes was analyzed by air aging box and TGA-FTIR. The SEM results show that nano-particles can be compatible with poly(vinyl chloride)(PVC) matrix homogeneously by the stirring-ultrasound blend method with two steps. Furthermore, the air aging box results proved that MgAl-CO(NH_2)_2-LDH has the best effect on thermal stability of PVC. TGA-FTIR results show that MgAl-CO(NH_2)_2-LDH could adsorb more HCl that resulted from the degradation of PVC and improve the pyrolysis temperature of the first degradation stage by 15 K compared with PVC.     

Porous boronate affinity monolith for on-line extraction coupled to high-performance liquid chromatography for sensitive analysis of heterocyclic aromatic amines in food samples

A novel on-line solid-phase microextraction–high-performance liquid chromatography(SPME–HPLC)system was developed for the determination of heterocyclic aromatic amines(HAAs) in food samples. A poly(vinylphenylboronic acid-co-ethylene glycol dimethacrylate) polymer monolith was prepared for on-line efficient extraction and large-volume injection was used to increase the sensitivity of detection.The polymermonolith, based on a ternary porogen, was prepared by in situ polymerization of vinylphenylboronic acid(VPBA) and ethylene glycol dimethacrylate(EGDMA) in a fused-silica capillary column. It showed good permeability, high extraction capacity, and high selectivity. The column-tocolumn reproducibility was satisfactory, and the enrichment factors for HAAs were 3746–7414.Conditions influencing the on-line extraction efficiency, including p H of sample solutions, flow rate of extraction and desorption, and desorption volume, were investigated. The proposed method had low limit of detection(0.10–0.15 ng/L) and good linearity. Trace HAAs in roast beef and lamb samples were determined, and the amounts of 2-amino-3-methylimidazo[4,5-f]quinoline, 2-amino-3,4-dimethylimidazo[4,5-f]quinoline, 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline, 2-amino-3,4,8-trimethylimidazo[4,5-f]quinoxaline, and 2-amino-3,4,7,8-tetramethyl-3H-imidazo[4,5-f]quinoxaline in these samples were 0.235–2.08 ng/g. The recoveries for the five HAAs ranged from74.3% to 119%, and the relative standard deviation(RSDs) were less than 8.2%. The results showed that the proposed on-line method was highly sensitive for monitoring HAAs in different food samples.     

Simultaneous analysis of Cu and Pb as ABEDTA complexes in Rhizoma coptidis by capillary electrophoresis coupled with solid phase extraction

A novel capillary electrophoresis method for simultaneous determination of Cu and Pb has been developed in this paper.Cu（Ⅱ） and Pb（Ⅱ） ions were reacted with ABEDTA to form complex to achieve an ideal sensitivity of heavy metal complexes.The digestion solution of Rhizoma coptidis drug sample was purified by neutral Al₂O₃ column chromatography and the chromatographic behavior of metal-L complexes was investigated.The calibration curve was linear in the range of 5-60μg/mL for Cu²⁺ and 5-25μg/mL for Pb²⁺ with the correlation coefficients 0.9970 and 0.9972 for each（n = 5）.The average recoveries were 86.2%for Pb and 90.1%for Cu,while the relative standard deviations were 5.1%and 3.6%respectively.The method was successfully applied to determine Cu and Pb in R.coptidis drug samples.     

波长对Ag/TiO2催化剂上二氧化碳光催化还原的影响

Photocatalytic reduction of CO2 by water was performed in the presence of a Ag/TiO2 catalyst under illumination by lamps with different wavelengths(254,365,and 400 nm).The yields of the main products(methane and methanol)were higher with the 254 nm lamp than with the 365 lamp while no products were observed with the 400 nm lamp.This was because the electron-hole generation rate increased with increasing energy of irradiation(decreasing wavelength)and there were higher densities of electron states at higher energies in TiO2. The increased efficiency of electron-hole generation with a shorter wavelength irradiation increased the efficiency of the catalyst.The energy of the electrons excited by visible light(400 nm)was too low for CO2 photocatalytic reduction.     

Characterization and catalytic performance of CeO2-Co/SiO2 catalyst for Fischer-Tropsch synthesis using nitrogen-diluted synthesis gas over a laboratory scale fixed-bed reactor

The surface species of CO hydrogenation on CeO2-Co/SiO2 catalyst were investigated using the techniques of temperature programmed reaction and transient response method. The results indicated that the formation of H2O and CO2 was the competitive reaction for the surface oxygen species, CH4 was produced via the hydrogenation of carbon species step by step, and C2 products were formed by the polymerization of surface-active carbon species （-CH2-）. Hydrogen assisted the dissociation of CO. The hydrogenation of surface carbon species was the rate-limiting step in the hydrogenation of CO over CeO2-Co/SiO2 catalyst. The investigation of total pressure, gas hourly space velocity （GHSV）, and product distribution using nitrogen-rich synthesis gas as feedstock over a laboratory scale fixed-bed reactor indicated that total pressure and GHSV had a significant effect on the catalytic performance of CeO2-Co/SiO2 catalyst. The removal of heat and control of the reaction temperature were extremely critical steps, which required lower GHSV and appropriate CO conversion to avoid the deactivation of the catalyst. The feedstock of nitrogen-rich synthesis gas was favorable to increase the conversion of CO, but there was a shift of product distribution toward the light hydrocarbon. The nitrogen-rich synthesis gas was feasible for F-T synthesis for the utilization of remote natural gas.     

Determination of eugenol and isoeugenol in aquaculture water by ultra performance liquid chromatography coupled with quadrupole time-of-flight mass spectrometryEI北大核心CSCD

An analytical method was established for the determination of eugenol and isoeugenol in aquaculture water by ultra performance liquid chromatography coupled with quadrupole time-of-flight mass spectrometry UPLC-Q-TOF-MS. Water samples were derivatized with dansyl chloride. The derivatization products were separated on a ThermoAccucore C18 column100 mm×2.1 mm2.6 μµm under gradient elution condition utilizing acetonitrile and 0.1% formic acid as mobile phases. Q-TOF-MS operating in mass data using alternating collision cell energyMSEmode with positive electrospray ionization was used for the identification of analytes. The results showed that the calibration curves for eugenol and isoeugenol were linear in the range of 0.1-20 μµg/L with the correlation coefficientsrhigher than 0.995. Their recoveries in aquaculture water were 83.2%-102% and 91.8%-104%respectivelywith relative standard deviationsRSDsless than 15%. The limits of detection were 0.02 and 0.05 μµg/L and the limits of quantitation were 0.05 and 0.1 μµg/Lrespectively. The method can be applied to the determination of eugenol and isoeugenol in real water samples. © 2022, Youke Publishing Co.,Ltd. All rights reserved.