Conjugated linoleic acid determination in human milk by fast-gas chromatography

An efficient direct method for measuring c9,t11- and t10,c12-conjugated linoleic acid (CLA) isomer content in human and rat milk was developed and validated using an RTX-2330 capillary column (40 m × 0.18 mm × 0.1 μm). In comparison with the commonly used 100 m × 0.25 mm × 0.20 μm columns, this new type of fast column allowed the separation of FAMEs with the same resolution but in much less time. An additional advantage for biological samples was that only a small volume of sample was needed. Two different procedures were tested in order to select the best methylation of CLA isomers, and the alkali plus acid-catalyzed procedure was selected. The precision results showed relative standard deviations (R.S.D.) of repeatability and reproducibility ranging between 0.10 and 8.71%. The application of this method to human and rat milk samples showed that it was a rapid, simple and reliable method for the analysis of biological samples.     

Extraction of fatty acids from grape seed by superheated hexane

Superheated hexane extraction has been tested for obtaining fatty acids from grape seed and compared with conventional Soxhlet and hot hexane extractions. Seeds from grape residues from a winery were dried for 46 h at 105 °C, milled and sieved by particle size (d < 0.42 mm, 0.42 < d < 0.84 mm and d > 0.84 mm). An optimization study of influential variables on superheated hexane extraction (namely extraction time, temperature, pression, particle size and sample amount) was carried out by a multivariate approach. All the extracts were concentrated in a rotary evaporator and dried by adding 1 g of Na₂SO₄. Then, 2 ml of the dried extract were subjected to reaction with 1 ml of a 0.5 M solution of sodium methylate in methanol to obtain fatty acid methyl esters (FAMEs). After derivatization, FAMEs were quantified by GC-FID. The results show that the optimal conditions for superheated hexane extraction are: time extraction, 10 min; temperature, 80 °C; pressure, 40 bar; particle size, d < 0.42 mm; amount of sample, 0.4 g. Under these conditions, around 84% of the fatty acids (out of the amount obtained by Soxhlet extraction) is extracted. Comparison with Soxhlet and hot hexane extractions showed that the percentages of FAMEs are similar in all the extracts and they agree with the data in the bibliography.     

Development of fast enantioselective gas-chromatographic analysis using gas-chromatographic method-translation software in routine essential oil analysis (lavender essential oil)

The study aimed to find the best trade-off between separation of the most critical peak pair and analysis time, in enantioselective GC–FID and GC–MS analysis of lavender essential oil, using the GC method-translation approach. Analysis conditions were first optimized for conventional 25 m × 0.25 mm inner diameter (d_c) column coated with 6^I–VII-O-tert-butyldimethylsilyl-2^I–VII-3^I–VII-O-ethyl-β-cyclodextrin (CD) as chiral stationary phase (CSP) diluted at 30% in PS086 (polymethylphenylpolysiloxane, 15% phenyl), starting from routine analysis. The optimal multi-rate temperature program for a pre-set column pressure was determined and then used to find the pressures producing the efficiency-optimized flow (EOF) and speed-optimized flow (SOF). This method was transferred to a shorter narrow-bore (NB) column (11 m × 0.10 mm) using method-translation software, keeping peak elution order and separation. Optimization of the enantioselective GC method with the translation approach markedly reduced the analysis time of the lavender essential oil, from about 87 min with the routine method to 40 min with an optimal multi-rate temperature program and initial flow with a conventional inner diameter column, and to 15 min with FID as detector or 13.5 min with MS with a corresponding narrow-bore column, while keeping enantiomer separation and efficiency.     

