Capillary Column Gas Research Articles

Determination of epoxidized soybean oil by gas chromatography/single quadrupole and tandem mass spectrometry stable isotope dilution assay

PVC lids of glass jars often contain epoxidized soybean oil (ESBO), able to migrate and contaminate food. To establish a stable isotope dilution assay (SIDA), the 13C18-labelled internal standard ethyl 9,10,12,13-diepoxyoctadecanoate (13C(18:2E)Et) was synthesized, providing after sample preparation the same retention time as methyl 9,10,12,13-diepoxyoctadecanoate ((18:2E)Me), commonly used as a marker for ESBO in gas chromatographic (GC) analysis. For eleven different food matrices, the GC capillary columns VF-17ms, DB1701 and DB1 were tested with single quadrupole (GC/MS) as well as tandem mass spectrometric detection (GC/MS/MS). Overall, the VF-17ms column coupled with MS/MS detection showed the best results in terms of separation and sensitivity. The method validation for the matrix spiked olive oil resulted in a limit of detection (LOD) of 5 mg kg-1, a limit of quantification (LOQ) of 11 mg kg-1, a mean recovery (n=5, c=106.5 mg kg-1) of 99.7+/-5.5%, with a repeatability (within-run precision) of 6.0%. By means of GC/MS an LOQ of 21 mg kg-1 and a mean recovery (n=5, c=106.5 mg kg-1) of 103.3+/-0.8% with a repeatability of 0.9% were determined.

Isolation and Identification of Nitrogen Species in Jet Fuel and Diesel Fuel

Many performance characteristics of liquid fuelsincluding lubricity, the ability to swell seal materials, storage stability, and thermal stabilityare determined, to a large degree, by the trace polar species that the fuel contains. Because the polar fraction comprises such a small portion of the fuel matrix, it is difficult to detect these species without first isolating them from the bulk fuel. This manuscript describes the extension of previous work that established a protocol for the isolation and identification of oxygenates in jet fuels. The current work shows that a liquid−liquid extraction using methanol, followed by an isolation step using high-performance liquid chromatography (HPLC) with a silica column, can successfully separate polar nitrogen-containing species from the fuel, in addition to separating oxygenates. The analytical protocol further isolates the polar target species using a polar capillary gas chromatography (GC) column and a nontraditional oven heating program. The method is amenable to milliliter quantitites of fuel samples and produces a matrix that can be analyzed directly, using typical GC methods. The method was evaluated using spiked surrogate fuels, as well as actual petroleum-derived jet fuel samples. Furthermore, it is shown that the method also can be extended for use on diesel fuels.

Multiresidue analysis of pesticides in fruits and vegetables by gas chromatography-mass spectrometry

A multiresidue method was assessed for the determination of several pesticides (organochlorine, organophosphorus, pyrethroids, triazole, amidine) using gas chromatography/mass spectrometry. The extraction of pesticides was carried out by liquid-liquid extraction (LLE) and solid-phase extraction (SPE) using two types of columns (CN and C18). The extracts were cleaned by the addition of florisil, the pesticides were separated by capillary column gas chromatography and detected by mass spectrometry in the electron impact mode. The extraction using C18 column provided the best results for most of the analyzed pesticides. The majority of pesticides recoveries from the four fruits and vegetables (apples, pears, tomatoes and pepper) were greater than 60%. Linearity and precision were satisfactory. The estimated limits of detection and limits of quantification ranged from 0.01 to 0.1 mg/kg and from 0.02 to 0.3 mg/kg, respectively. The proposed procedure was found to be useful for the multiresidue analyses of pesticides in agricultural products for routine monitoring programs.

Effect of the carrier gas pressure on the dynamic and separation characteristics of divinylbenzene-based monolithic capillary columns for gas chromatography

The efficiency and dynamic characteristics of divinylbenzene-based monolithic capillary columns for gas chromatography were analyzed using a test mixture composed of five light hydrocarbons. The chromatographic properties of these columns were evaluated within the framework of two varieties of the van Deemter equation, the classical one and that proposed by Giddings (with consideration given to the pressure drop across the column). An analysis of the van Deemter curves demonstrated that the main contribution to peak smearing comes from the diffusion processes in the mobile phase. The contribution from the resistance to mass transfer between the mobile and stationary phases is less important. Negative values obtained for A in the van Deemter equation and for C s in the Giddings model, parameters that characterize the stationary phase structure and mass transfer kinetics in the stationary phase, have no physical meaning, a result calling for further studies of this type of monolithic capillary columns since the classical theory supposed these parameters to be strictly positive. Under optimal conditions, the HETP of the monolithic columns was found to be 3 to 4 times smaller than that typical of open capillary columns of the same diameter.

