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Comprehensive two-dimensional gas chromatography (GC x GC) offers significant improvement for volatile chemical separation. Selecting suitable first (¹D) and second dimension (²D) columns normally requires consideration of the chemical composition of a sample. Replacing one of these dimensions with a two-column ensemble (for example, ¹D1 + ¹D2 for the ¹D column), provided with a pressure tuning makeup gas between them, varies the relative retentions of compounds before the modulation step according to the junction pressure. This makes it possible to alter the apparent polarity of the ¹D ensemble, and this alters peak positions in the 2D GC x GC space. This article presents an account of studies that suggest this offers potential for improved operation for a GC x GC laboratory. [ABSTRACT FROM AUTHOR]

Multiple dual mode counter-current chromatography (MDM CCC) separation processes with semi-continuous large sample loading consist of a succession of two counter-current steps: with “ x ” phase (first step) and “ y ” phase (second step) flow periods. A feed mixture dissolved in the “ x ” phase is continuously loaded into a CCC machine at the beginning of the first step of each cycle over a constant time with the volumetric rate equal to the flow rate of the pure “x” phase. An easy-to-use calculating machine is developed to simulate the chromatograms and the amounts of solutes eluted with the phases at each cycle for steady-state (the duration of the flow periods of the phases is kept constant for all the cycles) and non-steady-state (with variable duration of alternating phase elution steps) separations. Using the calculating machine, the separation of mixtures containing up to five components can be simulated and designed. Examples of the application of the calculating machine for the simulation of MDM CCC processes are discussed. [ABSTRACT FROM AUTHOR]

A series of Microsoft Excel spreadsheets were developed to simulate the process of separation optimization under isocratic and simple gradient conditions. The optimization procedure is performed in a stepwise fashion using simple macros for an automatic application of this approach. The proposed optimization approach involves modeling of the peak shapes in order for the simulation of predicted chromatograms to be possible. The performance of the selected optimization procedure was tested by means of experiments performed on a reversed-phase column that produced Gaussian peaks for all solutes, providing benefits for computational simplicity. The separation optimization by Microsoft Excel especially with simple and easily implemented macros is a challenging pedagogical tool for advanced analytical chemistry courses. An illustrative video given in the Supporting Information supports a novice Excel practitioner in following the proposed separation optimization procedure. [ABSTRACT FROM AUTHOR]

Abstract: New flexible chromatographic response functions for one-dimensional (DCRF f ) and two-dimensional chromatography (DCRF f,2D) are put forward and tested for estimating the quality index of separation in non-targeted chromatographic analysis of complex samples. These functions, based on already tested functions, have three clear-cut criteria: number of chromatographic peaks, degree of chromatographic separation, and time spent in the analysis. However, unlike the existing functions, they allow an accurate weighing and adjustment of these criteria according to the needs of the analyst. Special attention was given to the time spent in the analysis by introducing a time-saving criterion, which allowed its application in time dependent chromatographic systems. The performance and flexibility of the strategies based on the developed response functions are tested in different chromatographic scenarios and for several application possibilities using simulated chromatograms. [Copyright &y& Elsevier]

Chromatography combined with spectral analyzers provides great separation powers. However, the amount of data provided makes analysis difficult and laborious. The automated peak extraction and quantification (APEQ) method is a novel method for targeted and untargeted analysis. The method extracts retention times (tR), spectra, and signal intensity from data from chromatography with spectral detectors. It is a tiered approach consisting of five tiers: (1) the chromatograms are split into sections. (2) Peaks are detected and their elution profiles, spectra, and signal intensities are approximated. (3) The number of important peaks in each section is estimated. (4) For each section, the peaks and background are modeled using parallel factor analysis (PARAFAC). Several PARAFAC models with a different number of factors are made. (5) For each section, the optimal model is selected. The optimal model will in most cases be the model with lowest dimensionality (i.e., fewest factors) that has a factor describing the baseline. The APEQ method has been used to analyze gas chromatography/mass spectrometry (GC/MS) full-scan chromatograms of 12 samples, each containing 30 polycyclic aromatic hydrocarbons (PAHs). It detected all 30 PAHs and 14 compounds not intentionally added. It extracted the tRs, mass spectra, and relative concentrations. The quantification was compared to integration of extracted ion chromatograms. It had comparable quality for peaks with little or no overlap and significantly better for peaks with overlap. The total analysis time with default parameters was less than 10 min on an ordinary laptop. By optimizing the parameters, all 30 PAHs could be quantified in 142 s. [ABSTRACT FROM AUTHOR]

