Gas Chromatographic Technique Research Articles

A systematic derivatization technique for characterization of ethoxylates by GC and GCMS

AbstractEthoxylation is one of the common industrial process in which ethylene oxide (EO) is added to compounds containing active hydrogen atom (OH, COOH, SH, NH, etc.) to form surfactants. Alcohol ethoxylates are a major class of non‐ionic surfactants composed of an alkyl chain combined with few EO units. They are widely used in homecare products, personal care products, textiles, oilfield, construction, lubricants, food, paper, leather. The analysis of these ethoxylates possess several challenges since they contain ‘n’ number of EO units (n > 1). With increase in “n,” the product becomes more and more viscous and the boiling point increases making it difficult to analyze by normal gas chromatography (GC) technique. This paper describes a method of derivatizing these ethoxylates so that they can be eluted on a high temperature GC. BSTFA (N, O‐bis (trimethylsilyl) trifluoroacetamide) is used as the derivatizing agent (silylating agent). The ethoxylate combines with BSTFA to form the corresponding trimethylsilylated (TMS) product, which have comparatively lower boiling point. Thus, we detect trimethyl silyl product, which is the resemblance for the ethoxylated product. In this paper, we present a quantitative GC method for the ethoxylates of a few simple alcohols (2‐ethyl hexanol, glycerin), and complex vegetable oils (castor oil). The products formed during the reaction have also been identified on a gas chromatograph coupled with mass spectrometer (GCMS). GCMS shows the mass corresponding to the TMS derivatized product. The derivatization technique not only helps in increasing the volatility of these compounds but also improves the chromatographic efficiency, selectivity, and enhances the detectability.

Black Truffle Aroma Evaluation: SPME-GC-MS vs. Sensory Experts.

Nowadays, the truffle aroma attribute is not included as a quality parameter in the current recommendation that explains the truffle quality (UNECE standard 53 FFV3) and establishes the truffle commercial categories. However, the aroma is the main reason why truffles are worldwide appreciated. Indeed, more than 30 aromatic molecules compose it, and this is the reason why the human evaluation and identification of these odorants, without previous training, is quite subjective. Analytical techniques such as gas chromatography techniques, however, can establish an aromatic profile and detect potential aromatic markers. In this study, 16 tasting experts were trained to make more objective the truffle aroma evaluation and odorants identification. For this, a comparison between solid-phase microextraction gas chromatography coupled with mass spectrometry (SPME-GC-MS) and sensory expert evaluation was carried out in six sessions during different harvesting times in the black truffle season (December, January, and February). Both techniques were able to separate truffles depending on the harvesting time. Also, a list of volatile organic compounds related to the aromatic attributes was reported. This information will help to provide a more objective T. melanosporum truffle sensory evaluation.

Low-Cost Sensor System for Air Purification Process Evaluation.

With the development of civilisation, the awareness of the impact of versatile aerosol particles on human health and the environment is growing. New advanced materials and techniques are needed to purify the air to reduce this impact. This brings the necessity of fast and low-cost devices to evaluate the air quality from particulate and gaseous impurities, especially in a place where gas chromatography (GC) techniques are unavailable. Small portable and low-cost systems may work separately or be incorporated into devices responsible for air-cleaning processes, such as filters, smoke adsorbers, or plasma air cleaners. Given the above, this study proposes utilising a self-assembled low-cost system to evaluate air quality, which can be used in many outdoor and indoor applications. ESP32 boards with the wireless communication protocol ESP-NOW were used as the framework of the system. The concentration of aerosol particles was measured using Alphasense sensors. The concentrations of the following gases were measured: NO2, SO2, O3, CO, CO2, and H2S. The system was used to evaluate the quality of air containing tobacco smoke after passing through an actual DBD plasma reactor where the purification occurred. A high amount of reduction in aerosol particles and a reduction in the SO2 concentration were detected. An increase in the NO2 concentration was seen as an undesirable effect. The aerosol particle measurements were compared with those using a professional device (GRIMM, Hamburg, Germany), which showed the same trends in aerosol particle behaviour. The obtained results are auspicious and are a step towards producing a low-cost, efficient system for evaluating air quality as well as indoor and outdoor conditions.