Optimized use of a 50 μm ID secondary column in comprehensive two-dimensional gas chromatography–mass spectrometry

The objective of the present research is directed towards the optimized use of a 50 μm ID secondary column, in a comprehensive two-dimensional gas chromatography–quadrupole mass spectrometry (GC × GC–qMS) system. The analytical aim was achieved by exploiting a split-flow GC × GC approach, and a rapid-scanning qMS instrument. The stationary phase combination consisted of an apolar (silphenylene polymer) 30 m × 0.25 mm ID column, linked by means of a Y-union, to an MS-connected 1 m × 0.05 mm ID polar one [poly(ethyleneglycol)], and to a 0.20 m × 0.05 mm ID uncoated capillary segment; the latter was connected to a manually operated split-valve. It will be herein demonstrated that the split-flow GC × GC approach, successfully employed in previous H₂-based, flame ionization detection experiments, provides equally satisfactory results using mass spectrometric detection and helium as carrier gas. An optimized split-flow GC × GC–qMS method was developed and exploited for the analysis of a perfume sample. The results attained were compared with those observed using the same analytical column combination, but with no flow-splitting. It was found that it is not convenient to employ a 50 μm ID secondary column in a conventional GC × GC–MS instrument. On the contrary, the use a 50 μm ID secondary column, in a split-flow, twin-oven system, provided a good performance. A recently developed comprehensive chromatography software was used for data processing.     

Screening analysis to detect adulteration in diesel/biodiesel blends using near infrared spectrometry and multivariate classification

This paper proposes an analytical method to detect adulteration of diesel/biodiesel blends based on near infrared (NIR) spectrometry and supervised pattern recognition methods. For this purpose, partial least squares discriminant analysis (PLS-DA) and linear discriminant analysis (LDA) coupled with the successive projections algorithm (SPA) have been employed to build screening models using three different optical paths and the following spectra ranges: 1.0 mm (8814-3799 cm⁻¹), 10 mm (11,329-5944 cm⁻¹ and 5531-4490 cm⁻¹) and 20 mm (11,688-5952 cm⁻¹ and 5381-4679 cm⁻¹). The method is validated in a case study involving the classification of 140 diesel/biodiesel blend samples, which were divided into four different classes, namely: diesel free of biodiesel and raw vegetal oil (D), blends containing diesel, biodiesel and raw oils (OBD), blends of diesel and raw oils (OD), and blends containing a fraction of 5% (v/v) of biodiesel in diesel (B5). LDA-SPA models were found to be the best method to classify the spectral data obtained with optical paths of 1.0 and 20 mm. Otherwise, PLS-DA shows the best results for classification of 10 mm cell data, which achieved a correct prediction rate of 100% in the test set.     

Determination of elaidic and vaccenic acids in foods using GC×GC-FID and GC×GC-TOFMS

Trans fatty acids (TFAs) are present in meat and dairy products as m ruminant animals and in vegetable fats due to partial hydrogenation. This study aimed to discriminate between natural (N-TFA) and hydrogenated trans fatty (H-TFA) acids by GC × GC-flame ionization detection (GC × GC-FID) and comprehensive GC × GC-time-of-flight mass spectrometry (GC × GC-TOFMS). The separation of two kinds of trans fats, vaccenic acid (18:1 trans-11) and elaidic acid (18:1 trans-9), was performed using GC × GC-FID and GC × GC-TOFMS. A 100 m × 0.25 mm I.D. × 0.2 μm (film thickness) SP-2560 (bis-cyanopropyl polysiloxane) fused capillary column (first separation dimension, 1D) was coupled to a 1.5 m × 0.18 mm I.D. × 0.18 μm (film thickness) RTX-5 (5% diphenyl/95% dimethyl polysiloxane) fused capillary column (second separation dimension, 2D). The RSD of the intra-day repeatability by both GC × GC-FID and GC × GC-TOFMS for elaidic and vaccenic acids was ≤9.56% and ≤9.97%, and the RSD of the inter-day repeatability was ≤8.49 and ≤9.06%, respectively. It was found that the V/E value (vaccenic acid to elaidic acid ratio) could be used to distinguish H-TFA from N-TFA and to evaluate the quality of the fatty foods.     

