Separation of polystyrenes by means of open tubular capillary chromatography

Simulating polymer separation in flow-through channels of monolithic columns, separation of a mixture of polystyrene standards was investigated using open tubular capillary column of 2 μm inner diameter. High column efficiency was observed for polymers of molar mass ranged from few tens to few hundred kDas. Column efficiency significantly decreased for polymers with molar mass larger than 500 kDa nevertheless preserving value of few tens of thousands theoretical plates. Calibration curve observed for open capillary column is rather steep and can be well described by simple equation without quadratic term. In spite of low selectivity, capillary columns were able in separating wide range of polystyrene standards due to column high efficiency and in such a way supported an idea of hydrodynamic mechanism of polymer separation in flow-through channel of monolithic packings.     

Purity and Stability of Urea,Creatinine and Uric Acid Standards

Abstract

The significance to the routine laboratory of instability and inter-manufacturer variation of various standards previously demonstrated by HPLC analysis was investigated by chemical analysis. Urea, creatinine and uric acid standards from several manufacturers were studied. The causes and consequences of the demonstrated impurities, variations and instability of the standards are discussed.     

Monolithic columns with optimized pore structure for molecular size-based separations of synthetic polymers

Monolithic capillary columns based on divinylbenzene were synthesized using different alcanols as porogens. Prepared columns were tested in separation of polystyrene standards according to their molar mass (MM) and were characterized by corresponding calibration graphs. It was demonstrated that a decrease of alcanol chain length from dodecanol to octanol resulted in a decrease of column permeability and in an improved column ability to separate polystyrene standards. In contrast, removing a good solvent from porogen mixture results in an increase of column permeability and in a decrease of column performance toward polystyrene standards. Optimized synthetic conditions included porogen composed of nonanol and toluene or mesytilene, and the column prepared with this porogen was capable of separating a mixture of 14 polystyrene standards with MM ranged from several millions to oligomers.     

Deuteriated Analogs as Internal Standards for the Quantitation of Environmental Alkanes by Gas Chromatography

Abstract

Quantitation by gas chromatography requires the use of suitable internal standards. Deuteriated analogs are superior, but usually require a mass spectrometer as the gas chromatographic detector to distinguish them from the compounds being measured. Completely deuteriated alkanes are, however, completely separated from the corresponding unlabelled alkanes and serve as suitable internal standards for the quantitation of environmental alkanes by gas chromatography alone.     

Long-term stability of pure standards and stock standard solutions for the determination of pesticide residues using gas chromatography

The regular replacement of pure standards used in pesticide residue analysis laboratories and frequent preparation of stock standard solutions, both required by many accreditation bodies, impose considerable demands on a laboratory's resources. In this study, pure standards for all but one (heptenophos) of 118 different pesticides amenable to analysis by GC, and stock standard solutions (1000 microg/ml) prepared from these in toluene, acetone or ethyl acetate have been shown to be stable at < or = -20 degrees C over long periods: 4-13 and 2-8 years, respectively, for pure standards and solutions. Suitable solvents, containers and handling procedures are essential to avoid evaporation from solutions.     

The size exclusion chromatography calibration of ‘Mixed-A’ and ‘Mixed-D’ columns using various polymers and compounds: An application to coal-derived materials

This work attempts to obtain the calibration curves of two different size exclusion chromatography (SEC) columns operating with 1-methyl-2-pyrrolidinone (NMP) as eluent by using various standards. Polystyrene (PS) and polymethylmethacrylate (PMMA) standards were used for obtaining calibration curves, and checked against polysaccharide (PSAC) standards, some small aromatic polycyclic standards and miscellaneous polymers. Polystyrenes and polymethylmethacrylates gave identical calibrations while polysaccharides and miscellaneous polymers lay within 1 or 2 min of the polystyrene calibration. Small molecules of mass less than 1000 units lay on or near to the polystyrene calibration lines, with a shift to late elution for the smallest molecules. This shift may be caused by the interaction with the column packing. A sample has been examined by analytical size exclusion chromatography, which was calibrated using polystyrene and polymethylmethacrylate standards. Molecular mass (MM) distributions of the sample have been examined in terms of these calibrations.     