Characterization of chemical composition of high viscosity heavy oils: Macroscopic properties, and semi-quantitative analysis of molecular composition using high-resolution mass spectrometry

Heavy oil is an important resource in current petroleum exploitation, and the chemical composition information of heavy oil is crucial for revealing its viscosity-inducing mechanism and solving practical exploitation issues. In this study, the techniques of high-temperature gas chromatography and high-resolution mass spectrometry equipped with an electrospray ionization source were applied to reveal the chemical composition of typical heavy oils from western, central, and eastern China. The results indicate that these heavy oils display significant variations in their bulk properties, with initial boiling points all above 200 °C. Utilizing pre-treatment and ESI high-resolution mass spectrometry, an analysis of the molecular composition of saturated hydrocarbons, aromatic hydrocarbons, acidic oxygen compounds, sulfur compounds, basic nitrogen compounds, and neutral nitrogen compounds within the heavy oil was conducted. Ultimately, a semi-quantitative analysis of the molecular composition of the heavy oil was achieved by integrating the elemental content. The semi-quantitative analysis results of Shengli-J8 heavy oil and a conventional Shengli crude oil show that Shengli-J8 heavy oil lacks alkanes and low molecular weight aromatic hydrocarbons, which contributes to its high viscosity. Additionally, characteristic molecular sets for different heavy oils were identified based on the semi-quantitative analysis of molecular composition. The semi-quantitative analysis of molecular composition in heavy oils may provide valuable reference data for establishing theoretical models on the viscosity-inducing mechanism in heavy oils and designing viscosity-reducing agents for heavy oil exploitation.

Qingxiangxing Baijiu sensory quality grade classification by 1H NMR and GC combined with multivariate statistical analysis

The traditional uniform artificial sensory evaluation makes it difficult to standardize the classification of different sensory quality grades of Baijiu. In this study, a total of 92 authentic Qingxiangxing Baijiu samples with 3 sensory quality grades were carefully collected. Gas chromatography (GC) was used to determine 46 main flavor components and proton nuclear magnetic resonance (1H NMR) spectroscopy was employed to obtain hydrogen atom characteristic information of organic compounds. The principal component analysis (PCA), k-nearest neighbor (KNN) and linear discriminant analysis (LDA) models were conducted and fully validated by internal leave-one-out cross validation (LOOCV) and external repeated double random cross validation (RDRCV). The sensory quality grades of Qingxiangxing Baijiu were effectively classified by using GC and 1H NMR techniques coupled with PCA/KNN analysis with the averaged accuracy higher than 80%. In addition, synthetic minority oversampling technique (SMOTE) algorithm was successfully used to address the model overfitting problem caused by an unbalanced sample composition. This study demonstrated that 1H NMR and GC combined with multivariate statistical analysis were effective for sensory quality classification of Qingxiangxing Baijiu.

Isolation of Geranyl Acetate and Chemical Analysis of the Essential Oil from Melaleuca armillaris (Sol. ex Gaertn.) Sm.

A method was developed for the isolation of geranyl acetate from the crude essential oil (EO) of Melaleuca armillaris (Sol. ex Gaertn.) Sm. leaves, and the purity of the isolated compound was analyzed by GC/MS spectral and NMR analysis and was found to have high purity (98.9%). In addition, the EO isolated presented 0.907 g/cm3, 1.474 and [α]D20=−17.6 of density, refraction index and optical rotation, respectively. The chemical composition of the EO obtained for steam distillation from M. armillaris was analyzed by gas chromatographic and spectroscopic techniques (GC/MS and GC/FID). Thirty-eight compounds were identified, representing 99.92% of the total EO analyzed on a DB-5 ms (5% phenylmethylpolysiloxane) capillary column. This analysis showed that the EO consisted mainly of oxygenated monoterpenes (77.01%), followed by monoterpene hydrocarbons (21.31%) and sesquiterpene hydrocarbons (1.31%). Furthermore, the essential oil of M. armillaris was rich in 1,8-cineol (67 ± 2%), followed by limonene (10 ± 1%), α-Terpineol (9 ± 1%) and α-Pinene (5 ± 1%). Finally, the results suggest that the geranyl acetate isolated with high purity from crude essential oil is recommended to be explored as a component in medicinal or industrial use.

