Gas Chromatrography Research Articles

Determination of Free Glycerol in Biodiesel by Molecularly Imprinted Polymer – Based Solid-Phase Extraction (SPE) Using an Enzymatic Spectrophotometric Assay

The present work reports the development of a new analytical method for the determination of free glycerol in biodiesel samples using enzymatic-spectrophotometric assay combined with solid phase extraction (SPE) by molecularly imprinted poly(methacrylic acid) (MIP). The spectrophotometric method was performed using a commercial enzyme kit. The enzymatic-spectrophotometric method showed good analytical performance in terms of the linearity (0.998), limit of detection (7.70 × 10−6% w/w), limit of quantification (2.54 × 10−5% w/w), repeatability (0.42% to 7.91%), and recovery (99.4% to 112%). The analyses of several biodiesel samples by SPE and enzymatic-spectrophotometric method provided recovery values between 91.4% and 105%. Therefore, the high selectivity of molecularly imprinted polymer (MIP) was successfully applied to isolate free glycerol from biodiesel samples containing acylglycerols and methyl esters, and thereby allow enzymatic-spectrophometric based quantification. The developed method using SPE with MIP was efficient for the determination of free glycerol in biodiesel and the obtained results are in agreement with gas chromatrography (GC) that was used as a reference protocol.

Application of oleic acid functionalized magnetic nanoparticles for a highly sensitive and efficient dispersive magnetic solid phase extraction of fenazaquin in almond samples for determination by gas chromatrography mass spectrometry

A sensitive and efficient dispersive magnetic solid phase extraction (DMSPE) method was developed to determine fenazaquin at trace level by gas chromatography mass spectrometry. Fenazaquin belongs to the quinolone group of pesticides having an ovicidal activity in some agricultural crops and it is known to cause several adverse health effects. Magnetic nanoparticles were utilized as adsorbents in the extraction process and were synthesized based on the basic precipitation procedure. The Fe3O4 nanoparticles were also functionalized in a nitrogen atmosphere with oleic acid in order to enhance the adsorption capacity. The main parameters that affect the DMSPE preconcentration method including the type and amount of magnetic nanoparticles, type and volume of elution solvent were optimized. Under the optimum conditions, a linear range was obtained between 0.20 and 500 ng/mL and the limits of detection (LOD) and quantification (LOQ) calculated were 0.06 µg/L and 0.21 µg/L, respectively. The enhancement in detection power was found to be 793.7. The accuracy of the developed method was tested on diegsted almond samples, spiked at two concentrations and extracted with acetonitrile. The respective percent recovery results calculated for 5.0 and 20 mg/kg spiked samples were 91.2 ± 0.4% and 109.4 ± 3.4%.

Valorization of Sugar Beet Pulp via Torrefaction with a Focus on the Effect of the Preliminary Extraction of Pectins

An agro-industrial residue, i.e., sugar beet pulp, was taken into consideration in this work as a feedstock for valorization as a solid fuel and, potentially, as a source of valuable biochemicals obtainable from the torgas condensable fraction. To this end, an experimental program based on torrefaction of such a residue after pectin extraction (PE-SBP) was performed. The alternative scenario of raw sugar beet pulp (raw-SBP) torrefaction was also investigated for comparison. Raw biomasses and torrefaction products were analyzed by different techniques including thermogravimetric analysis and derivative thermogravimetry (TGA-DTG), Fourier transform infrared spectroscopy (FTIR), gas chromatrography coupled to mass spectrometry (GC/MS), and proximate and ultimate analyses. This allowed the comparative investigation of the role played by the pectin extraction method and the torrefaction temperature on the process performance and main properties of the resulting solid products. Outcomes showed that light torref...

