The use of inverse gas chromatography to study surface thermal oxidation of polypropylene

Thermo-oxidative effects on the surface energy of polypropylene were measured by inverse gas chromatography as a function of exposure time and temperature. Unaltered polypropylene had a surface energy of 33 mJ/m². Oxidized polypropylene, after exposure to air at temperatures of 100 °C and 110 °C, had a range of maximum surface energies from 38 to 41 mJ/m². Comparisons between FTIR carbonyl peak growth and the surface energy showed that both methods detect oxidation, though the increase in surface energy is detected before the carbonyl peak growth is noticeable. The work of adhesion predicted by the surface free energies obtained in this work between a coated calcium carbonate and polypropylene changes by 10% due to the oxidation of the polymer at 110 °C.     

The study of reversed phases by inverse gas chromatography

Summary The surface properties of three silica-based reversed phases have been studied by inverse gas chromatography. Theoretical deduction indicates that there is a linear relationship between the molar deformation polarisation of the test solute (P_D) and the dispersive interaction energy between the solute and the C18 and non-bonded silica surfaces. The specific interaction energy between the solute molecule and the silica surface (-G^SP) can be measured as the vertical distance between the solute experimental retention data point (RTl_nV_N) and the n-alkane RTl_nV_N vs P_D calibration line. From multiple regression analysis of-G^SP data with proton acceptor solubility parameter {ie290-1} and orientation solubility parameter {ie290-2} as variants, two coefficients can be obtained related to the influence of the residual silanol groups and the trace metal impurities.     

A rapid multidimensional liquid-gas chromatography method for the analysis of mineral oil saturated hydrocarbons in vegetable oils

The present paper describes an investigation directed toward the development of a rapid heart-cutting LC-GC method for the analysis of mineral oil saturated hydrocarbons contained in vegetable oils. The automated LC-GC experiments were carried out by using a system equipped with a syringe-type interface, capable of both heart-cutting and comprehensive (LC × GC) two-dimensional analysis. The first dimension separation was achieved on a 100 mm × 3 mm ID × 5 μm d(p) silica column, operated under isocratic conditions (hexane). A single 30-s cut, corresponding to a 175 μL volume, was transferred to a programmed temperature vaporizer. After the large volume injection, the target analytes were separated in a rapid manner (~9 min) using a 15 m × 0.1mm ID × 0.1 μm micro-bore GC capillary. The overall LC-GC run time enables the analysis of ca. 4 samples/hour. Quantification was performed by using external calibration, in the 1-200 mg/kg range. The method was validated in terms of linearity, precision, limits of detection and quantification, and accuracy. A series of commercial samples were subjected to analysis. Various degrees of contamination were found in all samples, in the 7.6-180.6 mg/kg range.     

Elucidation of fatty acid profiles in vegetable oils exploiting group-type patterning and enhanced sensitivity of comprehensive two-dimensional gas chromatography

The present research is focused on the use of comprehensive 2-D GC (GCxGC) for the thorough elucidation of fatty acid (FA) profiles contained in vegetable oils; the samples analysed consisted of extra-virgin olive oil and refined hazelnut oil. The enhanced sensitivity and the formation of group-type patterns provided by GCxGC enabled the identification and quantification of both well-known and rather unexpected FAs contained in the lipid matrices. Peak assignment was, in most cases, supported by using pure standard compounds. Of particular interest was the identification of a series of odd-numbered FAs in both samples. The results attained to demonstrate the usefulness of GCxGC also for the analysis of supposedly low-complex samples.     

Acid/base characterization of sepiolite by inverse gas chromatography

Summary The surface properties of sepiolite were investigated by inverse gas chromatography. It is shown that the value of the dispersive component change uniformly with temperature, while the values obtained for the parameters K_A and K_D indicate an acidic character for the sepiolite surface.     

Surface energy of solid catalysts measured by inverse gas chromatography

The time separation of experimental surface energy on Pt-Rh bimetallic catalysts, together with the time-independent rate constants for adsorption and desorption of O(2), CO, and CO(2) on them, is described, applying the reversed-flow version of inverse gas chromatography. The standard free energy of adsorption DeltaG(z.plims;) and its probability density function over time, together with the geometrical mean of the London parts of the total surface free energy (gamma(L)(1)gamma(L)(2))(1/2) of the adsorbed probe and the solid surface, accompanied by the relevant probability density functions over time are also calculated. The time-resolved phenomena lead to quite varying values of DeltaG(z.plims;), (gamma(L)(1)gamma(L)(2))(1/2), and the distribution functions as time passes, their maximum values being given by the catalyst containing a Pt:Rh = 3:1 weight ratio of the active phase for all adsorbed gases. The conclusion is reached that the surface energy measured as described can be used as a good measure for catalyst characterization.     

