Number Of Theoretical Plates Research Articles

Metal-Organic Framework [Cd(LTP)2]n for Improved Enantioseparations on a Chiral Cyclodextrin Stationary Phase in GC.

Metal-organic frameworks (MOFs) are a class of novel porous materials consisting of clusters or chains of metal ions and organic linkers. The chiral MOF [Cd(LTP)2]n (LTP = l(-)-thiazolidine-4-carboxylic acid) possesses infinite extension three-dimensional supramolecular reticular structure with right-handed helix. In this work, three capillary columns (A, B and C) containing MOF [Cd(LTP)2]n, permethylated β-cyclodextrin (CD) and sodium chloride, and MOF [Cd(LTP)2]n and permethylated β-CD, respectively, have been prepared and their respective enantioseparation abilities have been investigated. The polarities of all of the MOFs and permethylated β-CDs are moderate. The numbers of theoretical plates (plate m-1) of the three columns have been measured using n-dodecane at 120°C, which followed an increasing order of A (3100) < B (3800) < C (4300). Some racemates were separated with different resolutions on Columns A, B and C. The results indicated that the incorporated MOF [Cd(LTP)2]n enhanced the separations of racemates on a permethylated β-CD stationary phase with high column efficiency and good reproducibility in gas chromatography.

Simultaneous Determination and Drug Dissolution Testing of Combined Amlodipine Tablet Formulations Using RP-LC

In the proposed work, the simultaneous analysis of amlodipine–rosuvastatin and amlodipine–atorvastatin in their dosage forms was achieved. Simultaneous dissolution profiles of the amlodipine–rosuvastatin and amlodipine–atorvastatin tablets are realized using Apparatus II with a simple, accurate and precise RP-LC method. The mobile phase consisting of 0.2 % H3PO4 and pH 5:methanol:acetonitrile (46:27:27) was used. The samples of 10 µL were injected onto a Zorbax SB C18 (100 mm, 4.6 mm, 3.5 µm particle size) column with 1.2 µL min−1 flow rate. The samples were detected at 236 nm. By plotting peak area ratios vs. concentration, the linearity for amlodipine–rosuvastatin and amlodipine–atorvastatin was determined. With the developed RP-LC method, AML, ROS and ATOR were detected within the range of 0.25–10, 0.5–10 and 0.25–25 µg mL−1, respectively. LOD and LOQ values were also calculated as 0.028, 0.058, 0.021 and 0.095 µg mL−1, 0.195 µg mL−1, 0.070 µg mL−1 for AML, ROS and ATOR, respectively. System suitability tests parameters, such as capacity factor, selectivity to previous peak, selectivity to next peak, resolution to previous peak, resolution to next peak, tailing factor, theoretical number of plates, were performed and found coherent with the ICH guideline parameters. The proposed method has been extensively validated in terms of recovery, and recovery results were between 99 and 101 %. For proving the precision, between-day and within-day repeatability results of the method were proposed. The method can be used for the simultaneous determination of amlodipine–rosuvastatin and amlodipine–atorvastatin.

Low solvent consumption gel permeation chromatography method

ABSTRACTThis study presents the possibility of reducing the volume of solvent necessary for gel permeation chromatography analysis by up to 20 times when using two 2.1-mm internal diameter (ID) columns instead of the traditional three 7.5-mm ID columns. The low solvent consumption method was optimized by evaluating the number of theoretical plates at different flow rates. By injecting a broad polystyrene standard 16 times, good reproducibility and accuracy of weight average molecular weights (Mw) and peak surface areas were obtained for the optimized method.

