Preparation,evaluation, and comparison of wide bore (320 μm) and narrow bore (50 μm) cyanosilicone-coated capillary columns for gas chromatography

The preparation of wide bore (320 μm) and narrow bore (50 μm) fused silica capillary columns is described for immobilized cyanopropyl substituted silicones containing 60 and 88% substitution. The effect of high temperature deactivation with cyanopropylcyclosiloxanes was studied with a special test mixture. Curing was achieved with dicumyl peroxide or azo-tert-butane. The columns were evaluated and compared in terms of efficiency, activity, polarity, and temperature stability. Different coating methods were compared for the narrow bore columns. The activity of the 60% cyanopropyl columns that had been immobilized with dicumyl peroxide was significantly larger than for azo-tert-butane immobilized columns. The polarity of polar columns appeared to depend greatly on column temperature and is completely different for wide and narrow bore columns.     

Porous structure of the monolithic sorbent and separation properties of monolithic capillary columns in gas and liquid chromatography

Macroporous polymer based on polydivinylbenzene was used for the preparation of monolithic capillary columns with the diameter from 0.01 to 0.53 mm for separations by gas and liquid chromatography. The separation properties of the columns were studied by analysis of model systems of aromatic (in liquid chromatography) and light (in gas chromatography) hydrocarbons. The permeability was determined and the C parameter of the Van-Deemter equation was found for each column. The permeability of the majority of columns determined by gas chromatography is independent of the column diameter. The permeability of the same columns in liquid chromatography is also almost constant for the columns 0.53–0.1 mm in diameter; however, the permeability decreases sharply on going to columns of smaller diameter. In gas chromatography the value of the C parameter reflecting the effect of the mass transfer of the sorbate between the mobile and stationary phases on the smearing of a chromatographic peak in the column approximately the same for all columns. In liquid chromatography the value of the C coefficient in the Van-Deemter equation for the same capillary columns changes with a change in the column diameter and reaches a minimum for the columns 0.1 mm in diameter. The differences observed for the characteristics of the columns in gas and liquid chromatography are due to different structures of the macroporous monolith formed in columns of different diameter and to the effect of solvation of the monolith by the mobile phase under the conditions of liquid chromatography.     

Cyclodextrin derivatives in GC separation of racemic mixtures of volatiles – part XII: Thick-film wide-bore columns for enantiomer GC preparation

Preliminary results on thick-film wide-bore (0.53mm i.d.) columns for GC preparation of pure enantiomers are described. In particular the loading capacity for several racemates of a 3μm, 30% 2,6-di-O-methyl-3-O-Pentyl-β-CD/OV1701 column and of a 2 μm, 30% 2,3-di-O-acetyl-6-O-dimethyl-t-butylyl-β-CD/PS-086 collumn were determined. Consideration is also given to the relation-ship between resolution values of two enantiomers on anayltical columns and their loading capacity and scaling-up to the corresponding micropreparative columns.     

Preparation and evaluation of OV-240-OH coated glass capillary columns for isomer specific determination of PCDDs and PCDFs

Glass capillaries were leached, dehydrated, persilylated with 1, 3-bis (3-cyanopropyl) tetramethyldisiloxane, and coated with OV-240-OH. After crosslinking and binding the phase to the glass surface the columns showed high separation efficiency, high temperature stability, and inertness comparable to persilylated apolar columns. Column performance is shown to be superior to liquid phase cyanopropyl columns such as SP 2330. The excellent separation capabilities together with the selectivity of the phase makes OV-240-OH coated columns a valuable tool for the determination of toxic isomers in complex mixtures of polychlorinated dibenzo-p-dioxins (PCDDs) and dibenzofurans (PCDFs). The order of elution of individual TCDD isomers was found to be similar to that described for SP 2330 or Silar 10c. The detection of PCDDs and PCDFs in a fly ash extract further illustrates the utility of OV-240-OH coated columns. The high temperature limit of these columns opens the way for the analysis of high boiling compounds such as mixed brominated/chlorinated dibenzo-p-dioxins and dibenzofurans.     

Validity of using modified capillary column with larger diameter to study the Cs diffusion in local Taiwan laterite

We have examined the working diameter of capillary columns with diameter of 5, 7, 10 and 20 mm. These modified capillary columns were carefully filled with local Taiwan laterite (LTL). The porosity and density of these packed columns was 0.51±0.02 g/g and 1.27±0.05 g/cm³, respectively. The diffusion experiments were then carried out in synthetic groundwater with Cs loading of 0.1mM at room temperature. Experimental results have shown that the diffusion profiles of modified capillary columns fit Fick’s second law very well. This result revealed that the working diameter of a capillary column can be expanded to at least to 20 mm without affecting the validity of the derived diffusion coefficients. Among these columns, the ones with 5 mm diameter show the most consistent results of the derived K _d , apparent and effective diffusion coefficients. Although the derived distribution and effective diffusion coefficients slightly decrease as the diameter of these columns increases due to the increase of the solid/liquid ratio. These values are still informative of the Cs diffusion in local Taiwan laterite. Moreover, our results clearly demonstrate the potential of using “modified capillary method” to study the diffusion behaviors of concerned radionuclide because columns with large diameter enable the filling with more versatile geological substances.     