Chemical composition and antimicrobial activity of essential oil of Alpinia menghaiensis S.Q. Tong & Y.M. Xia in S.Q. Tong from Vietnam

The chemical constituents and antimicrobial activity of the essential oil isolated from the rhizomes of Alpinia menghaiensis S.Q. Tong & Y.M. Xia in S.Q. Tong from Vietnam was studied and reported. The techniques of gas chromatography (GC) and gas chromatography coupled with mass spectrometry (GC/MS) were used to characterize the chemical constituents of the essential oil while the microdilution assay was used to evaluate the antimicrobial activity. The main compounds identified in the rhizome essential oil consist of β-pinene (46.5%), β-phellandrene (25.7%) and α-pinene (8.5%). The studied essential oil inhibited the growth of Pseudomonas aeruginosa ATCC27853 with minimum inhibitory concentrations (MIC) value of 15.32 μg/mL ±0.01, and median inhibitory concentration (IC50) value of 32.0 ±0.01 μg/mL. The essential oil also displayed activity against Staphylococcus aureus ATCC25923 (MIC 31.57 ±0.01 μg/mL) and Bacillus cereus ATCC14579 (MIC, 34.21 μg/mL ±0.01 μg/mL), and IC50 value of 64.0 ±0.01 μg/mL. This is the first report on the rhizome oil composition, as well as the antimicrobial of essential oils from A. menghaiensis. The paper discusses further the comparative analysis of essential oils from A. menghaiensis.

Inhibitory Properties of Polyphenolic Phytochemicals of Cola nitida on Carbohydrate Hydrolyzing Enzymes of Wistar Rat In-Vivo

Polyphenolic phytochemicals of Cola nitida, with their potential therapeutic ability can modulate metabolic and transcriptional expression of proteins and enzymatic activities that culminate to hyperglyceamic effects. This study investigated the hyperglyceamic effects of polyphenolic phytochemical extracts of Cola nitida in Wistar rat in-vivo and established a parallel inhibition of the enzymes (α-amylase and α-glucosidase) in their activities as the concentration increased. On administration of the extracts, the activity of α-amylase was inhibited from control, 32 ± 0.00 to 16 ± 0.02u/L as the concentration increased. Also, the activity of α- glucosidase was inhibited from 17 ± 0.01 to 10 ± 0.00u/L in relation to the concentration of the extracts. The inhibitory effect of Cola nitida on carbohydrate hydrolyzing enzymes delayed glucose utilization resulting to elevated glucose concentration from 6.07 ± 0.02 to 9.11 ± 0.01 mMol/L. The composition of the polyphenolic phytochemicals in the Cola nitida analyzed with gas chromatographic techniques was found to contain; apigenin, 6.0 ± 0.01; catechin, 7.1± 0.01; epicatechin, 4.8 ± 0.02; narigenin, 4.9 ± 0.10 mg/100mg and these are the active ingredients of the bioactive compounds that are responsible for the hyperglyceamic effects of Cola nitida.

Appraising separation performance of MOF-808-based adsorbents for light olefins and paraffins

The development and design of efficient olefin/paraffin separation processes requires an understanding of the physicochemical properties of the adsorbent for target gas components. This paper presents experimental assessment of the adsorption characteristics of pristine and modified MOF-808s for ethane, ethene, propane and propene gases. The modification of MOF-808s was carried out using a post-synthesis approach, involving the use of two distinct types of ligands and subsequent addition of Cu metal. The pulse inverse gas chromatography technique at infinite dilution was employed to determine adsorption properties, including Henry's adsorption constants, adsorption enthalpies and entropies of the synthesized MOFs. The highest olefin/paraffin selectivity at 1 bar was identified in MOF-808-His-Cu, with selectivity values of 15.7 for ethene/ethane at 30 °C and 26.2 for propene/propane at 50 °C. This notable selectivity is probably attributable to the formation of π complexes between the olefin and Cu atoms present in the adsorbent. This is evidenced by the distinctive asymmetric chromatogram peak with a long tail, which aligns with their adsorption isotherm concavity. Depending on the molecule and the MOF-808 variant, different isotherm shapes and adsorption capacities were obtained.

