Separation of mixed solutes using reciprocating size exclusion chromatography: Computer simulation based upon experimental parameters

Mixed solutes of different molecular size were separated by reciprocating size exclusion chromatography and the results were compared with conventional size exclusion chromatography with repeated feeds using computer simulation. Operational conditions, such as overlapping between elution curves and diffusivities of solutes, were varied in simulation. Simulation showed the separation efficiency was higher in RSEC than SEC with repeated feeds in the region of high diffusivity of either solutes at low degree of overlapping. Further study to improve RSEC by employing temperature swing is being made.     

Coating porous silica by in situ polymerization of peo macromonomers for size exclusion separation of proteins

A coating method using comb-like polymers with poly(ethylene oxide) (PEO) grafts is described and studied in order to use porous silica as phase in size exclusion chromatography (SEC) of proteins. The coating is carried out by in situ polymerization and crosslinking of methacrylates of PEO with OH end groups (macromonomers) after deposition from a solution. A series of phases was prepared using two different graft lengths and two different crosslinking agents in different proportions. The efficiency of the coatings to mask the silanol groups of the matrix is characterized by pH metric titration and the best coating conditions are deduced. From calibration with PEO standards and with proteins, the SEC behavior of each phase is analyzed from column experiments and compared to results of pH metric measurements. A close interdependence between the two methods is observed. The optimized phases exhibit very good performance in SEC, except with low molecular weight basic proteins which interact with some residual unmasked silanol groups. The presence of these groups is attributed to the intrinsic porosity of the polymeric layer which increases with the length of the grafts.     

Number-average molecular weight by size exclusion chromatography

It is now theoretically possible to obtain absolute accurate values of number-average molecular weight of complex polymers (e.g., branched polymers or copolymers) using size exclusion chromatography (SEC) with only a detector that measures the difference between the eluting polymer solution viscosity and the viscosity of the pure mobile phase (a differential viscometer [DV] detector). However, both precision and accuracy of these “DV M?_n” values are of concern. In this work, the precision of NBS 706 polystyrene was found to be two to three times worse for the DV M?_n than for the conventionally calculated M?_n. Also, regarding accuracy, the DV M?_n values were affected by the location of the universal calibration curve along the retention volume axis (a problem intimately associated with the problem of specifying the correct interdetector volume), the sensitivity of the DV detector to low molecular weights present in the sample, and axial dispersion. Each of these sources of error are examined in turn and two methods of calculating M?_n values are proposed. © 1994 John Wiley & Sons, Inc.     

Characterization of block copolymers by size exclusion chromatography

Summary Poly(ethyl methacrylate-b-deuterated methyl methacrylate), poly(styrene-b-methyl methacrylate), and poly(styrene-b-dimethylsiloxane)diblock copolymers have been characterized by means of size exclusion chromatography (GPC) apparatus fitted with four detectors in series, viz continuous viscometer, UV spectrophotometer, low angle light scattering photometer, and differential refractometer. The continuous measurements of the scattered light intensity, the limiting viscosity number, the concentration, and the chemical composition permits complete determination of the molecular characteristics of block copolymers.     

Studies on hyperbranched polyurethane by multidetector size exclusion chromatography

Hyperbranched polyurethane (HP) and its linear analog (LPU) were studied by size exclusion chromatography (SEC), utilizing a combination of refractive index (RI), right angle light scattering (RALLS), and differential viscosity (DV) detectors. The relationships between retention volume (V_e), intrinsic viscosity (η), radius of gyration (R_g), and the molecular structure were investigated. It was shown that the hyperbranched polyurethane had lower V_e, η, and R_g than its linear analog when they had the same molecular weight. The branching parameter g and g′ were calculated. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 2445–2450, 2002     

Characterization of poly(diethoxyphosphazene) by size exclusion chromatography and viscometry

Two samples of poly(diethoxyphosphazene) (PDEP) having very different molecular weights have been studied by viscometry and size exclusion chromatography in THF solution. The results obtained, together with light scattering data of these samples, allow the calculation of the Mark-Houwink constants a=0.65 and K=2.5 10^-4 in THF at 25°C. The method of calculation employed takes into account the great polydispersity of the samples. The characteristic ratio of the unperturbed dimensions was also calculated giving C_n = r²_o/n² 18, a value slightly higher than those previously reported for poly(dihexoxyphosphazene), C_n13 and poly (dichlorophosphazene), C_n13.5.     

