Reversed Polarity Mode Research Articles

Investigation of electrospray for a capillary electrophoresis-mass spectrometry interface in reverse polarity and negative ion mode.

Capillary zone electrophoresis (CZE) paired with mass spectrometry (MS) is a powerful analytical technique for examining mixtures of ionic analytes such as glycosaminoglycans. This study examines the mechanics of the electrospray process for a sheath flow CZE-MS interface under reverse polarity negative ionization conditions. Liquid flow in a sheath flow nano-electrospray CZE-MS interface is driven by two mechanisms, electroosmotic flow and electrospray nebulization. The contribution of these two processes to the overall flow of solution to the electrospray tip is influenced by the surface coatings of the sheath flow emitter tip and by the solvent composition. We have investigated the application of this interface to the reverse polarity separation of glycosaminoglycans and find that the role of electroosmotic flow is far less than has been reported previously, and the electrospray process itself is the largest contributor to the flow of the sheath liquid.

Glycoform Analysis of Alpha1-Acid Glycoprotein by Capillary Electrophoresis Using Electrophoretic Injection.

Human alpha1-acid glycoprotein (AGP) is an acute phase glycoprotein that has a heterogeneous glycosylation pattern. This pattern can change in certain diseases, which has resulted in interest in using AGP glycoforms as potential biomarkers for these diseases. This report describes a method that uses capillary electrophoresis to characterize and analyze AGP glycoforms both in purified samples of AGP and in human serum. This method uses static and dynamic coatings of poly(ethylene oxide) that are applied to a silica capillary for separation of AGP glycoforms in the reversed-polarity mode of CE and in the presence of negligible electroosmotic flow. Electrophoretic injection is performed onto such capillaries by using a stationary stacking interface between the sample and running buffer. In addition, acidic precipitation and desalting are used to allow for the isolation and the analysis of AGP from only 65μL of serum. Up to eleven AGP glycoform bands can be reproducibly separated by this method, with the difference in migration time between neighboring bands being 12- to almost 60-fold larger than the standard deviation for the migration time of any given band. A limit of detection down to about 2nM per glycoform band can be obtained by this method for AGP in serum based on absorbance detection and without the need for further sample modification or labeling.

Glycoform analysis of alpha1-acid glycoprotein based on capillary electrophoresis and electrophoretic injection

A method based on capillary electrophoresis (CE) with electrophoretic injection and absorbance detection was developed for the direct analysis of AGP glycoforms in human serum. Electrophoretic injection of AGP was performed in the reversed-polarity mode of CE with a capillary coated with poly(ethylene oxide) and that had minimal electroosmotic flow. This situation created an essentially stationary interface between the sample and running buffer during injection and sample stacking. This approach allowed an 11,000-fold increase in sample loading for a 5min injection versus hydrodynamic injection and without introducing any significant levels of extra band-broadening. This method was used with sample pretreatment methods based on acid precipitation and desalting to examine AGP glycoforms in only 65μL of serum. A limit of detection of 2.1–11.3nM was obtained for the major AGP glycoform bands in serum, and the sample pretreatment method gave a recovery of 72.3–80.9% for these glycoforms. The precision for the migration times was ±0.08–0.13% and the precision for the peak areas was ±0.34–1.18% when using serum samples and an internal standard. This method was used for both normal pooled serum and serum from individuals with systemic lupus erythematosus. Results were obtained in a separation time of 25min and allowed the comparison of up to eleven glycoform bands in these samples. A similar approach may be useful in examining additional glycoproteins in serum or other types of biological samples.

Development and validation of a micellar electrokinetic capillary chromatography method for the determination of goserelin and related substances.

An MEKC method for the analysis of goserelin and related substances has been developed using a combination of additives including CTAB, β-CD, and sodium hexanesulfonate. For this assay, the running buffer (pH and additives) and separation conditions (voltage and temperature) were optimized. The optimized system was the following: 200 mM 6-aminocaproic acid buffer (pH 4.2) supplemented with 175 mM CTAB, 3.0% w/v β-CD, and 20 mM sodium hexanesulfonate; the voltage was 10 kV in reverse polarity mode, the temperature was 20°C, and UV detection was measured at 220 nm. The method was qualified by evaluating the specificity, precision, linearity, accuracy, LOD, and LOQ. According to validation experiments, the optimized method was specific, accurate, and repeatable and satisfied the requirements for the analysis of goserelin and related substances. Compared with the RP-HPLC method, the MEKC method better solved the problem of overlapping impurity signals, and the migration time required was shorter. This method can be used for quality control and for the analysis of goserelin and its related substances.

