Fused-silica Column Research Articles

Practical approach to the miniaturization of chiral separations in liquid chromatography using packed fused-silica capillary columns

A micro liquid chromatographic system was evaluated and the possibility of transferring some established methods of chiral separation to this system was examined. Fused-silica columns (0.32 mm I.D.) were slurry packed using an ordinary isocratic high-performance liquid chromatographic (HPLC) pump. Reversed-phase C 18 columns with an average reduced plate height of 3.5 could be packed reproducibly. The chiral selectors chosen were β-cyclodextrin, used as a mobile phase additive, bovine serum albumin adsorbed on silica and a Pirkle phase, covalently bound L -dinitrobenzoyl-phenylglycine. Enantiomeric separations gave results in good agreement with those obtained on conventional HPLC columns.

Improved congener‐specific GC analysis of chlorobiphenyls on coupled CPSil‐8 and HT‐5 columns

AbstractThe congener‐specific analysis of polychlorinated biphenyls (PCB) by high resolution gas chromatography on a 50 m × 0.25 mm fused silica column coated with a 0.26 μm film of 5% diphenyl polydimethylsiloxane (CPSil‐8) has been significantly improved by series coupling with a 25 m × 0.22 mm column coated with a 0.10 μm film of 1,2‐dicarba‐closo‐dodecarborane polydimethylsiloxane (HT‐5). Using helium as carrier gas, a total of 64 congeners in technical PCB mixtures could be analyzed as resolved peaks by ECD (86 by MS) with the CPSil‐8 column, and 84 by ECD (108 by MS) with the combination. The high upper temperature limit for these stationary phases (>300°C) enabled fast temperature programming and rapid analysis (60 min).

Drug matrix effect on the determination of residual solvents in bulk pharmaceuticals by wide-bore capillary gas chromatography.

A wide-bore capillary gas chromatographic method has been developed to study the drug matrix effect on the determination of residual solvents in bulk pharmaceuticals. A selective method is achieved on a Restek wide-bore (0.53-mm i.d. x 30 m) open-tubular fused-silica column coated with a 5-micron film of 95% dimethyl-5% diphenyl polysiloxane protected by a phenyl-methyl siloxane deactivated, uncoated fused-silica guard column. Utilizing this method, several common process solvents in weakly acidic, weakly basic, and neutral drug matrices are evaluated by recovery and linearity studies to show whether or not a drug matrix effect exists in their determination.

Capillary modification and evaluation using streaming potential and frontal chromatography for protein analysis in capillary electrophoresis

The modification of capillary surfaces in capillary electrophoresis requires accurate chemical characterization of the synthesized materials. A three-step procedure was developed for the evaluation of capillaries used for protein separations in capillary electrophoresis. These measurements include ζ potential determination via streaming potential measurements, adsorption characteristics using frontal chromatography measurements of test solutes, and overall performance under running conditions using selected test solutes. The ζ potential determined from the streaming potential reflects the degree to which the capillary wall can undergo electrostatic interactions with proteins as well as the magnitude of the electroosmotic flow. Frontal chromatography measurements with selected probe proteins can indicate both the amount of adsorption as well as the probable types of interactions involved in the adsorption. Kinetic information can also be obtained in some instances. Electrophoresis with test solutes reflects the overall effect of adsorption. For this study, three types of capillaries were evaluated: (1) bare fused-silica capillaries, (2) capillaries coated with several thickness of cross-linked polyethylene glycol and (3) cross-linked polyethyleneimine. The polyethylene glycol column displayed much weaker electrostatic and similar hydrophobic and/or hydrogen bonding interactions as compared with underivatized fused-silica columns. The polyethyleneimine column exhibited poor performance for the test proteins used. Good electrophoretic performance seems to be possible only if adsorption measurements were below 0.2 ng/cm 2 (correspondng to 0.1% of available surface area) for all of the test proteins.

Composição química dos óleos essenciais de Eugenia Iniflora L. E Eugenia involucra do Rio Grande do Sul

The essential oils in leaves of Eugenia uniflora L. and Eugenia involucrata- Myrtaceae from Rio Grande do Sul - Brazil, were analysed by gas chromatography with fused silica column, using H2 as carrier gas and gradient of temperature of 50°-20°C per 40°C/minute. For Eugenia uniflora L., the identified componentes were: limonene (9,84%), β-pinene (8,59%), camphene (2,73%), α-phellandrene (2,13%), myrcene (1,77%), α-pinene (1,43%), cyneol (9,13% and a great quantity of α-terpineol (39,20%), as major component. For Eugenia involucrata following compounds were detected: limonene (8,39%), β-pinene (4,63%), α-pinene (4,41%), camphene (2,19%), α-terpineol (2,16%), α-phellandrene (2%), myrcene (0,52%) and cyneol (6,38%).