Monitoring free silanols on reversed-phase supports with peptide standards

Summary A series of synthetic peptide HPLC standards has been designed for use in monitoring free silanols on silica-based reversed-phase supports. The four standards (+ 1 to + 4 net charge) showed great versatility in monitoring silanol activity over a pH range of 2.0 to 7.0. We have developed a silanol monitoring system based on the sensitivity of the standards to ionic interactions with reversed-phase packings at pH 7.0. This monitoring procedure involves chromatographing the peptides at pH 7.0 with a combined acetonitrile and sodium perchlorate linear AB gradient and is generally applicable to reversed-phase packings exhibiting a wide range of silanol concentrations. These standards not only demonstrate the presence and extent of free silanols, they also allow the researcher to determine what changes must be made to the mobile phase composition to minimize ionic interactions. In addition, the standards, in conjunction with the double gradient monitoring system at pH 7.0, will aid researchers and manufacturers in the improvement and development of reversed-phase matrices.     

氨基己酸为配基的新型弱阳离子交换/疏水双功能色谱固定相对蛋白质的分离纯化

以硅胶为基质、氨基己酸为配基制备了一种新型弱阳离子交换/疏水（WCX/HIC）双功能混合模式色谱固定相。该固定相配基具有一定的疏水性且含有羧基,在高盐浓度下表现为HIC的性质,可作为HIC固定相使用;在低盐浓度条件下表现为离子交换的性质,可作为WCX固定相使用。分别考察了该介质在WCX和HIC两种模式下对标准蛋白质的分离性能,并与商品柱进行比较。结果表明,所合成的WCX/HIC双功能固定相在WCX和HIC两种模式下对蛋白质均有较高的分离度和选择性,且分离能力与商品柱相当,两种模式下标准蛋白质的质量和活性回收率均大于93%,表明该柱具有“一柱二用”的功能,适于生物大分子的分离纯化。基于此双功能色谱柱构建的在线单柱二维液相色谱（2DLC-1C）可在60 min内实现8种蛋白质的快速分离。在70 min内完成了对蛋清中溶菌酶的二维纯化,纯度可达到98.3%。该技术中一根色谱柱可当作两根色谱柱使用,对蛋白质组学研究和重组蛋白药物的生产具有重要的应用价值。     

The effect of the physical matrix on accurate measurements using fixed volume analytical techniques

In order to perform high accuracy analytical measurements most analytical techniques require some form of calibration using standards of the same quantity as that being measured. The highest accuracy calibration standards are those prepared by mass (gravimetrically) as opposed to by volume (volumetrically). The use of gravimetrically prepared standards to calibrate analytical techniques that rely on fixed volume injections can cause systematic errors, even when the analytical technique does not suffer from a chemical matrix interference. The origin of these errors is explained and is demonstrated experimentally for the analysis of sulphate in synthetic seawater samples, and the measurement of the anionic content of particulate matter following extraction with water and wetting agents; where average measurement biases of +2.7 and -3.2%, respectively, were observed. Proposals are offered for methods to overcome this 'physical matrix effect'.     

在线凝胶渗透色谱-二维气相色谱/质谱法测定鲫鱼样品中的14种农药残留

建立了在线凝胶渗透色谱-二维气相色谱/质谱(GPC-MDGC/MS)测定鲫鱼样品中14种农药残留的方法。样品用环己烷/乙酸乙酯(1：1,v/v)提取两次,合并提取液。提取液冷冻、过膜后,经在线凝胶渗透色谱净化后直接进行MDGC/MS分析,通过中心切割的方式将农药组分选择性切割进入二维色谱柱进行进一步分离分析,采用内标法进行定量。实验结果表明：14种农药在0.01~0.9 mg/L范围内具有较好的线性关系,相关系数均大于0.99。14种农药在3个添加水平(0.01、0.05、0.1 mg/kg)的加标回收率为83.0%~112.9%,相对标准偏差为3.2%~12.0%。该方法前处理简单,实现了在线GPC和MDGC的有效结合,准确度好、精密度高,具有很好的推广性。     

An optimized extraction and gas chromatography analysis method for the quantification of diluent hydrocarbons in froth treatment tailings