Particle size separation by alternating electrophoretic deposition

This paper describes a study of the size distribution of the particles deposited under different frequencies by alternating electrophoretic deposition. A low concentration suspension of SnO₂ particles was prepared in acetone and particles of SnO₂ were deposited on electrodes by the low frequency alternating electrophoretic deposition method. Scanning electron microscopy (SEM) showed that increasing the frequency from 0 to 1000 Hz reduces the average size of the SnO₂ particles deposited. Particle size distributions obtained from the SEM images show the sizing capability of the alternating electrophoretic deposition method.     

Characterization of polyester/polycarbonate blends by size exclusion chromatography and melt rheometry

A major obstacle to the study of polymer blends has been the lack of a convenient technique for measurement of molecular weight. Melt rheometry, while giving useful information related to processing and end-use performance, is incapable of providing detailed information on the individual components. This work describes the use of size exclusion chromatography (SEC) to study the molecular-weight distributions of polycarbonates and aromatic polyesters in blends of the two. SEC of the polycarbonate is achieved in a solvent which dissolves the polycarbonate, but not the polyester, while SEC is performed in a solvent which dissolves both components, but using selective detection. Thus, SEC is used to examine the individual components of the blend, while rheometry can be used to study the blend as a whole. This combination of techniques has been successfully used to analyze the effect of moisture, processing conditions, and recycling on blend properties.     

Separation of acylglycerols,FAME and FFA in biodiesel by size exclusion chromatography

Size‐exclusion chromatography separates solutes according to their molecular sizes. Free fatty acids (FFA), fatty acid methyl esters (FAME) and monoacylglycerols (MG) of vegetable oils or animal fats have very close molecular sizes and they cannot be baseline‐separated on a single Phenogel column (100 Å, 300 mm × 7.8 mm ID, 5 µm) by using tetrahydrofuran (THF) as the mobile phase. When toluene is used as the mobile phase, triacylglycerols (TG), diacylglycerols (DG), MG and FAME are well separated but there is no baseline resolution between DG and FAME. In addition, the elution order of MG and FAME is reversed. However, baseline separation of all the above lipid classes can be achieved by using toluene containing THF, acetone, dichloromethane, ethyl acetate or acetic acid as the solvent modifier. Acetic acid (0.25%) as the solvent modifier gives the best resolution and all the reference peaks are symmetrical. The detection limit of each class of lipids is 0.1 µg. The correlation coefficient values (between 1 and 100 µg) of all the lipid classes are better than 0.99. Thus, the determination of biodiesel products in the biodiesel reactor is very much simplified.     

Comments on the measurement of long chain branching by size exclusion chromatography

Summary A technique for measuring long chain branching as a function of polymer molecular weight uses SEC with a low angle laser light scattering (LALLS) detector to compare M_W of an eluting species with the molecular weight of the linear counterpart that has the same retention time. This technique is correct only if all species in the SEC detector cells have the same constitution. Evidence is presented that indicates that this condition prevails for low density, high pressure polyethylene and polyvinyl alcohol. Alternative forms of data representations are suggested. A major uncertainty in the data treatment is the value to be assigned to the ratio of radii of gyration of linear and branched polymers with the same molecular weight. A method is suggested to measure this ratio directly, as a function of molecular weight, if the eluting species at any instant are uniform in branching character.     

High-performance liquid chromatography analysis of peanut phospholipids. I. Injection system for simultaneous concentration and separation of phospholipids

This paper discusses the details of a high-performance liquid chromatography method for the simultaneous concentration and separation of phospholipids or other trace compounds by direct oil injection using two different solvent systems. The system equilibrates and concentrates phospholipids on a silica column using hexane. At the same time, an analytical column is equilibrating and separating phospholipids using two binary solvent mixtures. This system eliminates a preconcentration step previously accomplished by solid-phase extraction, open-column chromatography, and other previously used methodology. Other advantages include: a 40% reduction in analysis time, elimination of a second transfer of labile compounds, decreased solvent use, and a simpler array of solvents to separate phospholipids. The method described has broader applications, such as trace organic compounds in water supplies, and trace metals with appropriate modifications for the particular analysis.     

Theoretical study of dynamic countercurrent cyclic extraction processes for the separation and concentration of components of a liquid mixture

Some results of theoretical studies on different dynamic countercurrent cyclic extraction variants and the effect of principal process parameters on the efficiency of separation for liquid mixture components have been given. The studies are based on a modified model of the equilibrium stages. It has been established that the proposed extraction mode enables the concentration of target mixture components with their simultaneous separation.

