Automated method for short-chain aldehydes emission measurement by dynamic solid-phase microextraction on-fiber derivatization GC-MSD coupled with a flow-cell.

A novel automated method was developed to test short-chain aldehyde emissions using a chamber and a flow-cell coupled with a dynamic solid-phase microextraction (SPME) on-fiber derivatization technique. Calibration curves of short-chain aldehydes were developed for quantitation of target analytes, including formaldehyde, acetaldehyde, propionaldehyde, and acrolein emitted from the chamber outlet. The linearity range for the aldehydes was 0.8 to 2130.0 µg/m3. The limits of quantitation (LOQ) for various aldehydes ranged from ∼0.2 - 1.9 µg/m3. By using this method, emission rate curves are measured with an automated system. Compared with a traditional 2,4-dinitrophenyl hydrazine (DNPH)-high performance liquid chromatography (HPLC) method for aldehyde emission measurement, this method provided an automated technique to study the emission of short-chain aldehydes from multiple samples in one experiment. Furthermore, by using dynamic SPME coupled to an on-fiber derivatization technique, the repeatability and sensitivity of the method is comparable and even better than traditional techniques.

Comprehensive two dimensional gas chromatography review.

Advances, developments and applications in 2-D comprehensive GC (GC x GC) from 2007 through October 2008 are reviewed, with emphasis on modulation, and data handling, and applications of current relevance. Industrial perspectives as well as suggestions where further developments would be beneficial are summarized in the concluding remarks.

Quantification of the composition of liquid hydrocarbon streams: Comparing the GC-VUV to DHA and GCxGC.

Hydrocarbons analysis is important in the oil and gas industry, as stream composition has a strong impact on plant operations. The composition of hydrocarbon streams vary across a plant, which makes the selection of analytical methods challenging. Traditional methods for the evaluation of liquid hydrocarbon streams include the Detailed Hydrocarbon Analysis (DHA); however, non-traditional methods, such as comprehensive gas chromatography (GCxGC), are also utilized in the chemical industry, including Dow. This work details a comparison of analytical techniques available for such analyses, specifically, DHA and GCxGC compared to the recently introduced GC-Vacuum Ultra Violet (GC-VUV) system. Numerous liquid hydrocarbon streams were blended together to generate a composite and extensive matrix in terms of composition. Paraffin, isoparaffin, olefin, naphthene, and aromatic (PIONA) results are presented for the three techniques. All of those methods obtained relative standard deviations lower than 1.3% for five injections a day for three days. Standard addition curves were utilized to accurately quantify specific compounds in a liquid hydrocarbon stream, and these results were compared to the GC-VUV PIONA+ and DHA quantification procedures.

Determination of short-chain branching content in polyethylene by pyrolysis comprehensive multidimensional gas chromatography using low thermal mass column technology.

A research effort was undertaken to utilize the pyrolysis process to create fragments of polyethylene that could be indicative of branching, and allow quantitiation of said short-chain branches by pyrolysis comprehensive 2-D GC (Py-GC x GC). Several strategies for sample introduction and pyrolysis such as the in-column pyrolysis device and the programmed temperature vaporizer (PTV) were studied. The chromatographic separations were executed using low-thermal mass (LTM) comprehensive 2-D GC (GC x GC). A series of polyethylene-co-hexene samples were analyzed and a linear correlation of 1-hexene content with branching peak ratio was found. Correlation coefficients were determined as 0.97 for the measurements performed.

A new decoupling method for accurate quantification of polyethylene copolymer composition and triad sequence distribution with 13C NMR.

(13)C NMR is a powerful analytical tool for characterizing polyethylene copolymer composition and sequence distribution. Accurate characterization of the composition and sequence distribution is critical for researchers in industry and academia. Some common composite pulse decoupling (CPD) sequences used in polyethylene copolymer (13)C NMR can lead to artifacts such as modulations of the decoupled (13)C NMR signals (decoupling sidebands) resulting in systematic errors in quantitative analysis. A new CPD method was developed, which suppresses decoupling sidebands below the limit of detection (less than 1:40,000 compared to the intensity of the decoupled signal). This new CPD sequence consists of an improved Waltz-16 CPD, implemented as a bilevel method. Compared with other conventional CPD programs this new decoupling method produced the cleanest (13)C NMR spectra for polyethylene copolymer composition and triad sequence distribution analyses.

Gas chromatographic applications with the dielectric barrier discharge detector.

With gas chromatography, there are many more choices for detectors when compared to other separation disciplines in analytical chemistry. The presence of sensitive and selective detectors aids in easing the separation requirements imposed on the capillary column. The current gas phase detectors, however, do not completely fulfill contemporary analytical needs. One example is in the area of ultratrace analysis of permanent gases for semiconductor industry. Another example is in the area of environmental/industrial hygiene monitoring for compounds such as 1,3-butadiene or vinyl chloride. The dielectric barrier discharge detector, a new highly sensitive detector with tuneable selectivity, has recently been innovated and commercialized. In this paper, the principle of operation of the detector, along with critical challenging industrial applications such as the analysis of oxygenated compounds, sulfur-containing compounds, and other compounds of industrial significance is presented.

