جستجوی مقالات مرتبط با کلیدواژه "gas chromatography" در نشریات گروه "شیمی"

The research presents a comparative analysis of the quality of locally produced groundnut oil (Arachis hypogaea) sold in the north-central zone of Nigeria markets (Benue, Nasarawa, Kogi, Kwara, Niger and Plateau S tates). The aim was to assess and compare the qualities of the oils and to know the safety of human consumption. The groundnut oil produced biodiesel, shampoo lubricants, and soap-making indus tries. The concentrations of the heavy metals were analyzed with atomic absorption spectrometry (AAS). It showed that the lead, zinc, and copper (Pb, Zn, Cu) were within the FAO/WHO recommended limit, while Cd (0.201-0.331 mg kg-1) was above the limit (0.07 mg kg-1). Also, the gas chromatography (GC-FID) results indicated that twelve fatty acids (linoleic > oleic > palmitic > s tearic > lignoceric > arachidic acid > behenic > erucic > arachidonic > margaric > linolenic > palmitoleic) were obtained in the groundnut oils in all markets and fatty acids include caprylic acid, capric acid, lauric acid, and myris tic acid were absent in oils. In addition, the magnitude of six phospholipids (phosphatidylcholine > phosphatidylethanolamine > phosphatidylinositol > phosphatidylserine > phosphatidic acid > lysophosphatidylcholine) were also achieved, respectively. The results showed that iodine, peroxide, saponification value and refractive index were below the FAO/WHO recommended level, and the acid value was higher than the normal range.

The principle of this research is based on the development of multi-residue method by QuEChERS sample preparation follow by gas chromatography with mass spectrometric detection in the selected ion monitoring mode (GC–MS-SIM) for the routine analysis of 42 pesticides in rice samples. The rice samples were initially extracted with acetonitrile, and the targeted pesticides were purified following the dispersive solid phase extraction (d-SPE) cleanup method. The calibration curve for each analyte quantified by matrix-matched calibration was linear over the concentration range of 10.0–1000.0 μg L−1 with a correlation coefficient range between 0.990 and 0.999. Mean recoveries from three replicates ranged from 79% to 112%, with satisfactory precision (RSD<7%). The limit of detection and the limit of quantification were in the range of 3.04–12.52 μg L−1 and 10.14–41.76 μg L−1 respectively, for all 42 pesticides.

Toluene is one of the mos t dangerous and, simultaneously, the mos t consumed subs tances in various factories. Toluene s trongly affects the central nervous sys tem. The numerous side effects caused by exposure to toluene indicate the removal of toluene vapours from the air in the workplace. This s tudy aims to use the removal of toluene vapours from the air using a Fe-MOFs metal-organic subs trate for the firs t time in the world and to inves tigate efficient methods to increase the efficiency of removing toluene vapours from the air. This experimental s tudy was carried out on a laboratory scale. After the iron metal-organic framework (Fe-MOFs) was synthesized, the components affecting the adsorption rate, such as reaction time (5-20 min), initial concentration (100-400 mg L-1), adsorbent amount, and temperature (25-80oC) were analyzed and optimized. Then, the efficiency of removing toluene vapours from the air was determined using a gas chromatography device. The absorption capacity of toluene was obtained by the desired adsorbent, 337.2 mg g-1. Also, the effect of different parameters on toluene absorption was inves tigated and optimized. The maximum absorption for concentration (300 mg L-1), temperature (75oC), and contact time (160s) were obtained as 340 mg g-1, 331 mg g-1, and 325 mg g-1, respectively. The obtained results indicate the suitability of the Fe-MOFs for the absorption of toluene vapours from the air before being determined by gas chromatography (GC-FID).

Polycyclic aromatic hydrocarbons (PAHs) have been listed among the hazardous compounds according to the US environmental protection agency (USEPA) and the world health organization (WHO). Even low concentrations of PAHs have shown serious toxicity, highlighting the necessity of the measurement of these compounds which require highly sensitive and precise methods. In this study, for the first time, a solid phase microextraction (SPME) fiber was fabricated by a highly porous monolithic nanofiber nanocomposite based on polyethersulfone (PES)/multiwalled carbon nanotubes (MWCNTs) and used for direct sampling of indoor air before identification of polycyclic aromatic compounds by gas chromatography-flame ionization detector (GC-FID). A new homemade sampling chamber was also designed to increase the exposure of airborne PAHs to the proposed SPME fiber. The microextraction conditions were optimized. The correlation coefficients and the linear range (LDR) of the compounds ranged from 0.9991 to 0.9996 and from 0.02 to 10 mg/m3, respectively. In addition, the limit of detection (LOD) varied in the range of 0.014-0.032 mg/m3. The relative standard deviation (RSD) for single fiber and fiber to fiber was 2.95 and 5.95%, respectively. This method was successfully applied to measure some PAHs in indoor spaces.