Analysis of triorganotin compounds in water samples by hydrophilic interaction liquid chromatography–electrospray ionization-mass spectrometry

Hydrophilic interaction liquid chromatography (HILIC)–electrospray ionization-mass spectrometry (ESI-MS) was evaluated for the analysis of tributyltin (TBT) and triphenyltin (TPT) in water samples. Separation was performed in isocratic mode on an Atlantis HILIC silica (2.1 mm × 150 mm, 5 μm) column with a mobile phase of acetonitrile–0.1% aqueous HCOOH (86:14, v/v) at a flow rate of 0.2 mL/min. Under optimum conditions, limits of detection for TBT and TPT were 10 and 20 pg injected onto the column, respectively. The extraction of triorganotin compounds from seawater samples was carried out using a polymer-based solid phase extraction cartridge of mixed modes with reversed-phase and weak anion exchange. Tributyltin-d₂₇ chloride and triphenyltin-d₁₅ chloride were used as internal standards. The relative standard deviations for the analysis were less than 4%. Using the proposed method, it was possible to analyze concentrations of TPT and TBT in seawater at ppt levels.     

Two methods for the separation of monounsaturated octadecenoic acid isomers

The identification and quantification of complex mixtures of cis and trans octadecenoic (18:1) fatty acid isomers presents a major challenge for conventional one-dimensional GC/FID analysis of their methyl esters. We have compared the use of two methods to achieve optimized separations of positional and geometrical octadecenoic fatty acid isomers—comprehensive two-dimensional gas chromatography (GC × GC), and silver ion high performance liquid chromatography interfaced to atmospheric pressure photoionization (APPI) mass spectrometry. Nine isomers of octadecenoic acid methyl ester were well separated on a single silver ion column with a mobile phase of 0.018% acetonitrile and 0.18% isopropanol in hexane. Reproducible retention times were obtained with relative standard deviations of around 1% over 5 injections. The extra selectivity and reproducibility afforded by APPI-MS, together with the wide separation of cis and trans isomers by silver ion chromatography, resulted in a promising method for measurement of octadecenoic acid FAME. The GC × GC separation was performed using various column combinations, and optimal separation was obtained by coupling an ionic liquid column (Supelco SLB-IL100 [1,9-di(3-vinyl-imidazolium) nonane bis(trifluoromethyl) sulfonyl imidate]) in the first dimension with a SGE BPX50 (50% phenyl polysilphenylene-siloxane) in the second dimension. These methods have been applied to the analysis of octadecenoic acid in milk and beef fat.     

High-efficiency liquid chromatography–mass spectrometry separations with 50 mm, 250 mm,and 1 m long polymer-based monolithic capillary columns for the characterization of complex proteolytic digests

In this study, high-efficiency LC–MS/MS separations of complex proteolytic digests are demonstrated using 50 mm, 250 mm, and 1 m long poly(styrene-co-divinylbenzene) monolithic capillary columns. The chromatographic performance of the 50 and 250 mm monoliths was compared at the same gradient steepness for gradient durations between 5 and 150 min. The maximum peak capacity of 400 obtained with a 50 mm column, increased to 485 when using the 250 mm long column and scaling the gradient duration according column length. With a 5-fold increase in column length only a 20% increase in peak capacity was observed, which could be explained by the larger macropore size of the 250 mm long monolith. When taking into account the total analysis time, including the dwell time, gradient time and column equilibration time, the 50 mm long monolith yielded better peptide separations than the 250 mm long monolithic column for gradient times below 80 min (n_c = 370). For more demanding separation the 250 mm long monolith provided the highest peak production rate and consequently higher sequence coverage. For the analysis of a proteolytic digest of Escherichia coli proteins a monolithic capillary column of 1 m in length was used, yielding a peak capacity of 1038 when applying a 600 min gradient.     

