Low-capacity Column Research Articles

Liquid Chromatographic Estimation of Octanol/Water Partition Coefficients with a High Efficiency, Nonporous, Ultrasmall Particle Size Reverse Phase Stationary Phase

Abstract HPLC retention data, obtained over a range of organic modifier fractions φ in binary mobile phases, can be used to estimate a compounds octanol/water partition coefficient (log Po/w). Such a determination is facilitated by a high efficiency, low capacity column. The utility of a nonporous, ultrasmall particles size (1.5 μ), C18 stationary phase capable of such performance was assessed using aqueous mobile phases containing either acetonitrile or methanol. In general, compounds were effectively eluted from this stationary phase at lower values of φ than with more typical stationary phases, thus increasing the accuracy and speed with which log Kw, the capacity factor in a 100% aqueous mobile phase, could be determined. Values of log Kw obtained for seventeen model compounds were highly correlated with the compound's log P0/w. Comparison of retention trends in the methanol and acetonitrile mobile phases suggests differences in the retention mechanisms for both organic modifiers.

Simultaneous determination of small organic and inorganic anions in environmental water samples by ion-exchange chromatography

Anion-exchange chromatography at elevated pH values is the method of choice for the simultaneous determination of weak and strong low-molecular-mass organic and inorganic acids. These are important species found in the environment where most of them are formed and further degraded, particularly if microbial activities are involved. A step gradient procedure with a weak eluent such as borate on a low-capacity column was developed for the simultaneous one-run one-column determination of most of these types of components in environmental water samples. High selectivity and detection limits below 1 μM were achieved. Other yet unknown coelutions of 3-hydroxybutyrate with fluoride and 2-hydroxybutyrate with propionate were found. The different retention characteristics of a high-capacity column was used to obtain additional evidence to identify interfering components. These separation procedures were used to investigate fog, lake sediment pore water and rain after roof run-offs.

Improved analysis of process liquors for the pulp and paper industry by ion chromatography

In this paper, techniques are presented to overcome interferences from caustic matrices and neighboring ions found in process solutions. Column switching and the use of low-capacity columns to characterize strongly retained analytes are described. Oxalate, sulfide, sulfite, sulfate and thiosulfate are characterized on one set of separator columns. High-capacity cation-exchange resins are shown to be an effective pre-treatment tool for neutralizing a caustic chlorine dioxide scrubbing liquor, enabling baseline resolution of chlorate.

A rapid and sensitive ion chromatographic technique for the determination of sulfate and sulfate reduction rates in freshwater lake sediments

Newly developed low capacity columns were used in suppressed ion chromatography for rapid and highly reproducible determination of SO42− in porewater samples from freshwater sediments without preconcentration of samples. With a 50 μl injection the detection limit for SO42− was ca. 50 pmol (= 1 μM) with a precision of 1–3% at the 10–200 μM level and <1% at concentrations above 200 μM. SO42− could be measured in 4–5 min with the routinely used eluent (3.0 mM NaHCO3/0.8 mM Na2CO3). When the strength of the eluent was increased to 3.0 mM NaHCO3/2.0 mM Na2CO3, sulfate analysis was possible in less than 3 min, provided that samples were nitrate-free. Under these conditions S2O32− could also be sensitively determined in about 6 min. Examples of application of the method are given for measurements of sulfate reduction rates in freshwater sediment samples from Lake Constance.

Two-Dimensional Capillary GC/FT-IR

Two-dimensional glass capillary gas chromatography/ Fourier transform infrared spectroscopy (GC4/FT-IR) is an effective technique for the analysis of very minor sample constituents as well as complex volatile mixtures. The two-dimensional system described here uses multicolumns and, for added separation capability, multiovens with independent temperature control. A fraction or fractions of the sample are transferred from the first column to a second column via a microswitching valve. With this approach, some of the problems routinely encountered with GC/FT-IR with the use of a single chromatographic separation are eliminated. The coupling of high- and low-capacity columns gives an extended working dynamic range for GC/FT-IR. In addition, column switching with repetitive cryofocusing onto the second chromatographic column may be used to enrich trace components prior to spectroscopic analysis.

