Internal Diameter Column Research Articles

Retention Behavior of Metformin and Related Impurities in Ion‐Pairing Liquid Chromatography

The ion‐pair (IP) mechanism was applied to achieve HPLC‐diode‐array detector (DAD) separation and determination of metformin and five related impurities (cyanoguanidine, 1‐methylbiguanidine, melamine, N,N‐dimethylmelamine, and 4,6‐diamino‐1,3,5‐triazin‐2‐yl guanidine). Sodium octanesulphonate (0.010 mol/L) at pH = 3 was used as an ion pair agent in the aqueous component of the mobile phase. Isocratic elution with 80% acetonitrile and 20% aqueous component was applied with a flow rate of 1.2 mL/min. A double end‐capped, 5 µm particle size Inertsil ODS‐2 stationary phase (250 mm length, 4.6 mm internal diameter column) was used. Limit of quantitation (LOQ), as absolute amount of analytes loaded to the column, in the 35–250 pg interval were obtained using detection at 218 nm. Retention data were used in estimating the thermodynamic parameters (enthalpy and entropy) corresponding to the mobile/stationary phase transfer. Correlations between experimental data and data predicted by means of basicity constant, pH, and water/octanol partition coefficient were also achieved.

Flow injection potentiometric stripping analysis for study of adsorption of heavy metal ions onto modified diatomite

Computerised flow injection coupled with potentiometric stripping analysis (FIPSA) was employed for examination of the adsorption behaviour of Pb(II), Cd(II) and Zn(II) ions onto diatomite modified with manganese oxides. Signal optimisation was undertaken with respect to flow rate, deposition time, deposition potential, oxidising agent concentration, thickness of mercury film, solution pH and metal ion concentration. Examination of the column adsorption characteristics was facilitated by introduction of an adsorption microcolumn, as a complementary component of the flow injection system. The resulting breakthrough curves were employed to calculate parameters including adsorption capacity and adsorption rate constant, taking into consideration initial ion concentration, flow rate, mass and particle size of adsorbent, and column internal diameter. Adsorption capacities, determined using the Thomas mathematical model, showed that manganese modified Jordanian diatomite had an efficiency towards the removal of heavy metal ions from aqueous solutions; Cd(II) > Zn(II) ≈ Pb(II). The relative adsorption rates of the ions followed the order: Pb(II) > Zn(II) ≈ Cd(II).

New insights to trickle and pulse flow hydrodynamics in trickle-bed reactors using MRI

Ultra-fast Magnetic Resonance Imaging (MRI) is used to image liquid distribution during air–water, co-current downflow through a fixed bed of cylindrical porous pellets of length and diameter 3 mm, packed within a 43 mm internal diameter column in both the trickle- and pulsing-flow regimes. Two different data acquisition times are used, 20 ms and 6.4 s, giving two-dimensional images of in-plane spatial resolution 1.4 mm × 2.8 mm and 351 μ m × 351 μ m , respectively. Superficial gas velocities in the range 27 – 275 mm s - 1 ( 0.033 – 0.338 kg m - 2 s - 1 ) and superficial liquid velocities in the range 0.4 – 13.3 mm s - 1 ( 0.4 – 13.3 kg m - 2 s - 1 ) were used. This work reports images of local pulsing events within the bed occurring during the trickle-to-pulse flow transition. The evolution of the local instabilities is studied as a function of increasing and decreasing liquid velocity, at constant gas velocity. Temporal fluctuations in local liquid holdup were seen even in the trickle flow regime; these fluctuations had much shorter time periods than the pore-scale liquid pulses, and are perhaps associated with fluctuations in local surface wetting of the packing elements. A preliminary assessment of the effect of periodic operation on liquid distribution within the bed is also reported.