Host–Guest Interactions and Their Catalytic Consequences in Methanol to Olefins Conversion on Zeolites Studied by 13C–27Al Double-Resonance Solid-State NMR Spectroscopy

Methanol conversion over zeolites with different topologies (H-ZSM-5, H-SSZ-13, and H-MOR) was studied using solid-state NMR spectroscopy and gas chromatrography mass spectroscopy (GC-MS). Host–guest interactions between active hydrocarbon pool (HP) species and zeolite framework (Bronsted acid/base site) were observed, and the supramolecular reaction centers (SMCs) generated by the interactions were unambiguously identified by 13C–27Al double-resonance NMR. The internuclear spatial interaction/proximity between the 13C nuclei (associated with HP species) and the 27Al nuclei (associated with Bronsted acid/base site) was analyzed and compared over the three zeolites. The product shape selectivity of zeolites greatly influences the catalytic performance that can be linked to the nature of HP species and the host–guest interactions. Closer spatial proximity and stronger interaction between methylbenzenes (MBs) and Bronsted acid/base sites were observed over H-SSZ-13 and H-MOR zeolites, which facilitate aromat...

Production of diesel-like fuel from spent engine oil by catalytic pyrolysis over natural magnetite

The present work addresses the conversion of spent engine oil into reusable useful diesel like fuel via two stage pyrolysis. In the 1st stage pyrolysis, pre-baked clay was used as adsorbent in order to remove impurities and to get a clear distillate product. In the 2nd stage, the clear distillate fraction was further pyrolyzed using different amounts of natural magnetite (1–5wt%). The catalyst was prepared in the laboratory, and characterized by scanning electron microscopy (SEM), energy dispersive x-ray (EDX), X-ray diffractometry (XRD), and surface area analysis. The yields of overall products, liquid, gas and solid residue as a function of catalyst concentration were investigated and 3wt% catalyst (optimum) gave 97.09, 72.31, 24.77 and 2.91% yields, respectively. The liquid fraction obtained at the optimum catalyst concentration was further characterized by Fourier Transform Infra Red (FT-IR) and Gas Chromatrography–Mass Spectrometry (GC–MS) in order to determine its detailed composition in terms of hydrocarbon ranges, hydrocarbon group type’s distribution and individual hydrocarbons in comparison with the thermal run. The fuel properties of the derived liquid fraction were also investigated using ASTM/IP standard methods. The results showed that the natural magnetite exhibited good catalytic activity and selectivity towards formation of hydrocarbons having fuel value in conformity to the diesel fuel.

A method for continuous and stable perfusion of tissue and single cell preparations with accurate concentrations of volatile anaesthetics

BackgroundIt is difficult to design a system to reliably deliver volatile anaesthetics such as halothane or isoflurane to in vitro preparations such as tissues or cells cultures: the very volatility of the drugs means that they can rapidly dissipate from even carefully-prepared solutions. Furthermore, many experiments require the control of other gases (such as oxygen or carbon dioxide) which requires constant perfusion. New methodWe describe a constant perfusion system that is air-tight (i.e., allows the accurate administration of hypoxic or hypercapnic gas mixtures), in which volatile anaesthetic is delivered via calibrated vaporisers by constant bubbling into the perfusing solution (and continuously monitored for stability by infrared spectroscopy in the headspace above the solution). ResultsWe have confirmed the accuracy (i.e., linear relationship of dissolved concentrations with vapour dial settings) and stability (i.e., over time) of the anaesthetic concentrations in solutions in samples taken from the bottles into which anaesthetic is bubbled, and from samples taken from the tissue perfusion bath, using gas chromatrography–mass spectrometry (GC–MS). ConclusionsIt is possible to deliver volatile anaesthetics in accurate concentrations to cell/tissue preparations whilst adjusting ambient air composition rapidly, stable over sustained time periods.

