Thermal and structural properties of binary mixtures of 1,3-distearoyl-2-oleoyl-glycerol (SOS) and 1,2-dioleoyl-3-stearoyl-sn-glycerol (sn-OOS)

We have conducted thermal and X-ray diffraction experiments on binary mixtures of symmetric stearic-oleic mixed-acid triacylglycerol (TAG) (1,3-distearoyl-2-oleoyl-glycerol: SOS) and asymmetric stearic-oleic mixed-acid TAG (1,2-dioleoyl-3-stearoyl-sn-glycerol: OOS), in which optically active sn-OOS was employed. We found that SOS–OOS mixtures exhibited immiscible monotectic or peritectic mixing behavior. This result was consistent with previous study on binary mixtures of 1,3-dipalmitoyl-2-oleoyl-glycerol (POP) and 1,2-dioleoyl-3-palmitoyl-rac-glycerol (OOP), in which racemic rac-OOP molecules were employed. The differences between the SOS–OOS and POP–OOP mixtures were in the polymorphic behavior of the fractions of POP and SOS. No effect was found from using an optically active (sn-OOS) or racemic mixture (rac-OOP) as an asymmetric oleic–oleic-saturated acid TAG. From the two results, we may conclude that an immiscible phase was formed in the binary mixtures of symmetric saturated-oleic-saturated TAGs and asymmetric oleic–oleic-saturated TAGs, of both racemic and optically active types. This result stands in contrast to mixtures of SOS–OSO (1,3-dioleoyl-2-stearoyl-glycerol), SOS–SSO (1,2-distearoyl-3-oleoyl-rac-glycerol), POP–OPO (1,3-dioleoyl-2-palmitoyl-glycerol), and POP–PPO (1,2-dipalmitoyl-3-oleoyl-rac-glycerol), all of which exhibited molecular-compound-forming behavior with molecular compound crystals at an equal ratio of the binary mixtures. Molecular-level mechanisms to explain this difference are discussed, based on possible roles of glycerol groups acting during the mixing processes of saturated–unsaturated mixed-acid TAGs.     

Enantiomeric separation of asymmetric triacylglycerol by recycle high-performance liquid chromatography with chiral column

In our previous studies, we employed recycle HPLC for the separation of triacylglycerol (TAG)-positional isomers (PIs). In this study, a recycle HPLC system equipped with a polysaccharide-based chiral column was applied to the enantiomeric separation of some asymmetric TAGs having straight-chain C16-C18 acyl residues. As a result, 1,2-dipalmitoyl-3-oleoyl-rac-glycerol (rac-PPO), 1,2-dioleoyl-3-palmitoyl-rac-glycerol (rac-OOP), and 1,2-dipalmitoyl-3-linoleoyl-rac-glycerol (rac-PPL) were resolved into their respective enantiomers. However, neither 1,2-dioleoyl-3-linoleoyl-rac-glycerol (rac-OOL), consisting of only unsaturated fatty acids, nor 1,2-dipalmitoyl-3-stearoyl-rac-glycerol (rac-PPS), consisting of only saturated fatty acids, was resolved. These results suggest that the asymmetric TAGs, used in this study, having both a palmitic acid moiety and an oleic acid (or a linoleic acid) moiety at the sn-1 or sn-3 positions are resolved by the chiral column. This new chiral separation method can be used in combination with atmospheric pressure chemical ionization mass spectrometry to determine the sn-OOP/sn-POO ratio in palm oil. This method is applicable for the chiral separation of asymmetric TAGs in palm oil.     

正相液相色谱法测定婴幼儿配方乳粉中1,3-二油酸-2-棕榈酸甘油三酯

建立并比较了正相色谱与反相色谱测定婴幼儿配方乳粉中1,3-二油酸-2-棕榈酸甘油三酯的方法。利用乙醚和石油醚提取婴幼儿配方乳粉中的油脂,经旋转蒸发浓缩后,分别采用银离子色谱柱和C18色谱柱,配合蒸发光散射检测器检测。其中采用银离子色谱柱以二氯甲烷-丙酮为流动相梯度洗脱的正相色谱法完全分离了1,3-二油酸-2-棕榈酸甘油三酯(OPO)和1,2-二油酸-3-棕榈酸甘油三酯(OOP)两种同分异构体,方法的重复性和线性关系良好,回收率为93.0%~101.5%,精密度(RSD)为2.89%~4.56%,检出限为20 mg/kg。该方法可准确测定婴幼儿配方乳粉中OPO的含量。     

