[Determination of individual components in finished motor gasoline by dual-channel three-column gas chromatography].

A method based on a dual-channel gas chromatograph equipped with three columns and three detectors was established for the determination of individual components in finished motor gasoline. The gasoline samples were separately introduced into the two injection ports of the chromatograph using two autosamplers. The components of the sample introduced into the first injection port (channel 1) were separated on a nonpolar PONA column (50 m×0.20 mm×0.5 µm) for gasoline analysis and detected by an flame ionization detector (FID). The components of the sample introduced into the second injection port (channel 2) were separated on another PONA column. Oxygenates (e.g., ethers and alcohols), other unconventional and prohibited additives that would co-elute with the hydrocarbons (e.g., methylal, dimethyl carbonate, sec-butyl acetate, and anilines), and some difficult-to-separate hydrocarbon pairs (e.g., 2,3,3-trimethylpentane and toluene) eluted from the PONA column and entered a DM-624 column (30 m×0.25 mm×1.4 µm) to achieve further separation according to the switch timetable using the Deans switch procedure and detected by an FID. The peak of 3-methylpentane, a common component in gasoline samples, also entered the DM-624 column by the Deans switch procedure for calculation purposes. The peak areas of target components on the PONA column in channel 1 were calculated using the peak areas on the DM-624 column as well as those of 3-methylpentane on both the DM-624 and PONA columns in channel 1 with a calibration factor between the two channels. The peak areas of co-eluted components were obtained by subtracting the calculated peak areas of the target components from those of the co-eluted peaks. The mass percentages of the individual components were calculated according to the normalization method using all peak areas on the PONA column in channel 1 with relative response factors. The mass percentages of the oxygenates, anilines, and individual hydrocarbons were determined, and the group-type distribution was calculated according to the carbon number. Separation and quantitation interferences between the additives and hydrocarbons were eliminated using this procedure. Twenty oxygenates and unconventional additives, each with a mass percentage of approximately 3%, were added to a real motor gasoline-92 sample and analyzed using the proposed method. The recoveries of the target components were between 90.1% and 118.2% with relative standard deviations (RSDs) between 0.2% and 5.1% (n=6). The analysis of a real ethanol-gasoline sample showed that the RSDs of contents of most components was less than 3% (n=6). Because the heart-cut of peaks using Deans switch technique requires the precise repeatability of retention times, the retention-time repeatability of components on the PONA column in channel 2 was investigated over an extended period of time after thousands of runs of real-sample analysis. The retention times of the same component in several randomly selected motor gasoline-92 samples varied from 0.01 to 0.03 min, indicating that the proper timetable for the Deans switch remained stable for two years. The precise repeatability of retention times was achieved owing to the high precision of the electric pneumatic control of the chromatograph and the stability of the column used. Real finished motor gasoline samples with different octane numbers (gasoline-92, gasoline-95, and ethanol gasoline-95) were analyzed using the developed method, and the results acquired were consistent with those of standard methods (GB/T 30519-2016, NB/SH/T 0663-2014, and SH/T 0693-2000). If some unconventional additives (such as methylal) were added to gasoline samples, the contents of these unconventional additives could also be detected, which means one run of the proposed method could provide results corresponding to three or four runs of different standard methods. The acquisition of information on the individual components of finished motor gasoline will assist in research on precise gasoline blending.

Optically Controlled Nano-Transducers Based on Cleaved Superlattices for Monitoring Gigahertz Surface Acoustic Vibrations.

