Enantiomer separation by pressure-supported electrochromatography using capillaries packed with Chirasil-Dex polymer-coated silica.

Pressure-supported electrochromatography using capillaries packed with permethyl-cyclodextrin covalently linked via an octamethylene spacer to dimethylpolysiloxane and immobilized on silica (Chirasil-Dex silica) has been employed as an efficient and rapid method for the enantiomer separation of various racemic compounds. By comparing this method with micropacked liquid chromatography (LC), employing the same column in a unified instrumental setup, micropacked capillary electrochromatography (CEC) shows higher column efficiencies and hence better resolution factors. The influence of type and concentration of buffer, amount and nature of organic modifier, and pressure support is investigated.     

Micropacked column gas chromatography with vapour of organic substance as the mobile phase

Summary Retention behaviours of aromatic hydrocarbons were examined by using the vapour of an organic substance as the mobile phase and silica gel as the stationary phase. Gas chromatographic separation of aromatic hydrocarbons was demonstrated by using a system comprising a liquid chromatographic (LC) pump, a micropacked column for LC, a column oven and a UV detector.     

Temperature optimization for the separation of PAHs on micropacked LC ODS columns

The effect of column temperature on the separation of the sixteen polycyclic aromatic hydrocarbons (PAHs) of mixture SRM 1647a of the US Environmental Protection Agency has been studied on different micropacked ODS columns. Isothermal temperature optimization was successfully used for complete separation of the PAHs on a polymeric ODS stationary phase, whereas temperature programmed conditions were selected for separation on a monomeric ODS stationary phase.     

The application of glass micropacked columns in gas liquid solid chromatography to the GC-MS analysis of polar compounds

Summary High efficiency, glass micropacked columns are evaluated in terms of Van Deemter plots showing that the same number of theoretical plates is obtained for hydrocarbons and polar compounds, such as aliphatic primary amines, alcohols and carboxylic acids. A direct GC-MS coupling system is employed showing no loss in resolution in the ion source even for very polar compounds. It is shown that the high capacity of GLSC micropacked columns is very effective in obtaining interpretable mass spectra of minor compounds in complex organic mixtures. Mass spectra obtained with the direct coupling are compared with those obtained with a conventional packed column of the same efficiency making use of a Biemann separator.     

Preparation and evaluation of nickelmesogen for micropacked gas chromatography

The preparation and mesomorphic properties of a substituted bis(dithiolene)nickel complex derived from 4, 4'-dimethoxybenzil are reported. The phase transition temperatures were based on data obtained by polarized light microscopy and differential scanning calorimetry. The mesogenic phase existed over the temperature range from 77 to 175 degrees C. A novel micropacked column (1.5 or 3 m x 1 mm i.d.) prepared from the slurry of bis[1,2-bis(4-n-undecyloxyphenyl)ethane-1,2-dithiolene] nickel(II) (5%, w/w), coated on Chromosorb W was applied for the separation of dialkyl sulfides. The non-linearity (discontinuity) of Van't Hoff plots suggests that the liquid crystal property existed even in the coated phase. Factors affecting the retention and the sample selectivity on the prepared column were examined by using a flame photometric detector (FPD). The separation might be based on the mechanism of ligand exchange, shape selectivity and polarity interaction besides the vapor pressure. LOD for the determination of dialkyl sulfides was below 1 ng for most of the analytes.     

Selective gas chromatographic separation of polycyclic aromatic hydrocarbons on Bentone 34

Summary Using modified Bentone 34 as a thin layer on glass beads in a short micropacked column at maximum working temperature reasonable retention times of polycyclic aromatic hydrocarbons were achieved up to perylene. Some differences in the elution order were observed as compared with other sorbents.     