As main air pollutants, volatile organic compounds (VOCs) must be paid special attention. In this study, the removal efficiency of xylene from the air was investigated by nano-activated carbons (NACs) as an efficient adsorbent and compared to commercial activated carbons (ACs). In the chamber, the xylene vapor in pure air was generated, stored in the airbag (5 Li), and moved to adsorbents. Then, the xylene vapor was absorbed on the NAC/AC adsorbents and desorbed from it by a heat accessory. The efficiency of xylene removal with NACs and ACs was investigated in the dynamic and static systems based on 100-700 mg L-1 of xylene, flow rates of 100 ml min-1, and 100 mg of adsorbent at a humidity of 32% (25°C). Xylene concentrations were determined by gas chromatography equipped with a flame ionization detector (GC-FID). In the batch system, the maximum absorption capacity for NACs and ACs was obtained at 205.2 mg g-1 and 116.8 mg g-1, respectively. The mean adsorption efficiency for NACs and ACs adsorbents was obtained at 98.5% and 76.55%, respectively. The RSD% for NACs ranged between 1.1-2.5% in optimized conditions. The characterizations of the NACs adsorbent showed that the particle-size range was between 35-100 nm. The results showed that the adsorption efficiency of NACs for removing xylene from the air was achieved more than ACs. The GC-MS validated the proposed procedure in real air samples.

New Solid-Phase Microextraction (SPME) coating was made by electrodeposition of Zeolite Imidazolate Framework (ZIF-67) nanocrystals with the aid of polyaniline (PANI) on steel fiber. The SPME fiber was used to extract four Polycyclic Aromatic Hydrocarbons (PAHs) from the Head Space (HS) of tea infusions and determined by Gas Chromatography coupled with a Flame Ionization Detector (GC-FID). The coating of the SPME fiber was characterized by Fourier Transformed InfraRed (FT-IR) spectroscopy and Scanning Electron Microscopy (SEM). Vital parameters affecting extraction performance, including desorption conditions, salt concentration, extraction time, and temperature, have been evaluated and optimized. The validated method was specific for the PAHs analysis, with the Limit of Detection (LOD) as low as 20.0 to 50.0 ng/L. The linear range was relevant to 70.0-180.0 ng/L with a relative standard deviation (RSD) % of less than 12.8. The factor of enrichment was found to be 446.7-808.8. The synthesized coating was shown to be thermally and chemically stable. The recommended approach was successfully applied to quantify PAHs in some frequent tea infusions in the market. The fiber coating of ZIF-67 can be easily made and applied efficiently to detect PAHs pollution in the environment and food products.

Polylactide based essential oil films were formulated by incorporating polyethylene glycol, nanopowder (zinc oxide), and essential oil by solvent casting method.The films were tested against pathogens for their antibacterial activity.The effectiveness of selected oil-nanomaterial based film was tested by performing the tests. In vitro antibacterial efficacies of nanopowders/essential oil were determined by the decimal reduction concentrations and the minimum bactericidal concentrations for the pathogens. In a typical process, Brassica napus extract was obtained from supercritical fluid extraction using pressurized carbon dioxide as solvent. The composition of the essential oil was analyzed by gas chromatography (GC) and gas chromatography-mass spectrophotometry (GC-MS).39 compounds were identified in the oil.Polylactide based essential oil films were formulated by incorporating polyethylene glycol, nanopowder (zinc oxide), and essential oil by solvent casting method.The films were tested against pathogens for their antibacterial activity. The effectiveness of selected oil-nanomaterial based film was tested by performing the tests. In vitro antibacterial efficacies of nanopowders/essential oil were determined by the decimal reduction concentrations and the minimum bactericidal concentrations for the pathogens.In a typical process, Brassica napus extract was obtained from supercritical fluid extraction using pressurized carbon dioxide as solvent.The composition of the essential oil was analyzed by gas chromatography (GC) and gas chromatography-mass spectrophotometry (GC-MS). 39 compounds were identified in the oil. The major compounds of the oil were 1,3,6,10-Cyclotetradecatetraene, 3,7,11-trimethyl-14- (1-methylethyl) - 30,07%, Cyclohexanone, 5 -methyl-2- (1-methylethylidene) - 12.91%, 3,4-Methylenedioxypropiophenone - 9,67%, Hexadecanoic acid, ethyl ester - 8.28%, Octacosanol - 5,50%, 11,15-Tetramethylhexadeca-1,3,6,10,14-pentaene - 4,55% and 1,6,10,14-Hexadecatetraen-3-ol, 3,7,11,15-tetramethyl – 3,14 %.