Surface acoustic waves (SAWs) convey energy at subwavelength depths along surfaces. Using interdigital transducers (IDTs) and opto-acousto-optic transducers (OAOTs), researchers have harnessed coherent SAWs with nanosecond periods and micrometer localization depth for various applications. These applications include the sensing of small amount of materials deposited on surfaces, assessing surface roughness and defects, signal processing, light manipulation, charge carrier and exciton transportation, and the study of fundamental interactions with thermal phonons, photons, magnons, and more. However, the utilization of cutting-edge OAOTs produced through surface nanopatterning techniques has set the upper limit for coherent SAW frequencies below 100 GHz, constrained by factors such as the quality and pitch of the surface nanopattern, not to mention the electronic bandwidth limitations of the IDTs. In this context, unconventional optically controlled nanotransducers based on cleaved superlattices (SLs) are here presented as an alternative solution. To demonstrate their viability, we conducted proof-of-concept experiments using ultrafast lasers in a pump-probe configuration on SLs made of alternating AlxGa1-xAs and AlyGa1-yAs layers with approximately 70 nm periodicity and cleaved along their growth direction to produce a periodic nanostructured surface. The acoustic vibrations, generated and detected by laser beams incident on the cleaved surface, span a range from 40 to 70 GHz, corresponding to the generalized surface Rayleigh mode and bulk modes within the dispersion relation. This exploration shows that, in addition to SAWs, cleaved SLs offer the potential to observe surface-skimming longitudinal and transverse acoustic waves at GHz frequencies. This proof-of-concept demonstration below 100 GHz in nanoacoustics using such an unconventional platform might be useful for realizing sub-THz to THz coherent surface acoustic vibrations in the future, as SLs can be epitaxially grown with atomic-scale layer width and quality.

Experimental and Theoretical Insights into the Effect of Dioldibenzoate Isomers on the Performance of Polypropylene Catalysts.

Experimental investigations and density functional theory (DFT) calculations were carried out to study the comprehensive effect of different 3,5-heptanedioldibenzoate (HDDB) optical isomers as the internal electron donor on the catalytic performance of Ziegler-Natta catalysts. The experimental catalytic activity of HDDB has a positive correlation with the relative content of the mesomer incorporated during catalyst preparation, while the hydrogen response of HDDB displayed a negative correlation with the relative content of the mesomer. In order to apply the DFT calculation results to the macroscopic activity of the catalyst, the content of the active centers of the catalyst was analyzed. Assuming that the content of the active centers is proportional to the internal electron donor content of the catalyst, binary linear regression was carried out, which showed a good linear correlation between experimental activity data and internal electron donor content. Furthermore, the fitted activity of the single active centers aligned well with the calculated activation energies. These results revealed that the catalytic activity of polypropylene (PP) catalysts is dependent on both the active center content and the catalytic activity of an individual active center. Additionally, the lower hydrogen response of HDDB leads to a higher molecular weight of polypropylene obtained from the RS-containing catalyst compared to the SS-containing catalyst. Further study reveals that the hydrogen transfer reactions of 2,4-pentanediol dibenzoate (PDDB)/HDDB are influenced by the orientation of the methyl/ethyl groups in different isomers, which affect the activation energy differences between the hydrogen transfer reaction and the propylene insertion reaction, and finally influence the molecular weight of PP.

Coherent Phonons in van der Waals MoSe2/WSe2 Heterobilayers.

The increasing role of two-dimensional (2D) devices requires the development of new techniques for ultrafast control of physical properties in 2D van der Waals (vdW) nanolayers. A special feature of heterobilayers assembled from vdW monolayers is femtosecond separation of photoexcited electrons and holes between the neighboring layers, resulting in the formation of Coulomb force. Using laser pulses, we generate a 0.8 THz coherent breathing mode in MoSe2/WSe2 heterobilayers, which modulates the thickness of the heterobilayer and should modulate the photogenerated electric field in the vdW gap. While the phonon frequency and decay time are independent of the stacking angle between the MoSe2 and WSe2 monolayers, the amplitude decreases at intermediate angles, which is explained by a decrease in the photogenerated electric field between the layers. The modulation of the vdW gap by coherent phonons enables a new technology for the generation of THz radiation in 2D nanodevices with vdW heterobilayers.

Predictive Value of a Quick Pitt Bacteremia Score for Prognosis of Patients with Bloodstream Infection Secondary to Urinary Tract Infection: A Retrospective Cohort Study.