Development and validation of a generic stability-indicating MEEKC method for five fluoroquinolone antibiotics.

In this paper, a reliable stability-indicating generic MEEKC method for the analysis of five commonly used fluoroquinolones (FQs) has been developed and optimized by a central composite circumscribed experimental design. The separation was carried out using a fused silica capillary (60.2 cm total length) and a microemulsion (ME) composed of 81.75% (w/w) of a 125 mM NaH2 PO4 solution having a pH of 2.75, 2.65% (w/w) SDS, 1.00% (w/w) n-octanol, 6.60% (w/w) n-butanol and 8.00% (w/w) 2-propanol. A voltage of 28 kV was applied in a reverse polarity mode. A linear relationship was established from 0.04 to 0.48 mg/ml with R2 values higher than 0.98 for all five FQs. Both repeatability and intermediate precision were less than 3% and accuracy ranging from 97 to 100%. Of note, ciprofloxacin impurity A and ofloxacin impurity A could be separated from the respective drug substance in a single run which cannot be achieved using the official HPLC method from the European Pharmacopoeia. Forced degradation of all FQs under heat, in acidic and alkaline medium, in the presence of oxidizing agents and under neutral hydrolysis conditions was investigated. The highest yield of degradation products was observed using oxidative hydrogen peroxide. Hence, the proposed MEEKC method can be used for the quantitative determination of the five FQs and their potential impurities within a total runtime of 20 min.

Quality by design in the chiral separation strategy for the determination of enantiomeric impurities: Development of a capillary electrophoresis method based on dual cyclodextrin systems for the analysis of levosulpiride

Quality by design (QbD) concepts, in accordance with International Conference on Harmonisation Pharmaceutical Development guideline Q8(R2), represent an innovative strategy for the development of analytical methods. In this paper QbD principles have been comprehensively applied in the set-up of a capillary electrophoresis method aimed to quantify enantiomeric impurities. The test compound was the chiral drug substance levosulpiride (S-SUL) and the developed method was intended to be used for routine analysis of the pharmaceutical product. The target of analytical QbD approach is to establish a design space (DS) of critical process parameters (CPPs) where the critical quality attributes (CQAs) of the method have been assured to fulfil the desired requirements with a selected probability. QbD can improve the understanding of the enantioseparation process, including both the electrophoretic behavior of enantiomers and their separation, therefore enabling its control. The CQAs were represented by enantioresolution and analysis time. The scouting phase made it possible to select a separation system made by sulfated-β-cyclodextrin and a neutral cyclodextrin, operating in reverse polarity mode. The type of neutral cyclodextrin was included among other CPPs, both instrumental and related to background electrolyte composition, which were evaluated in a screening phase by an asymmetric screening matrix. Response surface methodology was carried out by a Doehlert design and allowed the contour plots to be drawn, highlighting significant interactions between some of the CPPs. DS was defined by applying Monte-Carlo simulations, and corresponded to the following intervals: sulfated-β-cyclodextrin concentration, 9–12mM; methyl-β-cyclodextrin concentration, 29–38mM; Britton–Robinson buffer pH, 3.24–3.50; voltage, 12–14kV. Robustness of the method was examined by a Plackett–Burman matrix and the obtained results, together with system repeatability data, led to define a method control strategy. The method was validated and was finally applied to determine the enantiomeric purity of S-SUL in pharmaceutical dosage forms.

The development of a counterflow‐assisted preconcentration technique in capillary electrophoresis electrospray‐ionization mass spectrometry

A preconcentration approach for CE-MS using counterflow-assisted electrokinetic injection was proposed. The proposed preconcentration method was based on a counterflow-compatible sheathless interface. The interface was fabricated using a capillary-assembled PDMS microdevice that allowed the application of a counterflow and provided liquid-film electrical conduction. During electrokinetic injection, a hydrodynamic counterflow was introduced into the separation capillary to retard the movement of the stacking boundary to the CE outlet. Accordingly, a long injection time was achieved without a loss of CE separation. With the use of reverse polarity mode and a dynamic polybrene-coated separation capillary (filled with a 1% formic acid solution), a counterflow-assisted electrokinetic injection of peptide samples (in a aqueous solution containing 1% ammonia and 50% methanol) for 10 min provided a sensitivity enhancement of 750-1480 and a detection limit of 20 pM for the five peptide standards. The proposed technique was applied to the analysis of low nanomolar concentrations myoglobin tryptic peptides.