Benzene has a carcinogenic effect on the human body and adsorption from the air is the best way to control it. By this research, benzene vapor was removed from the air based on a tantalum metal-organic framework (Ta-MOF) by gas flow solid-phase interaction (GF-SPI). Benzene adsorption with Ta-MOF was studied in the static and dynamic systems at room temperature. The benzene concentration was analyzed by gas chromatography equipped with an FID detector (GC-FID). The factors affecting benzene removal efficiency like initial concentration of benzene, amount of adsorbent, exposure time, flow rate, and temperature were studied and optimized. The results showed us, the adsorption capacities range of Ta-MOF for benzene in the static and dynamic system were obtained between 90-160 mg g -1 and 65-135 mg g -1 , respectively. Also, the high removal efficiency was achieved by more than 95% at 45°C, 67.5 mg L -1 benzene concentration, 0.5 g of Ta-MOF, and the flow rate of 250 mL min -1 for a dynamic system. By dynamic system, the benzene is generated in the chamber, stored in a bag, and then moved on the surface of Ta-MOF. The GF-SPI method was validated by GC-MS and spiking real samples.

The analysis of organochlorine pesticides (OCPs) residues has received an increasing attention in the last decades. Thesolid-phase microextration (SPME) is a convenient and fast analytical method, which has been widely used for the determination of volatile and semivolatile organic compounds in aqueous samples. In this study, the multiwalled carbon nanotubes/polypyrrole composite (MWCNTs-PPy) coated on steel fiber was used for extraction OCPs from water samples by the SPME technique. The effects of various parameters on the efficiency of SPME process such as extraction time, extraction temperature, ionic strength, desorption time, and desorption temperature were studied. Under optimized conditions, the detection limits for the OCPs varied between 0.051 and 0.39 pg mL-1, the inter-day and intra-day relative standard deviations for various OCPs using a single fiber were 6.5-11.5% and 3.6-11.5, respectively. The linear ranges varied between 0.001 and 1 ng mL-1. The proposed method was successfully applied to the analysis of ground water samples with the recoveries from 86 to 110%

Migration of chemicals from plastic containers into drinks and liquids containing them, is supposed to be a hazardous phenomenon and results in many health problems. Sample preparation is of great importance due to trace amounts analysis of these compounds. In this research, dispersive liquid–liquid microextraction is applied for the extraction and preconcentration of the migrated compounds prior to their detection and determination by gas chromatography equipped with mass spectrometry or flame ionization detector. The method is on the basis of forming droplets of a water–immiscible organic solvent (extractant) into an aqueous phase by means of a disperser solvent. As a result, there would be a large contact area between the extractant and aqueous phase containing the analytes which boosts mass transfer. After centrifuging, the extractant is sedimented at the bottom of the aqueous phase and an aliquot of it is removed and injected into the separation system. Various experimental conditions which influence the extraction efficiency were optimized. Under the optimum conditions, the extraction recoveries were ranged from 52–63%. The relative standard deviations were ≤ 7.2% for intra– (n = 6) and inter–day (n = 4) precisions at a concentration of 20 µg L–1 of each analyte. The limits of detection were in the range of 0.18–0.38 µg L–1. Eventually the applicability of the proposed method for appraising the compounds migrated from the plastic containers was evaluated by analyzing the target compounds in different drinks and liquids stored in the plastic bottles.