Essential oils of Lauraceae: antimicrobial activity and constituents of essential oil from two Machilus species from Vietnam

The chemical constituents and antimicrobial activity of the essential oils isolated from the leaves of Machilus cicatricosa S.K. Lee and Machilus bonii Lecomte from Vietnam were studied and reported. The techniques of gas chromatography (GC) and gas chromatography coupled with mass spectrometry (GC-MS) were used to characterize the chemical constituents of the essential oil while the microdilution assay was used to evaluate the antimicrobial activity. The main constituents of the leaf oil of M. cicatricosa were α-pinene (20.6%), bicyclogermacrene (15.2%), linalool (14.9%), and β-pinene (8.4%). On the other hand (E)-β-ocimene (26.3%), bicyclogermacrene (23.6%) and (E)-nerolidol (9.1%) were the major constituents of M. bonii leaf essential oil. The studied essential oils displayed antimicrobial activity against Enterococcus faecalis ATCC 29212, and Staphylococcus aureus ATCC 25923, with minimum inhibitory concentration (MIC) value of 64.0 μg/mL. In addition, essential oil from the leaf of M. bonii was the most active towards Bacillus cereus ATCC14579 with MIC value of 64.0 μg/mL, while M. cicatricosa showed stronger anti-candidal activity against Candida albicans ATCC 10231 with MIC value of 32.0 μg/mL. This is the first report on the chemical constituents and antimicrobial activity of the essential oils of M. cicatricosa and M. bonii.

The Essential Oil of Balsamorhiza sagittata from Southwestern Idaho: Chemical Composition and Enantiomeric Distribution

Background/Objective: Arrowleaf balsamroot ( Balsamorhiza sagittata (Pursh) Nutt., Asteraceae) is a conspicuous forb growing in open hillsides and prairies at mid to upper elevations in the Intermountain West and Rocky Mountain regions. The plant is important forage for deer and elk and several Native American tribes used arrowleaf balsamroot as food and medicine. The volatile phytochemicals of B. sagittata have not been previously examined. Methods/Results: Nine individual samples of B. sagittata were collected, the essential oils obtained by hydrodistillation using a Likens-Nickerson apparatus in yields of 0.069-0.956%, and the essential oils analyzed by gas chromatographic techniques (GC-MS, GC-FID, and chiral GC-MS). The major components in the leaf essential oil of B. sagittata were (−)-germacrene D (10.8-34.5%), (+)-β-phellandrene (6.4-19.4%), (−)-( E)-β-caryophyllene (1.4-15.0%), and ( E)-β-ocimene (3.1-8.4%). Conclusion: There was modest variation in composition or yield with respect to geographical location or elevation in the samples from southwestern Idaho, but comparison with essential oils from locations outside of Idaho should more completely define the volatile phytochemistry of this plant.

Discriminating the leaves of Ocimum sanctum Linn. conferring to their age by gas chromatographic fingerprint analysis assisted with multivariate analysis

Ocimum species is having massive variations in their chemical composition that includes day time, terrestrial and cyclical variation according to the season etc. In this study, variation in overall essential oil constituents among matured, intermediate and young leaf samples of O. sanctum was studied. The leaf samples according to their age- matured, intermediate and young leaves were collected from three different plants at 11 a.m. each. Extract of collected leaf samples were then scrutinized using gas chromatographic technique having flame ionization detector (GC-FID). Result reveals that the noteworthy variance was observed in overall essential oil constituents of the leaf samples according to their age. The Average chromatographic fingerprint data of triplicate run for different leaf samples were then treated to multivariate methods such as hierarchical cluster analysis and principal component analysis. In this study, instead of considering one or two biomarkers, we have exasperated to obtain as many constituents in chloroform extracts of chosen leaf samples. Scree plot reveals that nine components were responsible for the whole variation. Score plot and dendogram efficiently discriminated all the three leaf types according to their age in different clusters. The outcome as an inference was, O. sanctum leaves according to their age exhibit variation in its chemical composition and developed tool can be used for routine quality control.