Regiospecific Positioning of Palmitic Acid in Triacylglycerol Structure of Enzymatically Modified Lipids Affects Physicochemical and In Vitro Digestion Properties

Tripalmitin-(PPP, 81.2%), 1,3-dipalmitoyl-2-oleoylglycerol-(POP, 64.4%), 1,2-dipalmitoyl-3-oleoylglycerol-(PPO, 86.5%), and 1,3-dioleoyl-2-palmitoylglycerol-(OPO, 50.2%)-rich lipids with different regiospecific positions of palmitic acid (P) were synthesized via acetone fractionation and lipase-catalyzed acidolysis, and their physicochemical and hydrolytic characteristics were compared. Triacylglycerols (TAGs) with higher content of P, wherein P was at the sn-1 (or 3) position, had higher melting points, crystallization temperatures, and packing densities of fat crystals compared to those with a lower content of P, and with P at the sn-2 position. The in vitro digestion degree calculated as released fatty acid (FA) (%) at 30, 60, and 120 min was in the following order: OPO-rich > PPO-rich > POP-rich lipids. At 120 min, in vitro digestion of the OPO-rich lipid released 92.6% of fatty acids, resulting in the highest digestibility, while 89.7% and 87.2% of fatty acids were released from the OPO-rich and PPO-rich lipids, respectively. Over the digestion period, the TAG and monoacylglycerol (MAG) contents decreased, while the diacylglycerol (DAG) content initially increased and then decreased, and the 1,2-DAG content exceeded the 1,3-DAG content. Therefore, the content and stereospecific position of P attached to a specific TAG affected the physicochemical and in vitro digestion characteristics of the lipids.     

Mixing Ratio and Cooling Rate Dependence of Molecular Compound Formation in OPO/POP Binary Mixture

Owing to the increasing reports of the harmful effects of trans and saturated fatty acids, the demand for trans- and saturated-fatty-acid-free oil and fat products is increasing among consumers. However, it is difficult to maintain the product stability and shape retention of such oil and fat products. As a result, there is a high demand in the processed oil and fat industry to develop solutions to such problems. Herein, we used molecular compound (MC) crystals in an attempt to find alternatives to trans and saturated fatty acids. The MCs used were 1,3-dioleoyl-2-palmitoyl-sn-glycerol (OPO) and 1,3-dipalmitoyl-2-oleoyl-sn-glycerol (POP)—the main components of lard and palm oil, respectively. We believe that OPO and POP can be used to obtain no-trans, low-saturation, and high-oleic-acid oil and fat products. Optimal conditions for efficient MC crystallization were examined by changing the oil and fat composition under rapid cooling conditions assuming industrial cooling process by using differential scanning calorimetry and synchrotron radiation time-resolved X-ray diffraction methods. It was concluded that the increase in OPO concentration destabilized MC formation, while the increase in POP concentration stabilized it under rapid cooling conditions. As a result, it was shown that MC crystals can be efficiently obtained by reducing the degree of POP supercooling.     

Temperature effect in separation of fullerene by high-performance liquid chromatography

Summary The effect of column temperature, especially at low temperatures, on the separation of fullerenes on monomeric and polymeric octadecyl silica (ODS) bonded phases has been studied. Decreasing the column temperature induces an increase in selectivity. The best temperature for the separation of fullerenes was determined for both types of ODS phase with n-hexane eluent. The selectivity for higher fullerenes on monomeric phases becomes similar to that on polymeric phases to low temperature. It has been found that as the carbon content of monomeric phases is increased, the selectivity also becomes similar to polymeric phases.     

Tris(2-methyl-8-quinolinolato)gallium(III) as a fluorescent probe for sensitive silanol-testing.

The peak shape of tris(2-methyl-8-quinolinolato)gallium(III) by reversed-phase high-performance liquid chromatography was found to be very sensitive to trace amounts of silanol groups on the surface of octadecylsylanized silica gel (ODS silica gel). The variation of the peak of the gallium(III) complex can be used as a probe of the residual silanol groups in an ODS column. The chromatographic peak parameters of the complex were compared with the silanol activities output by some silanol-detecting tests using nitrogen-containing compounds as probes. The comparison was performed with several commercially available ODS columns and laboratory-packed columns in which the amount of silanol groups was controlled by mixing fully endcapped ODS materials and a non-endcapped ODS material. The peak height was the most effective parameter among the peak parameters, and much more sensitive than the silanol-detecting tests using nitrogen-containing compounds, in detecting a trace amount of silanol groups that could not be detected by other silanol-detecting tests.     