Combined Impact of Branching and Unsaturation on the Autoignition of Binary Blends in a Motored Engine

The impact of a branched and unsaturated compound (diisobutylene) mixed with simple hydrocarbons such as n-heptane and isooctane in binary blends on the autoignition behavior were investigated in a modified cooperative fuel research (CFR) engine at an equivlanece ratio of 0.5 and intake temperature of 120 °C. From this test condition, a homogeneous charge of fuel and intake air can be achieved. The test fuels were prepared by addition of 5–20 vol % diisobutylene into n-heptane and isooctane. The engine compression ratio (CR) was gradually increased from the lowest point to the point where significant high temperature heat release (HTHR) was observed, and this point is also referred to as the critical compression ratio (CCR). Heat release analysis showed that each n-heptane blend had a noticeable low temperature heat release (LTHR), which was not observed in the isooctane blends. The gradual addition of diisobutylene into each primary reference fuel contributed to retarded high temperature heat release in these binary blends, increasing the in-cylinder temperature and decreasing formation of CO. The 15 and 20 vol % blends of diisobutylene in isooctane were not able to reach high temperature heat release in the CFR engine system under these test conditions. The fundamental ignition behavior such as CCR and calculated % LTHR show the impact of the presence of the C–C double bond on ignition reactivity. Species concentration profiles obtained in condensed products from the engine exhaust were measured via gas chromatrography–mass spectrometry and −flame ionization detector. The major intermediate species for each blend were captured at a compression ratio selected just before the high temperature heat release was observed. Most intermediate species were derived from n-heptane and isooctane, while diisobutylene rarely participated in forming any major species, with the exception of the formation of 4,4-dimethyl-2-pentanone. Addition of diisobutylene exhibited opposite trends with regard to the abundance of intermediate species when blended with n-heptane versus with isooctane, due to the different degree of oxidation reactivity of n-heptane in comparison to isooctane.

Organic Solvent Traces in Fibrillar Scaffolds for Tissue Engineering

In the present study the amount of xylene remaining in fibrillar scaffolds after their manufacture has been estimated by means of Gas Chromatrography coupled to Mass Spectrometry (GC-MS). For this purpose model scaffolds of poly(ethylene terephthalate) (PET) comprised of microfibrils with diameters of ~1 µm or nanofibrils with diameters of 50-150 nm as well as microfibrillar scaffolds of poly(glycolic acid) (PGA) have been used. An extremely low initial amount of xylene has been found (< 20 ppm). The xylene amount dropped below 2 ppm after drying for 24 h in a vacuum at 80°C. The microfibrillar PGA scaffolds, initially containing more xylene (23.4 ppm), retained only 3.6 ppm after drying for 24 h. After drying for 48 h the amount of xylene in all the scaffolds studied reached the detection limits of the GC-MS apparatus (< 0.5 ppm).

Determination of isotretinoin in pharmaceutical formulations by reversed-phase HPLC

The development of facile and rapid quantification of biologically active biomolecules such as isotretitoin in therapeutic drugs contained in many generic formu- lations is necessary for determining their efficiency and their quality to improve the human health care. Isotretritoin finds its applications in the maintenance of epithelial tissues. Different processes to date such as normal phase HPLC, or gas chromatrography am- ong others are able to separate and quantify isote- troin. However, the extraction is quite complex and in the case of HPLC, the analysis requires long retention times. In such context, an isocratic reversed- phase high-performance liquid chromatography (HP- LC) technique coupled with an UV-vis detector is described here for easy separation and quantification of 13-cis-retinoic (isotretinoin) from soft gelatin capsule formulations. The isotretinoin was extracted from three different commercial drug samples with tetrahydrofuran (THF) solvent by a procedure that can be completed in less than 10 minutes. Subsequent separation and quantification were accomplished in less than 5 minutes under isocratic reversed-phase conditions on a Lichrospher RP18 column and a mobile phase consisting of 0.01% TFA/acetonitrile (15/85, v/v) at a flow rate of 1.0 mL/min. Isotretoin was detected for the three samples via its UV-vis absorbance at 342 nm. The method was validated and the results showed good linearity, precision and accuracy for sensitive and selective quantitative determination of isotretinoin in the different pharmaceutical formulations. We found that the average isotretinoin content in two of the three commercial pro- ducts fell outside the 90-110% United States Pha- rmacopeia specifications. Consequently, the facile extraction and the precise method for the biomole- cule quantification open up tremendous possibilities in improving the quality control of drugs which can exist as different generic brands.