低碳烃的常温动态预浓缩方法

设计了一种常温动态预浓缩方法,用于低沸点气体样品的富集,该方法使用对样品有中等保留强度的吸附剂作为浓缩柱,配以反吹和快速升温技术,实现了对沸点≥－１０３℃样品的常温动态富集和升温快速脱附。整个过程不间断连续完成,从进样至脱附只需几分钟能以较小的进样量获得较高的浓缩倍数。本文以Ｃ２样品为例进行了实验,在进样量１１ｍＬ时,得到浓缩倍数≥１００,回收率〉９８％,重复误差≤３％（ＲＳＤ）,该装置适配微型色谱仪,用于痕量分析。本方法同样适用于常规色谱仪。该方法操作简便,可靠性高,可用于环境样品和特殊场合的现场样品的富集和分析,替代了低温冷阱富集的传统方法。     

Applications of capillary supercritical fluid chromatography to the characterization of edible oils and traditional chinese medicines

A home-made supercritical fluid chromatograph fitted with a capillary micropacked column and equipped with FID detection has been used to separate the components of silicone DC-200, beeswax, tea oil, cod-liver oil, rancid butter, and several traditional Chinese medicines such as Honghua oil, Jiuxin oil, and Wanhua oil.     

Multidimensional GC with macrobore WCOT and PLOT Columns

Multidimensional GC (MDGC) with macrobore WCOT and PLOT columns has shown several benefits: (1) Higher flow rates, which are used, makes possible the use of common valves as the switching device; (2) very simple system configurations are possible; (3) because the columns have relatively large capacity, the TCD can be used to measure both organic and inorganic components; (4) micropacked or open tubular columns are precolumns which provide a wide range of selectivity; (5) both precolumn and analytical columns can be operated at the same flow rate without splitting of the sample. Four rapid sample analyses: (1) Oxygenates in gasohol; (2) natural gas; (3) refinery gas; (4) hydrocarbon types in naphtha, have been developed and performed on a less complex and economical gas chromatograph.     

高效迎头分析法测定药物-人血清白蛋白混合液中游离药物浓度

 用高效迎头分析法 (HPFA)测定了药物 人血清白蛋白 (HSA)混合液中游离药物的浓度。样品溶液不经任何处理直接进样到装有内表面反相固定相的色谱柱中 ,用 67mmol/L磷酸盐缓冲液 ( pH 7 4 ,I =0 17mol/L)作流动相。当进样体积足够大时 ,游离药物以平顶峰的形式被洗脱出来 ,平顶峰区域洗脱液中的药物浓度等于样品溶液中游离药物的浓度。收集平顶峰区域的洗脱液 ,然后将一定体积的洗脱液注入到反相色谱柱中 ,测定游离药物的浓度。用该法测定酮基布洛芬 HSA和头孢哌酮 HSA两种混合液中游离药物的浓度。     

超高效液相色谱-串联质谱法快速测定沉积物中11种藻毒素

建立了超高效液相色谱-串联质谱(UPLC-MS/MS)快速测定沉积物中11种藻毒素的方法。沉积物经冷冻干燥、粉碎过筛,用0.1 mol/L EDTA-Na4P2O7溶液涡旋超声提取,经HLB固相萃取小柱净化后,用甲醇-0.2%甲酸洗脱、浓缩并氮吹定容至1 m L。经Waters BEH C18色谱小柱,以乙腈-0.2%甲酸水溶液为流动相,梯度洗脱分离后,在电喷雾正离子模式下,以超高效液相色谱-串联质谱多级监测模式(MRM)外标法进行定性定量分析。结果表明:沉积物中11种藻毒素的检出限为1.0~5.0 ng/kg。对同一环境样品进行了0.1、1.0、4.0μg/kg不同水平的加标回收试验,平均回收率为70.3%~112.5%,相对标准偏差(RSD)为2.2%~9.3%。该方法快速、灵敏、准确,可应用于沉积物中11种藻毒素的快速监测。     

Analysis of free carbohydrates in milk using micropacked columns

Summary A gas chromatographic method using a micropacked column is described for the analysis of lactose, galactose, lactulose and epilactose in processed milks. The method is evaluated for precision and accuracy using phenyl-β-glucoside as an internal standard. Recoveries near 100% were found for lactulose concentrations higher than 0.1 mgml⁻¹, showing coefficients of variation from 5.9 to 9.4%.     