Endcapping of high performance liquid chromatography packings derived from silica gel

The effect of endcapping a reversed phase chromatographic packing material derived from silica gel depends on the degree of derivatization of the phase. The effect can be dramatic for phases with low loading. Whether an octadecylated silica gel has been endcapped or not can be ascertained by chromatographing the pair naphthalene/1-nitronaphthalene with a water/methanol eluent producing at least k' ≈ 10 for naphthalene. The ratio of the two k' values is 1.4 or higher for an endcapped material, while it is only 1.1 -1.2 for a non-endcapped phase. A similar approach fails to give conclusions of similar utility for octylated silica gels.     

Comparison of Column Packings for Isocratic High-Performance Liquid Chromatographic Analysis of Carotenoids Using Non-Aqueous Reversed-Phase

Abstract

Ten different columns are compared for the isocratic non-aqueous reversed-phase separation of carotenoids, using solvent mixtures of ethyl acetate-acetonitrile both with and without 0.1% n-decanol as modifier. Conditions were established for separation of a mixture of alfalfa carotenoids containing mainly neoxanthin, violaxanthin, lutein and β-carotene. The best material for use for rapid isocratic separation of all major components was a high carbon loading non-endcapped material with ODS functionality, although one endcapped C8 material gave similar results. The use of n-decanol as mobile phase modifier is imperative to rapidly condition new columns to give optimum peak shape and definition and system linearity.     

Effect of the endcapping of reversed-phase high-performance liquid chromatography adsorbents on the adsorption isotherm

The retention mechanisms of n-propylbenzoate, 4-t ert-butylphenol, and caffeine on the endcapped Symmetry-C(18) and the non-endcapped Resolve-C(18) are compared. The adsorption isotherms were measured by frontal analysis (FA), using as the mobile phase mixtures of methanol or acetonitrile and water of various compositions. The isotherm data were modeled and the adsorption energy distributions calculated. The surface heterogeneity increases faster with decreasing methanol concentration on the non-endcapped than on the endcapped adsorbent. For instance, for methanol concentrations exceeding 30% (v/v), the adsorption of caffeine is accounted for by assuming three and two different types of adsorption sites on Resolve-C(18) and Symmetry-C(18), respectively. This is explained by the effect of the mobile phase composition on the structure of the C(18)-bonded layer. The bare surface of bonded silica appears more accessible to solute molecules at high water contents in the mobile phase. On the other hand, replacing methanol by a stronger organic modifier like acetonitrile dampens the differences between non-endcapped and endcapped stationary phase and decreases the degree of surface heterogeneity of the adsorbent. For instance, at acetonitrile concentrations exceeding 20%, the surface appears nearly homogeneous for the adsorption of caffeine.     

Selectivity enhancement for trans-2-(2,3-anthracenedicarboximido)-cyclohexane-derived diastereomers in HPLC by using an ordered organic stationary phase.

2-(2,3-anthracenedicarboximido)cyclohexane derivatives (AC) have been known as the evolutionary diastereomerizing reagents for enantiomer discrimination in HPLC with ODS. However, a substantial separation of diastereomers can be observed only at lower temperatures, such as -40 degrees C. Therefore, in this work, poly(octadecyl acrylate)-grafted silica, ODAn was applied as an alternative stationary phase to ODS for the separation of AC-derived diastereomers. As a result, complete separation was achieved even under the conventional condition: for example, methanol as the mobile phase and 0 degrees C as the column temperature. An investigation on the temperature dependency of the selectivity demonstrated that ODAn shows a remarkable increase in selectivity at temperatures below 30 degrees C, which almost agreed with the peak-top temperature of the endothermic peak in a DSC thermogram for ODA35 immersed in a mobile phase. The better separation would be derived from a highly ordered structure of ODAn and a carbonyl-pi interaction with AC-derived diastereomers.     