Narrow (5‐50‐μm i.d.) open tubular columns in liquid chromatography using immobilized polymethyloctadecylsiloxane as stationary phase

AbstractThis paper presents in detail the preparation of highly efficient, stable open tubular (OT) columns for reversed‐phase liquid chromatography. Chromatographic properties of 5‐50‐μm i.d. fused silica columns (1.5‐5 m in length) are described, and details of the coating procedure are discussed. On‐column fluorescence detection was used for the model substituted‐anthracene test solutes. Gas chromatography was used as a complementary technique for column characterization.The stationary phase studied, immobilized polymethyloctadecylsiloxane, PMSC18, was chosen because of its more lipophilic character compared to other siloxanes. As expected, a higher retention power was found compared to polydimethylsiloxane coatings.The polymeric stationary phase showed good properties. More than 900,000 plates were achieved in 25 min (k = 0.1) in a 5‐μm i.d. fused silica OT column. The stationary phase contribution to band broadening was less than 10% in an 11‐μm i.d. column at a flow rate thirty times uopt (k = 1.3).

Quantitative High-Performance Liquid Chromatographic, Gas Chromatographic, and Gas Chromatographic-Mass Spectrometric Analysis of Ticlopidine in Baboon Plasma after Solid-Phase Extraction

High-performance liquid chromatography with UV detection (HPLC-UV) and gas chromatography with either nitrogen phosphorus (GC-NPD) or mass spectrometry (GC-MS) detection were used for the determination of ticlopidine in plasma. Solid-phase extraction of ticlopidine from plasma was performed using Extrelut columns without pH adjustment, and using hexane as the solvent of elution. With HPLC, a mobile phase of 0.01 M pH 7.8 phosphate buffer:acetonitrile (70:30) was passed through a μBondapack C-18 column at a rate of 1.3 mL/min. Ultraviolet detection at 235 nm was sensitive to plasma ticlopidine concentrations of 0.05 μg/mL. The GC-NPD and GC-MS were performed on a DB-17 fused-silica column using on-column injection. For GC-NPD and GC-MS, limits of quantification were found to be 0.020 and 0.005 μg/mL, respectively. Compared with HPLC-UV, the GC methods were found to be more reproducible, sensitive, and specific and therefore more suitable for pharmacokinetic applications.

Rapid protein analysis by capillary electrophoresis

Rapid protein analysis by free-zone capillary electrophoresis in an untreated fused-silica column is presented. Separation of model proteins by the proposed method shows that the retention times of these proteins correlate well with each of their isoelectric points. By using a high voltage gradient, most proteins could be separated in 200 s with excellent reproducibility. Similarly, human serum proteins could be resolved and determined in less than 100 s.

Fused silica microcolumn LC‐MS and MS/MS using an aeronebulized interface

AbstractAn aeronebulized interface has been developed for use with 0.15–0.25‐mm i.d. slurry‐packed fused silica columns. The interface was built in a removable probe that uses tha direct inlet on a triple quadrupole mass spectrometer for easy switching between LC, GC, or the solids probe. The probe is indirectly heated by the ion source, and premature evaporation of the mobile phase, acetonitrile/water, is prevented by controlled water cooling. A standard EI/CI ion source was used in the chemical ionization mode using methane to control the pressure in the source. Several variables that influence the performance of the interface were evaluated using various drugs as model compounds. Typically, 50,000 to 70,000 theoretical plates could be generated. The minimum detectable quantities were generally in the low picogram range. The best result was 3 pg using negative ion SIM, corresponding to a concentration of 8 × 10−8 M in the injected sample.

