Evaluation of New Microparticulate Packings for Aqueous Steric Exclusion Chromatography

Abstract

Two types of high performance aqueous size exclusion columns have recently been developed, one a rigid spherical silica-based packing containing a new hydrophilic bonded phase (MicroPak TSK Gel Type SW) and the other an organic-based, semi-rigid gel (MicroPak TSK Gel Type PW). Characteristics of MicroPak TSK SW and PW columns were compared to other commercially available aqueous SEC columns packed with similar supports. Chromatographic performance of prepacked columns containing microparticulate support materials were compared for exclusion separations of water-soluble organic polymers, biopolymers, and small water-soluble oligomers. Amino acid probes were used to investigate non-exclusion effects of MicroPak TSK SW and PW columns.     

Evaluation of Reversed-Phase,Radially-Compressed,Flexible-Walled Columns for the Separation of Low Molecular Weight,UV-Absorbing Compounds in Serum

Abstract

Radially-compressed, flexible-walled columns were compared to rigid-walled columns for the reversed-phase separation of twenty compounds of biological importance. The radially-compressed columns were found to be efficient and reproducible, and enable the analysis time of human serum to be reduced by 50%. The effect of pH, flow-rate, and changing methanol concentration upon the separation of some compounds on the radially-compressed column is also presented.     

Modeling of structures of poly(oxyhexaorganocyclotetrasiloxy-2,6-diyl) mesophases

The idealized liquid-crystal structures of two cyclolinear organosilicon polymers, viz., poly(oxyhexaorganocyclotetrasiloxy-2,6-diyls), where the alkyl substituent is Et (1b) or Pr (1c), were modeled. The columns of monomer units in polymers have different conformations, viz., a distorted long boat in 1b and a distorted long chair in 1c. Both polymers have columnar structures with the most probable antiparallel arrangement of the columns.     

Evaluation of Alkaline Earth and Transition Metals for Use in the Ion Moderated Partition Chromatography of Sugars

Abstract

The elution behavior of 28 sugars and related compounds from high performance chromatography columns packed with alkaline earth and transition metals was investigated. As expected from the well-known chromatography of the commercially available calcium, silver, and lead form columns, elution behavior is highly metal-ion form specific. A significant data base of sugar elution versus column cationic-form was generated to permit the selection of new columns to enhance the separation of specific eluting species. Sugars resulting from the hydrolysis of wood were closely examined. Arabinose and galactose, known to be difficult to separate on commercially available lead and silver-form columns, were well separated on custom-packed rubidium and cesium-form columns.     

A Comparison of Radially-Compressed and Stainless Steel Columns for the Reversed-Phase Ion-Pair Separation of Phencyclidine Synthetic Mixtures

Abstract

The reversed-phase ion-pair HPLC separation of phencyclidine synthetic mixtures was optimized utilizing Radial-Pak radially compressed columns. Variables examined in the optimization included column type (C-18, C-8, or CN), pairing ion (methane-, pentane-, hexane-, or octane sulfonates) and mobile phase composition (varying concentrations of methanol or acetonitrile in water). The chromatographic behavior of the phencyclidine mixtures in the various systems utilizing radially compressed columns is compared and contrasted to a similar previous study which examined similar variables on stainless steel columns. The optimum system for radially compressed columns was found to consist of a Radial-Pak C-18 column and a mobile phase of 85:15 MeOH:H₂O, 2.5% acetic acid, 1% triethylamine and 5mM sodium hexane sulfonate.     

Gas Chromatography of δ1-Tetrahydrocannabinol

Abstract

Quantitative gas chromatography of small amounts of δ¹ - tetrahydrocannabinol has been demonstrated on a variety of silicone columns. Retention data in the form of methylene unit values were obtained on these columns.     

A Portable Slurry Packing Apparatus for High Performance Liquid Chromatography

Abstract

A portable apparatus for slurry packing high performance microparticulate liquid chromatographic columns is described. The packer offers lab to lab portability and ease of operations. Columns up to 50 cm in length can be accommodated with the described configuration. Material costs per column are $40 – $70, offering a substantial saving over commercially prepared columns, in situations where labor costs are minimal. Efficiencies of columns packed with this apparatus have been equivalent to or better than those obtained with commercially available columns. Columns are packed using a staged pressurization/depressurization method. This method also leads to longer column life. Evaluation of relative column efficiency is also discussed.     

