Elution Behavior of Low Molecular Weight Compounds in Gel Permeation Chromatography

Abstract

Elution behavior of organic compounds in gel permeation chromatography was investigated using chloroform as eluent. In aliphatic hydrocarbons, the elution counts decreased linearly with increasing the molecular volumes. In aromatic hydrocarbons, the relation between molecular volume and elution count slightly shifted toward lower counts. The elution counts in esters, ketones, amides, alcohols and carboxylic acids always fell in lower elution counts than expected by aliphatic hydrocarbons. This fact suggests that all these compounds are solvated by eluent molecules. Amines and chlorides exhibit an adsorption effect on cross-linked polystyrene gel. These compounds are eluted behind the corresponding hydrocarbons for given molecular volumes, which were obtained by dividing molecular weight by density.     

Characterization of Bituminous Compounds by Gel Permeation Chromatography (GPC)

Abstract

Gel permeation chromatography is applied to the qualitative and quantitative characterization of asphalt, asphaltenes and maltenes. The nature of their molecular size distributions, micellar dimensions, and degree of aromatic polycondensation are described. The resultant data are used to provide insight into the nature of associative processes involving these materials.     

Model of a Reversed Phase Grafted on Silica Gel

Russian Journal of Physical Chemistry A - A model is proposed for the surface structure of reversed phase sorbents obtained via the chemical modification of silica gel with...     

Characterization of Brominated Vegetable Oils by Normal and Reversed Phase Liquid Chromatography

Abstract

Brominated vegetable oils are characterized by normal and reversed phase chromatography using UV absorbance detection at 220 nm. A series of seven brominated vegetable oil preparations are transesterified using acid methanolysis and the resulting dibromo-, tetrabromo- and hexabromostearate components quantitated by HPLC. The identification of the oils compare favorably with results obtained by gas chromatography.     

Gel Permeation Chromatography of Unsaturated Polyester Resins. Possibilities and Limitations

Abstract

The use of gel permeation chromatography (GPC) for the characterization of unsaturated polyester resins is demonstrated on several examples. Number-average molecular weights determined by this method are compared to data obtained by means of vapor pressure osmometry (VPO) and by end group analysis (EG). The determination of the polyester resin composition as a function of molecular weight by stop-and-go UV scanning procedure is described. A comparison of theoretical and experimental molecular distribution is applied to the estimation of branching extent.     

Solvation and Adsorption Effects in Gel Permeation Chromatography

Abstract

Saturated hydrocarbons are generally eluted according to molecular volumes in gel permeation chromatography (GPC). Other compounds, containing polar groups such as hydroxyl and carbonyl groups, deviate from the molecular volume/elution count relationship which is prepared using saturated hydrocarbons. The deviation is more or less observed regardless of the kinds of eluents. In this paper, this problem is investigated in detail with respect to infrared(IR) and proton magnetic resonance(NMR) spectra, and concentration dependences of peak heights and elution volumes in GPC. IR and NMR spectra reveal that alcohols, ketones and esters are strongly solvated by eluent molecules such as chloroform and tetrahydrofuran(THF). The solvation effect leads to faster elution for these compounds than expected for aliphatic hydrocarbons. On the other hand, the concentration dependences of elution counts and peak heights prove the adsorption of amines on polystyrene gel in chloroform. In fact, the elution rates of amines and polychlorides are retarded. In the case of aliphatic carboxylic acids, the elution mechanism is more complicated: association and adsorption effects would be overlapped.     

正相色谱和反相色谱法分离提纯东北红豆杉中紫杉醇和三尖杉宁碱

以东北红豆杉树叶为原料,采用正相色谱和反相色谱法分离提纯了紫杉醇和三尖杉宁碱。反相色谱中使用了一种新颖的高分子填料。东北红豆杉枝叶经过一次正相色谱分离后,再经两次反相色谱分离,分离得到两种白色针状固体。经1H NMR和13C NMR测试表明,两种物质分别为紫杉醇和三尖杉宁碱,纯度达到98%以上,产率分别为树叶干重的0.0022%和0.0018%,回收率大于70%。     

Analysis of Low Molecular Weight Polymers with Gel Permeation Chromatography

Intrinsic viscosities and gel permeation chromatography (GPC) elution times were determined in toluene on commercially available standards of polystyrene (PSTY) and polymethyl methacrylate (PMMA) having M_n in the range of 10³ to 10⁵ and 10⁴ to 10⁶, respectively. In addition, elution times were determined on the discrete GPC peaks of dimer, trimer, tetramer, etc. as seen in lower molecular weight PSTY and PMMA. Intrinsic viscosities of oligomers were estimated by extrapolation of the Mark-Houwind-Sakurada equations determined from our data, and the results were used to establish a universal calibration curve over a wide range of molecular weights. A similar approach was taken by using literature data for the intrinsic viscosities of PSTY and PMMA in tetra-hydrofuran. It was verified by proton NMR that the universal calibration curve so constructed is useful at M_n, values as low as 300. No correction was necessary for chain length dependence of the detector response.     