Microchip electrophoresis with background electrolyte containing polyacrylic acid and high content organic solvent in cyclic olefin copolymer microchips for easily adsorbed dyes

Plastic microchips can significantly reduce the fabrication cost but the adsorption of some analytes limits their application. In this work, background electrolyte containing ionic polymer and high content of organic solvent was adopted to eliminate the analyte adsorption and achieve highly efficient separation in microchip electrophoresis. Two dyes, rhodamine 6G (Rh6G) and rhodamine B (RhB) were used as the model analytes. By using methanol as the organic solvent and polyacrylic acid (PAA) as a multifunctional additive, successful separation of the two dyes within 75μm id. microchannels was realized. The role of PAA is multiple, including viscosity regulator, selectivity modifier and active additive for counteracting analyte adsorption on the microchannel surface. The number of theoretical plate of 7.0×105/m was attained within an effective separation distance of 2cm using background electrolyte consisting 80% methanol, 0.36% PAA and 30mmol/L phosphate at pH 5.0. Under optimized conditions, relative standard deviations of Rh6G and RhB detection (n=5) were no more than 1.5% for migration time and 2.0% for peak area, respectively. The limit of detection (S/N=3) was 0.1nmol/L for Rh6G. The proposed technique was applied in the determination of both Rh6G and RhB in chilli powder and lipstick samples with satisfactory recoveries of 81.3–103.7%.

Application and comparison of high‐speed countercurrent chromatography and high‐performance liquid chromatography in semi‐preparative separation of decarboxymethyl oleuropein aglycone (3,4‐DHPEA‐EDA), a bioactive secoiridoid from extra‐virgin olive oil

This paper primarily extends research on applying and comparing high‐speed countercurrent chromatography (HSCCC) and high‐performance liquid chromatography (HPLC) in semi‐preparative isolation of decarboxymethyl oleuropein aglycone (3,4‐DHPEA‐EDA), a bioactive secoiridoid, from extra‐virgin olive oil (EVOO). An EVOO phenolic extract (EVOO‐PE) was obtained by solid‐phase extraction (SPE), and this extract was subjected to one run using the maximum loading capacity of each methodology without loss of resolution. For this sample set, the HSCCC method proved to be a more efficient approach regarding loading capacity, solvent consumption, and throughput compared with the HPLC method. However, the purity of the target from HPLC was superior to that of HSCCC, as the number of theoretical plates could not match that of HPLC. Therefore, we propose that HPLC should be used when higher purities are required, despite higher costs. In addition, HPLC is orthogonal and complementary to HSCCC, and can often provide straightforward resolution of otherwise difficult separations by HSCCC.Practical applications: Our results indicate that the optimized HSCCC is an economic process, and hence, a good candidate for further scaling‐up to preparative and industrial scales, as long as the chromatographic profile of the sample itself is simple enough to achieve good resolution, or a very high purity of the compound of interest is not required. For those cases, HPLC would provide superior target purity but would result in higher costs.This paper compares high‐speed countercurrent chromatography (HSCCC) and high‐performance liquid chromatography (HPLC) in semi‐preparative isolation of decarboxymethyl oleuropein aglycone (3,4‐DHPEA‐EDA), a bioactive secoiridoid, from extra‐virgin olive oil (EVOO). An EVOO phenolic extract (EVOO‐PE) was obtained by solid‐phase extraction (SPE), and this extract was subjected to one run using the maximum loading capacity of each methodology without loss of resolution. For this sample set, the HSCCC method proved to be a more efficient approach regarding loading capacity, solvent consumption, and throughput compared with the HPLC method. However, the purity of the target from HPLC was superior to that of HSCCC, as the number of theoretical plates could not match that of HPLC.

Simultaneous separation of antihyperlipidemic drugs by green ultrahigh-performance liquid chromatography–diode array detector method: Improving the health of liquid chromatography

Statins in combination with fibrates show beneficial effects on the lipoprotein profile of patients because they have positive complimentary effects on lipid profile. A new green ultrahigh-performance liquid chromatography–diode array detector method for simultaneous analysis of simvastatin (SMV) and fenofibrate (FNF) in standard form, marketed formulations, and self-emulsifying drug delivery system formulations was developed and validated in the present investigation. The method utilized C18 as stationary phase and a combination of methanol:water (8:2) as an eluent. It was found that selected eluent provided short run time (2.5 minutes), better peak symmetry and satisfactory values of other chromatographic parameters such as resolution (Rs=2.325), capacity factor (k, 3.0 and 4.2 for SMV and FNF, respectively), selectivity (α =1.4), and number of theoretical plates (N, 4265 and 5285 for SMV and FNF, respectively). An excellent linear relationship (r2 0.998 and 0.997 for SMV and FNF, respectively) was observed for linear regression data for the calibration plots. The developed system was validated for accuracy, precision, robustness (˃ 2% for both drugs) and recovery (98–102% for both drugs). Results obtained from the statistical treatment of the values obtained for different parameters proved that the method is suitable, reproducible, and selective for the simultaneous analysis of SMV and FNF in bulk, marketed, and self-emulsifying drug delivery system formulations. The replacement of commonly applied toxic solvents with innocuous and environmentally benign solvents provides a better option than the more toxic processes in drug analysis.