SUBCRITICAL WATER EXTRACTION OF ESSENTIAL OILS FROM ZATARIA MULTIFLORA BOISS

ABSTRACT The essential oil of Zataria multiflora Boiss., cultivated in Iran, was extracted by subcritical water extraction (SCWE) and compared with two conventional methods, including hydrodistillation and Soxhlet extraction. The extraction efficiencies of different temperatures (100, 125, 150 and 175C), mean particle sizes (0.25, 0.50 and 1 mm) and water flow rates (1, 2 and 4 mL/min) were investigated at 20 bar. The separation and identification of the components were carried out by gas chromatrography (GC)‐flame ionization detection and GC‐mass spectrometry. The best operating conditions for the SCWE of Z. multiflora Boiss. were determined to be at 150C temperature, 0.50‐mm mean particle size and 2 mL/min flow rate for 150 min extraction time. The SCWE method resulted in a more valuable essential oil with respect to the oxygenated components.PRACTICAL APPLICATIONSSubcritical water can be used in many different fields of applications. In recent years, the extraction of flavors, fragrances and antioxidant components from plant materials, and the hydrolysis of carbohydrates, vegetable oils and fatty acids have been widely investigated by many researchers. Using subcritical water for analytical purposes and for soil remediation, and applying it as a reaction media are some other interesting fields for practical applications.

Determination of glucose and ethanol after enzymatic hydrolysis and fermentation of biomass using Raman spectroscopy

Raman spectroscopy has been used for the quantitative determination of the conversion efficiency at each step in the production of ethanol from biomass. The method requires little sample preparation; therefore, it is suitable for screening large numbers of biomass samples and reaction conditions in a complex sample matrix. Dilute acid or ammonia-pretreated corn stover was used as a model biomass for these studies. Ammonia pretreatment was suitable for subsequent measurements with Raman spectroscopy, but dilute acid-pretreated corn stover generated a large background signal that surpassed the Raman signal. The background signal is attributed to lignin, which remains in the plant tissue after dilute acid pretreatment. A commercial enzyme mixture was used for the enzymatic hydrolysis of corn stover, and glucose levels were measured with a dispersive 785 nm Raman spectrometer. The glucose detection limit in hydrolysis liquor by Raman spectroscopy was 8 g L −1. The mean hydrolysis efficiency for three replicate measurements obtained with Raman spectroscopy (86 ± 4%) was compared to the result obtained using an enzymatic reaction with UV–vis spectrophotometry detection (78 ± 8%). The results indicate good accuracy, as determined using a Student's t-test, and better precision for the Raman spectroscopy measurement relative to the enzymatic detection assay. The detection of glucose in hydrolysis broth by Raman spectroscopy showed no spectral interference, provided the sample was filtered to remove insoluble cellulose prior to analysis. The hydrolysate was further subjected to fermentation to yield ethanol. The detection limit for ethanol in fermentation broth by Raman spectroscopy was found to be 6 g L −1. Comparison of the fermentation efficiencies measured by Raman spectroscopy (80 ± 10%) and gas chromatrography–mass spectrometry (87 ± 9%) were statistically the same. The work demonstrates the utility of Raman spectroscopy for screening the entire conversion process to generate lignocellulosic ethanol.