Abstract: In a recent contribution a design method for steady-state recycling chromatography in the so-called mixed-recycle mode (MR-SSR) has been proposed by . The method holds under ideal, dispersion-free conditions for chromatographic systems with competitive Langmuir adsorption isotherms. Here this approach is extended to practically relevant nonideal conditions with significant dispersive effects and convex-upward adsorption isotherms in general. The developed shortcut design method allows designing MR-SSR processes based on a simple procedure applied to a single conventional chromatogram. The method is validated experimentally for the separation of two cycloketones on a polymeric stationary phase. The performance of the MR-SSR process is compared to batch chromatography by means of a simulation study. [Copyright &y& Elsevier]

Abstract: Samples with a large number of compounds or similarities in their structure and polarity may yield insufficient chromatographic resolution. In such cases, however, finding conditions where the largest number of compounds appears sufficiently resolved can be still worthwhile. A strategy is here reported that optimises the resolution level of chromatograms in cases where conventional global criteria, such as the worst resolved peak pair or the product of elementary resolutions, are not able to detect any separation, even when most peaks are baseline resolved. The strategy applies a function based on the number of “well resolved” peaks, which are those that exceed a given threshold of peak purity. It is, therefore, oriented to quantify the success in the separation, and not the failure, as the conventional criteria do. The conditions that resolve the same amount of peaks are discriminated by either quantifying the partial resolution of those peaks that exceed the established threshold, or by improving the separation of peaks below it. The proposed approach is illustrated by the reversed-phase liquid chromatographic separation of a mixture of 30 ionisable and neutral compounds, using the acetonitrile content and pH as factors. [Copyright &y& Elsevier]

Abstract: A new and systematic application for separation and online identification of coumarins from Peucedanum praeruptorum Dunn by preparative high-speed counter-current chromatography coupled with electrospray ionization multi-stage mass spectrometry (prep-HSCCC/ESI-MS n ) was established. The procedure of separation was guided by the chromatogram of ion current. The structures of acquisitions were deduced by MS information. The hyphenation between prep-HSCCC/ESI-MS n was designed to keep the split ratio from 1:20 to 1:200 exactly. Seven compounds were obtained and two new compounds were detected. It was proved that prep-HSCCC/ESI-MS n was an effective method for sensitive detection, rapid identification and separation of natural products. [Copyright &y& Elsevier]

Abstract: Rational strategies for the optimization of separations are vital to any chromatographic technique. In counter-current separations (CS), once a suitable solvent system is selected for a given separation, the operator is faced with the task of optimizing the separation through the manipulation of those adjustable operation parameters allowed for by the current CS technology. This study employed a mixture of 21 natural products of varying polarity, molecular mass, and functionality, termed the GUESSmix, as a tool to assess the effectiveness of optimization strategies. The behavior of the GUESSmix was observed in the hexane/ethyl acetate/methanol/water 4:6:4:6 (HEMWat +3) solvent system. The effect of operation parameters on both the elution and extrusion stages of a recently introduced CS methodology, termed elution–extrusion counter-current chromatography (EECCC), was investigated. The resulting chromatograms were plotted with K-based reciprocal symmetry plots (ReS and ReSS), which allow comparison of the K values of significant peaks and assessment of resolution of eluting compounds in the interval 0≤ K ≤ ∞. The operation parameters studied were: (1) the effect of temperature controlled water circulation around the centrifuge; (2) the combination of flow rate and revolution speed; (3) sample loading capacity; (4) the direction of rotation either agreeing with or opposing the direction of coil winding; (5) injection before equilibration, a practice that saves operator time and reduces solvent consumption. The GUESSmix was found to be a highly useful reference mixture to compare and contrast stationary phase retention volume ratios, resolution, K-values, peak shapes, and extrusion characteristics between CS experiments. EECCC is shown to be a robust technique that may be enhanced with appropriate temperature, rpm, flow rate, sample loading, direction of rotation, and injection timing. Plotting ReS[S] chromatograms enables systematic study of CS parameters, which are not reproducibly represented in retention time or volume plots. [Copyright &y& Elsevier]

Abstract: Peak capacity (i.e. maximal number of resolved peaks that fit in a chromatographic window) is a theoretical concept with growing interest, but based on a situation rarely met in practice. Real chromatograms tend to have uneven distributions, with overlapped peaks and large gaps. The number of resolved compounds should, therefore, be known from estimations. Several equations have been reported for this purpose based on three perspectives, namely, the intuitive approach (peak capacity as the size of the retention time window measured in peak width units), which assumes peaks with the same width, and the outlines of Giddings and Grushka, which consider changes in peak width with retention time. In this work, the peak capacity concept is discussed and three new approaches are derived based on realistic descriptions of peak shape. The first one is based on the Grushka''s approach and considers the contributions of column and extra-column peak variances. The second one relies on Giddings’ and assumes asymmetrical peaks where left and right peak half-widths depend linearly on retention time. The third equation, based on the intuitive approach, uses a mean peak width obtained by integration, instead of a mean value from several representative peaks. The accuracy of the classical Giddings’ approach for ideal peaks, a modification of the Grushka''s approach that considers variation of peak width at half-height, and the three new approaches were checked on combined chromatograms built by adding real peaks. The results demonstrate that the change in efficiency (and not in skewness) is the relevant factor, at least in the studied examples. Also, peak width should be measured at low peak height ratios (i.e. 10%) to better account peak deformation. [Copyright &y& Elsevier]