Tubing modifications for countercurrent chromatography: Investigation of geometrical parameters

ABSTRACTCountercurrent chromatography (CCC) is a separation technique which may be described as a combination of a great number of liquid–liquid distributions of analytes in a two-phase solvent system with liquid chromatography (LC) features. Even optimized CCC separations currently provide a lower number of theoretical plates when compared to LC. For this reason, instrumental advancements are indispensable to, at least partly, overcome this drawback. Recently, we found that improvement of the classic CCC coil, that is using a long hollow tubing, may be achieved by the introduction of tubing crimpings which increase the stationary phase retention. In this study, we systematically investigated the effects of three geometrical parameters (crimping depth, distance between two crimpings as well as partial or complete crimping of the tubing) on the stationary phase retention by a factorial design of experiments approach. Separation efficiency tests were performed with two groups of analytes: fatty acid methyl esters (FAME) in the n-hexane/acetonitrile (HAcn) and alkyl p-hydroxybenzoates in the n-hexane/tert-butylmethylether/methanol/water solvent system. The most narrow crimping distance and the deepest crimping of the tubing were the best configurations in the examined flow rate range.

Rationale behind the optimum efficiency of columns packed with new 1.9 μm fully porous particles of narrow particle size distribution

Columns packed with new commercially available 1.9 fully porous particles of narrow particle size distribution (nPSD) are characterized by extremely high efficiency. Under typical reversed phase conditions, these columns are able to generate very high number of theoretical plates (in the order of 300,000plates/m and more). In this paper, we investigate the origin of the high performance of these nPSD columns by performing a series of measurements that include, in addition to the traditional determination of the van Deemter curve, peak parking, pore blocking and inverse size exclusion experiments. Two nPSD columns (both 100×3.0mm) have been considered in this study: the first one, packed with particles of 80Å pore size, is commercially available. The second one is a prototype column packed with 1.9 fully porous particles of 120Å pore size.The main conclusion of our study is that these nPSD columns are characterized by extremely low eddy dispersion, while longitudinal diffusion and mass transfer kinetics are substantially equivalent to those of other fully porous particles of similar chemistry.

General Solution of the Extended Plate Model Including Diffusion, Slow Transfer Kinetics and Extra-Column Effects for Isocratic Chromatographic Elution

The plate model proposed by Martin and Synge has been used for the characterization of columns up-to-date. In this approach, the column is divided into a large number (N) of identical theoretical plates. Mobile phase transference between plates takes place in infinitesimal steps with mixing of the solutions in the adjacent plates during the flow. The plate height is related to the band broadening that occurs in the mixing process due to the microscopic heterogeneities in the mobile phase flow. According to the original Martin and Synge model, solutes reach the equilibrium instantaneously in each theoretical plate, where dispersion is produced by: (i) convection or mixing of the mobile phase reaching a theoretical plate with that existing in that plate; and (ii) the equilibrium of the solute that is partitioned between mobile phase and stationary phase. In this work, a general method is proposed to solve the problem of chromatographic elution by means of an extended plate model assuming slow mass transfer, longitudinal diffusion in both mobile phase and stationary phase, and the extra column dispersion. The final equation was validated by comparing the results with those obtained through the numerical simulation of the solute migration using the finite differential approach. Experimental data were also used to check the validity of the derived equations.