Determination of alkylphenols and alkylphenol ethoxylates in sewage sludge: effect of sample pre-treatment

A complete characterization of sewage sludge collected from five biological waste water treatment plants was done to determine physico-chemical parameters, heavy metals and alkylphenols, making special emphasis on sampling, homogenization, and sample pre-treatment. Ultrasonic extraction followed by gas chromatrography coupled with mass spectrometry was used to evaluate the effect of sample pre-treatment (untreated sample, freeze-drying, drying at 40 degrees C or drying at 100 degrees C) on the concentration of octylphenol (OP), nonylphenol (NP) and nonylphenol ethoxylates (NP1EO, NP2EO). Untreated samples and samples dried at 100 degrees C gave concentration levels up to 62% and 89% lower, respectively, than freeze-dried samples. In 50% of cases, freeze-dried samples led to significantly higher concentrations than those obtained by drying at 40 degrees C. Thus, freeze-drying is the recommended sample pre-treatment to prevent possible losses of OP, NP, and NP1EO. Using this methodology, concentrations detected were from 3.2 to 199 mg kg(-1) being NP followed by NP1EO found in highest concentration. The total concentration of NP and NP1EO exceeded the limit of 50 mg kg(-1) proposed by the draft European directive on sewage sludge in three out of five samples studied. Contrarily, heavy metals were below the legislated values.

Production and Characterization of a Thermostable Alcohol Dehydrogenase That Belongs to the Aldo-Keto Reductase Superfamily

The gene encoding a novel alcohol dehydrogenase that belongs to the aldo-keto reductase superfamily has been identified in the hyperthermophilic archaeon Pyrococcus furiosus. The gene, referred to as adhD, was functionally expressed in Escherichia coli and subsequently purified to homogeneity. The enzyme has a monomeric conformation with a molecular mass of 32 kDa. The catalytic activity of the enzyme increases up to 100 degrees C, and a half-life value of 130 min at this temperature indicates its high thermostability. AdhD exhibits a broad substrate specificity with, in general, a preference for the reduction of ketones (pH optimum, 6.1) and the oxidation of secondary alcohols (pH optimum, 8.8). Maximal specific activities were detected with 2,3-butanediol (108.3 U/mg) and diacetyl-acetoin (22.5 U/mg) in the oxidative and reductive reactions, respectively. Gas chromatrography analysis indicated that AdhD produced mainly (S)-2-pentanol (enantiomeric excess, 89%) when 2-pentanone was used as substrate. The physiological role of AdhD is discussed.

Inverse gas chromatrography of chromia. Part II. Finite surface coverage

The interactions of n-hexane, benzene, chloroform, and tetrahydrofuran with dried (amorphous) chromia (I) and chromia heated at 1073 K (crystalline) (II), both obtained from a colloidal dispersion, and a commercially available chromia (III) were studied by inverse gas chromatography (IGC) under finite surface coverage conditions. The isotherms, in the temperature range 383 ? 423 K, were used to estimate the surface area, the adsorption energy distribution, the isosteric heat of adsorption, and the spreading pressure on the surfaces of the solids. The uniformly reduced adsorption ability of the heated chromia was attributed to the dehydroxylation of the surface at the higher temperatures. Both solids showed an increased affinity toward chloroform molecules, as a result of strong acid-base interaction.

Role of corrosion products in biofilms in microbiologically induced corrosion of carbon steel

AbstractThe effects on microbiologically induced corrosion (MIC) of carbon steel resulting from the presence of corrosion products in the biofilm of sulphate reducing bacteria (SRB) have been investigated. The SRB were isolated from the Changqing oilfield in China. Electrochemical impedance spectrometry and a hydrogen monitoring device were used to study the accumulation of the biofilms. The corrosion products were analysed by both electron probe microanalysis and X-ray diffraction, and the metabolites of the SRB in the biofilm were detected by gas chromatrography and mass spectrometry techniques. The results have shown that the first corrosion product to form in the biofilm is mackinawite, followed by the appearance of troilite and greigite. Only the mackinawite layer has protective properties; the others accelerate the corrosion of carbon steel. Both the activity of the SRB and the structure of the SRB biofilm influence the initiation and development of corrosion. The process of MIC involves first the d...