Effect of temperature in reversed phase liquid chromatography

The high temperature liquid chromatography (HTLC) reveals interesting chromatographic properties but even now, it misses some theoretical aspects concerning the influence of high temperature on thermodynamic and kinetic aspects of chromatography: such a knowledge is very essential for method development. In this work, the effect of temperature on solute behavior has been studied using various stationary phases which are representative of the available thermally stable materials present on the market. The thermodynamic properties were evaluated by using different mobile phases: acetonitrile–water, methanol–water and pure water. The obtained results were discussed on the basis of both type of mobile phases and type of stationary phases. Type of mobile phase was found to play an important role on the retention of solutes. The kinetic aspect was studied at various temperatures ranging from ambient temperature to high temperature (typically from about 30 to 200 °C) by fitting the experimental data with the Knox equation and it was shown that the efficiency is improved significantly when the temperature is increased. In this paper, we also discussed the problem of temperature control for thermostating columns which may represent a significant source of peak broadening: by taking into account the three main parameters such as heat transfer, pressure drop and band broadening resulting from the preheating tube, suitable rules are set up for a judicious choice of the column internal diameter.

A RAPID METHOD TO ANALYZE SAPONIN PRECURSORS IN SOYBEAN (GLYCINE MAX (L.) MERRILL)

A RAPID METHOD TO ANALYZE SAPONIN PRECURSORS IN SOYBEAN (GLYCINE MAX (L.) MERRILL)

Studies on surface to bulk ionic mass transfer in bubble column

Mass-transfer coefficient with immersed surface of diameter 0.016 m placed axially in bubble column (internal diameter=0.0515 m), was measured using electrochemical technique with ferro-ferricyanide system. Perforated-plate sparger (hole diameter=0.0015 m) and single-nozzle spargers (hole diameter=0.001, 0.0015 and 0.002 m) were used. Mass-transfer coefficient was found to be independent of initial bed height. It decreases as axial position of transfer surface from bottom increases at low gas velocities. The effect of type of sparger on mass-transfer coefficient was observed at all axial positions. It increases with increase in hole diameter for single-nozzle sparger. It is higher for perforated-plate distributor than that for single-nozzle sparger with same hole diameter. The present values are in comparison with data of Patil and Sharma [Chem. Eng. Res. Des. 61 (1983) 21]. Following correlation correlated present set of data: St m =0.057(1−ε)(Re Fr Sc 2) −0.25.

Preparation, characterization and performance of a silica gel bonded molecularly imprinted polymer for selective recognition and enrichment of β-lactam antibiotics

A silica gel-bound molecularly imprinted polymer to oxazolone(s) exclusively derived from certain cephalosporins (cefaclor) and penicillins (amoxycillins and ampicillins) was prepared using ethylacetate as a porogen. This was used as a packing material for solid phase extraction in column chromatography. The high selectivity and the quantitative sorption of oxazolone at pH 7.5 and a flow rate of 5.0 ml min −1 in a long (13.0 cm) and wide bore (1.4 cm internal diameter) column have led to efficient clean-up, selective enrichment, and indirect differential pulse adsorptive stripping voltammetric measurement of the β-lactams in the form of corresponding oxazolones either in a larger volume of dilute aqueous systems or in the pharmaceutical formulations, without complications of complex matrices, excipients or column deterioration.

Experimental Characterization and Computational Fluid Dynamics Simulation of Gas Distribution Performance of Liquid (Re)Distributors and Collectors in Packed Columns

The usability of a state of the art computational fluid dynamics simulation package as a tool for analyzing the fluid-dynamic performance of internals encountered in packed distillation columns, such as initial gas distributors, liquid distributors and liquid collectors is demonstrated. A 1.4 m internal diameter column hydraulics simulator was used to provide detailed experimental evidence on the gas distribution pattern imposed by various types of column internals. The comparison of measured and predicted profiles for single-phase gas flow conditions indicates a strikingly good agreement.