Loading capacities of monolithic capillary columns in gas chromatography

The loading capacities of monolithic capillary columns based on silica gel and divinylbenzene are studied for two carrier gases, CO2 and N2. It is shown that the efficiency of the column is more sensitive to the overload of the column than the retention time of the sorbate is, especially for the CO2 carrier gas. It is established that the loading capacity of a monolithic column based on silica gel decreases significantly in going from N2 to CO2. For columns based on divinylbenzene, the loading capacity is found to be virtually the same for both carrier gases. For monolithic columns, the loading capacity per one meter of column length is found to be 10 and more times higher than that for a standard open capillary column.

Separation of Enantiomers of a Chiral Lactone on Sol-Gel Gas Chromatography Capillary Columns of Poly(methydrosiloxane) Stationary Phase with Pendant Permethylated β-Cyclodextrin

Four different pendant cyclodextrin PMHS-based chiral stationary phases were synthesized. These four phases were different with respect to the anchoring positions of cyclodextrin to poly(methydrosiloxane) (PMHS) and with respect to the structures and lengths of the anchoring arms. The four stationary phases were used for the preparation of GC capillary columns by sol-gel method. These columns were then used to separate enantiomers of (±) γ-phenyl- γ-butyrolactone. For these columns, separation efficiency, enantioselectivity, retention factor, resolution, and polarity values were experimentally determined and compared. Among the four types of chiral stationary phases used, the one possessing the small-rim-tethered cyclodextrin (CD) with an anchoring arm containing four methylene groups and an etheric oxygen linkage provided the best chromatographic performance.

THE PRESENCE OF POLYCYCLIC AROMATIC HYDROCARBONS (PAH) IN OIL OBTAINED AT PYROLYSIS OF JORDAN OIL SHALE

The presence of polycyclic aromatic hydrocarbons (PAH) in the oil obtained at pyrolysis of Jordan oil shale in a fluidised-bed reactor in the atmosphere of nitrogen and nitrogen/steam has been investigated. The final pyrolysis temperature was 520 °C, at which the maximum oil yield was established. The derived oils were fractionated into chemical classes using mini-column liquid chromatography followed by analysis using capillary column gas chromatography with mass spectrometry (GC/MS) for identification and quantification of PAH. The derived oils were found to contain significant amounts of PAH, mainly naphthalene, fluorene and phenanthrene and their alkylated derivatives, and lower amounts of fluoranthrene, pyrene and chrysene. Some of the PAH found in the derived oils are known to be carcinogenic and/or mutagenic, and consequently the oils may represent a significant environmental and health hazard. The PAH have probably formed via Diels-Alder type reactions or via gas-phase cracking of aliphatic compounds.

The binding of the flavour of lactones by soya protein, amino acids and casein

SummaryThe binding of certain lactones to soya protein isolate, amino acids and casein in different concentrations was investigated using capillary column gas chromatography. The analysis of lactones was conducted by solid phase microextraction and by the standard method of headspace analysis. The percentage of binding of lactones γ‐9, γ‐10, δ‐10 and δ‐11 on the soya protein is almost the same. According to the Klotz equation, the bound ligand concentration was calculated as the number of moles of ligand bound per mole of protein. γ‐lactones are bound less than δ‐lactones and that the competitive binding ability of lactones δ‐11 and γ‐10 is similar. δ‐11 has a greater binding capacity with each of the amino acids used and with casein than γ‐10 because of its greater ability to form hydrophobic binding than γ‐10. The techniques of gas chromatography/mass spectrometry and infrared spectroscopy confirmed that the binding of the ligand on the protein substrate was attributed to secondary bonds, such as hydrogen bonds, hydrophobic bonds and van der Waals forces.