正反相模式下键合纤维素手性固定相对手性化合物的拆分

在自行合成的键合型纤维素-(3,5-二甲基苯基氨基甲酸酯)(CDMPC-CSP)手性固定相上,在正相模式下对苯偶姻和甲霜灵外消旋体进行了拆分,考察了流动相中醇以及温度在手性识别中对手性分离的影响。同时考察了反相模式下外消旋体的拆分。     

Characterization of Polyphenylene Sulfide Using Gel Permeation Chromatography with Triple Detection

The increasing world demand for polyphenylene sulfide (PPS) due to its unique properties has augmented the pressure on development of analytical methods to evaluate its molecular weight distribution and structure. Whilst gel permeation with triple detection (GPC3D) has been considered for PPS analysis, its development and effectiveness has been impaired because of, firstly, the high temperature needed to maintain solubility (>205°C), and, secondly, a very low dn/dc for the polystyrene calibration standards in 1-chloronaphthalene. This article presents practical recommendations to overcome these early difficulties by discussing the results obtained on PPS samples analyzed with a commercially available GPC3D instrument.     

Characterization of Copolymers and Polymer Mixtures by Gel Permeation Chromatography

Abstract

Estimation of molecular weights from GPC data is complicated when the polymer sample consists of a mixture of homopolymers or of statistical copolymers with nonuniform compositions. This is because sizes of solvated polymer coils depend on solvent interaction with both the homo-and hetero-units of the copolymers and because the extent of solvation of different homopolymers can differ. The overall degree of solvation may change effectively with composition and use of a single “average” set of Mark-Houwink constants in calibration procedures will then produce false molecular weight data from the GPC data. A new molecular weight average, M _x, is defined to overcome this problem. This average can be determined from the GPC chromatogram and intrinsic viscosity of the sample in the GPC solvent. Mark-Houwink coefficients are not needed. M _x lies between M _w and M _z.     

Comparison of Ion-Pairing and Reversed Phase Liquid Chromatography in Determination of Sulfamethoxazole and Trimethoprim

Abstract

Two simple, rapid, and sensitive HPLC methods have been developed for the simultaneous determination of sulfamethoxazole and trimethoprim in their pure and dosage forms, one utilizing reversed phase HPLC and the other ion-pair HPLC. In the reversed phase HPLC method (A) the mobile phase consists of 0.05% aqueous solution of formic acid with pH adjusted to 4.5±0.2 with triethylamine : acetonitrile:tetrahydrofuran 50 : 49 : 1 (v/v), and the mobile phase pumped at flow rate of 1.0 ml min^?1. An Appolo LC18 column (5.0 µm), 250 mm length × 4.6 mm diameter, was utilized as the stationary phase. Detection was affected spectrophotometrically at 254 nm. In the ion-pair HPLC method (B) the mobile phase consisted of methanol : buffer 35 : 65 (v/v) with the buffer composed of potassium dihydrogen phosphate 0.3 M and sodium heptan sulfonic acid 5.0 mM. To 500 ml of buffer was added 2.0 ml triethylamine, and then the pH was adjusted to 5.0 with phosphoric acid, and the mobile phase was pumped at a flow rate of 1.2 ml min^?1. A Hypersil C₁₈ column (5.0 µm), 150 mm length × 4.6 mm diameter, was utilized as the stationary phase. Detection was affected spectrophotometrically at 254 nm. Linearity ranges for sulfamethoxazole and trimethoprim were 1.0–110 and 1.5–98 µg ml^?1, respectively, with method A and 0.5–100 and 1.0–125 µg ml^?1, respectively, with method (B). Minimum detection limits obtained were 0.1969 and 0.3451 µg ml^?1 for sulfamethoxazole and trimethoprim, respectively, with method A, and 0.1377 and 0.2454 µg ml^?1 with method (B). The proposed methods were further applied to the analysis of tablets containing the two drugs, and the results were satisfied.     

A Comparison of High Performance Gel Permeation Chromatography and Nuclear Magnetic Resonance Spectroscopy in the Analysis of Plasma from Normal Subjects and Cancer Patients

Abstract

High Performance Gel Permeation Chromatography (GPC) was evaluated as an alternative to the more expensive Nuclear Magnetic Resonance (NMR) spectros-copy technique presented by Fossel and co-workers (1) for cancer detection using human plasma. These two techniques show a biphasic relationship which can be explained on the basis of the relative amounts of the lipoprotein levels present in the plasma and a good correlation (Table 1) with total triglyceride concentrations obtained from standard blood tests. The major difference in the GPC elution-profiles (254 nm) of plasma from normal individuals and that from cancer patients occurred in the peak eluting at the void volume. This peak has a retention time consistent with very low density lipoprotein (VLDL) and is elevated in most cancer patients and in normal patients with triglyceride levels greater than 200 mg/ml. The use of these techniques as a screening test for cancer in an asymptomatic population needs further evaluation.     