Liquid Chromatographic Separation of Isoniazid, Pyrazinamide and Rifampicin on a Reversed-Phase Silica Column

A gradient liquid chromatographic method which can separate isoniazid, pyrazinamide and rifampicin is described. A Hypersil C18, 5 mm, 250 mm x 4.6 mm internal diameter column was maintained at 40°C. The method was developed by systematic evaluation of the influence of the buffer concentration, column temperature and the mobile phase pH. The method proposed uses isocratic elution with potassium phosphate buffer (pH 6.0; 0.05 M) for 10 min, followed by linear gradient to potassium phosphate buffer (pH 6.0; 0.05 M)-methanol (40:60, v/v) in 5 min, isocratic elution at the same composition for a further 15 min and then linear gradient back to potassium phosphate buffer (pH 6.0; 0.05 M) in 5 min. The flow-rate was 1 ml/min and UV detection was at 254 nm. The method was validated and it has been used for routine analysis of tablets containing isoniazid, pyrazinamide and rifampicin. Analysis time is 35 minutes. (E & C Afr Jnl Pharm Sci: 2002 5(1): 8-14)

L to d Amino Acid Isomerization in a Peptide Hormone Is a Late Post-translational Event Occurring in Specialized Neurosecretory Cells

Modification of the chirality of a single amino acid residue within a peptide chain appears to be novel additional mechanism leading to structural and functional diversification of eukaryotic bioactive peptides. This phenomenon has been studied at the cellular level in a neuroendocrine organ which elaborates a mixture of diastereoisomers of a 72-residue neuropeptide, crustacean hyperglycemic hormone. For the first time, amino acid isomerization has been shown to occur in the perikarya of fully specialized neurosecretory cells, as a late step of the maturation of the hyperglycemic hormone precursor and after propeptide cleavage. The specificity and efficiency of this phenomenon indicates the existence of a new enzyme family involved in the biogenesis of peptide hormones.

Quantification of vincristine and vinblastine in Catharanthus roseus plants by capillary zone electrophoresis

A systematic and comprehensive study of the separation and quantification of two dimeric catharanthus alkaloids, vincristine (VC) and vinblastine (VB), in Catharanthus leaves by capillary zone electrophoresis (CZE) was conducted. Various separation parameters such as buffer concentration and pH, column internal diameter and applied voltage were studied. Due to the complexity of the samples, the optimum conditions for separating VC and VB from other alkaloids that co-exist in the plant samples are matrix-dependent. We found the following conditions, in general, gave the best results in terms of resolution and analysis time: column, 72 cm (57 cm effective length) × 75 μm I.D.; buffer, 0.2 M ammonium acetate solution, pH 6.2 and an applied voltage of 10 kV. Although the separation of VB and VC was the primary focus, the separation parameters determined in this study can be applied to the separation of other alkaloids as well. Separation of many of the other alkaloids in the plant samples was observed under conditions presented in this paper. A secondary objective of this study was to develop a method with experimental conditions which could be applied to electrophoresis-mass spectrometry. For this reason, ammonium acetate buffers, which are more compatible with mass spectrometry than the widely used phosphate buffers, were used exclusively. Also, methanol-water-acetic acid was used as external buffer for the same reason. The effects of this buffer and its compositions on the resolving power of CZE for the VB/VC pair are discussed.

A new simple and rapid HPLC method for determination of DEHP in PVC packaging and releasing studies