Froth treatment tailings are one type of waste stream generated during the extraction of surface-mined oil sands bitumen. To remove water and solids from bitumen froth recovered during the water-based extraction process, hydrocarbon diluent is added, and settling and/or centrifugation are applied to the diluted bitumen froth, producing diluted bitumen and froth treatment tailings. While recovery processes are in place to remove and recycle the diluent from froth treatment tailings, some residual diluent can remain. Since tailings are stored in outdoor ponds, the residual diluent can have implications for methanogenic microbial processes and resulting greenhouse gas emissions. This work presents a methodology to accurately extract and quantify diluent hydrocarbons from froth treatment tailings using gas chromatography. A cold-start temperature program is used to separate diluent hydrocarbons from any residual bitumen in the sample, and diluent is quantified using commercial standards as well as unprocessed diluent. A series of extraction parameters were tested and results from multiple conditions are shown with a rationale for the selected optimized parameters. Quantification of diluent in tailings samples is demonstrated from 60 to 5329 μg/g, and results from quality control standards show an average diluent recovery of 100 ± 10%.     

Study on retention behavior of cyclic siloxanes by high resolution pyrolysis-gas chromatography with a fused silica capillary column

The general gas chromatographic retention behavior of cyclic methylsiloxanes partially substituted with phenyl or 2-cyanoethyl groups has been systematically studied, with pyrolysis-gas chromatography being utilized to form the cyclic siloxanes from the corresponding polysiloxanes at a temperature of 600°C. Kovats retention indices (KI) were determined for the cyclic siloxanes by use of the retention data of the pyrolyzates from polyethylene as standards. The effect of phenyl and 2-cyanoethyl substituents in the cyclic siloxanes on retention behavior has also been considered.     

Isolation of oxidative degradation products of atorvastatin with supercritical fluid chromatography

The isolation of four oxidative degradation products of atorvastatin using preparative high‐performance liquid chromatography applying at least two chromatographic steps is known from the literature. In this paper it is shown that the same four impurities could be isolated from similarly prepared mixtures in only one step using supercritical fluid chromatography. The methods for separation were developed and optimized. The preparation of the mixtures was altered in such a way as to enhance the concentration of desired impurities. Appropriate solvents were applied for collection of separated impurities in order to prevent degradation. The structures of the isolated impurities were confirmed and their purity determined. The preparative supercritical fluid chromatography has proven to be superior to preparative HPLC regarding achieved purity of standards applying fewer chromatographic as well as isolation steps. Copyright © 2015 John Wiley & Sons, Ltd.     

Matrix effects on the multi-collector inductively coupled plasma mass spectrometric analysis of high-precision cadmium and zinc isotope ratios

Resin-derived contaminants added to samples during column chemistry are shown to cause matrix effects that lead to inaccuracy in multi-collector inductively coupled plasma mass spectrometry measurement of small natural variations in Cd and Zn isotopic compositions. These matrix effects were evaluated by comparing pure Cd and Zn standards and standards doped with bulk column blank from the anion exchange chromatography procedure. Doped standards exhibit signal enhancements (Cd, Ag, Zn and Cu), instrumental mass bias changes and inaccurate isotopic compositions relative to undoped standards, all of which are attributed to the combined presence of resin-derived organics and inorganics. The matrix effect associated with the inorganic component of the column blanks was evaluated separately by doping standards with metals at the trace levels detected in the column blanks. Mass bias effects introduced by the inorganic column blank matrix are smaller than for the bulk column blank matrix but can still lead to significant changes in ion signal intensity, instrumental mass bias and isotopic ratios. Chemical treatment with refluxed HNO₃ or HClO₄/HNO₃ removes resin-derived organic components resulting in matrix effects similar in magnitude to those associated with the inorganic component of the column blank.Mass bias correction using combined external normalization-SSB does not correct for these matrix effects because the instrumental mass biases experienced by Cd and Zn are decoupled from those of Ag and Cu, respectively. Our results demonstrate that ion exchange chromatography and associated resin-derived contaminants can be a source of error in MC-ICP-MS measurement of heavy stable element isotopic compositions.     