     

纳滤分离中性溶质的截留分子量参数细孔模型

基于纳滤膜截留分子量（MWC）所对应的分子Stokes半径(rs)与膜的等效细孔半径(rp)相等的假设,通过建立rs与分子量(MW)之间、rp与MWC之间的定量关系方程,并以立体阻碍－细孔模型（SHP）和Spiegler-Kedem模型为基础,组建了一个以截留分子量为特征参数的纳滤分离中性溶质的细孔模型（MWC-SHP）。通过NF270纳滤膜对葡萄糖和蔗糖的透过实验,采用MWC-SHP模型对NF270纳滤膜的开孔率与膜厚之比（Ak/Δx）和rp进行了估算,估算结果同SHP模型一致。应用MWC-SHP模型预测中性溶质分子的截留率随透过通量的变化关系,与实验结果吻合.因此,MWC-SHP模型同SHP模型一样,可用于纳滤膜结构评价和分离性能预测。与SHP模型相比,MWC-SHP模型的求解更方便,具有较好的实用性。     

Chromatogram broadening of proteins and dextrans in size exclusion chromatography

The mechanisms governing the broadening of experimental chromatograms for proteins and paucidisperse dextrans were studied on TSK-G2000SW and TSK-G3000SW columns. Within the conditions studied, the chromatogram variance for all solutes increased linearly with increasing effluent flow rate. As predicted by current theories of the kinetics of size exclusion chromatography, this flow rate dependence is caused mainly by slow mass transport of the solute within the stationary phase of the column. Restricted diffusion within the stationary phase was dependent upon the ratio of solute molecular size to column pore radius and was similar for both proteins and dextrans. In comparison with results for monodisperse proteins, the broader chromatograms produced by dextrans were due to sample polydispersity and not to differences in solute column spreading. Corrections for column spreading on these columns are small for the determination of integral properties of polymers but may be significant when molecular weight distributions are of interest.     

Adsorption characteristics of sulphonated melamine formaldehyde condensates by high performance size exclusion chromatography

High performance size exclusion chromatography has been used to measure the average molecular weight and molecular weight distribution of sulphonated melamine formaldehyde condensate admixtures. The method was then used to study the adsorption of these molecules on to the surfaces of cement particles. It was found that the molecules in the higher molecular weight fractions preferentially adsorbed on to the cement particles.     

Molar mass analysis of polyamides-11 and -12 by size exclusion chromatography in HFiP

The SEC analysis of polyamide-11 and polyamide-12 can be conducted free of association and aggregation phenomena when hexafluoroisopropanol + 0.05 mol/L potassium trifluoroacetate are used as the mobile phase. The calibration of the SEC system can be conducted in different ways. As stationary phases non-polar polystyrene and polar perfluoro silicagel were tested. The investigations showed that the polystyrene gel exhibits hydrophobic interactions with the polyamides while with the silicagel selective interactions were not found. Investigating different options for SEC calibration it was found that conventional PMMA calibration does not yield correct results. The universal calibration approach based on PMMA calibration did not work either. Correct molar masses were obtained when the PMMA calibration curve was corrected with data from polyamide blends using a simplex algorithm. Alternatively, calibration can be conducted with broadly distributed polyamides that were first fully characterized by SEC-MALLS. The resulting molar mass distributions for different sets of polyamides were compared with molar masses that were determined directly by SEC-MALLS and excellent correlation was obtained.     

The simultaneous separation and quantitation of human milk lipids

A protocol using a dry column method was modified for the extraction of total lipids and the simultaneous separation and quantitation of neutral and polar lipids in human milk. The triacylglycerol, cholesterol, phospholipid and vitamin E contents of the lipid extracts were determined and compared with lipids extracted using a modified Folch procedure. Good precision for the extraction of neutral, polar and total lipids, as well as the different lipid classes, was demonstrated. No significant differences were found between the two methods with respect to the amount of cholesterol, phospholipid, total lipid or vitamin E extracted, thus validating the method as an extraction technique. We discuss the relationship between vitamin E and the three major milk lipids as an indicator of the vitamin's place of origin in the mammary gland. Our findings do not support the idea that vitamin E in mature milk has its original location in the apical membrane. Scientific Contribution No. 1254, Storrs Agricultural Experiment Station, University of Connecticut, Storrs, CT 06269.     

System development for size exclusion chromatography of starch hydrolysates

A system for the aqueous size exclusion chromatography (SEC) of starch hydrolysates has been developed. Sepharose CL is the chromatographic support material, and aqueous sodium hydroxide solution is the eluent. Various factors affecting the resolution of the proposed system are discussed. Support materials having small particle size and narrow particle size distribution are necessary for maximizing separation efficiency. The ionic strength of the eluent, however, has a negligible effect on separation efficiency. The fractionation range of the system has been broadened by connecting in series columns containing two different Sepharose-CL gel types according to the bimodal pore size distribution concept. Well-characterized sodium polystyrene sulfonate and dextran standards are used to calibrate this SEC system. The Coll–Prusinowski calibration procedure leads to a linear calibration curve over a wide molecular weight domain.