Structure of Glancing Incidence Deposited TiO2 Thin Films as Revealed by Grazing Incidence Small‐Angle X‐ray Scattering

For the first time, grazing incidence small‐angle X‐ray scattering (GISAXS) analysis is used to characterize the morphology of TiO₂ thin films grown by glancing angle physical vapor deposition (GLAD). According to cross‐section scanning electron microscopy (SEM) images, the films consist of near isotilted TiO₂ columns of different length and width depending on film thickness. The obtained GISAXS patterns show a characteristic asymmetry with respect to the incidence plane, which is associated with the tilted geometry of the TiO₂ columns. The patterns also show the existence of two populations of columns in these GLAD‐TiO₂ films. The population of the thinnest columns appears related to the first grown layer and is common for all the films investigated, while the second population of columns grows with the thickness of the films and has been related to wider columns formed by shadowing at the expense of the initially formed columns.     

Direct resolution of the enantiomers of new diphosphine and diphosphine oxide ligands by high-performance liquid chromatography

Summary Resolution of the enantiomers of new racemic diphosphines, which are very useful ligands for stereoselective catalysts, and of the corresponding phosphine oxides has been investigated by high-performance liquid chromatography (HPLC) on four different chiral stationary phases (CSP)—Chiralpak AD, Whelk-01, and Supelcosil naphthylurea and phenylurea columns. The mobile phases were optimized to achieve separation of the enantiomers. α andR _S values ranged from 1.05 to 5.17 and from 0.37 to 6.57, respectively, for the Chiralpak AD and (R,R)-Whelk-01 columns. For the Supelcosil LC-(R)-phenylurea and Supelcosil LC-(S)-naphthylurea columns α values ranged from 1.05 to 1.62 andR _S from 0.35 to 3.61.     

Effect of high temperature in determination of the mathematical dead time and the constants of the n-alkane retention time curve in gas chromatography

In gas liquid chromatography, the column dead time and the constants of the n-alkane retention time curve are calculated by the multiparametric least-squares regression iterative method at high temperature between 180 and 270°C. The method was applied to two types of columns. The first group includes eight packed columns (seven OV polymethylphenylsiloxane and Apolane-87), while the second includes five glass capillary columns (four methylsilicone with different film thicknesses and Apolane-87). The calculated tM and b values were compared with those obtained by Guardino's, Grobler's, and Kaiser's methods. The influences of coating thickness and temperature thereon were investigated.     

Analysis of global components in Ganoderma using liquid chromatography system with multiple columns and detectors

In present study, a multiple columns and detectors liquid chromatography system for analysis of global components in traditional Chinese medicines was developed. The liquid chromatography system was consist of three columns, including size exclusion chromatography column, hydrophilic interaction chromatography column, and reversed phase chromato‐graphy column, and three detectors, such as diode array detector, evaporative light scattering detector, and mass spectrometry detector, based on column switching technique. The developed multiple columns and detectors liquid chromatography system was successfully applied to the analysis of global components, including macromolecular (polysaccharides), high (nucleosides and sugars)‐, and low (triterpenes)‐polarity small molecular compounds in Ganoderma, a well‐known Chinese medicinal mushroom. As a result, one macromolecular chromatographic peak was found in two Ganoderma species, 19 components were identified in Ganoderma lucidum (two sugars, three nucleosides, and 14 triterpenes), and four components (two sugars and two nucleosides) were identified in Ganoderma sinense. The developed multiple columns and detectors liquid chromatography system was helpful to understand comprehensive chemical characters in TCMs.     