Development of High Pressure Liquid Chromatography (HPLC) for Fractionation and Fingerprinting of Petroporphyrin Mixtures

Abstract

A method is described which permits the analysis of fossil porphyrin mixtures by HPLC. This method involves the fractionation of the demetallated petroporphyrin mixtures on silica columns followed by rechromatography of the trapped fractions on ODS columns. This coupling of the two modes of HPLC provides a fast and effective method for the separation of isomeric porphyrins and for the petroporphyrin fingerprinting of geological (oil/shale) samples. Representative examples of analysis are discussed in terms of the potential applicability of the technique in the areas of structure elucidation and geochemical correlations.     

Evaluation of Packed GLC Columns for Nanomolar Analysis of Unknowns Lincluding a New Type of Packed Column

Abstract

Fatty acid methyl esters, 2,6-dimethylaniline, and 2,6-xylenol were used for rapid evaluation of the usefulness of packed GLC columns for analysis of unknowns at the nanomolar level. Three types of column construction with three liquid phases of widely varying polarity were tested by the above procedure. A new type of GLC column, a dynamically coated packed column prepared with a surface active agent, was found to yield better overall performance for less polar liquid phases than packed silanized glass or packed stainless steel columns.     

A New Technique for Simultaneous Assay of Biogenic Amines and Their Metabolites in Unpurified Mouse Brain

Abstract

We developed a chromatographic system which separates cate-cholamines and indolamines as well as a large number of their metabolites (acids, aminoacids and glycols). Waters Radial Pak columns compressed radially to avoid formation of cavities in the packing, were used. These columns must be washed with methanol in order to obtain reproducible results when an ion-pairing mobile phase is employed. The conditioning of bhe columns was not affected by washing with triethylamine or variations in radial pressure. Good resolution of 13 samples was obtained in 28 minutes with a mobile phase composed of 0.1 M KH²PO⁴, 0.1 mM EDTA and 5 mM heptane sulfonic acid in water and Me OH (85:15), pH = 3.6. Products were identified with the use of a Metrohm 64l electrochemical detector.

The technique was used for rapid, simultaneous determination of NA, DA, DOPAC, HVA, 5HT and 5HIAA in deproteinated mouse brain samples.     

A Bidimensional HPLC System for Direct Determination of Theophylline in Serum

Abstract

A bidimensional HPLC system combining steric gel exclusion and reverse phase ODS columns for determination of theophylline in serum is reported. Factors involved in the development of the method and its performance are discussed. This technique is a practical alternative for the determination of theophylline levels in serum without any clean up procedure before chromatography.     

Flow Rate Dependence of Separation and Broadening Effects in GPC

Abstract

The primary objective of this work is an investigation of the separation and zone brodening effect in columns packed with porous and nonporous materials, and estimation of the accuracy of the broadening parameter, h, obtained by a reverse flow method. In order to study the separation and dispersion phenomenon in the mobile phase, and that caused by a mass-transfer process, columns packed with smooth glass beads and porous silica columns were used.     

Mixed Packings in High Performance Liquid Chromatography. II. Mixed Packings vs. Mixed Ligands

Abstract

The use of mixed packing of different selectivities for the separation of antidepressants and anticonvulsants was studied. The results show that columns packed with mixed ligand supports (C₈ and cation exchange), gave the better resolution and peak shapes than the physically mixed C,₈/cation exchange and serially connected columns. Also, the retention times obtained on the mixed ligands column, the physically mixed supports column and the two columns in series were different in each case.     

Comparison of Various Columns for the High-Speed HPLC Analysis of Drugs of Forensic Interest

Abstract

A comparison of the use of various commercially available columns for the high-speed reverse-phase ion-pair high performance liquid chromatographic separation of drugs of forensic interest is discussed. The columns include a Partisil 5 ODS-3 RAC, a Partisil 5 C8 RAC, a Radial Pak microBondapak C18 cartridge, a Perkin-Elmer HS/5 C18 and a Perkin-Elmer HS/3 C18. The mobile phases employed contain water, acetonitrile, phosphoric acid, and sodium hydroxide, with or without hexylamine. When a mobile phase without an amine modifier is employed, retention times were at least halved, except with a HS/3 C18 column, over those obtained with conventional columns. Basic drugs did not elute when the above mobile phase is used with a HS/3 C18 column. In addition, the selectivities of the other high speed columns were similar. Further reductions in retention times and different selectivities were obtained when an amine modifier is utilized. Column performance parameters such as n, V and v are presented for the colupns examined. A new column performance parameter S which is (n/V)^1/2 is introduced and discussed.     