CHEMICAL COMPOSITION OF EXTRACTS AND ESSENTIAL OILS OBTAINED FROM COMMON JUNIPER (JUNIPERUS COMMUNIS L.) IN AZERBAIJAN

Juniperus communis L. (common juniper) is a widespread plant species in the Western region of Azerbaijan. The dependence of the composition and content of various biologically active substances in juniper on natural climatic conditions was studied. The results of the study of the substances obtained from the extraction of leaves and branches in ethanol were presented. The composition of volatile compounds was studied by the gas chromatography technique. In all samples, monoterpene hydrocarbons always predominated with percentages higher than 70% (from 71.12% for the plant material collected in August to 74.38% for those in September), followed in similar quantities by oxygenated monoterpenes or sesquiterpene hydrocarbons with values between 10.45% and 12.77% and between 10.50% and 12.72%, respectively. Ascorbic acid content varying from 33.1 to 123.2 mg/100 g was also determined. The investigation of the yield of essential oils in different months of the year showed that its amount varies depending on the season (3.5-4.4% of the mass of dry raw materials).

Effects of syngas and methanol fuel substitution on ammonia counterflow diffusion flames

Ammonia (NH3) is increasingly recognized as a promising alternative fuel. Various blending options have been proposed that are aimed at improving its flammability and applicability across diverse energy systems. This study conducts a comprehensive investigation, employing both experimental and numerical approaches, to understand the impact of blending ammonia with CH3OH or syngas, at various H2:CO ratios, on flame extinction limits, structure, and NOx emissions in counterflow laminar diffusion flames. Concentration profiles of ammonia and intermediate species (O2, CO, CO2, H2, NO, and N2O) were measured using Fourier-transformed infrared (FTIR) and gas chromatographic (GC) techniques. The findings indicate that increasing the H2:CO ratio in syngas-blended flames increases the extinction limits and reduces NO and N2O emissions. Compared with ammonia/methanol flames the ammonia/syngas flames exhibit higher extinction limits, flame temperatures, and lower NO and N2O emissions. Multiple kinetic models were found to underestimate the extinction strain limits, with Wang et al.’s 2021 model offering the closest predictions. Notably, discrepancies in ammonia dissociation and oxygen leakage to the rich side of stoichiometry impact reaction zone characteristics, extinction limits, and NOx predictions. Further kinetic analyses reveal that reactivity in syngas-blended flames is dominated by heat and radicals-producing reactions, while methanol-blended flames are sensitive to reactions involving ammonia fragments, resulting in decreased reactivity compared to syngas-blended flames. The results and findings from this study yield valuable insights into optimizing ammonia blends for enhanced flame stability and reduced emissions across various energy applications. It also provides data for chemical kinetics model validation in non-premixed diffusion environment where both species chemistry and transport are encountered.

Evaluation of Lipids for the Study of Photosynthetic Membranes.

The biological role of lipids goes far beyond the formation of a structural membrane bilayer platform for membrane proteins and controlling fluxes across the membranes. For example, in photosynthetic thylakoid membranes, lipids occupy well-defined binding niches within protein complexes and determine the structural organization of membrane proteins and their function by controlling generic physicochemical membrane properties. In this chapter, two-dimensional thin-layer chromatography (2D TLC) and gas chromatography (GC) techniques are presented for quantitative analysis of lipid classes and fatty acids in thylakoid membranes. In addition, lipid extraction methods from isolated thylakoid membranes and leaves are described together with a procedure for the derivatization of fatty acids to fatty acid methyl esters (FAME) that is required for GC analysis.