Performance comparison using the GUESS mixture to evaluate counter-current chromatography instruments

Comparing the performance of different counter-current chromatography (CCC) J-type centrifuges has and will always be difficult. This is due to the number of variables such as speed of rotation, swung radius, β-value, column bore, column length that can be chosen during the design of an instrument. This situation is further complicated by the implication that some of these variables are intrinsically linked, such that if one is changed another or others can also change. The chromatographer has no influence on these hardware parameters once the instrument designer has chosen them. However, the chromatographer wants a CCC column that retains the most liquid stationary phase in order to achieve the best separation of the components in a mixture. What matters most is column performance in terms of: sample loading per injection, speed of separation, purity of target and yield of target. The instrument that has the best performance in all these areas is called a “high-performance” CCC system. This paper demonstrates to the modern chromatographer that a “high-performance” CCC instrument has shorter, lower volume columns that are rotated faster to provide quicker separations, even with the same sample loading.     

Effects of large sample loads on column lifetime in preparative-scale liquid chromatography

In preparative-scale liquid chromatography of proteins, the use of high sample concentration and large sample mass may result in irreversible adsorption to the support surface. This can change the stationary phase characteristics, reduce the capacity, shorten the column lifetime and diminish the economic viability of a particular separation method. Column recycling and regeneration can influence the throughput (mass purified per time unit) and selectivity, and affect the reproducibility. The effects of large sample loads on column lifetime and performance were evaluated for three strong anion-exchange columns: (1) a silica support with a quaternized polyethyleneimine (PEI) coating, (2) a polymeric support with an adsorbed PEI coating which also was quaternized, and (3) a polymeric support with a proprietary quaternary amine stationary phase. The column capacity for proteins was measured by frontal chromatography and monitored as a function of cycle number. The column lifetime was determined by examining chromatographic properties subsequent to the frontal chromatography. The change in protein binding capacity was then compared to the change in nitrate binding capacity. The column performance was evaluated under analytical conditions by measuring the change in resolution of standard protein mixtures.     

Use of partially porous column as second dimension in comprehensive two-dimensional system for analysis of polyphenolic antioxidants

In the present work, a comprehensive LC system using a microbore HPLC column in the first dimension and a partially porous column in the second dimension was developed and applied to the separation of polyphenolic components in a red wine sample. The performance of the partially porous short column (3.0 cm) was compared to that of a monolithic column, of comparable dimensions. The results obtained demonstrated the possibility to use partially porous columns to obtain fast analyses, using high flow rates, under repetitive gradient conditions and with very brief reconditioning times. A conventional HPLC system was used since the backpressure generated by the shell-packed column, even at very high flow rates, was well within the operational limits. The use of an increased column temperature (60 degrees C) allowed a further pressure-drop decrease, with no stationary phase degradation, or loss in column performance.     

Optimization of fat-soluble vitamin separation by supercritical fluid chromatography

Summary Fat-soluble vitamin separation, achievable using a micropacked SFC column loaded with Cw 20M, is optimized using a rotatable central composite experimental design. Two chromatographic response functions, based on relative retention and the number of peaks resolved are proposed. Temperature and pressure gradients giving the best response in the experimental region are obtained and the effect of their variation on separation is evaluated. Relative standard deviations resulting from both absolute and normalized peak areas are also given.     