High Performance Liquid Chromatography Separations Using Short Columns Packed with Spherical ODS Particles. II. Effect of Mobile Phase Composition on Resolution

Abstract

The effect of instrumental parameters, mobile phase composition, and flow rate on high performance liquid chromatography separations using 3 cm, 5 cm, and 10 cm columns packed with 3y spherical ODS materials is discussed. The results indicate that when instrumental parameters were optimized, the 10 cm column gave better separation than the shorter columns under the same experimental conditions. However, when the mobile phase composition was adjusted so that the solute residence time was comparable in the three columns, short and long columns gave comparable results.     

Comparison of Column Packings for Isocratic High-Performance Liquid Chromatographic Analysis of Carotenoids Using Non-Aqueous Reversed-Phase

Abstract

Ten different columns are compared for the isocratic non-aqueous reversed-phase separation of carotenoids, using solvent mixtures of ethyl acetate-acetonitrile both with and without 0.1% n-decanol as modifier. Conditions were established for separation of a mixture of alfalfa carotenoids containing mainly neoxanthin, violaxanthin, lutein and β-carotene. The best material for use for rapid isocratic separation of all major components was a high carbon loading non-endcapped material with ODS functionality, although one endcapped C8 material gave similar results. The use of n-decanol as mobile phase modifier is imperative to rapidly condition new columns to give optimum peak shape and definition and system linearity.     

Solid-Phase Extraction Techniques for Assay of Diuretics in Human Urine Samples

Abstract

Solid-phase extraction techniques were evaluated for the treatment of urine samples in the analysis of diuretics before injection into an HP-Hypersyl ODS-C18 column. Six different reversed-phase extraction columns were tested, and the results obtained are compared with those obtained in a classical liquid-liquid extraction with ethyl acetate.

The solid-phase extraction procedures are the best overall choice for all the diuretics tested, due to their versatility, the minor time-consuming, and the good recovery percentages obtained. C18 and C8 packings give the highest recoveries for a majority of the diuretics studied. However, CH or PH columns, due to their greater selectivity, can be used if the elution of the matrix is not complete in the washing solution. This could be more suitable.     

Use of the Peak Shaving-Recycle Technique for Separation of Labdadiene and Labdatriene Isomers by HPLC

Abstract

Separation on a preparative scale of labdadiene and labdatriene isomers by extensive use of the peak shaving-recycle technique is described. The procedure can be used to effect rapid and high yield separations of closely related isomers with α ～1 using a commercial instrument (Prep LC/system 500) and commercially available columns.     

Analysis of pyraflufen-ethyl residues in apples and soil by high-performance liquid chromatography

Abstract

Detailed procedures are provided for preparing packed cadmium columns to reduce nitrate to nitrite. Experiments demonstrated the importance of conditioning both open tubular cadmium reactor (OTCR) and packed copper-coated cadmium columns to achieve 100% reduction efficiency. The effects of segmentation bubbles in the OTCR upon reduction efficiency and baseline noise in nitrate analysis are investigated using an auto-analyzer. Metal particles derived from segmentation bubbles in OTCR result in interference with continuous flow analyses. Therefore packed columns are recommended for determination of low level nitrate in natural waters.     

Modification of Selectivity in Reversed-Phase Liquid Chromatography of Polycyclic Aromatic Hydrocarbons Using Mixed Stationary Phases

Abstract

Monomeric and polymeric C₁₈ materials provide significantly different selectivities for polycyclic aromatic hydrocarbons (PAH) in reversed-phase liquid chromatography. Selectivity factors vary in a regular manner with respect to surface concentration of C₁₈ groups on different C₁₈ columns. In this study, we investigated the feasibility of “customizing” a C₁₈ column to provide an intermediate selectivity by mixing 5-μm polymeric C₁₈ material from two different lots with high and low C₁₈ surface concentrations. Polymeric C₁₈ materials from different production lots were mixed in ratios of 30/70, 50/50, and 70/30 (w/w). Selectivity factors for these columns were found to be similar to those predicted by the linear addition of the selectivities of the two individual phases. The PAH selectivities on these mixed columns were also found to be comparable to data obtained from coupled short columns of appropriate lengths each containing one of these different C₁₈ materials. These studies indicate that columns of specific selectivity can be prepared by either mixing two different C₁₈ materials or by coupling columns containing each of these different phases. The use of mixed phase columns is illustrated for the analysis of a fraction containing five condensed ring PAH isomers (molecular weight 278) isolated from an air particulate sample.