Stability-indicating micellar electrokinetic chromatography method for the analysis of sumatriptan succinate in pharmaceutical formulations

A micellar electrokinetic chromatography method for the determination of sumatriptan succinate in pharmaceutical formulations was developed. The effects of several factors such as pH, surfactant and buffer concentration, applied voltage, capillary temperature, and injection time were investigated. Separation took about 5 min using phenobarbital as internal standard. The separation was carried out in reversed polarity mode at 20 °C, 26 kV and using hydrodynamic injection for 10 s. Separation was achieved using a bare fused-silica capillary 50 μm × 40 cm and background electrolyte of 25 mM sodium dihydrogen phosphate—adjusted with concentrated phosphoric acid to pH 2.2, containing 125 mM sodium dodecyl sulfate and detection was at 226 nm. The method was validated with respect to linearity, limits of detection and quantification, accuracy, precision and selectivity. The calibration curve was linear over the range of 100–2000 μg mL −1. The relative standard deviations of intra-day and inter-day precision for migration time, peak area, corrected peak area, ratio of corrected peak area and ratio of peak area were less than 0.68, 3.48, 3.28, 2.97 and 2.83% and 2.01, 5.50, 4.46, 4.92 and 4.07%, respectively. The proposed method was successfully applied to the determinations of the analyte in tablet. Forced degradation studies were conducted by introducing a sample of sumatriptan succinate standard solution to different forced degradation conditions using neutral (water), basic (0.1 M NaOH), acidic (0.1 M HCl), oxidative (10% H 2O 2) and photolytic (exposure to UV light at 254 nm for 2 h). It is concluded that the stability-indicating method for sumatriptan succinate can be used for the analysis of the drug in various samples.

Capillary zone electrophoresis for U(VI) and short chain carboxylic acid sorption studies on silica and rutile

Capillary zone electrophoresis was used to study the uranyl and short chain carboxylic acid sorption on silica and rutile. The separation and the simultaneous determination (in a single run) of a number of short chain carboxylic acids (oxalic, formic, acetic and propionic) and U(VI) with direct UV detection is developed for the analysis of solutions after the sorption experiments. The reverse polarity mode is used (the injection is performed at the negative end). The matrix effect of Si(IV) (possible silica dissolution product) and perchlorate (added for constant ionic strength in sorption experiments) on the separation of U(VI) and organic acids is investigated. The influence of methanol addition in carrier electrolyte on the separation selectivity of given analytes is also studied. Under the chosen conditions (carbonate buffer (ionic strength of 0.1M), pH 9.8, 0.15mM of tetradecyltrimethylammonium bromide, 25% (v/v) of methanol) the calibration curves are plotted. They are linear in two ranges of concentration from ∼1×10−5 to ∼1×10−3M for oxalate, acetate, propionate, U(VI) and ∼1×10−4 to ∼1×10−3 for formate. The accuracy of the procedure is checked by the “added-found” method in simulation solutions. The relative standard deviations of the concentrations found are within the range of 1–10% and the recovery is in the range of 90–115%. This method is applied for the analysis of aqueous samples issued from sorption experiments on silica and rutile. The obtained results indicate that the given organic acids decrease uranium sorption both on silica and rutile. These experiments demonstrate that short chain carboxylic acids can influence the mobility and the chemistry of U(VI) in the environment.