Protein separation using a novel silica-based RPLC/IEC stationary phase modified with N-methylimidazolium ionic liquid

Ionic liquids (ILs) immobilized on silica as novel high performance liquid chromatography (HPLC) stationary phases have attracted considerable attention. However, it has not been applied to protein separation. In this paper, N-methylimidazolium IL-modified silica-based stationary phase (SilprMim) was prepared and investigated as a novel multi-interaction stationary phase charged positively for protein separation. The results indicate that all of the basic proteins tested cannot be absorbed on this novel stationary phase, whereas all of the acidic proteins tested can be retained, and the baseline separation of eight kinds of acidic protein standards can be achieved when performed in reversed phase/ ion-exchange chromatography (RPLC/IEC) mode. Compared with commonly used commercial octadecylated silica (ODS) column, the novel stationary phase can show selectivity and good resolution to acidic proteins, which has a promising application in the separation and analyses of acidic proteins from the complex samples in proteomics. In addition, the chromatographic behavior of proteins, the effect of the ligand structure and the retention mechanism on this stationary phase were also investigated.     

Dynamic calibration system for trace analysis in ion chromatography

Summary A dynamic method for the preparation of diluted standards in trace analysis by Ion Chromatography is described. The proposed system uses a diffusion cell that through a capillary tube of known dimension, continuously provides large volumes of highly diluted standard.The diffusion cell setting-up and its working conditions are described, and the advantages and difficulties of the dynamic method are pointed out. Loading the cell with concentrated standard solutions (200–10000 ppm), it was possible to produce diluted Na₂SO₄ standards in the 0.1–10 ppb concentration range. The cell is able to work for nearly a month before the source amount decreased by 1%.The linearity of the calibration device is good and the method is free of systematic errors. Under strictly controlled experimental condition, the diffusion cell provides primary standards because it allows to obtain concentrations only depending on its geometry.     

The Direct Determination of Axial Dispersion in Size Exclusion Chromatography Based on Poissonian Chain Length Distributions

Summary A fast and straightforward method for the direct determination of _ad the extent of axial dispersion under normal working conditions is presented. The method makes use of the peak variance of Poisson distributions, which can be determined from the points of inflection. The applicability of this method is experimentally demonstrated for four series of commercially available polymer standards. Theoretical calculations and experimental results are presented that confirm that this method also works with narrow distributions which are the weighted sum of several adjacent Poisson distributions.Presented at: International Symposium on Separation and Characterization of Natural and Synthetic Macromolecules, Amsterdam, The Netherlands, February 5–7, 2003     

Retention indices in micellar electrokinetic chromatography

The use of retention indices in micellar electrokinetic chromatography (MEKC) is evaluated both from a theoretical and a practical point of view. Fundamental equations for the determination of retention indices in MEKC are described, showing that retention indices are independent of the surfactant concentration. Possibilities as well as limitations of different homologous series as reference standards are described. In addition, the practical application of retention indices for identification, investigation of solute-micelle interactions, characterization and classification of pseudo-stationary phases and determination of solute lipophilicity are discussed.     

Gas Chromatography of Alpha-Keto Acids with A Sensitive and Selective Detector

Abstract

Gas chromatography of α-keto acids has been performed with high sensitivity by converting the acids to the trimethylsilyl derivatives of the quinoxalones derived from them and using a rubidium sulfate flame detector. Quantitative determinations have been made with the use of alkyl cyanides as internal standards.     

Feasibility of preparing and analyzing gas standards containing heavy hydrocarbons (C10–C16)

State and federal agencies are beginning to monitor ambient air for compounds related to diesel exhaust. The National Institute of Standards and Technology (NIST) was asked to develop standards containing heavy (C10-C16) alkanes which could then be used in air monitoring and exhaust studies. Several primary gravimetric standards, containing heavy (C10-C16) alkanes in nitrogen, were developed and analyzed by gas chromatography (GC) with flame-ionization detection (FID). The results of this research indicate that accurate gas standards containing these hydrocarbons can be prepared. However, the analytical results show that the temperature of the transfer system from the gas cylinder to the GC column (including the gas-sample valve) must be heated in order to prevent adsorption of these compounds within the analytical system. The results indicate that even at elevated temperatures these compounds are being absorbed within the system. The results show that quantitative results cannot be obtained by using one compound such as hexane, as an internal standard to determine the concentration of other hydrocarbons. Quantitative and accurate results are best obtained if standards for each hydrocarbon of interest are used to determine concentrations of unknowns for the respective hydrocarbon.