Bioremediation of Engine Oil-Contaminated Soil using Selected Indigenous Moulds

The polycyclic aromatic hydrocarbons (PAHs) utilizing the potential of moulds from engine oil-polluted soils were assessed. These PAHs are known to be toxic, mutagenic and carcinogenic in the environment. Consequently, the study aims to evaluate the potential of indigenous moulds from engine oil in the remediation of contaminated soil. Samples were collected from engine oil-polluted soils from Samonda, Ibadan, Oyo State Nigeria. The ability of four potential indigenous moulds to degrade the PAH fraction of the engine oil-polluted soil sample was assessed using the gas chromatography technique. Four moulds were identified based on their cultural and microscopic characteristics and were confirmed as Aspergillus flavus, Aspergillus parasiticus, Aspergillus oryzae and Aspergillus nidulans. The highest biodegradation potential was observed in treated soil sample containing Aspergillus flavus (55.15%) followed by Aspergillus parasiticus (55.00%), Aspergillus oryzae (44.51%) and the least biodegradation potential was observed in the sample containing Aspergillus nidulans (24.16%) after 60 days of treatment. This study revealed that indigenous mould has the ability to utilize toxic fractions of petroleum products as their sole carbon sources therefore are the major bio-remediating agents in the sampling area.

Analisis Lipid Mikroalga Tetraselmi Chuii Dan Chlorella Vulgaris Sebagai Antioksidan

Microalgae have received attention as potential sources of bioactive compounds, especially lipids with antioxidant activity. This research aims to analyze the lipid content of the microalgae Tetraselmi Chuii and Chlorella Vulgaris and unlock their potential as antioxidant agents. The extraction method uses organic solvents namely olive oil followed by lipid composition analysis using gas chromatography techniques. Next, the antioxidant test was carried out using the in vitro method using DPPH (1,1-diphenyl-2-picrylhydrazyl). The analysis results show that the microalgae Tetraselmi Chuii and Chlorella Vulgaris contain various types of lipids, including omega-3 and omega-6 fatty acids which are known to have positive effects on health. Antioxidant tests showed that the lipid extracts of both microalgae showed significant antioxidant activity against DPPH free radicals. In particular, lipid compounds from Tetraselmi Chuii showed higher antioxidant effects compared to Chlorella Vulgaris. With antioxidant power of 83.77% and 83.61% respectively.

The Effect of Temperature on the Surface Energetic Properties of Carbon Fibers Using Inverse Gas Chromatography

This paper constitutes an original and new methodology for the determination of the surface properties of carbon fibers in two forms, namely, oxidized and untreated, using the inverse gas chromatography technique at infinite dilution based on the effect of temperature on the surface area of various organic molecules adsorbed on the carbon fibers. The studied thermal effect showed a large deviation from the classical methods or models relative to the new determination of the surface properties of carbon fibers, such as the dispersive component of their surface energy, the free surface energy, the free specific energy, and the enthalpy and entropy of the adsorption of molecules on the carbon fibers. It was highlighted that the variations in the London dispersive surface energy of the carbon fibers as a function of the temperature satisfied excellent linear variations by showing large deviations between the values of γsd (T), calculated using different models, which can reach 300% in the case of the spherical model. All models and chromatographic methods showed that the oxidized carbon fibers gave larger specific free enthalpy of adsorption whatever the adsorbed polar molecules. The obtained specific enthalpy and entropy of the adsorption of the polar solvents led to the determination of the Lewis acid–base constants of the carbon fibers. Different molecular models and chromatographic methods were used to quantify the surface thermodynamic properties of the carbon fibers, and the results were compared with those of the thermal model. The obtained results show that the oxidized carbon fibers gave more specific interaction energy and greater acid–base constants than the untreated carbon fibers, thus highlighting the important role of oxidization in the acid–base of fibers. The determination of the specific acid–base surface energy of the two carbon fibers showed greater values for the oxidized carbon fibers than for the untreated carbon fibers. An important basic character was highlighted for the two studied carbon fibers, which was larger than the acidic character. It was observed that the carbon fibers were 1.4 times more acidic and 2.4 times more basic. The amphoteric character of the oxidized fibers was determined, and it was 1.7 times more important than that of the untreated fibers This tendency was confirmed by all molecular models and chromatographic methods. The Lewis acid and base surface energies of the solid surface, γs+ and γs−, as well as the specific acid–base surface energy γsAB of the carbon fibers at different temperatures were determined. One showed that the specific surface energy γsAB of the oxidized fibers was 1.5 times larger than that of the untreated fibers, confirming the above results obtained on the strong acid–base interactions of the oxidized carbon fibers with the various polar molecules.