Comprehensive untargeted lipidomic analysis using core–shell C30 particle column and high field orbitrap mass spectrometer

The goal of untargeted lipidomics is to have high throughput, yet comprehensive and unambiguous identification and quantification of lipids. Novel stationary phases in LC separation and new mass spectrometric instruments capable of high mass resolving power and faster scanning rate are essential to achieving this goal. In this work, 4 reversed phase LC columns coupled with a high field quadrupole orbitrap mass spectrometer (Q Exactive HF) were thoroughly compared using complex lipid standard mixture and rat plasma and liver samples. A good separation of all lipids was achieved in 24min of gradient. The columns compared include C30 and C18 functionalization on either core–shell or totally porous silica particles, with size ranging from 1.7 to 2.6μm. Accucore C30 column showed the narrowest peaks and highest theoretical plate number, and excellent peak capacity and retention time reproducibility (<1% standard deviation). As a result, it resulted in 430 lipid species identified from rat plasma and rat liver samples with highest confidence. The high resolution offered by the up-front RPLC allowed discrimination of cis/trans isomeric lipid species, and the high field orbitrap mass spectrometer afforded the clear distinction of isobaric lipid species in full scan MS and the unambiguous assignment of sn-positional isomers for lysophospholipids in MS/MS. Taken together, the high efficiency LC separation and high mass resolving MS analysis are very promising tools for untargeted lipidomics analysis.

Acylated-naproxen as the surface-active template in the preparation of micro- and nanospherical imprinted xerogels by emulsion techniques

A strategy based on water-in-oil emulsion for the dispersion of a sol–gel mixture into small droplets was employed with the view of the production of naproxen-imprinted micro- and nanospheres. The procedure, aiming at a surface imprinting process, comprised the synthesis of a naproxen-derived surfactant. The imprinting process occurred at the interface of the emulsions or microemulsions, by the migration of the NAP-surfactant head into the sol–gel drops to leave surficial imprints due mainly to ion-pair interaction with a cationic group contained within the growing sol–gel network. The surface-imprinted microspheric particles exhibited a log-normal size distribution with geometric mean diameter of 3.1μm. A mesoporous texture was found from measurements of the specific surface area (206m2/g) and pore diameter (Dp 2nm). Evaluation of the microspheres as packed HPLC stationary phases resulted in the determination of the selectivity factor against ibuprofen (α=2.1), demonstrating the successful imprinting. Chromatographic efficiency, evaluated by the number of theoretical plates (222platescm−3), emerged as an outstanding feature among the set of all relatable formats produced before, an advantage intrinsic to the location of the imprinted sites on the surface. The material presented a capacity of 3.2μmolg−1. Additionally, exploratory work conducted on their nanoscale counterparts resulted in the production of nanospheres in the size order of 10nm providing good indications of a successful imprinting process.

Particle-loaded monolithic materials for separations via planar electrochromatography

The synthesis and characterization of novel stationary phases for analytical applications as well as for planar electrochromatography are presented. The stationary phases are C8-functionalized silica-based monoliths, which are supported by silica particles in order to avoid shrinkage and to increase mechanical stability. After optimizing the separation conditions in capillaries for capillary electrochromatography (CEC), the novel materials were implemented in a planar test cell and tested for the electrochromatochraphic separation of polyaromatic hydrocarbons (PAHs). Although the change of geometries implied a scale-up of the filling procedure, high separation performances with theoretical plate numbers of up to 30,000 m−1 and throughputs of 50 mL h−1 could be achieved.

Femtoliter high-performance liquid chromatography using extended-nano channels.

A high-performance liquid chromatography system with 35 fL sample volume was developed using extended-nano (10-1000 nm) fluidic channels. For many years, miniaturization and enhancement of separation performance have been important issues in separation science. Recently, we have reported an ultimate miniaturization of chromatography using extended-nano channels with extremely high separation efficiency of 7 × 106 plates per m. However, the real theoretical plate number was limited to 103 due to the short nanochannel length. In this paper, the theoretical plate number was dramatically increased by developing a new high-pressure system with a very long nanochannel. A separation experiment of two fluorescent dyes demonstrated that the theoretical plate number could be improved to 1.4 × 104, which is much higher than that with conventional HPLC. The theoretical plate number is also comparable to those of capillary monolithic columns. The extremely small sample volume of extended-nano chromatography could support innovative analytical techniques capable of analyzing a single living cell in the near future.