A new simple, rapid and sensitive reverse-phase liquid chromatographic technique for the determination of di-2-ethylhexyl phthalate (DEHP), the major plasticizer of most PVC materials, is proposed. The proposed method is characterised by a single liquid/liquid hexane extraction procedure which can be used either for direct DEHP determination in PVC raw material or for the analysis of leached DEHP in the infusion bags during the perfusion process. The detection of DEHP is performed based on UV absorbance at 270 nm after direct injection of the hexane extract in a miscible eluent consisting of an acetonitrile/methanol mixture (9:1, v:v). The chromatographic process takes place on a classical C I, stationary phase. Linearity of the method is assumed from 0.25 to 5 ppm of DEHP with an acceptable repeatibility and reproducibility (RSD lower than 1.5 and 2.5%, respectively). Trace analysis is shown to be possible with respect to the limit of detection of 0.05 ppm. Moreover, the interesting possibility of using a reduced internal diameter column (2.1 mm) is underlined with respect to the resulting increase in sensitivity (0.01 ppm detectable). Some practical pharmaceutical applications are presented in order to demon-strate the reliability of the proposed method for the determination of DEHP in PVC packaging, as well as for traces of DEHP leached in infusion bags.

MASS TRANSFER IN A RECIPROCATING PLATE BIOREACTOR

Abstract An experimental program has been initiated to evaluate the performance of a reciprocating plate bioreactor for its use in viscous fermentations. The investigation is divided into three parts: (1) to study the hydrodynamics within the bioreactor, (2) to determine the axial dispersion coefficient and the overall oxygen mass transfer coefficient as a function of the operating conditions, and (3) the evaluation of a reciprocating plate column as a bioreactor for viscous fermentations. This paper reports on the determination of the axial dispersion coefficient and on the measurement of the overall oxygen transfer coefficient. Experiments were done in water on a semi batch scheme (no water flow) in a 1.26m high and 101.6mm internal diameter column. It was found that the axial dispersion coefficient is a strong function of the reciprocation speed whereas it is relatively unaffected by the aeration flow rate. The overall oxygen transfer coefficient was determined with two separate methods: (1) the sulfit...

Advances in Chromatography for Clinical Drug Analysis

Advances have been made in chromatography complement immunoassay for clinical drug analysis. Chromatographic theory shows that the minimum detectable mass is directly proportional to the square of column radius. Small internal diameter columns are capable of analyzing lower analyte concentrations, and high resolution is achievable in open capillary columns, concomitant with greatly reduced mobile phase consumption and waste. This review, based on the author's experience and literature, focuses on supercritical fluid chromatography (SFC), capillary electrophoresis (CE), and selected high-performance liquid chromatography (HPLC) methodologies--microbore and direct-sample analysis (DSA) using commercially available Restricted Access Media (RAM) and REMEDi. In investigating the feasibility of SFC, the "normal-phase-like" selectivity of carbon dioxide was established, affecting the design of the extraction protocol and the elution order of drugs and metabolites. For example, the "more polar" tautomer eluted after FK-506, opposite to the order in the reversed-phase HPLC analysis. CE was investigated by Shihabi et al. for the analysis of pentobarbital and iohexol, while Evenson and Wiktorowicz performed preliminary evaluation of several therapeutic drug monitoring (TDM) drug groups. Innovation in HPLC column technology and hardware have greatly enhanced clinical drug analysis. Microbore column, offering enhanced mass sensitivity and high resolution, utilizes small sample size of 5 microliters of serum for the analysis of chloramphenicol. Commercially available RAM include internal surface reversed phase, shielded hydrophobic phase, and dual zone media, readily applicable for serum drug analysis without any sample preparation. Recently, an automated HPLC REMEDi offers urine and serum drug screening for toxicology.

Effect of column diameter on plate height in high speed liquid chromatography using pellicular and perfused particles in packed capillaries