Determination of methanol and ethanol by gas chromatrography following air sampling onto florisil cartridges and their concentrations at urban sites in the three largest cities in Brazil

A new sampling protocol was developed to determine methanol and ethanol in the gas phase, at low concentration levels, in urban atmospheres. The procedure involves collection of air samples (20.0–30.0 l) with three florisil cartridges connected in series, at a flow rate ranging from 1.0 to 2.0 l min −1 and subsequent elution of the alcohols with water. Separation and quantification were done by gas chromatography (GC) coupled with a flame ionization detector, ‘SPI’ injector and column DB WAX (30 m×0.53 mm×1 μm). The minimum mass detected by the method, based on two times the average background mass on the blank cartridges, was 0.3 μg for both alcohols which, for a sampled volume of 30 l, resulted in detection limits of 7.6 and 5.3 ppbV for methanol and ethanol, respectively. The determined alcohol concentrations, in 42 different samples from the three largest cities in Brazil—São Paulo, Rio de Janeiro and Salvador—ranged from 72 ppbV to below the detection limit for methanol and from 355 to 12 ppbV for ethanol.

Kinetics of Hydrolytic Depolymerization of Melt Poly(ethylene terephthalate)

The hydrolytic depolymerization of poly(ethylene terephthalate) (PET) was carried out in a stirred batch reactor at 235, 250, and 265 °C above its melting point and under autogenous pressure. The solid products which were mainly composed of terephthalic acid were analyzed by potentiometric titration and elemental analysis. The liquid products which were mainly composed of ethylene glycol and a small amount of its dimer were analyzed by gas chromatrography. A kinetic model consisting of forward and backward reactions for the PET hydrolysis fitted well with the experimental data. Moreover, an autocatalytic mechanism was suggested, which indicates that some of the hydrolytic depolymerization of PET was catalyzed by the carboxyl groups produced during the reaction. The dependence of the rate constant on the reaction temperature was correlated by the Arrhenius plot giving the activation energy of 123 kJ/mol for the PET hydrolysis.

Use of Local Lagrange Interpolation for calculation of retention indices in linear temperature-programmed gas chromatrography

The influence of the isothermal temperature, program rate, initial temperature and flow rate on retention indices was studied. The methods of Kovats, Van Den Dool and Local Lagrange Interpolation are compared. Ten experimental measurements were carried out on a capillary column coated with OV-101 stationary phase.

Effect of igneous intrusion on the organic geochemistry of a siltstone and an oil shale horizon in the Midland Valley of Scotland

The effect of rapid thermal stress on the organic geochemistry of a siltstone intruded by a quartz-dolerite dyke and an oil shale intruded by an alkali-dolerite sill has been studied using optical petrography, Rock-Eval pyrolysis, gas chromatrography and gas chromatography-mass spectrometry. Maturity-dependent ratios derived from both the aliphatic and aromatic hydrocarbon fractions corroborate the observation of Raymond and Murchison (1988b) that the alkali-dolerite sills, which were intruded soon after sedimentation, had a lesser effect than the later quartz-dolerite intrusions. The maturity parameters based on the alkylnaphthalene and alkylphenanthrene isomer ratios are more suitable for studying maturity variations in heat-affected samples than those based on the commonly-used aliphatic biological markers. These aromatic compounds survive to higher ranks and the isomer ratios continue changing.

Structure-retention correlation of dihydropyrazolo-trazinone derivatives in thin-layer and gas chromatrography

Relationships between logarithmic retention factors and carbon atom numbers for some homologous series of the title compounds were studied in thin-layer and gas chromatographic systems. Reversed-phase R M values and Kováts retention indices showed linear correlation with the carbon atom numbers of the homologous species. In silica gel chromatography, these correlations were non-linear in several cases. The chromatographic behaviour of the compounds investigated could be explained on the basis of their structural properties.