Protein separation using toroidal columns by type-J synchronous counter-current chromatography towards preparative separation

Separation of large bioactive molecules such as proteins, DNAs and RNAs using aqueous two-phase systems (ATPSs) and liquid–liquid partition-based counter-current chromatography (CCC) can avoid risks of sample loss and denaturation, and greatly reduce processing time. We have constructed toroidal columns (length 26–140 m, column volume 51–280 ml, bore size 1.6 mm) suitable for mounting onto a commercially available preparative CCC apparatus. With the use of an ATPS containing 12.5% (w/w) PEG1000 and 12.5% (w/w) K₂HPO₄ and at a rotational speed of 800 rpm for the rotor of the CCC device, the lower phase (i.e. the phosphate-enriched phase) has been used as the mobile phase and a pair of proteins, myoglobin and lysozyme, as model proteins for demonstrating the separation capability of the CCC system. For a toroidal column with a length of 53.5m and a column volume of 107.5 ml, and operated for the Coriolis force parallel flow mode at 0.62 ml/min, protein sample loading (containing 2.2 mg/ml myoglobin and lysozyme, respectively) at 1.7% and 7.4% to the column volume led to peak resolution (with theoretical plate number TP and stationary phase retention S_f shown in the parenthesis) of R_s = 1.5 (N = 211 and N = 113 TP for myoglobin and lysozyme, respectively, and S_f = 45.0%), and R_s = 1.4 (218 and 152 TP, and S_f = 34.0%). However, further increase of the loading to 13% failed to separate the two proteins. Although proteins eluted at positions predictable from the distribution coefficients, they showed broader peaks when compared with small dipeptides under identical CCC operating conditions. This confirms that the molecular weight of the partitioned species is an important factor causing peak broadening on CCC chromatograms. These results paved the way for further scaling-up toroidal CCC columns for processing larger quantities of samples containing large biomolecules.     

Comparison of pyrimethanil-imprinted beads and bulk polymer as stationary phase by non-linear chromatography

A pyrimethanil-imprinted polymer (P1) was prepared by iniferter-mediated photografting a mixture of methacrylic acid and ethylene dimethacrylate onto homemade near-monodispersed chloromethylated polydivinylbenzene beads. The chromatographic behaviour of a column packed with these imprinted beads was compared with another column packed with irregular particles obtained by grinding a bulk pyrimethanil-imprinted polymer (P2). The comparison was made using the kinetic model of non-linear chromatography, studying the elution of the template and of two related substances, cyprodinil and mepanipyrim. Extension of the region of linearity, capacity factors for the template and the related substances, column selectivity, binding site heterogeneity, apparent affinity constant (K) and lumped kinetic association (k_a) and dissociation rate constant (k_d) were studied during a large interval of solute concentration, ranging between 1 and 2000 μg/ml. From the experimental results obtained, in the linearity region of solute concentration column selectivity and binding site heterogeneity remained essentially the same for the two columns, while column capacity (at 20 μg/ml, P1 = 23.1, P2 = 11.5), K (at 20 μg/ml, P1 = 8.3 × 10⁶ M⁻¹, P2 = 2.5 × 10⁶ M⁻¹) and k_a (at 20 μg/ml, P1 = 3.5 μM⁻¹ s⁻¹, P2 = 0.47 μM⁻¹ s⁻¹) significantly increased and k_d (at 20 μg/ml, P1 = 0.42 s⁻¹, P2 = 0.67 s⁻¹) decreased for the column packed with the imprinted beads. These results are consistent with an influence of the polymerisation method on the morphology of the resulting polymer and not on the molecular recognition properties due to the molecular imprinting process.     

Comprehensive two-dimensional gas chromatography improves separation and identification of anabolic agents in doping control