AbstractThe purpose of this work was to examine column designs that allow for rapid separations by packed capillary liquid chromatography. Previous work with packed capillary columns with inner diameters (i.d.'s) of 20 to 150 μm revealed significantly reduced eddy diffusion broadening in these columns compared to larger bore columns. These results suggested that resistance to mass transfer dominates band broadening in microcolumns at high flow rates. Thus, it should be possible to attain rapid separations in capillaries by using pellicular or perfused particles which reduce resistance to mass transfer in the stagnant mobile phase. Furthermore, the use of capillary columns with small eddy diffusion effects should give better performance than larger bore columns packed with similar particles. To test these possibilities, the plate height of an unretained solute as a function of flow velocity was evaluated in columns with internal diameters of 50 to 250 μm packed with pellicular particles (8 and 15 μm diameter) and perfusion particles (10 and 20 μm diameter). Decreasing both column i.d. and column i.d. to particle diameter ratio (ρ) were found to improve the performance of columns packed with pellicular particles; however, ρ was the most important factor. Column i.d. and ρ had no effect on the performance of perfusion particles within the range tested. However, the capillary perfusion columns had better performance than previously reported for larger bore perfusion columns. The best results were obtained for 8 μm pellicular particles inside 50 μm i.d. columns. These columns generated nearly 7,000 theoretical plates in 10 s. Further improvements should be possible by using smaller particles and smaller column internal diameters.

Influence of coiling on performance in capillary electrophoresis using open tubular and polymer network columns

AbstractThe influence of coiling on column efficiency in capillary electrophoresis (CE) has been examined. In open tubular columns of 75‐μm i.d., no significant effect of column coiling on efficiency was observed, even at plate counts of 2 × 106 m−1. The small column internal diameter and radial diffusion in free solution was able to minimize the potential deleterious effect of coiling. With gel‐filled columns of very high efficiency (˜107 plates m−1), the influence of coiling on column efficiency was, however, significant, e.g., a factor of 3 or more loss in plate count per coil. For relatively rigid gels (e.g., 9% T linear polyacrylamide with 7 M urea), this observed loss of column efficiency was attributed mainly to the inability of the polymer network to permit diffusional relaxation of the coiling effects. A significant influence of coiling on column efficiency was also found with medium concentration polymer networks (e.g., 3‐6% T linear polyacrylamide with no urea). The polymer network structure was assumed to change under the influence of mechanical stress caused by coiling, resulting in anisotropy across the column. Furthermore, the changes in structure and in efficiency were found to be time dependent and, in general, reversible. The effect appears to be caused by the shear force imposed on a polymer network structure, since changes are only observed when the column shape is altered after the polymer has been loaded into the capillary.

Packed-capillary liquid chromatography/ion-spray tandem mass spectrometry determination of biomolecules

Precolumn flow splitting is successfully implemented for gradient separation in peptide-mapping applications with a column internal diameter of 320 μm. Peptide standards, protein tryptic digests, and a crude peptide mixture from industry are used to demonstrate the feasibility for utilizing the packed-capillary LC/MS system in a variety of applications. High-sensitivity micro LC/MS peptide mapping and molecular weight determination can be performed routinely via ion-spray LC/MS with injected sample amounts as low as 10 pmol. Peptide sequence information is obtained via on-line packed-capillary LC/MS/MS

Concentration of organics from aqueous solutions using uncoated capillary columns

A novel technique has been developed for the concentration of trace organics in aqueous solutions. Concentration of organics is carried out by passage of aqueous samples through uncoated plastic and metal capillary tubing. The organic compounds are removed on the walls of the column while the water is allowed to elute from the capillary. Detailed investigations were also carried out on parameters that affect the efficiency of trapping such as the column length, column internal diameter, column internal surface area, trapping temperature, solute concentration, ionic strength of aqueous solutions, and the flow rates of solutions through trapping capillaries. It was determined that plastic type materials, and silicone in particular, are capable of removing trace organics from solution extremely efficiently. The trapping temperature and the flow rate of solutions through the columns are important parameters that contribute to the removal of organics.

Short columns for gas chromatography

Abstract

Preparative Liquid Chromatography and theH/uCurve

Abstract H/u curves for columns of increasing internal diameter are shown to be useful for evaluating their LC performance. In particular, the H/u curve reveals whether the packing technique or the packing material is defective. H/u curves for very large internal diameter columns show deviations which result from friction heat and thermal expansion of the column tubing, creating a void at the column wall.