In this study, we demonstrate the application of newly developed magnetic potassium substituted hydroxyapatite (KHA/Fe3O4) for the extraction of phthalate esters (PE) from water samples. Nanoparticles of KHA were synthesized through an easy alkoxide–based sol–gel technique. The structure of nanocomposite was characterized by X–ray diffraction (XRD), Fourier transform infrared (FTIR) analysis, and energy dispersive X–ray Analysis (EDXA). Moreover, the size of nanoparticle and micro–strain of synthesized KHA and KHA/Fe3O4 using Williamson–Hall (W–H) plots and transmission electron microscopy (TEM) were measured. The hexagonal and cubic structures of synthesized KHA and its nanocomposite having P63/m space group confirmed by XRD pattern. Also, the size of spherical particles of KHA in pure and nanocomposite, and Fe3O4 nanoparticles evaluated by W–H and TEM methods are in good agreement as 60, 65, and 18 nm. The PEs were analyzed by gas chromatography‒flame ionization detector (GC‒FID). Different parameters influencing the extraction efficiency including: sample pH, amount of sorbent, extraction time, desorption conditions, and salt effect, were optimized. The obtained optimal conditions were: sample pH, 7; amount of sorbent, 25 mg; extraction time, 8.0 min; desorption solvent and its volume, 200 μL dichloromethane; and desorption time, 5.0 min. Under optimum conditions, good linearity was achieved for all analytes in the 0.015–100 ng mL−1 concentration range. The limits of detection (at an S/N ratio of 3) are between 0.005 and 0.03 ng mL−1. The recoveries of PEs from spiked real water samples are between 86.3 and 99.2%, with relative standard deviations between 5.3 and 9.3 %.

Two convenient sample preparation methods, air–assisted liquid–liquid microextraction (AALLME) and dispersive liquid–liquid microextraction (DLLME) have been developed for the simultaneous determination of multiclass pesticide residues in vegetable and fruit juice samples with gas chromatography–flame ionization detection and the advantages of each method were investigated. In AALLME, fine droplets of an extraction solvent were immediately formed by suction with a syringe and injection of the mixture of an aqueous sample solution and an extraction solvent into a test tube for several times. In DLLME, the cloudy solution was formed with the aid of a disperser solvent. The effect of main factors, such as type and volume of extraction solvent, salt addition, pH, etc was studied. Under the optimum conditions, enrichment factors and extraction recoveries were obtained in the ranges of 262–515, 52–103% and 45–438, 9.2–88% in AALLME and DLLME methods, respectively. Both methods are inexpensive, simple, fast, efficient, reliable, and sensitive. Therefore, the proposed methods are suitable for determination of trace levels of multiclass pesticide residues in fruit juice and vegetable samples.

In this study, fatty acid (FA) composition of aerial parts of selected Salvia species from Iran was analyzed by Gas chromatography. The amount of FAs was quantified for leaf and shoot of species as mg per kg (mg/kg) of dry weight. The results showed that FA contents of aerial parts for studied plants varied significantly and changed between 73.05 and 739.50 mg/kg of dried weight. Caprylic (C8:0, 1.00-380.49 mg/kg), elaididc (C18:1n9t, 0.73-97.29 mg/kg), stearic (C18:0, 1.1-62.97 mg/kg), palmitic (C16:0, 1.19-36.48 mg/kg), and α-linoleic (C18:3n3, 1.34-19.36 mg/kg) acid were major identified FAs. The numerical analyze was applied on FA composition of shoot and leaf of specimens and the shoot FA composition was selected to identify the systematic position of studied species. The UPGMA (Unweighted Pair Group Method with Arithmetic Mean) dendrogram showed that the species were grouped in two clusters. Caprylic acid (C8:0), behenic acid (C22:0), and lignoceric acid (C24:0) were chief characters in the infrageneric grouping the species in the genus. S. chloroleuca and S. atropatanawere placed in cluster I and separated from other species based on shoot FA composition. The discrimination of Salvia species based on their botanical classification was supported by results. The results confirmed that FA composition of shoot are distinguishable and can be used as chemotaxonomic markers.

Water pollution is a major global problem which requires ongoing evaluation and revision of water resource policy at all levels (international down to individual aquifers and wells. It has been suggested that it is the leading worldwide cause of deaths and diseases, and that it accounts for the deaths of more than 14,000 people daily. Genetic algorithm-partial least square (GA-PLS), Kernel partial least square (GA-KPLS) and Levenberg-Marquardt artificial neural network (L-M ANN) techniques were used to investigate the correlation between retention time (RT) and descriptors for 150 organic contaminants in natural water and wastewater which obtained by gas chromatography coupled to high-resolution time-of-flight mass spectrometry (GC-TOF MS). The L-M ANN model gave a significantly better performance than the other models. This indicates that L-M ANN can be used as an alternative modeling tool for quantitative structure–retention relationship (QSRR) studies.