Enantioselective analysis of ofloxacin and ornidazole in pharmaceutical formulations by capillary electrophoresis using single chiral selector and computational calculation of their inclusion complexes

A capillary electrophoretic method for the separation of the enantiomers of both ofloxacin and ornidazole is described. Several parameters affecting the separation were studied, including the type and concentration of chiral selector, buffer pH, voltage and temperature. Good chiral separation of the racemic mixtures was achieved in less than 16 min with resolution factors Rs = 5.45 and 6.28 for ofloxacin and ornidazole enantiomers, respectively. Separation was conducted using a bare fused-silica capillary and a background electrolyte (BGE) of 50 mM H 3PO 4–1 M tris solution; pH 1.85; containing 30 mg mL −1 of sulfated-β-cyclodextrin (S-β-CD). The separation was carried out in reversed polarity mode at 25 °C, 18 kV, detection wavelength at 230 nm and using hydrodynamic injection for 15 s. Acceptable validation criteria for selectivity, linearity, precision, and accuracy were studied. The limits of detection (LOD) and limits of quantitation (LOQ) of the enantiomers (ofloxacin enantiomer 1 (OF-E1), ofloxacin enantiomer 2 (OF-E2), ornidazole enantiomer 1 (OR-E1) and ornidazole enantiomer 2 (OR-E2)) were (0.52, 0.46, 0.54, 0.89) and (1.59, 1.40, 3.07, 2.70) μg mL −1, respectively. The proposed method was successfully applied to the assay of enantiomers of both ofloxacin and ornidazole in pharmaceutical formulations. The computational calculations for the enantiomeric inclusion complexes rationalized the reasons for the different migration times between the ofloxacin and ornidazole enantiomers.

Lysine-based zwitterionic molecular micelle for simultaneous separation of acidic and basic proteins using open tubular capillary electrochromatography.

In this work, a zwitterionic molecular micelle, poly-epsilon-sodium-undecanoyl lysinate (poly-epsilon-SUK), was synthesized and employed as a coating in open tubular capillary electrochromatography (OT-CEC) for protein separation. The zwitterionic poly-epsilon-SUK containing both carboxylic acid and amine groups can be either protonated or deprotonated depending on the pH of the background electrolyte; therefore, either an overall positively or negatively charged coating can be achieved. This zwitterionic coating allows protein separations in either normal or reverse polarity mode depending on the pH of the background electrolyte. The protein mixtures contained four basic proteins (lysozyme, cytochrome c, alpha-chymotrypsinogen A, and ribonuclease A) and six acidic proteins (myoglobin, deoxyribonuclease I, beta-lactoglobulin A, beta-lactoglobulin B, alpha-lactalbumin, and albumin). Protein separations were optimized specifically for acidic (reverse mode) and basic (normal mode) pH values. Varying the polymer thickness by changing the polymer and salt concentration had a great influence on protein resolution, while nearly all peaks were also baseline resolved in both modes using the optimized poly-epsilon-SUK coating concentration of 0.4% (w/v). Proteins in human sera were separated under optimized acidic and basic conditions in order to demonstrate the general utility of this coating. Nanoscale characterizations of the poly-epsilon-SUK micellar coatings on silicon surfaces were accomplished using atomic force microscopy (AFM) to gain insight into the morphology and thickness of the zwitterionic coating. The thickness of the polymer coating ranged from 0.9 to 2.4 nm based on local measurements using nanoshaving, an AFM-based method of nanolithography.

Effect of temperature on the enantioselectivity of basic analytes using CE with sulfated β‐cyclodextrins

Twelve basic analytes, including ephedrine and its structurally related compounds, were used to study the influence of capillary temperature on enantioselectivity in CE enantioseparations under reversed polarity mode using sulfated beta-CD (S-beta-CD) as chiral selectors. All of the effective mobility changes of (+)-enantiomers between 35 and 20 degrees C were higher than those of (-)-enantiomers whosoever enantioselectivity increased or decreased with an increase in temperature. However, the unusual temperature effect that enantioselectivity was increased with an increase of temperature was observed for the compounds with hydroxyl substitution on phenyl ring and had relationship with the molecular structures. With performing NMR studies on the selected selector-analyte complexes, the results led to a deeper understanding of the chiral discrimination process. Inspection of the complexation-induced chemical shifts (CICS) of the enantiomers showed that the phenyl ring sits deeply and slantways in the cavity of S-beta-CD and alkyl chain pointed out of the wider rim of S-beta-CD with ion-ion and hydrogen bond interactions between analytes and S-beta-CD.