Effect of Column Dimensions on HPLC Separations Using Constant Volume Columns

Abstract

The effect of column dimension on resolution, sample capacity, retention time, efficiency and mobile phase composition were studied, using both constant flow rate and constant linear velocity. The four columns selected (A = 238 × 3.2 mm, B = 153 × 4.0 mm, C = 116 × 4.6 mm and D = 50 × 7 mm) had the same volume. K¹ values were found to be constant, within experimental error, for all columns. At constant linear velocity, the retention time was found to be a linear function of column length, while at constant flow rate retention time was constant for all columns. The longest column (A) generated the largest N values while columns 3 and C gave the lowest H values, for dilute solutions, while they decreased with decreasing column length. On the other hand, it was observed that as the sample size increased, N generated by column A decreased more rapidly and eventually fell below the values generated by columns B and C. These two columns (B & C) can tolerate a larger sample size with less reduction in N value than the longest column. It is important to note that although there were minor differences in performance between columns B and C, there were significant differences between them (B and C) and the other two columns (A and D). Column A offered the highest sensitivity (narrower peaks) for dilute solutions, while columns B and C offered higher loadability. The volume of organic modifier in the mobile phase affected the retention equally in the four columns. It was also found that equal separation (a) was obtained for each column at constant flow rate and constant linear velocity, except with the latter the retention times were longer.     

Micropacked capillary nucleic acid analysis

Nucleic acid compositional analysis is discussed, followed by a brief review of the current state of the technology applied in which the benefits and limitations of current methodology are enumerated. An alternative method is presented, namely the use of a micropacked capillary ion exchange column to separate nucleoside monophosphates via an anion exchange mechanism. The separated nucleotides are then quantitated by means of post-column photodiode-array detection. The use of a photodiode array also enables the verification of peak identity and purity by acquisition of UV spectra at any point in the separation. The technique has applications in the compositional analysis of both deoxyribonucleic acid (DNA) and ribonucleic acid (RNA).     

Sample Solvent as Analyte in High Performance Liquid Chromatography

Abstract

Solvents vary in their behavior in high performance liquid chromatography (HPLC). Water and methanol, among others, are widely used in the mobile phase as well as solvents for the solute. Few reports indicate that the solvent used for the solute can behave as an analyte. Normally, it is generally accepted that the solute solvent, a non-constituent of the mobile phase will be the first eluent. However, a solvent which is a component of the sample can show up as an unexpected peak with its own identity. This solvent may show a similar retention time as some of the unknown components of the sample. This indicates that in some cases the quantitative results may be the sum of the absorptivity of the solute and solvent used for the sample. It is assumed that some solvents show no absorption in the ultraviolet region at which the analysis is being conducted. Depending on the mobile phase composition some solvents can be detected at the wavelengts or wavelengths used for analysis. Water, ethylacetate, and methanol showed absorption at 210 nm when present in the sample being analyzed with a mobile phase of acetonitrile-methanol using a C₁₈ column. These solvents overlapped or showed retention times the same as estriol and testosterone.     

Evaluation of several solid phase extraction liquid chromatography/tandem mass spectrometry on-line configurations for high-throughput analysis of acidic and basic drugs in rat plasma

Several configurations using 6- and 10-port switching valves were studied for high flow, on-line extraction of rat plasma coupled to an electrospray triple quadrupole mass spectrometer. Each plasma sample was diluted 1:1 with an aqueous internal standard solution. The sample was injected into a 2.1 x 20 mm cartridge column packed with 25 microm divinylbenzene/N-vinylpyrrolidone packing using 100% aqueous mobile phase at 4 mL/min. After sample loading and sample cleanup, the analytes were eluted from the extraction column with a 1.0-min gradient at 0.4 mL/min. The samples were either analyzed directly after elution from the extraction column or after additional separation using a short high performance liquid chromatography (HPLC) column. The different configurations were tested using an acidic drug (diflunisal) and a basic drug (clemastine) in rat plasma. On-line analysis was performed by injecting 200 microL of diluted plasma. The mass spectrometer was operated in the multiple reaction monitoring (MRM) mode. All calibration standards gave relative standard deviations (RSDs) below 5%. The total time per sample was 3 min.