Biosorption of Copper and Cadmium in Packed Bed Columns with Live Immobilized Fungal Biomass of <Emphasis Type="Italic">Phanerochaete chrysosporium</Emphasis>

Biosorption of copper (II) and cadmium (II) by live Phanerochaete chrysosporium immobilized by growing onto polyurethane foam material in individual packed bed columns over two successive cycles of sorption–desorption were investigated in this study. Initial pH and concentrations of the metals in their respective solutions were set optimum to each of those: 4.6 and 35 mg·l⁻¹ in case of copper and 5.3 and 11 mg·l⁻¹ for cadmium. The breakthrough curves obtained for the two metals during sorption in both the cycles exhibited a constant pattern at various bed depths in the columns. The maximum yield of the columns in removing these metals were found to be, respectively, 57% and 43% for copper and cadmium indicating that copper biosorption by the immobilized fungus in its column was better than for cadmium. Recovery values of the sorbed copper and cadmium metals from the respective loaded columns by using 0.1 N HCl as eluant was observed to be quite high at more than 65% and 75%, respectively, at the end of desorption in both the cycles. Breakthrough models of bed-depth service time, Adams–Bohart, Wolborska, and Clark were fitted to the experimental data on sorption of copper and cadmium in the columns, and only the Clark model could fit the sorption performance of the columns well over the entire range of ratios of concentrations of effluent to influent, i.e., C/C ₀ for both copper and cadmium biosorption. The kinetic coefficients of mass transfer and other suitable parameters in the system were determined by applying the experimental data at C/C ₀ ratios lower than 0.5 to the other three models.     

Clean-up of polynuclear aromatic hydrocarbons and 3-ring azaarenes and their GC-analysis on whisker-walled open tubular columns

A modified clean-up of polynuclear aromatic (PNA) hydrocarbons on XAD-2 is described. n-Alkanes (C₁₆? C₂₈) are separated quantitatively from the PNA hydrocarbons and are eluted in one fraction. The distribution of 17 PNA hydrocarbons and four of their alkyl derivatives, two S-heterocyclic compounds and two azaarenes between the different fractions is reported. Azaarenes containing three rings are separated from PNA hydrocarbons and S-heterocyclic compounds. Whisker-walled open tubular columns coated with OV-215 and OV-25 were used in the separation of isomeric azaarenes and in PNA hydrocarbon profile analysis, respectively. The preparation of such columns is described in detail. Rinsing of capillary columns with cold, concentrated HCI after whisker growth removes much larger amounts of boron and sodium than subsequent leaching with HCI at 180°C. Whisker-walled open tubular columns are successfully applied to the characterization of isomeric benzofluoranthenes and other PNA hydrocarbons isolated from air particulate matter.     

Seperation of protein amino acids as their N(O)-Acyl alkyl ester derivatives on glass capillary columns

A comparison of the elution properties of the major protein amino acids as their N(O)-acyl alkyl ester derivatives (O-n-propyl, -n-butyl, -isopentyl; N(O)-trifluoroacetyl, -heptafluorobutyryl) on open-tubular glass capillary columns coated with SE-30, OV-17, OV-210 and EGA is described. A single-column separation to the baseline of the protein amino acids as their N(O)-heptafluorobutyryl n-butyl ester derivatives in less than 35 min was obtained on the SE-30 column. OV-210 columns have properties complementary to those of SE-30 columns and can be used as an aid to compound identification from retention time data. Separations of the amino acids from beer and dialysate from uremic patients are used to illustrate the practical posibilities of the method.     

Measurement of Henry coefficients by capillary columns coated with slightly polar solvents

Summary The specific retention volumes and Henry coefficients measured on packed columns are compared with those calculated via retention indices determined on wall coated open tubular capillary columns. The stationary phase liquids used were derivatives of a branched paraffin, C₇₈H₁₅₈, where a methyl or ethyl group of the paraffin was replaced by OH, CN, OCH₃ and SH groups. The retention indices of a series of molecular probes of varying polarity (aromatics, 1-chloroalkanes, 1-acetoxy-alkanes, 1-alkanols, 2-alkanones) were determined atT=403.15 K on fused-silica open tubular columns prepared by static coating that gave stable and uniform solvent films. After obtaining the absolute data on packed columns forn-alkanes, the specific retention volumes and Henry coefficients of the solutes were calculated. The retention data obtained on both columns showed good agreement. Presented at Balaton Symposium on High Performance Separation Methods, Siófok, Hungary, September 1–3, 1999     

Characterization of different RP-HPLC columns by a gradient elution technique

Summary The literature contains no unified testing procedure for evaluation and characterization of reversed-phase (RP) columns of different pore size (surface area) and containing different types of ligand. In our laboratory a testing procedure has been developed using gradient elution under standardized conditions independent of column dimensions and applicable to both narrow-pore and wide-pore columns. Six wide-pore and four narrow-pore columns were investigated and compared. The test solutes were selected to cover a wide range of chemical properties. The evaluation and characterization of the columns was performed on the basis ofk _app retention factors. Principal components analysis (PCA) was performed to reveal similarities and differences among the columns and test substances. The factors obtained characterize the columns according to the extent of various interactions such as hydrophobicity, HB (hydrogen bond)-donor acidity and HB-acceptor basicity. Presented at the 21^st ISC held in Stuttgart, Germany, 15^th–20^th September, 1996     

A comparison of different retention index systems with unsaturated and aromatic hydrocarbons in capillary gas chromatography on PEG 20M

Summary The correction of the reproducibility of retention indices on polar capillary columns with different film thickness, using more polar reference standards instead ofn-alkanes, was investigated. It was found that the replacement ofn-alkanes by 1-alkenes, 3-alkynes and n-alkylbenzenes as standards significantly improves the reproducibility of retention indices and diminishes their temperature increments forn-alkanes,n-alkynes and arenes on PEG 20M columns.     