Single-Laboratory Evaluation of Method 8060 for the Determination of Phthalates in Environmental Samples

Abstract Method 8060 of the SW-846 methods manual for the determination of phthalates In aqueous and solid matrixes was modified and evaluated in a single laboratory. The range of compounds of interest was expanded to 16 phthalates. The results of a study to determine the extent and the sources of phthalate contamination in the laboratory and ways to minimize background contamination, conducted as part of this work, were reported elsewhere. The packed columns specified in Method 8060 for the gas chromatographic analysis were replaced with 2 fused-silica open-tubular columns of dissimilar stationary phases. These columns were connected to an inlet splitter and 2 electron capture detectors; this dual-column/ dual-detector setup allowed the primary and confirmatory analyses to be conducted simultaneously. Extracts were cleaned up by column chromatography on 10 g Florisil or alumina. Of the 16 target compounds, only 13 were recovered from the Florisil column (Method 3620), but all 16 were recovered from the alumina column (Method 3610). The use of commercially available Florisil and alumina solid-phase extraction cartridges for sample extract cleanup was evaluated, and a method that uses such cartridges (Florisil or alumina) was developed. This latter method gave quantitative recoveries for all 16 compounds. The effects of interferences represented by corn oil, dlesel hydrocarbons, and elemental sulfur were evaluated, and an internal standard and 3 surrogate compounds were identified and proposed for use with this method. The revised method was tested with samples of an estuarine water, a leachate, a groundwater, an estuarine sediment, a municipal sludge, and a sandy loam soil, each spiked with the 16 phthalates. For the aqueous samples spiked at 20 and 60 μg/L, the method accuracy ranged from 60 to 117% and method precision was better than 28%. The method accuracy and precision for solid samples extracted by Method 3550 were highly dependent on matrix type and on analyte concentration.

Multiple headspace extraction-capillary gas chromatography (MHE-CGC) for the quantitative determination of volatiles in contaminated soils

A multiple headspace extraction-capillary gas chromatographic method for the quantitative, accurate, and rapid determination of volatiles in multicontaminated soil samples has been developed. A thick film fused silica column has been used and a nine-step multiple headspace extraction (MHE) determination performed. Calibration was achieved by introducing 1 μl of a standard solution of mixed volatiles into empty headspace vials, the presence of the matrix being unnecessary in multiple headspace extraction. Accuracy of determination by MHE-CGC and a simple method employing standard additions have been compared.

Sulphur dioxide as a mobile phase in supercritical fluid chromatography

The properties of sulphur dioxide as mobile phase in supercritical fluid chromatography have been examined. With neat supercritical sulphur dioxide polysiloxane and silica stationary phases were stripped from the columns and clogged the restrictors. The injector rotors needed frequent replacement and epoxy glued fused silica columns went to pieces. With a mixture of 20% sulphur dioxide in carbon dioxide, the problems were significantly reduced, but not completely. A series of columns were examined and all were eventually degraded, with the exception of a porous graphitic carbon column. The adsorptive properties of this material was too high, however, to be of any practical use with the SO2−CO2 mixture. The retention of polycyclic aromatic hydrocarbons as well as several other compounds was significantly reduced in 20% SO2 in CO2, compared to the retention in neat carbon dioxide, and good peak shapes were obtained before the columns became degraded. Before further progress can be made, however, capillary columns with stationary phases which can better withstand mixtures of sulphur dioxide and carbon dioxide are needed.

Gas chromatographic determination of nitrophenols in atmospheric liquid water and airborne particulates

A method for the determination of nitrophenols in fogwater and atmospheric particles is presented. The gas chromatographic (GC) performances of the underivatized pure compounds and their corresponding acetate esters were compared using four fused-silica columns with three alternative detection modes, viz. mass-selective detection, nitrogen-specific detection and electron-capture detection (ECD). Splitless injection of pure nitrophenols suffered from adsorption in the GC system causing unacceptable imprecision in the quantification of semi-volatile nitrophenols. The separation of nitrophenols as their corresponding acetates and ECD improved the GC performance and the analytical results. Acetylation with acetic anhydride in alkaline aqueous solution was found to be a very specific, uncomplicated and rapid method of derivatization. Its high sensitivity and accuracy and excellent suitability for analysing complex aqueous samples such as fogwater is demonstrated in detail as part of a multi-residue procedure.

Capillary electrophoresis--a new clinical tool

The potential clinical diagnostic utility of capillary electrophoresis in an open-tubular column is established. Separation patterns for serum proteins by conventional agarose gel electrophoresis can be faithfully reproduced by a capillary electrophoresis procedure that provides the complete run data in 8 min. Hemoglobin variants can be separated within 10 min. The capillary electrophoresis separations are performed reliably and reproducibly in an untreated 75 micron (i.d.) x 25 cm fused-silica column. Diluted serum or hemoglobin samples can be loaded on an automated instrument with on-line injection, detection, and quantification, providing a truly "walkaway" electrophoresis system.