Time separation of adsorption sites on heterogeneous surfaces by inverse gas chromatography

Summary The measurement of local (homogeneous) adsorption energiesε _i , local monolayer capacities,c _max ^* , local adsorption isotherms,θ _i (p, T, ε), and probability density functions for adsorption, f(ε) and ϕ(ε,t), can be used to study the mechanism of adsorption of five gaseous hydrocarbons on the heterogeneous surface of magnesium oxide. The method does not use analytical or numerical solutions of a classical integral equation comprisingf(ε) as unknown, but it depends on a time function of gas chromatographic peaks obtained by short flow-reversals of the carrier gas. The results for adsorption of ethane, ethylene, acetylene, propene, and l-butene on MgO, in the absence and presence of O₃ are given and discussed on the basis of a mechanism proposed earlier for argon on titatium dioxide.     

Estimation of the lateral to basal surface ratio of talc by inverse gas chromatography

Inverse Gas Chromatography at Infinite Dilution, i.e. IGC‐ID, allows following the evolution of surface properties of talc impregnated with increasing concentrations of polyethyleneglycol of molecular weight 20,000. Coupling Inverse chromatography in infinite dilution conditions measurements with controlled surface modification, we have developed a new method to estimate the lateral to basal surface ratio of talc crystals.     

Investigation of thermodynamic properties of hyperbranched aliphatic polyesters by inverse gas chromatography

Thermodynamic properties of a series of commercial hyperbranched aliphatic polyesters (Boltorn^® H20, H30 and H40) were examined for the first time by inverse gas chromatography (IGC) using 13 different solvents at infinite dilution as probes. Retention data of probes were utilized for an extensive characterization of polymers, which includes the determination of the Flory–Huggins interaction parameter, the weight fraction activity coefficient as well as the total and partial solubility parameters. Analysis of the results indicated that the total and partial solubility parameters decrease with increase of temperature. Furthermore, upon increase of the molecular weight, while the hydrogen bonding component decreases, no influence on the total solubility parameter is noticed within the experimental error margins. Results from the present study while providing new insight to the thermodynamic characteristics of the examined systems, they are also expected to reflect more general aspects of the behavior of hyperbranched polymers bearing similar end-groups.     

Characterization of the surface properties of heavy residues of oil distillation by inverse gas chromatography

Summary Heavy residues from the distillation of oils (SAFANYA) have been analyzed by inverse gas chromatography (IGC). The dispersive components of the surface energies of the residues could readily be determined. Acid/base characteristics could be appreciated using an original method developed in this Laboratory.     

双重净化-气相色谱法测定植物油中指示性多氯联苯

为了考察食用油中7种指示性多氯联苯(PCBs)的残留情况,建立了食用油中痕量多氯联苯测定的双重净化-气相色谱法。以乙腈提取样品,提取液浓缩至干后用正己烷溶解,经浓硫酸、硅胶分散固相萃取双重净化后进行气相色谱分析,外标法定量。优化的色谱条件为:HP-5石英毛细管柱(30 m×0.32 mm×0.25 μm)程序升温分离,流速0.8 mL/min,进样量1.00 μL,电子捕获检测器检测。结果表明:在优化的条件下,7种多氯联苯在10~500 μg/L范围内线性良好,相关系数大于0.999,不同基质中的检出限(S/N=3)范围为1.8~8.9 μg/kg,定量限(S/N=10)范围为5.9~29.8 μg/kg。在橄榄油、花生油和棕榈油空白样品中添加10、20、100 μg/kg 3个水平的7种多氯联苯,其加标回收率范围为71.0%~105.5%,相对标准偏差(RSD)范围为4.0%~11.3%。该方法具有操作简便、快速、准确的特点,可用于植物油中指示性多氯联苯残留量的日常检测。     

Surface characterization of macroporous glycidyl methacrylate based copolymers by inverse gas chromatography

Two samples of macroporous crosslinked poly(glycidyl methacrylate-co-ethylene glycol dimethacrylate), PGME, with different porosity parameters were synthesized by suspension copolymerization and modified by ring-opening reaction of the pendant epoxy groups with ethylene diamine, EDA. Inverse gas chromatography at infinite dilution was used for the determination of adsorption properties of PGME, and copolymer modified with ethylene diamine, PGME-en. Thermodynamic parameters of adsorption, dispersive components of the surface free energies, and the acid/base constants for the copolymer samples were calculated. The calculated dispersive surface energy values, , for PGME and PGME-en are comparable with the literature data for nonconductive polymers.     

Study of the influence of surfactants on the transfer of gases into liquids by inverse gas chromatography

Analyses of amino acids and peptides were performed using a quartz microchip and an interface for microchip electrophoresis-electrospray ionization mass spectrometry (MCE-ESI-MS). In MCE-ESI-MS, negative pressure caused by ESI increased band broadening and deteriorated separation. We tried to suppress the negative pressure and improve separation using a microchip with a long separation channel. Separations of peptide standards were compared using two microchips with long separation channel (58.9 mm) and short one (22.9 mm). Theoretical plate numbers and resolution were improved significantly using the former. The theoretical plate numbers of [Val4]angiotensin was 8600 using the former and 1700 using the latter. When background electrolytes of low pH were used in an uncoated quartz microchip, electrokinetic injection was difficult because of weak electroosmotic flow. The use of successive multiple ionic polymer layers coating of the microchip channel stabilized electrokinetic injection and permitted analysis of amino acids and peptides even under low pH conditions. Separation of amino acids was successfully performed using formic acid solution (pH 2.5) as background electrolyte.     