Comprehensive two-dimensional gas chromatography using liquid nitrogen modulation: set-up and applications.

An improved modulation system for comprehensive two-dimensional gas chromatography (GC x GC) is presented. It is based on two-jet modulation with liquid nitrogen as cryogen. A valve system was designed to include subsequent re-heating of cooled capillary segments after modulation. It is demonstrated that even volatile components, such as propane or butane, are easily modulated with this system. Thus, the temperature range for GC x GC operation compared to diaphragm valve or liquid CO2 modulation is extended. The system allows highly efficient analysis of volatile and non-volatile components. Applications include separations of alkenes and gasoline samples. Also sulfur-containing hydrocarbon samples were compared via GC x GC and differences among samples of different producers were observed. Finally, headspace GC x GC investigations of volatiles found in polymer latex-coated papers round out the increasing portfolio of valuable applications.

Retention time reproducibility in comprehensive two-dimensional gas chromatography using cryogenic modulation. II. An interlaboratory study.

An interlaboratory survey was conducted to determine the reproducibility of retention times in both the first (1D) and second dimension (2D) axes of the two-dimensional separation space, using the longitudinal cryogenic modulation comprehensive two-dimensional gas chromatographic approach. Intralaboratory reproducibility has been demonstrated in part 1 of this investigation [J. Chromatogr. A 968 (2002) 161]. Confidence in absolute retention times (hence component positions) in the two-dimensional separation space is critical to component identification. Comparing data from four independent laboratories, five independent gas chromatographs, five independent LMCS units, and numerous operators has determined that the LMCS cryogenic modulation approach provides reliable comprehensive two-dimensional GC results.

Dual-purpose gas chromatographic injection device for pressurized liquid and gas injection.

A dual-purpose gas chromatographic injection device, capable of injecting pressurized liquid sample of up to 5000 psig and gas sample with a volume as high as 5000 microL, has been successfully developed and implemented. The injection device is synergized by the effectiveness of a classical flash vaporization of a syringe injection and the reliability of a proven rotary valve. Depending on the matrix involved, this injection device employs either a commercially available four-port internal valve for liquid sampling or a six-port external valve for gas sampling, a modified removable needle used in standard liquid syringe, and an auxiliary flow stream that can be either mechanical or electronic flow controlled for solute transfer. For pressurized liquid, the device was found suitable of up to nC(16) hydrocarbon with no observable carry-over despite the injection device was operating at ambient temperature. A relative standard deviation of less than 2% (n=20) was obtained for hydrocarbon compounds ranging from nC(8) to nC(16). For gas injection, the device performed well even under difficult chromatographic conditions such as with a low column inlet pressure of less than 1 psig. A relative standard deviation of less than 0.5% (n=10) was obtained for reactive sulfur compounds such as alkyl mercaptans. The device can be operated manually or automated with pneumatic or electrical actuator, is platform neutral, and can be moved amongst instruments without hardware modification as well as implemented for on-line or in situ applications. In this paper, the utility of the device was also demonstrated with selected GC applications of industrial significance.

Universal and discriminative detection using a miniaturized pulsed discharge detector in comprehensive two-dimensional GC.

A miniaturized pulsed discharge detector (Mini-PDD) has been successfully demonstrated for comprehensive 2-D GC (GC x GC) analysis of pyrolysis gasoline and the pyrolysis GC x GC analysis of a polyethylene copolymer. The detector cell volume of the Mini-PDD is reduced to 25% of the Valco plug-in PDD D-3. An n-C11 peak width at base is 96 ms for the Mini-PDD, about 23% larger than a peak width of 78 ms detected by a flame ionization detector (FID). The Mini-PDD has sufficient response time for most GC x GC applications. When Mini-PDD is operated in helium photoionization mode (Mini He-PDD), it is a universal detector for both inorganic and organic compounds. This is especially useful when detection of water is needed in GC x GC applications. When krypton is doped in the helium discharge gas (Mini Kr-PDD), it can suppress signals of compounds having higher ionization potentials and enhance relative signal intensities of aromatic compounds. The determination of aliphatic to aromatic hydrocarbon ratios is essential to the operation of petroleum crackers. Comparison of the signal from two modes of the Mini-PDD is a simple and fast way to verify the location of aromatics in comprehensive 2-D gas chromatograms.

Modulation techniques and applications in comprehensive two-dimensional gas chromatography (GC x GC).

More than a decade after Phillips' first published work this article reviews recent developments in comprehensive two-dimensional gas chromatography (GC x GC). Special attention is devoted to the further development and diversity of modulation devices. These include heated sweepers, cryofocused modulators, and a variety of diaphragm valve-switching strategies. It is demonstrated that all modulation approaches can be very well suited to GC x GC, depending on the particular application. Diaphragm-valve modulation is very powerful for volatile organic compounds. Slotted heater and cryofocused modulation are preferred for samples that contain non-volatile components. Applications ranging from petroleum to environmental and biological samples are illustrated. Extension of the technique to GC x GC-mass spectrometry (MS) is also discussed and trends for future research activity are pointed out.