Assay and stability‐indicating micellar electrokinetic chromatography method for the simultaneous determination of valacyclovir, acyclovir and their major impurity guanine in pharmaceutical formulations

A micellar electrokinetic chromatography (MEKC) method for the simultaneous determination of the antiviral drugs acyclovir and valacyclovir and their major impurity, guanine, was developed. The influences of several factors (surfactant and buffer concentration, pH, applied voltage, capillary temperature and injection time) were studied. Using tyramine hydrochloride as internal standard, the analytes were all separated in about 4 min. The separation was carried out in reversed polarity mode at 28 degrees C, 25 kV and using hydrodynamic injection (15 s). The separation was effected in a fused-silica capillary 100 microm x 56 cm and a background electrolyte of 20 mM citric acid-1 M Tris solution (pH 2.75), containing 125 mM sodium dodecyl sulphate and detection at 254 nm. The method was validated with respect to linearity, limit of detection and quantification, accuracy, precision and selectivity. Calibration curves were linear over the range 0.1-1 microg/mL (guanine) and from 0.1 to 120 microg/mL for both valacyclovir and acyclovir. The relative standard deviations of intra- and inter-day migration times and corrected peak areas were less than 5.0%. The proposed method was successfully applied to the determination of the analytes in tablets and creams. From the previous study it is concluded that the stability-indicating method developed for acyclovir and valacyclovir can be used for analysis of the drug in various stability samples.

CE of Small DNA Fragments Using Linear Polyacrylamide Matrices

Mutations at codons 248 and 249 of p53 gene showed a relatively high incidence in gastric cancer patients. Development of novel methods for the detection of codon mutations is of great importance for gastric cancer research. Studies have showed that the separation matrix can significantly influence the separation efficiency and resolution of small DNA fragments in CE. In order to achieve baseline separation of PCR-amplified products of small DNA fragments from gastric cancer tissue, linear polyacrylamides (LPA I and LPAII) were designed and synthesized in the current study. LPAI and LPAII were used as separation matrixes to separate small size fragments (less than 70 bp) of pBR322/BsuRI DNA Marker and the separation conditions were optimized. Optimum separations were performed at 25 kV in reversed-polarity mode with capillary temperature set at 15 °C. The signal of DNA fragments was detected using laser-induced fluorescence detector, with an argon ion laser as the excitation source that emits at 488 nm. A 520 nm bandpass filter was used as an emission cut-off filter. The resolution of small DNA fragments was higher when LPAI was used as separation matrix compared to LPAII, accompanied with longer migration time. The results indicated that LPAI as separation matrix was more efficient for the separation of small DNA fragments (less than 70 bp) than other LPAs. A rapid and sensitive analysis method for the separation and detection of small DNA fragments (less than 70 bp) was established in this study. The method was successfully applied to detect the mutations at codons 248 and 249 in p53 gene from gastric cancer tissues.

Enantiomeric Separation of Two Antiparkinsonian Drugs by Electrokinetic Chromatography Using Dextran Sulfate

Anionic polysaccharide dextran sulfate (DxS) was successfully employed as chiral selector for the enantioseparation of two antiparkinsonian drugs, including rotigotine and trihexyphenidyl (THP), by electrokinetic chromatography (EKC). The enantioseparation was performed under normal and reversed polarity modes and reversed enantiomer migration order was achieved under two modes. The parameters affecting the chiral separation, such as buffer pH, DxS concentration, organic additive, and temperature were investigated and optimized. Reversed polarity mode provided better separation for the two drugs. The optimized conditions for the enantioseparation under reversed polarity mode were 2.0% (w/v) DxS, 10 mM phosphate buffer, pH 2.5 with an applied voltage of −30 kV at 25 °C. Direct UV detection was performed at 200 nm. Under the optimal conditions, rotigotine and THP enantiomers were enantioresolved in 40 min with the resolution of 2.0 and 5.8, respectively. The analytes could be enantioseparated using DxS of molecular mass 1,000,000 or 500,000. It was inferred that the electrostatic, hydrophobic, and steric interactions may be involved in the chiral separation mechanism in this study.