Temperature optimization for the separation of PAHs on micropacked LC ODS columns

The effect of column temperature on the separation of the sixteen polycyclic aromatic hydrocarbons (PAHs) of mixture SRM 1647a of the US Environmental Protection Agency has been studied on different micropacked ODS columns. Isothermal temperature optimization was successfully used for complete separation of the PAHs on a polymeric ODS stationary phase, whereas temperature programmed conditions were selected for separation on a monomeric ODS stationary phase.     

A chromatographic estimate of the degree of surface heterogeneity of reversed-phase liquid chromatography packing materials. II-Endcapped monomeric C18-bonded stationary phase

In a previous report, the heterogeneity of a non-endcapped C30-bonded stationary phase was investigated, based on the results of the measurements of the adsorption isotherms of two neutral compounds (phenol and caffeine) and two ionizable compounds (sodium naphthalene sulfonate and propranololium chloride) by frontal analysis (FA). The same method is applied here for the characterization of the surface heterogeneity of two new brands of endcapped C18-bonded stationary phases (Gemini and Sunfire). The adsorption isotherms of the same four chemicals were measured by FA and the results confirmed by the independent calculation of the adsorption energy distribution (AED), using the expectation-maximization (EM) method. The effect of the length of the bonded alkyl chain was investigated. Shorter alkyl-bonded-chains (C18 versus C30) and the end-capping of the silica surface contribute to decrease the surface heterogeneity under the same experimental conditions (30% methanol, 25 mM NaCl). The AEDs of phenol and caffeine are bimodal with the C18-bonded columns while they are trimodal and quadrimodal, respectively, with a non-endcapped C30-bonded column. The "supersites" (adsorption energy > 20 kJ/mol) found on the C30-Prontosil column and attributed to a cation exchange mechanism completely disappear on the C18-Gemini and C18-Sunfire, probably because the end-capping of the silica surface eliminates most if not all the ionic interactions.     

Retention of C60 and C70 fullerenes on reversed-phase high-performance liquid chromatographic stationary phases.

The separation of C60 and C70 fullerenes on four different polysiloxane stationary phases was examined. It was determined that polar solvents can be used as mobile phases effectively for the separation of fullerene molecules. Unlike previously published work, a polymeric octadecyl siloxane (ODS) stationary phase provided higher separation factors for C70/C60 than did monomeric ODS stationary phases or phenyl substituted stationary phases. For example, for a methanol-diethyl ether (50:50, v/v) mobile phase and C60, k' approximately 5.0 separation factors, alpha = 3.3, were achieved with polymeric ODS compared to alpha = 2.2, with a monomeric ODS stationary phase. A linear solvation energy relationship (LSER) was used to model the importance of solvent interactions and stationary phase interaction to solute retention.     

Retention versatility of silica-supported comb-shaped crystalline and non-crystalline phases in high-performance liquid chromatography

Silica-supported comb-shaped polymer (Sil-ODA18) provided a specific selectivity towards aromatic and non-aromatic solutes. Selectivity of Sil-ODA18 and ODS (polymeric and monomeric) columns towards polycyclic aromatic hydrocarbons and geometric isomers have been discussed in respect of molecular shapes and sizes. The retention versatility of this phase arises from the orientation change on transition from the ordered crystalline to the less ordered non-crystalline state. Selectivity in the crystalline and non-crystalline regions of Sil-ODA18 is similar to that of polymeric and monomeric ODS phases, respectively. Sil-ODA18 column also exhibited the characteristic temperature dependency of liquid-crystalline phases, i.e., an increase in retention with increasing temperature on transition from crystalline to isotropic state.     

Separation of peptides utilizing ultrahigh-temperature micellar electrokinetic chromatography

The use of ultrahigh column temperatures, up to 110 degrees C, in micellar electrokinetic capillary chromatography was investigated. The number of plates generated per unit time increased from 0.22 to 12.8 plates/s for separations at 15 degrees C and 110 degrees C, respectively. Ultrahigh-temperature micellar electrokinetic capillary chromatography was used for the separation of cyclic undecapeptides (cyclosporins). A minimum resolution of 1.39 was calculated for a critical peak pair at 110 degrees C, which is more than a 50% increase over resolution generated at 40 degrees C. During a run time of more than 90 min at 110 degrees C and at pH 9.3, no sample degradation or solvent boiling was observed.     