Purpose: To analyze the effect of a quick Pitt bacteremia score (qpitt) on the prognosis of patients with bloodstream infection (BSI) secondary to urinary tract infection (UTI) and to further explore its use in aiding appropriate selection of initial antibiotic treatment. Methods: Medical records of patients with BSIs secondary to UTIs who were admitted to our hospital from January 2018 to December 2020 were retrospectively collected. To screen for independent risk factors, logistic analysis was conducted on statistically significant variables. The receiver operating characteristic (ROC) curve was drawn with prognosis and death as the state variables to evaluate the predictive value. Patients were grouped by qpitt 2-point cutoff, to explore the impact of initial antimicrobial treatment regimens on poor prognosis and death in different subgroups. Poor prognosis was defined as a hospital length of stay (HLOS) ≥14 days or death within 28 days from BSI onset (ie, 28-day death). Results: A total of 266 patients were included in this study. In BSIs secondary to UTIs, we observed a pathogenic composition of 77.44% Gram-negative bacteria, 19.55% Gram-positive bacteria, and 3.01% fungi. The qpitt had poor predictive value for poor prognosis [area under ROC (AUROC) = 0.653, p < 0.001], while it had a high predictive value for death (AUROC = 0.890, p < 0.001). For patients with a qpitt ≥2, the poor prognosis and death rates of patients who were initially treated with carbapenem antibiotics were lower (p < 0.01). In comparison, initial treatment with carbapenem antibiotics had no significant effect on prognosis and death rates in patients with qpitt <2 (p > 0.1). Conclusion: The qpitt is highly predictive for death in patients with BSIs secondary to UTIs and can be used to inform first-line antibiotic treatment strategy.

Determination of trace organic chlorides in hydrogen for fuel cell vehicles by gas chromatography coupled with ion mobility spectrometry.

A method for the determination of organic chlorides in hydrogen for fuel cell vehicles by gas chromatography coupled with ion mobility spectrometry was established. Organic chlorides were separated by a non-polar gas chromatography column and detected in the negative ion mode of the ion mobility spectrometer. The effect of operating parameters of ion mobility spectrometer including drift gas flow rate and drift tube temperature on sensitivity and resolution were evaluated. Under the optimized conditions, the detection limits of seven organic chlorides were from 0.65 to 6.73 nmol/mol, which met the requirement of detection for the specification limit of 50 nmol/mol of total halogen impurities in hydrogen for fuel cell vehicles. Compared with gas chromatography-mass spectrometry, and gas chromatography coupled with electron capture detector under the same gas chromatography conditions, gas chromatography coupled with ion mobility spectrometry method demonstrated higher sensitivity for detection of organic chlorides under study. Based on the portability of the device and its detection capabilities, gas chromatography coupled with ion mobility spectrometry has the potential to perform online detection of impurities in hydrogen for fuel cell vehicles.

Application of Chlorine Dioxide in Cell Surface Modification to Enhance Its Mechanical Stability and Metal Ion Adsorption.

There has been a trend toward the use of microorganisms as the biomaterial for removing dyes and metals from wastewater. However, native microorganism cells have low mechanical stability, which limit their further application in industries. In this study, chlorine dioxide (ClO2), a high-efficiency, low-toxicity, and environmentally benign disinfectant, was used for microorganism surface modification to enhance the mechanical stability and metal ion adsorption of the cell. ClO2 can either modify cell walls to improve their metal adsorption capacity or modify cell membranes to improve their mechanical stability. Fourier-transform infrared spectroscopy analysis indicated that several cell surface groups were involved in the cell wall modification of Bacillus sp. Microscopic observation indicated that ClO2 treatment could deter cell membranes from forming vesicles in sodium hydroxide (NaOH) aqueous solution, and freeze-etching showed that ClO2 treatment could alter the erythrocyte membrane proteins which might also contribute to improving the cell stability. The experimental results on Bacillus sp., Pseudomonas aeruginosa, and Mucor rouxii show that ClO2 treatment may increase, or at least not reduce, the ability of microbial cells to adsorb heavy metals, but it can significantly improve the resistance of these cells to NaOH cleavage. It seems ClO2 is a promising auxiliary for biosorption of heavy-metal ions.