The application of comprehensive two-dimensional gas chromatography coupled to time-of-flight mass spectrometry (GC × GC-TOFMS) for the analysis of six anabolic agents (AAs) in doping control is investigated in this work. A non-polar–polar column configuration with 0.2 μm film thickness (d_f) second dimension (²D) column was employed, offering much better spread of the components on ²D when compared to the alternative 0.1 μm d_f²D column. The proposed method was tested on the “key” AA that the World Anti-Doping Agency (WADA) had listed at the low ng mL⁻¹ levels (clenbuterol, 19-norandrosterone, epimethendiol, 17α-methyl-5α-androstane-3α,17β-diol, 17α-methyl-5β-androstane-3α,17β-diol and 3′-OH-stanozolol). The compounds were spiked in a blank urine extract obtained by solid-phase extraction, hydrolysis and liquid–liquid extraction; prior to analysis they were converted to the corresponding trimethylsilyl (TMS) derivatives. The limit of detection (LOD) was below or equal to the minimum required performance limit (MRPL) of 2 ng mL⁻¹ defined by WADA, and the correlation coefficient was in the range from 0.995 to 0.999. The method allows choosing an ion from the full mass spectra which shows the least interference from the matrix and/or the best sensitivity; this can only be done if full scan mass spectral data are available. The advantage of GC × GC over classical one-dimensional GC (1D GC), in terms of separation efficiency and sensitivity, is demonstrated on a positive urine control sample at a concentration of 5 ng mL⁻¹. The obtained similarity to the in-house created TOFMS spectra library at this level of concentration was in the range from 822 to 932 (on the scale from 0 to 999). Since full mass spectral information are recorded, the method allows the retro-search of non-target compounds or new “designer steroids”, which cannot be detected with established GC–MS methods that use selected ion monitoring (SIM) mode.     

Thermochemistry of intercalation of n-alkylmonoamines into lamellar hydrated barium phenylarsonate

Hydrated layered crystalline barium phenylarsonate, Ba(HO₃AsC₆H₅)₂·2H₂O was used as host for intercalation of n-alkylmonoamine molecules CH₃(CH₂)_n-NH₂ (n = 1-4) in aqueous solution. The amount intercalated (n_f) was followed batchwise at 298 ± 1 K and the variation of the original interlayer distance (d) for hydrated barium phenylarsonate (1245 ppm) was followed by X-ray powder diffraction. Linear correlations were obtained for both d and n_f as a function of the number of carbon atoms in the aliphatic chain (n_c): d = (2225 ± 32) + (111 ± 11)n_c and n_f = (2.28 ± 0.15) − (11.50 ± 0.03)n_c. The exothermic enthalpies of intercalation increased with n_c, which was derived from the monomolecular amine layer arrangements with the longitudinal axis inclined by 60° to the inorganic sheets. The intercalation was followed by titration with amine at the solid/liquid interface and gave the enthalpy/number of carbons correlation: ΔH = −(7.25 ± 0.40) − (1.67 ± 0.10)n_c. The negative Gibbs free energies and positive entropic values reflect the favorable host/guest intercalation processes for this system.     

Poly(butylene terephthalate)/poly(ε-caprolactone) blends: Influence of PCL molecular mass on PBT melting and crystallization behavior

The isothermal crystallization kinetics and melting behavior of poly(butylene terephthalate) (PBT) in binary blends with poly(ε-caprolactone) (PCL) was investigated as a function of PCL molecular mass by differential scanning calorimetry and optical microscopy. The components are miscible in the melt when oligomeric PCL (M_w = 1250) is blended with PBT, whereas only partial miscibility was found in mixtures with higher molecular mass (M_w = 10,000 and 50,000). The equilibrium melting point of PBT in the homopolymer and in blends with PCL was determined through a non-linear extrapolation of the T_m = f(T_c) curve. The PBT spherulitic growth rate and bulk crystallization rate were found to increase with respect to plain PBT in blends with PCL1250 and PCL10000, whereas addition of PCL50000 causes a reduction of PBT solidification rate. The crystallization induction times were determined by differential scanning calorimetry for all the mixtures through a blank subtraction procedure that allows precise estimation of the crystallization kinetics of fast crystallizing polymers. The results have been discussed on the basis of the Hoffman-Lauritzen crystallization theory and considerations on both the transport of chains towards the crystalline growth front and the energy barrier for the formation of critical nuclei in miscible and partially miscible PBT/PCL mixtures are widely debated.     