凝胶渗透色谱和固相萃取净化-气相色谱分离组合法测定糙米中的残留农药

提出糙米中38种有机氯农药、拟除虫菊酯和多氯联苯残留量的同时测定方法。用乙酸乙酯提取,凝胶渗透色谱和固相萃取净化,气相色谱．电子俘获检测,外标法定量。3个添加水平的平均回收率分别为77．3、81．4和83．8％;相对标准偏差3．8％～13．9％。有机氯农药和多氯联苯检出限为0．07μg／kg;拟除虫菊酯的检出限为0．4μg／kg。检测方法简便省时,自动化程度高,稳定可靠。     

Characterization and Properties of Macromolecules. XII. Numerical Treatment of Gel Permeation Chromatography Data

Abstract

Gel permeation chromatography provides a continuous recording of polymer concentration as a function of elution time. The latter may be converted by appropriate calibration into molecular weight. The chromatogram may be analyzed numerically to yield the various molecular weight averages. This process involves a number of assumptions and approximations. The magnitude of the errors introduced in the calculated molecular weight averages by the methods described in the literature are reported.     

Assessment of the Plasma-Induced Changes under Acidic Conditions in the Apparent Molecular Volume of β-Endorphin, β-Lipotropin and γ-Lipotropin by Gel Permeation and Reversed Phase High Performance Liquid Chromatography

Abstract

Addition of radiolabeled β-endorphin, β-lipotropin and γ-lipotropin to plasma at acid pH results in an apparent reduction in size of these molecules as evidenced by gel permeation chromatography. These acid plasma-treated molecules, however, are indistinguishable from the untreated radiolabeled polypeptides when subjected to high performance liquid chromatographic separations suggesting no differences in molecular composition. As these apparent changes in polypeptide molecular volume are prevented by addition of Trasylol or sodium azide to the plasma, a likely explanation would appear to be an enzyme-dependent production of anionic lipids in plasma which at acid pH bind to the lipotropins and endorphins reducing their molar volume.     

反相高效液相色谱法测定蜂胶水提物中的酚类化合物

建立了同时测定中国蜂胶水提物中23种酚类化合物的反相高效液相色谱(RP-HPLC)分析方法.采用ZORBAX Eclipse XDB C_(18)色谱柱(150 mm×4.6 mm×5 μm);流动相:甲醇-0.1%甲酸,梯度洗脱,流速1.0 mL/min,检测波长为256和280 nm,进样量20 μL,柱温35 ℃.各对照品质量浓度与色谱峰面积线性关系良好,具有较好的精确度和重现性,标准加入回收率在93.29%～106.61%之间.采用此法,从河北蜂胶中检测出18种对照品,其中表儿茶素含量最高35.50 mg/g WEP,其次是3,4-二甲氨肉桂酸15.41 mg/g WEP.而云南蜂胶中检测到9种对照品,表儿茶素含量最高11.23 mg/g WEP,其次是白杨素3.61 mg/g WEP,两地蜂胶WEP的HPLC图相似度分别为0.099(256 nm) 和0.194(280 nm),化学成分差异明显.     

凝胶渗透色谱-气相色谱-质谱测定玉米中3种农药的残留

建立以凝胶渗透色谱（GPC）和气相色谱-质谱（GC／MS）联用技术测定玉米中三唑酮、三唑醇-a，三唑醇-b残留量的方法。目标农药经乙腈提取，共提物中的油脂经液／液分配、GPC加以去除，叶黄素通过固相萃取（SPE）净化。目标农药采用GC／MS／SIM方式进行定性、定量分析。3种农药（0．05、0．5、2μs／s）的回收率在90％-110％；相对标准偏差（RSD）〈10％。     

A Direct Fractionation Procedure for the Isolation of Synthetic Products Utilizing Normal and Reversed Phase Liquid Chromatography

Abstract

A simple, one-step fractionation scheme was developed by utilizing liquid chromatography in order to provide new and improved isolation techniques for synthetic reactions, allowing elimination of tedious, multi-step processes presently in use. Thin-layer chromatography (TLC) data, used for monitoring and optimizing synthetic reactions, were directly extrapolated to high performance liquid chromatography (HPLC) systems. Inorganic reagents and highly polar side products were removed by a silica pre-column. A reversed phase column was used for clean-up process. The desired products were rapidly fractionated from the crude reaction mixture. General applicability of this procedure was demonstrated in the syntheses of various steroid derivatives.