Effect of amino functional groups on the surface properties and Lewis's acid base parameters of UiO-66(NH2) by inverse gas chromatography

Amino-functionalized metal organic frameworks (MOFs) have attracted much attention for various applications such as carbon dioxide capture, water remediation and catalysis. The focus of this study is to determine the surface and Lewis's acid-base properties of UiO-66(NH2) crystals by the inverse gas chromatography (IGC) technique at infinite dilution. The latter was applied to evaluate the dispersive component of the surface energy γsd(T) by using thermal model and several molecular models. The obtained results proved that γsd(T) decreases when the temperature increases. The best results were achieved by using the thermal model that takes into account the effect of the temperature on the surface areas of the organic molecules. We also observed a decrease of the Gibbs surface free energy of adsorption by increasing the temperature of the different organic solvents. The polar interactions of UiO-66(NH2) were obtained by using the methods of Saint-Flour Papirer, Donnet et al., Brendlé-Papirer and the different molecular models. The Lewis's acid base constants KA and KD were further calculated by determining the different variables of adsorption of the probes on the solid surface and the obtained values were 1.07 and 0.45 for KA and KD respectively, with an acid-base ratio (KA/KD) of 2.38. These values showed the high acidic surface of the solid substrate; whereas, the values of the entropic acid base parameters, ωA, ωD and ωA/ωD respectively equal to 1.0×10−3, 3.8×10−4 and 2.73, also highlighted the important acidity of UiO-66-(NH2) surface. These important findings suggest that the surface defects (missing linkers and/or clusters) in UiO-66(NH2) are the main determining factor of the acid-base properties of UiO-66 based structures.

High sensitive phosphorene and molecular imprinted polymers electrochemical sensor to determine benzene in oilfield-produced water

A new electrochemical sensor based on a carbon screen-printed electrode (CSPE) modified with phosphorene (BP) and PEDOT:PSS (BP-PEDOT:PSS) and molecularly imprinted polymers (MIPs) composed of poly(o-phenylenediamine) has been developed and applied to determine low benzene concentrations in oilfield-produced water (OPW). Morphological and electrochemical characterization of the sensor confirmed that the CSPE surface was modified with BP-PEDOT:PSS and MIPs. CSPE modification with BP-PEDOT:PSS increased the electrochemical current by 24.8%. Under optimized conditions, the sensor presented analytical curves with two linear ranges from 4.0 × 10−8 to 1.0 × 10−7 mol L−1 and from 2.0 × 10−7 to 1.0 × 10−6 mol L−1. The limit of detection, limit of quantification, and sensitivity were 7.4 × 10−9 mol L−1, 2.3 × 10−8 mol L−1, and 36.4 A L mol−1 (n = 3), respectively. The sensor showed good interday and intraday repeatability, with RSD values of 3.4% and 4.9%, respectively. Its stability was excellent, preserving 90.7% of its initial current after storage at room temperature and in contact with the ambient atmosphere for 15 days. The sensor also displayed excellent selectivity for the benzene molecule in the presence of interferents (o-xylene, m-xylene, phenol, and toluene). The proposed method was validated by comparison using the technique of gas chromatography coupled to flame injection detection (GC-FID) and successfully applied to determine benzene in an OPW sample.