We consider a new method for the chromatographic separation of mixtures, which is distinguished by a discrete (cyclic) supply of the mobile phase to a column. Analysis The the of a linear model of ideal (equilibrium) cyclic chromatography is performed. Theoretical description of chromatograms for a binary mixture of components is presented. Comparative analysis of the chromatography process under cyclic and steady-state conditions is conducted. It is shown that, under the assumptions made (the column consists of equal sections, with the equilibrium distribution of components between the phases being reached in each of the sections; the mobile phase is supplied in portions equal to its volume in a single section of the column; the supply of each portion occurs instantaneously), a higher degree of separation is attained in cyclic mode. A relationship between process parameters under cyclic and steady-state conditions is found. [ABSTRACT FROM AUTHOR]

A four-step strategy is described which is aimed at optimizing the separation parameters of the chromatographic fingerprint of herbal medicines. In the optimization procedure, a model is built to predict the retention time of components. The proposed model shows good retention prediction potency with an average relative deviation of 1.78%. The grid search method is used in optimizing gradient parameters. In addition, an iterative procedure is adopted to further improve the prediction accuracy of the gradient retention time and the quality of the chromatogram. The whole optimization process has been validated by real samples. [ABSTRACT FROM AUTHOR]

The article examines several activities of some leading separation science research institutes in Austria. One group is the Institute Chemistry and Radiochemistry which simplifies sample preparation technique to isolate trace components from complex environmental to allow interference-free chromatographic measurements. Other groups include the Institute of Analytical Chemistry, Institute of Chemistry-Analytical Chemistry, and Center for Analytical Chemistry.

Discusses calibration in chromatography. Importance of residual standard deviation in estimating the prediction interval and uncertainty of the result; Determination of the standard deviation of a signal at its lowest and highest concentration.

Part II. Investigates the baseline disturbances in chromatographic systems with refractive index detection using acetonitrile-water mixtures on amino-phase columns. Role of minor fluctuations in the column thermostat in causing composition fluctuations in the column effluent; Correlation between the magnitude of these composition fluctuations and the time derivative of the temperature fluctuations.

The article explores a problem related to the transfer of a method from one instrument to another in chromatographic analysis. It discusses how to troubleshoot this liquid chromatography (LC) problem. It suggests that a periodic system performance qualification test be performed for each LC system on a semiannual or annual basis so that method transfer problems will not occur.

Discusses the extracolumn effects on the chromatogram's appearance. Advantages of checking for reasonable chromatographic behavior; Importance of controlling temperature and checking its influence on the separation; Retention factor for the analyte in the liquid chromatography assay.

The article focuses on the impact of the size of pore packing materials for peptide separations in ultra performance liquid chromatography peptide mapping. The pore size materials of 130 A and 300 A are compared in the separation of its two complex peptide digests. The result shows that both peptide separation technology columns give useful separations of peptides over a wide range of sizes and chemical properties.

Features several literature on separation science. Dionex Corp.'s product catalogue on CD-ROM; Bionisis' application bulletin describing how scientists can monitor the metabolism of radioactively labelled drug candidates; Sun-Sri's catalogue for its range of chromatography vials and validated syringe filters.

Editorial. Discusses the management of chromatographic data. Need to deploy a long-term archival solution that offers ongoing access and reuse of information; Considerations in the long-term content preservation; Physical storage and media management.

The article presents information on multidimensional separations in analytical chemistry. Conventional, heart-cut multidimensional separations are valuable when extra resolution is needed in the examination of a small segment of peaks in a complex chromatogram. Prior knowledge of the sample composition is always beneficial. In comprehensive multidimensional separation techniques, the entire sample, not just a part of it, is subjected to different separations. Separation techniques that utilize more than two dimensions can certainly be expected in the future.

Lists conferences on separation science for February to June 2004. Eighth International Symposium on Hyphenated Techniques in Chromatography and Hyphenated Chromatographic Analyzers in Brudges, Belgium; Environmental Mass Spectrometry Meeting in Chester, England; 27th International Symposium on Capillary Chromatography in Italy.