Dynamic optical arbitrary waveform generation with amplitude controlled by interference of two FBG arrays.

In this paper, a novel structure of dynamic optical arbitrary waveform generation (O-AWG) with amplitude controlled by interference of two fiber Bragg grating (FBG) arrays is proposed. The FBG array consists of several FBGs and fiber stretchers (FSs). The amplitude is controlled by FSs through interference of two FBG arrays. The phase is controlled by FSs simultaneously. As a result, optical pulse trains with various waveforms as well as pulse trains with nonuniform pulse intensity, pulse spacing and pulse width in each period are obtained via FSs adjustment to change the phase shift of signal in each array.

[Bactericidal effects of chlorine dioxide by respiratory inhibition].

OBJECTIVE: Chlorine dioxide (ClO2) is a highly effective disinfectant for food and potable water treatment. However, knowledge on its action mechanism remains unexplored. The present study aims to determine the role of respiratory inhibition in the bactericidal effects of ClO2. METHODS: Transmission electron microscopy was used to observe the ultra structural alteration of the mitochondrion. Fluorescence-based flow cytometry analysis was employed to determine the disruption of mitochondrion membrane potential. Respiratory inhibition was detected by measuring the oxygen consumption. The results obtained were compared with those of plate counting. RESULTS: No visible physiological alteration in the shapes and structures of the mitochondria was found. The rate of collapse in mitochondrial membrane potential increased with the death rate, but the respiratory inhibition rates were always significantly lower than the death rates. The death rates detected by the aerobic and anaerobic methods did not differ significantly. CONCLUSION: ClO2-induced damages to the mitochondria were positive correlated with the death rates, but respiratory inhibition was not the primary target site for cell killing.

[Application of gas chromatography in research of biodiesel processing].

Applications of gas chromatography in the research of biodiesel processing are reviewed with 27 references, including the analysis of fatty acid methyl esters (FAME) in the reaction products and final biodiesel, the determination of mono-, di- and tri-glycerides, the contents and distribution of free fatty acids, and the determination of trace methanol in biodiesel. The effects of various factors for analysis of the reaction products are discussed, such as injection mode, column type and silylation. A method for the determination of trace methanol in biodiesel products with dual-columns and pressure backflush system is proposed. 1-Propanol was used as the internal standard. After methanol and 1-propanol entered the analytical column through pre-column, the pressure was changed to backflush the heavy components through the split vent. A polar PEG-20M column was applied for the analysis of the contents and distribution of FAME in biodiesels from 8 different vegetable oils.

[Analyses of gasoline range hydrocarbons by gas chromatography].

Analyses of gasoline range hydrocarbons by gas chromatography are reviewed with 66 references. Methods of high resolution capillary gas chromatography, multidimensional gas chromatography, and gas chromatography with atomic emission detection after bromination are summarized respectively. The advantages and limitations of each method are discussed and solutions for some existing problems are proposed.

[Alkene bromination used for detailed hydrocarbon and bulk hydrocarbon group-type analysis of gasolines containing alkenes].

The optimized reaction conditions of selective alkene bromination for gasolines containing aromatics and saturated hydrocarbons are presented. By this way, the interfering problem in alkene determination from coeluting saturated hydrocarbons has been solved. So the detailed hydrocarbon analysis can be improved by a simple system containing polar and non-polar columns or by a gas chromatograph coupled with an atomic emission detector (GC-AED). Under the optimized conditions, it was found that the alkene compounds were selectively and completely brominated but the aromatics and alkane compounds were remained unaffected. A simple treatment, 90 s-120 s for reaction and 10 s-20 s for removing the excess bromine, can be easily realized. The treatment is applied for the different types of gasoline containing 0-100% alkene. Besides, one of the most important applications of this treatment is to analyse the hydrocarbons in detail from the fluid catalytic cracking (FCC) gasoline. The samples in these cases may not be accurately analyzed when using the traditional method of hydrocarbon analysis because of the presence of coeluted interfering olefins above C7.