Comparative analysis of pyrolysis oils and its subfractions under different atmospheric conditions

In this paper comparative analysis of bio-oils and their subfraction from static, sweeping gas and steam pyrolysis of apricot pulp, a food industry waste, was investigated. Experimental studies were conducted in a well-swept fixed-bed reactor with a heating rate of 5 °C min− 1, to a final pyrolysis temperature of 550 °C. The oil yield which was 22.4% at the static atmosphere reached to the value of 23.2% in the sweeping gas atmosphere by using 100 cm3 min− 1 N2 flow rate. The yield of liquid product in steam pyrolysis was higher (27.2%) than the static and inert gas atmosphere.The elemental analyses of the pyrolysis oils were determined, and the chemical compositions of the oils were investigated using chromatographic and spectroscopic techniques. The liquid products were fractionated into pentane solubles and insolubles (asphaltenes). Pentane solubles were then solvent fractionated into pentane, toluene, and methanol subfractions by fractionated column chromatograpy. The aliphatic subfractions of the oils were then analysed by capillary column gas–liquid chromatography and GC/MS. For further structural analysis, the pyrolysis oils' aliphatic, aromatic and polar subfractions were conducted using FTIR and 1H NMR spectra.

The use of the Dhcr7 knockout mouse to accurately determine the origin of fetal sterols

Mice with a targeted mutation of 3beta-hydroxysterol Delta(7)-reductase (Dhcr7) that cannot convert 7-dehydrocholesterol to cholesterol were used to identify the origin of fetal sterols. Because their heterozygous mothers synthesize cholesterol normally, virtually all sterols found in a Dhcr7 knockout fetus having a Delta(7) or a Delta(8) double bond must have been synthesized by the fetus itself but any cholesterol had to have come from the mother. Early in gestation, most fetal sterols were of maternal origin, but at approximately E13-14, in situ synthesis became increasingly important, and by birth, 55-60% of liver and lung sterols had been made by the fetus. In contrast, at E10-11, upon formation of the blood-brain barrier, the brain rapidly became the source of almost all of its own sterols (90% at birth). New, rapid, de novo sterol synthesis in brain was confirmed by the observation that concentrations of C24,25-unsaturated sterols were low in the brains of all very young fetuses but increased rapidly beginning at approximately E11-12. Reduced activity of sterol C24,25-reductase (Dhcr24) in brain, suggested by the abundance of C24,25-unsaturated compounds, seems to be the result of suppressed Dhcr24 expression. The early fetal brain also appears to conserve cholesterol by keeping cholesterol 24-hydroxylase expression low until approximately E18.

Fast Gas Chromatography of Explosive Compounds Using a Pulsed‐Discharge Electron Capture Detector*

The detection of a mixture of nine explosive compounds, including nitrate esters, nitroaromatics, and a nitramine in less than 140 sec is described. The new method employs a commercially available pulsed-discharge electron capture detector (PDECD) coupled with a microbore capillary gas chromatography (GC) column in a standard GC oven to achieve on-column detection limits between 5 and 72 fg for the nine explosives studied. The PDECD has the benefit that it uses a pulsed plasma to generate the standing electron current instead of a radioactive source. The fast separation time limits on-column degradation of the thermally labile compounds and decreases the peak widths, which results in larger peak intensities and a concomitant improvement in detection limits. The combination of short analysis time and low detection limits make this method a potential candidate for screening large numbers of samples that have been prepared using techniques such as liquid-liquid extraction or solid-phase microextraction.

Determination of volatile residual solvents in pharmaceutical products by headspace liquid-phase microextraction gas chromatography-flame ionization detector

This paper demonstrates headspace liquid-phase microextraction (HS-LPME) as used for the determination of volatile residual solvents in pharmaceutical products. This method is based on headspace liquid-phase microextraction capillary column gas chromatography. Under optimum conditions, the linerary of the method ranged from 1 to 1,000 mg l(-1). The limits of detection are 0.2-6.0 [corrected] mg l(-1) and relative standard deviations (RSD) for most of the volatile solvents were below 10%. This novel method is applied to the analysis of volatile residual solvents in pharmaceutical products with satisfactory results.

Gas-Liquid Chromatographic Study of Thermodynamics of Some Alkanes on Polysiloxane Stationary Phase

A gas-liquid chromatographic study of the interaction and elution characteristics of 47 paraffinic compounds from C5-C14 normal, branched, and cyclic alkanes using 100% dimethyl polysiloxane and 35% diphenyl, 65% dimethyl polysiloxane as stationary phases is reported. It is shown that polysiloxane stationary phase in capillary column gas chromatography possesses excellent chromatographic properties and is unique in the separation of iso-paraffins. The mechanism, retention, and selectivity are discussed by measuring various thermodynamic parameters: the enthalpy of solution Δ H, the entropy of solution Δ S, and the free energy Δ G.