Investigation of Ba fully occupied A-site BaCo0.7Fe0.3−xNbxO3−δ perovskite stabilized by low concentration of Nb for oxygen permeation membrane

BaCo_0.7Fe_0.3−xNb_xO_3−δ (BCFN, x = 0–0.2) were prepared by the conventional solid state reaction process. The crystal structure, electrical conductivity and oxygen desorption property were studied by X-ray diffraction (XRD), different thermal analysis (DTA), four-terminal direct current conductivity and oxygen temperature programmed desorption (O₂-TPD), respectively. At x = 0.08–0.20, BCFN have a cubic perovskite structure, while it exhibits the hexagonal structure for x = 0.00 and the mixed phases of cubic perovskite with trace amount of hexagonal for x = 0.05. BCFN shows good structure stability in 5%H₂ + Ar reducing atmosphere, and it is enhanced with the increased Nb-doping content. The electrical conductivity of BCFN increases with increasing temperature and decreases with the Nb substitution content for iron. BCFN exhibits a p-type semiconductor and obeys the thermally activated small polarons hopping mechanism. The oxygen fluxes increase with the working temperature and the COG flow rate, but decrease with increasing Nb content. The flux of BCFN (x = 0.08) with 1.0 mm thickness membrane reaches 25.77 ml min⁻¹ cm⁻² at 875 °C, higher than most of the reported materials.     

An in-tube SPME device for the selective determination of chlorophyll a in aquatic systems

We report a new device for the estimation of the content of chlorophyll a pigment in water samples as an indicator of water quality. The extraction of the pigment from water was also optimized. 10 mL of water was filtered through a nylon filter (45 μm pore size and 13 mm of diameter), after the chlorophylls were dissolved by immersing the filter in 1 mL of a low non-hazardous solvent as ethanol. An in-valve in-tube SPME device coupled to capillary liquid chromatography with diode array detection was designed. A capillary column of 70 cm in length (0.32 mm i.d. coated with 5% diphenyl-95% polydimethylsiloxane, 3 μm coating thickness) was used as the loop of the injection valve for preconcentration and a Zorbax SB C₁₈ (SiO₂-based) 150 mm × 0.5 mm i.d., 5 μm column (Agilent) was used as analytical column. The achieved detection limit was 0.05 μg L⁻¹ and the working range of concentrations was 0.1-1 μg L⁻¹. % RSD values between 2 and 11 were obtained. Chlorophyll a in several water matrices was determined with good results in presence of other pigments such as chlorophyll b, pheophytin a and pheophytin b.     

Enhanced resolution comprehensive two-dimensional gas chromatography applied to the analysis of roasted coffee volatiles

The present research is based on the full exploitation of the separation power of a 0.05 mm internal diameter (ID) capillary, as a comprehensive two-dimensional (2D) GC (GC × GC) secondary column, with the objective of attaining very high-resolution second dimension separations. The aim was achieved by using a split-flow system developed in previous research [P.Q. Tranchida, A. Casilli, P. Dugo, G. Dugo, L. Mondello, Anal. Chem. 79 (2007) 2266], and a dual-oven GC × GC instrument. The column combination employed consisted of a polar 30 m × 0.25 mm ID column connected, by means of a T union, to a detector-linked high-resolution 1.1 m × 0.05 mm ID apolar analytical column and to a 0.33 m × 0.05 mm ID retention gap; the latter was connected to a manually operated split valve. As previously demonstrated, the use of a split valve enables the regulation of gas flows through both analytical columns, generating the most appropriate gas linear velocities. Comprehensive 2D GC experiments were carried out on Arabica roasted coffee volatiles (previously extracted by means of solid-phase microextraction) with the split-valve closed (equal to what can be defined as conventional GC × GC) and with the split-valve opened at various degrees. The reasons why it is absolutely not effective to use a 0.05 mm ID column as second dimension in a conventional GC × GC instrument will be discussed and demonstrated. On the contrary, the use of a 0.05 mm ID column as second dimension, under ideal conditions in a split-flow, twin-oven system, will also be illustrated and discussed.     