Simulation of Tert-Butyl Alcohol Forming Process by Slurry Catalytic Distillation with Custom Kinetic Program

Producing tert-butyl alcohol (TBA) by slurry catalytic distillation is a green new technology. In order to provide reference data for this production process, this paper applied advanced simulation software Aspen to simulate and optimize the slurry catalytic distillation process of producing TBA. And the kinetics equation of isobutylene hydration which is catalyzed by cation exchange resin in continuous stirred tank reactor (CSTR) is used to display the reaction process. Appropriate theoretical plate number of rectifying section, reaction section and stripping section, reflux ratio and liquid hold-up are obtained by the analog computation. Under this process condition, the conversion rate of isobutylene is 82.53%; the mole fraction of TBA in the bottom discharging is 82.5%.

Disposable microcolumns with welded metal frits.

This study reports the preparation of disposable microcolumns with welded metal frits for the first time. First, the bottom of glass-lined stainless-steel tubing of 30 cm length, 1.6 mm od, and 0.5 mm id was welded with a stainless-steel screen frit of 1.6 mm diameter. A micro-welding machine was used for this. Next, the column was connected to a slurry packer and packed with porous silica particles. Then, the inlet of the column was carefully welded with another frit. The column was tested for separation of a test mix composed of phenol, 2-nitrophenol, acetophenone, aceanilide, and benzamide. Another column of the same physical dimension was also prepared with frits that were not welded to the column. The chromatographic performances of the two groups of columns (welded frits versus non-welded frits) were examined. The columns of welded frits showed ca. 18% better separation efficiency (number of theoretical plates) than those of non-welded frits.

Conventional and enantioselective gas chromatography with microfabricated planar columns for analysis of real-world samples of plant volatile fraction

Within a project exploring the application of lab-on-chip GC to in-field analysis of the plant volatile fraction, this study evaluated the performance of a set of planar columns (also known as microchannels, MEMS columns, or microfabricated columns) of different dimensions installed in a conventional GC unit. Circular double-spiral-shaped-channel planar columns with different square/rectangular sections up to 2m long were applied to the analysis of both essential oils and headspace samples of a group of medicinal and aromatic plants (chamomile, peppermint, sage, rosemary, lavender and bergamot) and of standard mixtures of related compounds; the results were compared to those obtained with reference narrow-bore columns (l:5m, dc:0.1mm, df:0.1μm). The above essential oils and headspaces were first analyzed quali-and quantitatively with planar columns statically coated with conventional stationary phases (5%-phenyl-polymethylsiloxane and auto-bondable nitroterephthalic-acid-modified polyethylene glycol), and then submitted to chiral recognition of their diagnostic markers, by enantioselective GC with a planar columns coated with a cyclodextrin derivative (30% 6I–VII-O-TBDMS-3I–VII-O-ethyl-2I–VII-O-ethyl-β-cyclodextrin in PS-086). Column characteristics and analysis conditions were first optimized to obtain suitable retention and efficiency for the samples investigated. The planar columns tested showed performances close to the reference conventional narrow-bore columns, with theoretical plate numbers per meter (N/m) ranging from 6100 to 7200 for those coated with the conventional stationary phases, and above 5600 for those with the chiral selector.

역상 크로마토그래피에서 모멘트 방법과 van Deemter 식을 이용한 고리형 아데노신 일인산의 분리특성 연구

The moment analysis of cyclic adenosine monophosphate (cAMP) was performed using chromatograms that were obtained with the pulse input method from an octadecyl silica (ODS) high-performance liquid chromatogra- phy (HPLC) column. The general rate (GR) model was employed to calculate the first absolute moment and the second central moment. Three important coefficients for moment analysis, which are molecular diffusivity (Dm), external mass transfer coefficient (kf), and intra-particle diffusivity (De), were estimated by the Wilke-Chang equation, Wilson-Gean- koplis equation, and comparing van Deemter equation to theoretical plate number equation, respectively. Experiments were conducted by various conditions of flow rates, methanol volume ratio of the mobile phase, and solute concentra- tion. After the moment analysis, results were organized by van Deemter plots. Also van Deemter coefficients were com- pared each other to effect Hax, Hf, and Hd on height equivalent to a theoretical plate (HETP, Htotal). The value of intra- particle diffusion (Hd) was the primary factor which makes for HETP whereas external mass transfer (Hf) was disre- gardable factor.