Loss of Angiotensin-Converting Enzyme-2 Leads to the Late Development of Angiotensin II-Dependent Glomerulosclerosis

Angiotensin-converting enzyme-2 (ACE2), a membrane-bound carboxymonopeptidase highly expressed in the kidney, functions as a negative regulator of the renin-angiotensin system. Here we report early accumulation of fibrillar collagen in the glomerular mesangium of male ACE2 mutant (ACE2−/y) mice followed by development of glomerulosclerosis by 12 months of age whereas female ACE2 mutant (ACE2−/−) mice were relatively protected. Progressive kidney injury was associated with increased deposition of collagen I, collagen III and fibronectin in the glomeruli and increased urinary albumin excretion compared to age-matched control mice. These structural and functional changes in the glomeruli of male ACE2 mutant mice were prevented by treatment with the angiotensin II type-1 receptor antagonist irbesartan. Loss of ACE2 was associated with a marked increase in renal lipid peroxidation product formation and activation of mitogen-activated protein kinase and extracellular signal-regulated kinases 1 and 2 in glomeruli, events that are also prevented by angiotensin II type-1 receptor blockade. We conclude that deletion of the ACE2 gene leads to the development of angiotensin II-dependent glomerular injury in male mice. These findings have important implications for our understanding of ACE2, the renin-angiotensin system, and gender in renal injury, with ACE2 likely to be an important therapeutic target in kidney disease.

Effect of the pressure of the carrier gas on the parameters of the Van Deemter equation for monolithic silica gel gas chromatography columns

The chromatographic properties of monolithic capillary silica gel columns for gas chromatography were examined with the use of four different variants of the Van Deemter model. The corresponding experimental curves were measured for the elution of light hydrocarbons with the helium carrier gas in the isothermal mode at 60°C. Despite the models tested are based on different mechanisms of the smearing of chromatographic peaks, the values of the Van Deemter equation parameters proved to be very close to each other for three of the four models. All models yielded negative values of the parameter A. Physically reasonable values of the parameters of the Van Deemter equation were obtained only for the Giddings model, which takes into account the pressure drop across the column. At the same time, this model overestimated the contribution from diffusional smearing (parameter B). It was concluded that none of the models tested adequately described the chromatographic properties of monolithic capillary columns for gas chromatography.

Longitudinal Miniaturization of Fiber-Packed Capillary Column in High Temperature Gas Chromatography

Miniaturization of fiber-packed capillary column in gas chromatography was studied. Packed with a bundle of polymer-coated filaments into a short metal capillary, longitudinal miniaturization was demonstrated without any significant disadvantages for practical retentivity and sample loading capacity. With a metal capillary of 0.3 mm i.d., the typical column length could be reduced to be several centimeters. The retentivity for alkanes on the fiber-packed capillary column was compared to that obtained by a conventional open-tubular capillary column of the same length. Taking advantage of the heat-resistant property of both the fiber and the metal capillary, the separation of a polystyrene mixture on the polymer-coated fiber-packed short metal capillary column with a temperature-programmed run up to 400 °C was successfully carried out. As the typical application, rapid GC separations were also carried out with the short column of 0.05 m length.

Resolution of common dietary sugars from probe sugars for test of intestinal permeability using capillary column gas chromatography

The most widely accepted method for the evaluation of intestinal barrier integrity is the measurement of the permeation of sugar probes following an oral test dose of sugars. The most-widely used sugar probes are sucrose, lactulose, mannitol and sucralose. Measuring these sugars using a sensitive gas chromatographic (GC) method, we noticed interference on the area of the lactulose and mannitol peaks. We tested different sugars to detect the possible makeup of these interferences and finally detected that the lactose interferes with lactulose peak and fructose interferes with mannitol peak. On further developing of our method, we were able to reasonably separate these peaks using different columns and condition for our assay. Sample preparation was rapid and simple and included adding internal standard sugars, derivitization and silylation. We used two chromatographic methods. In the first method we used Megabore column and had a run time of 34 min. This resulted in partial separation of the peaks. In the second method we used thin capillary column and was able to reasonably separate the lactose and lactulose peaks and the mannitol and fructose peaks with run time of 22 min. The sugar probes including mannitol, sucrose, lactulose, sucralose, fructose and lactose were detected precisely, without interference. The assay was linear between lactulose concentrations of 0.5 and 40 g/L (r(2)=1.000, P<0.0001) and mannitol concentrations of 0.01 and 40 g/L (r(2)=1.000). The sensitivity of this method remained high using new column and assay condition. The minimum detectable concentration calculated for both methods was 0.5 mg/L for lactulose and 1 mg/L for mannitol. This is the first report of interference of commonly used sugars with test of intestinal permeability. These sugars are found in most of fruits and dairy products and could easily interfere with the result of permeability tests. Our new GC assay of urine sugar probes permits the simultaneous quantitation of sucralose, sucrose, mannitol and lactulose, without interference with lactose and fructose. This assay is a rapid, simple, sensitive and reproducible method to accurately measure intestinal permeability.