Simultaneous determination of uranium carbide dissolution products by capillary zone electrophoresis

Separation and simultaneous determination of a number of organic acid anions (oxalate, mellitate, trimellitate and benzoate) and U(VI) with direct UV detection is developed for analysis of uranium carbide (UC) dissolution products by capillary zone electrophoresis (CZE). Reverse polarity mode is used. It is found that complex formation of U(VI) with carbonate, used as a carrier electrolyte, allows U(VI) to be determined, as negatively charged species, in a single run with organic acid anions. Some parameters such as pH value, composition of electrolyte and detection wavelength are optimized. Under the chosen conditions (carbonate buffer (ionic strength of 100 mM), pH 9.8, 0.15 mM tetradecyltrimethylammonium bromide (TTAB)) a complete separation is achieved. Calibration plots are linear in two ranges of concentration for U(VI) (∼1 × 10 −5 to 1 × 10 −3), mellitate and trimellitate (∼5 × 10 −6 to 5 × 10 −4), and about one range (∼1 × 10 −4 to 5 × 10 −3) for oxalate and benzoate. Accuracy of the procedure is checked by the “added-found” method in standard mixture solutions. Relative standard deviation is within the range of 2–10% and the recovery is in the range of 90–110%. This method is applied for the analysis of real UC dissolution samples.

Separation and determination of clopidogrel and its impurities by capillary electrophoresis

Clopidogrel bisulphate, an anti-platelet drug, has been separated from its impurities, namely impurity A, B and C by capillary zone electrophoresis (CZE) using uncoated fused-silica capillary (50.0 μm internal diameter, 31.2 cm total length). Four factors affected the separation: buffer concentration, pH of the buffer, concentration of the chiral selector and the applied voltage. Optimization and robustness studies were performed with the aid of reduced central composite experimental design. The buffer used was triethylamine–phosphoric acid and the chosen chiral selector was sulphated β-cyclodextrin (SCD). The best separation was achieved by using 10 mM buffer, pH 2.3, containing 5% (mass/volume (m/v)) SCD. Reversed polarity mode was used with an applied voltage of −12 kV and the capillary temperature was maintained at 20 °C. The method was validated for quantitative determination of the drug. It offered a limit of detection (LOD) of 0.13 μg/ml, a limit of quantitation (LOQ) of 0.4 μg/ml, and a linearity range of 0.4–300 μg/ml. Commercial bulk samples were analyzed using the developed method.

The use of GC×GC with time‐of‐flight mass spectrometry to investigate dienes and Diels–Alder polymerisation products in high‐temperature Fischer–Tropsch‐based fuels

Comprehensive GC in the reversed polarity mode i.e. a polar main column and an apolar secondary column have been used to differentiate cyclic olefins, dienes and cyclic dienes in high temperature Fischer-Tropsch (FT)-based fuels. The elucidation of the blobs in the contour plot was based on spectral data obtained by TOF-MS. The effectiveness of selective catalytic hydrogenation in transforming dienes into olefins could be studied. Dienes are prone to polymerisation by Diels-Alder reactions and dimers and trimers were detected in the 2-D plot by operating the MS in the ion extraction mode. Polymerisation is thought to be partially responsible for gum formation in high temperature FT-derived products.

Enantiomeric Separation of Isochromene Derivatives by Cyclodextrin-Modified Micellar Capillary Electrophoresis

The enantiomeric separations of highly hydrophobic isochromene derivatives were performed and optimized using cyclodextrin-modified micellar capillary electrophoresis. Hydroxypropyl-γ-cyclodextrin proved to be the most effective chiral selector for the enantioseparation of these analytes. The effects of cyclodextrin and sodium dodecyl sulfate concentration and organic modifier were examined in order to optimize the separation conditions. Addition of an organic solvent modifier to the run buffer served to increase the analyte' solubility and enhance the separation efficiency. A highly acidic pH was necessary to effectively suppress the electroosmotic flow when operating in the reverse polarity mode.

Temperature effects on the enantioselectivity of basic analytes in capillary EKC using sulfated β‐CDs as chiral selectors

The thermodynamic processes were investigated to reveal the temperature effects during chiral separation by capillary EKC with reversed polarity mode using sulfated beta-CD (S-beta-CD) as chiral selectors. The temperature effects on enantioselectivities of basic analytes (ephedrine, norephedrine, synephrine, and epinephrine) were investigated in detail over a temperature range of 20-60 degrees C. An increase of the capillary temperature produced the decrease of enantioselectivities for ephedrine and norephedrine, but increase of enantioselectivities for synephrine and epinephrine. The thermodynamic variations showed that the interactions between the basic analytes and chiral selectors were always enthalpy- driven. However, the difference in enthalpy and entropy showed that the enantioseparation was an enthalpy-driven process for ephedrine and norephedrine, but an entropydriven process for synephrine and epinephrine. Just because of the different driving forces, there exist two kinds of temperature effects on enantioselectivities mentioned above.