Free release static coating of glass capillary columns; rapid coating at lower temperatures and elevated pressures

The coating speed upon static coating of glass capillary columans was evaluated in terms of inner diameter and length of the column, viscosity and pressure of solvent vapor, etc. From the equation obtained it can be shown that a smaller diameter of a microbore column restricts solvent vapor transfer to the orifice of the column drastically. To compensate for this restriction, a higher pressure at the meniscus is needed. As an alternative to using a higher coating temperature, application of more volatile solvents such as n-butane and isobutane is proposed. Several glass capillary columns (130 μm i.d.) were coated with SE-54 dissolved inpentane-acetone mixed with n-butane or isobutane and the column performances were evaluated. Selection of these solvents permitted free release static coating of ca. 100 μm columns at lower or even ambient temperatures and they were equally suitable as commonly applied solvents (e.g. pentane) to coat highly efficient columns.     

Comparison of dynamically coated SE-54, SP-2250 and carbowax 20M wall-coated open tubular (WCOT) glass capillary columns,prepared after surface pretreatment with Superox™-4 or with BaCO3

A new surface pretreatment for the preparation of wall-coated open tubular (WCOT) glass capillary columns has been evaluated. This technique involves the application of a non-extractable layer of Superox?-4, a 4,000,000 MW polyethylene glycol, to the glass surface as a pretreatment and deactivation agent. Unlike other polyethylene glycols, Superox-4 is stable at high temperatures (> 300°C) in the absence of oxygen, coats smoothly onto a bare glass surface and resists droplet formation. WCOT columns (SE-54, Carbowax 20M, and SP-2250) prepared using this technique are compared to columns prepared using a modified Grob [2,3] BaCO₃ procedure. The Superox-4 pretreated columns were equal or superior in quality to the BaCO₃ pretreated columns, based on the appearance of an activity standard and the effective theoretical plates (N_eff) per meter. Chromatograms showing practical application of the WCOT columns prepared using both methods is given.     

Resolution of GPC columns

A resolution index for gel-permeation chromatograph (GPC) columns is defined by the relation log (RI) = αW, where RI is the resolution index, α is the slope of the calibration curve of logarithm of molecular weight against peak position for narrow polymer fractions, and W is the width of the GPC curves for narrow fractions. This resolution index is calculated approximately for several GPC columns individually and in series combinations by using data obtained on narrow fractions of polystyrene. The index increases with number of columns and with flow rate over a limited range of flow rate, does not vary much with solvent, and does not correlate well with plate count obtained with low molecular weight molecules. It is believed that the resolution index provides an improved indication of the performance of GPC columns.     

Molded separation media: An inexpensive,efficient, and versatile alternative to packed columns for the fast HPLC separation of peptides,proteins, and synthetic oligomers and polymers

A simple molding process carried out within the confines of a chromatographic column has been used for the preparation of macroporous poly(glycidyl methacrylate-co-ethylene dimethacrylate) and poly(styrene-co-divinylbenzene) rods. The novel monolithic separation media that are obtained are useful for the HPLC separation of biological and synthetic polymers. The presence of large pores with a diameter of about 1 μm makes the molded rod columns easily permeable to eluents. Therefore, the back pressure of these columns is modest even at high flow rates. In contrast to the conventional HPLC columns packed with beads, all of the mobile phase flows through the continuous monolithic medium. As a result of this total convection, the efficiency of the molded media is almost independent of the flow rate. This improves significantly the separation ability of the rod columns and very fast separations of macromolecules such as peptides, proteins, and synthetic polymers have been demonstrated.     

A crosslinked chiral stationary phase for the separation of enantiomers by gas and supercritical fluid chromatography

Crosslinking experiments for the chiral stationary phase OV-225-L-Val-t-butylamide within both fused silica and glass capillary columns have been carried out. Amino acid enantiomers were separated on crosslinked columns by both GC and SFC methods. In SFC, the a values of amino acid enantiomers are independent of the density of the mobile phase, and they are hig her than those obtained by GC for the tested enantiomers with the same column due to the lower column temperature used in SFC.