Comparison of Dorris-Gray and Schultz methods for the calculation of surface dispersive free energy by inverse gas chromatography

Inverse gas chromatography (IGC) is an important technique for the characterization of surface properties of solid materials. A standard method of surface characterization is that the surface dispersive free energy of the solid stationary phase is firstly determined by using a series of linear alkane liquids as molecular probes, and then the acid-base parameters are calculated from the dispersive parameters. However, for the calculation of surface dispersive free energy, generally, two different methods are used, which are Dorris-Gray method and Schultz method. In this paper, the results calculated from Dorris-Gray method and Schultz method are compared through calculating their ratio with their basic equations and parameters. It can be concluded that the dispersive parameters calculated with Dorris-Gray method will always be larger than the data calculated with Schultz method. When the measuring temperature increases, the ratio increases large. Compared with the parameters in solvents handbook, it seems that the traditional surface free energy parameters of n-alkanes listed in the papers using Schultz method are not enough accurate, which can be proved with a published IGC experimental result.     

Analysis of Alaskan crude oils by glass capillary gas chromatography/mass spectrometry

Glass capillary gas chromatography/mass spectrometry is used to profile Alaskan crude oil for purposes of origin verification. Alaskan oil, sampled at Valdez, Alaska, and transshipped to the U.S. East Coast, is compared with 21 samples of foreign crude oil using GC/MS techniques in which original data is reconstructed at selected parent and fragment ions to generate a series of chromatographic profiles. Comparison of selected profiles and compositional parameters derived from peak ratios allows distinction of Alaskan oil from many foreign crudes and may be applied to the examination of crude mixtures.     

Characterization of surface thermodynamic properties of p-toluene sulfonate-doped polypyrrole by inverse gas chromatography

Summary p-Toluene sulfonate-doped polypyrrole (PPyTos) powder has been characterized by inverse gas chromatography at various temperatures. We have used apolar n-alkanes and polar probes of differing acidity and basicity to interrogate the London dispersive and Lewis acid-base properties of PPyTos, respectively. We have found that the London component of the surface energy (γs^d) is about 90 mJ · m⁻² at 25°C and the acid-base contribution to the free energy of adsorption (ΔG_a ^AB) for Lewis bases is higher than 8 kJ · mol⁻¹. These results show that PPyTos is a high energy material and is capable of very strong specific acid-base interactions. Lewis acidity is, however, dominant and is shown to increase with temperature. The determination of the heats of adsorption for tetrahydrofuran and ethyl acetate enabled us to determine Drago’s E_A, C_A, E_B and C_B parameters. Whilst E_A and C_A are similar to those published for chloride-doped polypyrrole and rank PPyTos as a hard acidic species, the E_B and C_B values suggest that PPyTos is a very soft Lewis base.     

Measurement of the infinite dilution diffusion coefficients of small molecule solvents in silicone rubber by inverse gas chromatography

The infinite dilution diffusion coefficients of n-hexane, n-heptane and n-decane in crosslinked silicone rubber with different crosslinking agent concentrations were measured in the temperature range of 348.15 K-368.15 K by inverse gas chromatography. The crosslinked silicone rubber was obtained by dissolving PDMS prepolymer, crosslinking agent and catalyst in n-heptane solvent and characterized by FTIR spectra. The Van Deemter equation was used to determine diffusion coefficients from the variation in chromatographic peak width with carrier gas flow rate. The good linear relation indicated the Van Deemter equation used in this work was reliable. The influences of small molecule solvent, crosslinking agent concentration and temperature on the infinite dilution diffusion coefficient were investigated. The results showed that the infinite dilution diffusion coefficient decreased with an increasing number of CH₂ group in the alkane series. The increase in crosslinking agent concentration resulted in decrease of the infinite dilution diffusion coefficient. The infinite dilution diffusion coefficient increased with the rising of temperature. The interdependence on the infinite dilution diffusion coefficient and temperature accorded with Arrhenius equation well. Diffusion constant and activation energy obtained from the Arrhenius equation provided straight lines with the specific critical volume and crosslinking agent concentration.     

Adulteration or natural variability? enantioselective gas chromatography in purity control of essential oils

The potential of enantioselective capillary gas chromatography with modified cyclodextrins as chiral stationary phases for authenticity control is demonstrated for a selection of economically important essential oils. Adulteration can be easily detected in cases where enantiomerically pure constituents are present in natural oils. In cases of (naturally) varying enantiomeric compositions of chiral constituents, enantioselective gas chromatography may prove insufficient.