Single column ion chromatographic determination of inorganic acids in workroom places.

Single Column Ion Chromatography (SCIC) combines low capacity-columns, low conductivity eluents and a detector with considerable electronic supression capability and enables quantitation of ions at the ppm level without the need of a suppressor column associated with other forms of Ion Chromatography. Vapors and aerosols of inorganic acids are collected on filter and silica gel tubes and analyzed directly by SCIC. A conventional liquid chromatograph with a low capacity column and a conductimetric detector is used to analyze aerosols of Cl-, Br-, NO-3 and SO=4 with good results.

Column switching applied to capillary gas chromatography/fourier transform infrared spectroscopy

AbstractA dual oven gas chromatograph incorporating a micro, mechanical switching valve has been interfaced to an FTIR spectrometer. With this system, each oven can be operated with independent temperature control. Complete choice of the columns' type and capacity gives flexibility in the separation prior to spectroscopic evaluation. An application which demonstrates some of the advantages of column switching in GC/FTIR is presented. Minor sample components have been successfully analyzed by heart‐cutting the appropriate section of the separation from a high to a low capacity column. In this way, the dynamic range of the technique is effectively increased while an efficient chromatographic inlet to the FTIR is maintained.

Application of Ion Chromatography to Beer, Wort, and Brewing Water

Several factors that affect the retention and resolution of different ions in anion chromatography were studied. These included the type of anion column and the pH, type, and concentration of the eluting buffer. Regression analysis was used to derive response-surface equations that improved understanding of the technique and aided its optimization. The utility of conductivity, spectrophotometric, and refractive-index detectors was also examined. A medium-capacity anion chromatography column gave better results than did a low-capacity column, although it made use of the conductivity detector more difficult. The medium-capacity column gave better resolution and enabled the elution of phosphate, chloride, and sulfate in a single 15-min run.

Application of Ion Chromatography to Beer, Wort, and Brewing Water

Several factors that affect the retention and resolution of different ions in anion chromatography were studied. These included the type of anion column and the pH, type, and concentration of the eluting buffer. Regression analysis was used to derive response-surface equations that improved understanding of the technique and aided its optimization. The utility of conductivity, spectrophotometric, and refractive-index detectors was also examined. A medium-capacity anion chromatography column gave better results than did a low-capacity column, although it made use of the conductivity detector more difficult. The medium-capacity column gave better resolution and enabled the elution of phosphate, chloride, and sulfate in a single 15-min run.

Ion exchange chromatography-conductivity detection with low capacity column and low concentration eluent

Ion exchange chromatography-conductivity detection with low capacity column and low concentration eluent

High-performance gel permeation chromatography of polystyrene with silica microspheres

Gel permeation chromatography separations have been performed with short low capacity columns containing silica microspheres (particle diameter ≈ 20 μm) having narrow particle size distributions and mean pore diameters in the range 8–120 nm. Plate height data for non-permeating polystyrene standards permitted an evaluation of chromatogram broadening due to mobile phase dispersion. These results together with plate height data for permeating polystyrene standards, tetraphenylethylene and toulene gave an assessment of chromatogram broadening due to mass transfer dispersion as a function of eluent flow-rate and solute molecular weight. It was found that mass transfer dispersion increased at higher flow-rates, the flow-rate dependence increasing as the diffusion coefficient of permeating polystyrene decreased. At very low flow-rates (0.05 cm 3 min −1, mobile phase dispersion is the major contributor to the chromatogram broadening,of permeating polystyrene. From theoretical considerations of chromatogram broadening, a relation is derived permitting the approximate determination of the true polydispersity of a permeating polymer at very low eluent flow-rates from the plate height for that polymer and from the plate height arising from mobile phase dispersion. The results show that fast separations may be accomplished in several minutes and that the most precise determinations of polydispersity are obtained at slow eluent flow-rates with separation times of about 1 h.