Thermodynamics of BaNd2Fe2O7(s) and BaNdFeO4(s) in the system BaNdFeO

Two compounds, BaNd₂Fe₂O₇(s) and BaNdFeO₄(s) in the quaternary system BaNdFeO were prepared by citrate-nitrate gel combustion route and characterized by X-ray diffraction analysis. Heat capacities of these two oxides were measured in two different temperature ranges: (i) 130-325 K and (ii) 310-845 K, using a heat flux type differential scanning calorimeter. Two different types of solid-state electrochemical cells with CaF₂(s) as the solid electrolyte were employed to measure the e.m.f. as a function of temperature. The standard molar Gibbs energies of formation of these quaternary oxides were calculated as a function of temperature from the e.m.f. data. The standard molar enthalpies of formation from elements at 298.15 K, ΔfHm° (298.15 K) and the standard entropies, Sm° (298.15 K) of these oxides were calculated by the second law method. The values of ΔfHm° (298.15 K) and Sm° (298.15 K) obtained for BaNd₂Fe₂O₇(s) are: −2756.9 kJ mol⁻¹ and 234.0 J K⁻¹ mol⁻¹ whereas those for BaNdFeO₄(s) are: −2061.5 kJ mol⁻¹ and 91.6 J K⁻¹ mol⁻¹, respectively.     

Poly(ε-caprolactone) + unsaturated isophtalic polyester blends: Thermal properties and morphology

Miscibility of blends composed by a linear unsaturated polyester (LUP) with poly(ε-caprolactone) (PCL) of different molecular weights (M_w = 50 × 10³, 18 × 10³ and 2 × 10³) has been studied. The blends were subjected to different thermal treatments and have been studied by FT-IR spectroscopy, differential scanning calorimetry (DSC) and scanning electronic microscopy (ESEM). FT-IR results allow proving the miscibility of the blends at temperatures above the melting temperature of neat PCL. DSC measurements confirm the existence of a crystalline phase corresponding to neat PCL. The crystallization of PCL is observed in a wide range of blends composition, being detected in all the blend compositions when the crystallization time increases. Thermograms show clearly the glass transition temperatures of samples that have been rapidly quenched from the melt. However, the change in the heat flow corresponding to the glass transition temperatures is difficult to detect in samples with high PCL crystallization degree. The analysis of the results indicates that the morphology of the amorphous phase is heterogeneous for LUP + PCL blends and changes depending on the thermal treatment. The ESEM measurements, confirm the heterogeneity of the amorphous phase. The decrease of the molecular weight of the PCL favours the miscibility of the blends.     

Kinetic study on external mass transfer in high performance liquid chromatography system

External mass transfer coefficients (k_f) were measured for a column packed with fully porous C₁₈-silica spherical particles (50.6 μm in diameter), eluted with a methanol/water mixture (70/30, v/v). The pulse response and the peak-parking methods were used. Profiles of elution peaks of alkylbenzene homologues were recorded at flow rates between 0.2 and 2.0 mL min⁻¹. Peak-parking experiments were conducted under the same conditions, to measure intraparticle and pore diffusivity, and surface diffusion coefficients. Finally, the values of k_f for these compounds at 298 K were derived from the first and second moments of the elution peaks by subtracting the contribution of intraparticle diffusion to band broadening. As a result, the Sherwood number (Sh) was measured under such conditions that the Reynolds (Re) and the Schmidt numbers (Sc) varied from 0.004 to 0.05 and from 1.8 × 10³ to 2.7 × 10³, respectively. We found that Sh is proportional to Re^α and Sc^β and that the correlation between these three nondimensional parameters is almost the same as those given by conventional literature equations. The values of α and β were close to those in the literature correlations, between 0.26 and 0.41 and between 0.31 and 0.36, respectively. The use of the Wilson–Geankoplis equation to estimate k_f values entails a relative error of ca. 15%. So, conventional literature correlations provide correct estimates of k_f in HPLC systems, even for particle sizes of the order of a micrometer.