Application of capacitively coupled contactless conductivity as an external detector for zone electrophoresis in poly(dimethylsiloxane) chips.

In this work, lab-made PDMS microfluidic chips were matched to a capacitively coupled contactless conductivity detector (C(4) D) having external in-plane electrodes (eDAQ, Australia). The advantages of this type of C(4) D are the choice to reversibly place or remove the microchip onto/from the detector and to freely variate the position of the detection (separation length) on the microchip. The thickness of the bottom layer of the PDMS chip was optimized to achieve sensitive detection during the electrophoretic separation. PDMS chips with 100 μm bottom layer used with the C(4) D platform were tested by CZE of a mixture of seven anions and different types of real samples. Using split-flow pressure sample injection and effective length of 6.5 cm, the numbers of theoretical plates were in the range of 4000-6000 (63,000-93,000/m) and the LODs amounted to 3.66-14.7 μmol/L (0.13-2.26 μg/mL) for the studied anions.

Preparation of a novel ionic hybrid stationary phase by non-covalent functionalization of single-walled carbon nanotubes with amino-derivatized silica gel for fast HPLC separation of aromatic compounds

Single-walled carbon nanotubes (SWCNTs) were immobilized on spherical silica gel with a 4-μm average particle size and a 60-Å average pore size. The amino-derivatized silica gel was non-covalently coated with carboxylated SWCNTs to preserve the structure of the nanotubes and their physico–chemical properties. The novel ionic hybrid stationary phase was characterized by scanning electron microscopy (SEM), infra-red (IR) spectroscopy and elemental analysis, and then, it was used to fill an empty 150×4.6mm2 high-performance liquid chromatography (HPLC) column. Chromatographic parameters, such as the theoretical plate number, retention factor and peak asymmetry factor, and analytical parameters, such as the limit of detection (LOD), limit of quantification (LOQ), linear range, calibration equation, and R2 value, and quantitative analysis parameters were calculated for all of the analytes. Using different mobile phases, five different classes of aromatic hydrocarbons were separated in a very short analysis time of 4–8min. Furthermore, a high theoretical plate number (up to 25000) and an excellent peak asymmetry factor (1.0) were obtained. The results showed that the surface of the SWNTs had very strong interactions with aromatic groups, therefore providing high selectivity for the separation of different classes of aromatic compounds. This study indicates that SWCNTs enable the extension of the application range of the newly prepared stationary phases for the fast separation of aromatic compounds by HPLC.

Extract methylnaphthalene from C10 aromatics with sidetrack distillation and continuous crystallisation

The method that extracted methylnaphthalene from C10 aromatics with sidetrack distillation and continuous crystallisation was proposed. Sidetrack distillation experiment of extracting methylnaphthalene from C10 aromatics was simulated by advanced system for process engineering (Aspen Plus). Sidetrack outlet plate, sidetrack outlet rate, reflux ratio, inlet plate and theoretical plate number were investigated. Then, the simulation results were checked by experiment at the optimised simulation process conditions. The experimental apparatus was built, and the results showed that the amount of 1-methylnaphthalene and 2-methylnaphthalene reached 27·38 and 49·46 wt-%, and the yield of them was 76·63% and 73·90%, respectively. After then, continuous crystallisation experiment was set up. The optimal results showed that when the crystallisation temperature was −12°C, crystallisation time was 3 hours, filter time was 20 minutes, the purity and yield of 2-methylnaphthalene were 96·29 and 86·45 wt-%, respectively. Therefore, the 2-methylnaphthalene can be extracted from C10 aromatics with high purity and yield.