Surface treatment effects in microcolumn liquid chromatorgraphy

Packed fused-silica columns with several surface pretreatments are prepared for micro liquid chromatography. Untreated fused silica is compared to polymethylhydorsiloxane-deactivated tubing as well as a polymer-coated commercially available capillary GC column. Columns are packed under identical conditions with 5-μm reversed-phase material. The chromatographic and physical properties of these columns are examined. Surface pretreatments have minimal effects on the chromatographic characteristics of packed fused-silica columns but substantial effects on the physical capabilities.

Separation of phenols and aromatic hydrocarbons from biomass tar using aminopropylsilane normal-phase liquid chromatography

A quantitative procedure for the determination of selected phenols and aromatic hydrocarbons in biomass tar is described. Solid-phase extraction (SPE) through columns of amino-bonded silica stationary phase was used to separate tar samples into two fractions. These fractions were subjected to capillary gas chromatography using a DB-1 fused-silica column and a flame ionization detector. The efficiency of the method was determined by the use of synthetic and spiked tar samples. Excellent reproducibility and high recoveries were obtained for most of the target compounds. Compared with the traditional liquid—liquid extraction technique, the SPE technique eliminates the problems involved and proveds higher overall recoveries in a shorter time.

Prediction of gas chromatographic retention indexes for polychlorinated dibenzofurans

A model has been developed by using molecular connectivity to describe the relationship between the molecular structure of polychlorinated dibenzofurans (PCDFs) and their gas chromatographic linear temperature-programmed retention characteristics on a 30-m fused silica column coated with a DB-5 stationary phase. Model variables account for the number of chlorine atoms present, the position and the relationship on each aromatic ring, the chlorine atom interaction between the two rings, and the skeletal structure of each PCDF isomer.

Thermal degradation observed with different injection techniques: Quantitative estimation by the use of thermolabile carbamate pesticides

AbstractAn experiment has been designed to study the thermal degradation of thermolabile compounds caused by various injection techniques. The four carbamate pesticides aminocarb, bendiocarb, carbaryl, and dioxacarb decompose thermally into methylisocyanate and the corresponding phenol. The carbamets and the phenols arising from them were separated on a 25 m SE‐54 fused silica column; all compounds exhibited sharp peak shape indicating that the degradation observed took place completely within the injector.When cold on‐column injection was employed no thermal degradation was observed whereas with hot splitless injection at 220°C decomposition of the carbamates was almost complete.PTV injection was found to produce intermediate results. When packed with glass wool and operated with glass wool and operated with starting temperatures lower than the boiling point of the solvent, decomposition was found to be almost complete. Applying isothermal conditions at 140°C (30°C above the boiling point of toluene) aminocarb and bendiocarb underwent only slight decomposition while carbaryl and dioxacarb were about half degraded. Results from PTV injection with an empty insert resembled those obtained using cold on‐column injection and in this mode the application of temperatures up to 200°C resulted in no visible degradation. This can be explained by the short residence time of the sample in the injector.

Open-tubular liquid chromatography with surfactant-enhanced electroosmotic flow

The velocity of electroosmotic flow in a polymer-coated, reversed-phase fused silica column is enhanced by low concentrations ({mu}M) of cetyltrimethylammonium bromide (CTAB) in the buffer. Open-tubular capillary liquid chromatography (OTCLC) based upon this enhanced flow makes possible the separation of several neutral, geometrical, and positional isomers with greater than baseline resolution (R > 1) in all cases and efficiencies of up to 230,000 plates generated in less than 4 min in a 54-cm column. As little as 5-pL samples can be directly injected, and as low as 0.75 amol of 9-methylanthracene can be detected. This brings to OTCLC the instrumental simplicity of capillary electrophoresis.

Computer‐controlled vacuum backflush for capillary GC

AbstractA vacuum‐pump‐operated backflush system has been developed for applications involving high‐speed, repetitive GC analysis of gas streams containing ppm and ppb levels of organic vapor. The system uses an injector capable of cryofocusing and a relatively short length of 0.25‐mm i.d. fused silica column for the separation of relatively simple mixtures of volatile compounds. Analysis times typically are in the 5–10 s range, and backflush times are in the 2–5 s range. Gases from the flame ionization detector are used as the backflush carrier gas, and no modification of the detector is necessary. A procedure is described which allows the average gas velocity to be measured during backflush operation. The minimum backflush time is directly proportional to the analysis time and to the square of the column length, making this system most useful with short columns and short analysis times.