A study of the efficiency of monolithic silica gel capillary columns for gas chromatography

The efficiency and dynamic characteristics of seven silica-gel-based monolithic capillary columns were analyzed by separating on them a mixture of five light hydrocarbons. For helium carrier gas flowing at an optimum velocity, the height equivalent to a theoretical plate was found to be 0.15–0.20 mm, values comparable to those typical of packed capillary columns. An analysis of the Van Deemter curves for the columns under study demonstrated that the main contribution to the smearing of the chromatographic zone comes from the diffusional processes in the mobile phase while the mass transfer between the mobile and stationary phases plays only a minor role. At the same time, the parameter A in the Van Deemter equation, which characterizes the degree of column packing uniformity, was found to be negative. This result contradicts the classical theory of chromatography and calls for further studies of monolithic capillary columns.

Use of changes in triacylglycerols during ripening of cheeses with high lipolysis levels for detection of milk fat authenticity

The triacylglycerol (TAG) compositions by carbon number during ripening of two Protected Designation of Origin (PDO) cheeses were analysed using short capillary column gas chromatography. Lipolysis levels were high in the Cabrales (blue cheese produced from cows’ milk or from blends of cows’ with goats’ milk) and Majorero goats’ milk cheeses at the end of ripening, with free fatty acid (FFA) levels of around 24 000 ppm and significant changes in the TAG composition. The level of lipolysis in an industrial blue cheese made from ewes’ milk was low, with an FFA value of around 6000 ppm and no significant changes in the TAG composition during ripening. The TAG values recorded for each cheese sample were substituted into the multiple regression equations that have been proposed for use in detecting foreign fats in milk fat. The values thus obtained were within the established ranges in early ripening. In the cheeses with high lipolysis levels during ripening, some of the values obtained fell outside the established ranges. These equations can be potentially useful for detecting foreign fats in these cheeses, when employed early in the ripening period. Furthermore, it is important to take into account that before coming to a conclusion about cheese authenticity, several individual samples should be analysed.

Docosahexaenoic Acid in Red Blood Cells of Term Infants Receiving Two Levels of Long‐Chain Polyunsaturated Fatty Acids

A randomized, double-blind, prospective trial assessed effects of different formula levels of polyunsaturated fatty acids on blood phospholipid docosahexaenoic (DHA; 22:6omega3) and arachidonic acids (ARA; 20:4omega6) in term infants at 120 days of age. Healthy, formula-fed term infants (n = 78) were randomized to 1) routine milk-based formula with 8 mg DHA, 21 mg ARA, 110 mg alpha-linolenic (ALA; 18:3omega3), and 1,000 mg linoleic acids (LA; 18:2omega6) per 100 kcal (Lower-long-chain polyunsaturated fatty acids [LCPUFA]; n = 39) or 2) routine milk-based formula with 17 mg DHA, 34 mg ARA, 85 mg ALA, and 860 mg LA per 100 kcal (Higher-LCPUFA; n = 39). Fatty acid methyl esters from red blood cell (RBC) and plasma phospholipid fractions were assessed using capillary column gas chromatography. Compared with infants fed Lower-LCPUFA formula, the Higher-LCPUFA group had significantly greater percentages of fatty acids as DHA in RBC phosphatidylethanolamine (PE), RBC phosphatidylcholine (PC), total RBC, and plasma phospholipids (P < 0.001). Infants fed Lower-LCPUFA formula had higher percentages of precursor omega6 fatty acids in the desaturation/elongation pathway but lower percentages of ARA (RBC PE, RBC PC, and plasma phospholipid, P < 0.001; total RBC, P = 0.017) compared with the Higher-LCPUFA group. Greater amounts of dietary ALA do not produce as great an increase in DHA in blood lipids as preformed dietary DHA. Infants fed DHA at levels similar to human milk had significantly greater percentage of DHAat 120 days of age compared with the Lower-LCPUFA group despite higher precursor levels of ALA.