A novel data reduction and representation method for gas chromatography time-of-flight mass spectrometry (GC-TOFMS) is presented that significantly facilitates separation visualization and analyte peak deconvolution. The method utilizes the rapid mass spectral data collection rate (100 scans/s or greater) of current generation TOFMS detectors. Chromatographic peak maxima (serving as the retention time, tR) above a user specified signal threshold are located, and the chromatographic peak width, W, are determined on a per mass channel (m/z) basis for each analyte peak. The peak W (per m/z) is then plotted against its respective tR (with 10 ms precision) in a two-dimensional (2D) format, producing a cluster of points (i.e., one point per peak W versus tR in the 2D plot). Analysis of GC-TOFMS data by this method produces what is referred to as a two-dimensional mass channel cluster plot (2D m/z cluster plot). We observed that adjacent eluting (even coeluting) peaks in a temperature programmed separation can have their peak W vary as much as ∼10-15%. Hence, the peak W provides useful chemical selectivity when viewed in the 2D m/z cluster plot format. Pairs of overlapped analyte peaks with one-dimensional GC resolution as low as Rs ≈ 0.03 can be visually identified as fully resolved in a 2D m/z cluster plot and readily deconvoluted using chemometrics (i.e., demonstrated using classical least-squares analysis). Using the 2D m/z cluster plot method, the effective peak capacity of one-dimensional GC separations is magnified nearly 40-fold in one-dimensional GC, and potentially ∼100-fold in the context of comparing it to a two-dimensional separation. The method was studied using a 73 component test mixture separated on a 30 m × 250 μm i.d. RTX-5 column with a LECO Pegasus III TOFMS.
Reversed phase high-performance liquid chromatography (RP-HPLC) is demonstrated for hydrophobic analytes such as aromatic hydrocarbons using only water as the mobile phase. Achievement of reasonable capacity factors for these types of compounds without the need for toxic and costly organic modifiers in the mobile phase is accomplished by substantially decreasing the phase volume ratio of stationary phase relative to the mobile phase volume and by increasing the polarity of the stationary phase relative to stationary phase materials commonly used for RP-HPLC. Applying a stationary phase of trifluoropropylsiloxane, which is a common gas chromatographic stationary phase material, to nonporous glass microspheres yields a stationary phase with a phase volume ratio reduced by about 2 orders of magnitude as compared to common liquid chromatographic packing materials. As a result, a separation was obtained for hydrophobic organic analytes such as benzene, toluene, ethylbenzene, and isopropylbenzene using a water mobile phase at ambient temperature. A separation of sodium benzoate, benzaldehyde, benzene, and butyrophenone is shown in less than 3 min using a water mobile phase and UV/visible absorbance detection. Additionally, the separation of the ionic surfactant species octyl sulfate and dodecyl sulfate in water in less than 3 min, using unsuppressed conductivity detection, is achieved with a separation mechanism based on interactions with the hydrophobic portion of the surfactant. A water mobile phase offers many potential advantages over traditional mixed aqueous/organic solvent systems. In addition to saving on the cost and expense of buying and disposing of toxic solvents and waste, there is less exposure of the operator to potentially harmful solvents. Increased consistency in reproducing retention times can be expected, since there will not be any variability in solvent strength due to slight variations in mobile phase composition. A water mobile phase produces an environment that should provide an inherent advantage of increased signal-to-noise ratio for detection. Additionally, excellent predictions of the octanol/water partitioning coefficient and aqueous solubility for hydrophobic analytes are obtained from a single measurement of the capacity factor in the water mobile phase.
ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTDual-beam absorbance measurements by position-sensitive detectionCurtiss N. Renn and Robert E. SynovecCite this: Anal. Chem. 1988, 60, 11, 1188–1193Publication Date (Print):June 1, 1988Publication History Published online1 May 2002Published inissue 1 June 1988https://pubs.acs.org/doi/10.1021/ac00162a019https://doi.org/10.1021/ac00162a019research-articleACS PublicationsRequest reuse permissionsArticle Views85Altmetric-Citations2LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access optionsGet e-Alertsclose Get e-Alerts
A novel injection technique for high-speed gas chromatography is demonstrated. Synchronized dual-valve injection is shown to provide peak widths as low as 1.5 ms (width at half-height) for an unretained analyte. This was achieved using a 0.5-m DB-5 column with an internal diameter of 100 μm and a film thickness of 0.4 μm operated at a temperature of 150 °C with a column absolute head pressure of 85 psi, resulting in a dead time of only to = 26 ms (∼1900 cm/s, 26 mL/min). Using the DB-5 column in a 1-m length under the same instrumental parameters, with a resulting linear flow velocity of 935 cm/s (12.7 mL/min, to = 117 ms), a minimum peak width of 3.3 ms was obtained. During an isothermal separation, 10 analytes were separated in a time window of 400 ms. A rigorous comparison of experimental and theoretical band-broadening data based on the Golay equation showed that band broadening is limited almost entirely by the chromatographic band broadening terms expressed by the Golay equation and not by extra column band broadening due to the injection process. Synchronized dual-valve injection offers a rugged and inexpensive design, providing extremely reproducible injections with peak height precision of 2.4% (RSD) and low run-to-run variation in retention times, with an average standard deviation less than 0.1 ms. Herein, synchronized dual-valve injection is demonstrated as a proof of principle using high-speed diaphragm valves. It is foreseen that the injection technique could be readily implemented using a combination of thermal modulation and high-speed valve hardware, thus optimizing the mass transfer and not significantly sacrificing the limit of detection performance for high-speed GC. Further implications are that, if properly implemented, high-speed temperature programming coupled with this new technology should lead to very large peak capacities for ∼1-s separations.