Evaluation of microstructural features of a new polymeric organic stationary phase grafted on silica surface: A paradigm of characterization of HPLC-stationary phases by a combination of suspension-state H NMR and solid-state C-CP/MAS-NMR

Silica-supported poly(octadecylacrylate) (Sil-ODA_n), polymeric octadecylsilyl silica (polymeric ODS), and monomeric octadecylsilyl silica (monomeric ODS) were studied by a combination of suspension-state ¹H NMR and solid-state ¹³C CP/MAS-NMR to probe the mechanisms underlying their functions as stationary phases for RP-HPLC. Sil-ODA_n, with a strong temperature dependent separation behaviour showed correspondent temperature dependent manifestations in both suspension-state ¹H NMR and solid-state ¹³C CP/MAS-NMR experiments. With a gradual increase in temperature, intensity of proton signals (¹H NMR) of octadecyl moieties (mainly methylene groups) rose dramatically. This dramatic rise was at the same temperature of an endothermic peak detectable in its DSC thermogram indicating a relatively complete solid to liquid phase transition. In addition temperature dependencies of the ratio of trans to gauche conformed well to temperature dependencies of the separation factor between naphthacene and triphenylene (as a simple indicator of shape selectivity). Therefore NMR spectra of Sil-ODA_n were used as a reference for ascertaining percentage of octadecyl moieties of liquid type mobility in the two other stationary phases. Using this method we determined percentage of liquid phase in polymeric ODS and monomeric ODS at various temperatures. We suggest a combination of suspension-state ¹H NMR and solid-state ¹³C CP/MAS-NMR for structure-dynamic characterization of various kinds of hydrocarbon chains grafted onto the silica particles.     

Computer-assisted high-performance liquid chromatography method development with applications to the isolation and analysis of phytoplankton pigments

We used chromatography modeling software to assist in HPLC method development, with the goal of enhancing separations through the exclusive use of gradient time and column temperature. We surveyed nine stationary phases for their utility in pigment purification and natural sample analysis. For purification, a complex algal matrix was separated on an efficient monomeric column, from which partially purified fractions were collected and purified on polymeric columns that exaggerated resolution between pigments of interest. Additionally, we feature an HPLC method that is simple, fast, demonstrates excellent transferability and is ideal for quantitative analysis of pigments in dilute natural water samples.     

Comparison of the performance of different reversed-phase columns for liquid chromatography separation of 11 pollutant phenols

A systematic optimization of the HPLC separation of a mixture containing 11 pollutant phenols (PPs) using a Hypersil ODS (250 mm x 4.6 mm, 5 microm) column and UV-DAD detection has been carried out. The binary mobile phases used were obtained by mixing 50 mM phosphate (pH = 3.0) and methanol, ACN, or THF as organic modifiers. After selecting ACN as an organic modifier, the effects of pH and temperature on PPs separation were studied. A mobile phase of 50 mM acetate (pH = 5.0)-ACN (60:40 v/v) at 50 degrees C allowed the separation of 11 phenols but not to baseline in 17 min. To improve the performance of this separation, the following RP columns were tested: Luna C18 (2), Purospher C18, Synergi C12, Synergi Fusion C18, Gemini C18, Luna Cyano, Lichrospher C8, and Envirosep-PP (polymeric). In all the cases, the performance (analysis time, retention, selectivity, resolution, asymmetry factors, and efficiency) was evaluated. A further reoptimization of the mobile phase was carried out for all the columns by studying the ACN content and pH, with the aim of improving the above-mentioned separations and selecting the most suitable one for PPs analysis.     

The novel assay method for nicotine metabolism to cotinine using high performance liquid chromatography

Nicotine is the primary psychoactive component in tobacco. It is taken into the body by tobacco smoking, and mainly metabolized to cotinine in the hepatic cytochrme P450 (CYP) 2A6. The objective of this study was to develop a sensitive method for the determination of nicotine metabolism to cotinine using HPLC. The internal standard, trans-4'-carboxycotinine methyl ester was synthesized with a simple method. The nicotine and cotinine were separated completely and detected by C(18) 5-μm analytical column (L-column Octa decyl silyl (ODS), 150 mm × 4.6 mm i.d.) equipped with a C(18) 5-μm guard column (L-column ODS, 10 mm × 4.6 mm i.d.) and ultraviolet detection at 260 nm. The detection limit of the assay was 0.05 μM for cotinine (n=5, R.S.D) and 0.1 μM for nicotine. Thus the present results provided a sensitive and useful method for the determination of nicotine metabolism catalyzed by CYP2A6.