A Vacuum Ultraviolet Absorption Array Spectrometer as a Selective Detector for Comprehensive Two-Dimensional Gas Chromatography: Concept and First Results

Fast and selective detectors are very interesting for comprehensive two-dimensional gas chromatography (GC × GC). This is particularly true if the detector system can provide additional spectroscopic information on the compound structure and/or functionality. Other than mass spectrometry (MS), only optical spectroscopic detectors are able to provide selective spectral information. However, until present the application of optical spectroscopy technologies as universal detectors for GC × GC has been restricted mainly due to physical limitations such as insufficient acquisition speed or high detection limits. A recently developed simultaneous-detection spectrometer working in the vacuum ultraviolet (VUV) region of 125–240 nm overcomes these limitations and meets all the criteria of a universal detector for GC × GC. Peak shape and chromatographic resolution is preserved and unique spectral information, complementary to mass spectrometry data, is gained. The power of this detector is quickly recognized as it has the ability to discriminate between isomeric compounds or difficult to separate structurally related isobaric species; thus, it provides additional selectivity. A further promising feature of this detector is the data analysis concept of spectral filtering, which is accomplished by targeting special electronic transitions that allows for a fast screening of GC × GC chromatograms for designated compound classes

Dual-Stage Consumable-Free Thermal Modulator for the Hyphenation of Thermal Analysis, Gas Chromatography, and Mass Spectrometry

The design of the so-called “Peltier modulator” is presented. It is a new dual-stage consumable-free thermal modulator for thermal analysis-gas chromatography-mass spectrometry (TA-GC-MS). It requires only electrical power for operation as it facilitates thermo-electric coolers instead of cryogenics for trapping and resistive on-column heating for reinjection. Trapping and desorption temperatures as well as modulation cycles are freely adjustable. The stationary phase for the trapping region can be selected to suit the specific application, since common fused silica capillary is used. The Peltier modulator’s performance is demonstrated with a broad range of different standard substances and with heavy crude oil as a complex real life sample. Successful modulation from <i>n</i>-pentane to pyrene (boiling points = 36/394 °C) is presented. The produced peaks show the narrowest bandwidths ever reported for a consumable-free thermal modulator, i.e., 12.8 ± 1.2 ms for <i>n</i>-pentadecane. The Peltier modulator is rugged, cost-effective, requires low maintenance, and decreases security issues significantly, compared to commercial available solutions using liquid N₂/CO₂

Optically Heated Ultra-Fast-Cycling Gas Chromatography Module for Separation of Direct Sampling and Online Monitoring Applications

This work describes an ultrafast-cycling gas chromatography module (fast-GC module) for direct-sampling gas chromatography/mass spectrometry (GC-MS). The sample can be introduced into the fast-GC module using a common GC injector or any GC × GC modulator. The new fast-GC module offers the possibility to conduct a complete temperature cycle within 30 s. Its thermal mass is minimized by using a specially developed home-built fused silica capillary column stack and a halogen lamp for heat generation, both placed inside a gold-coated quartz glass cylinder. A high airflow blower enables rapid cooling. The new device is highly flexible concerning the used separation column, the applied temperature program, and the integration into existing systems. An application of the fast-GC module is shown in this work by thermal analysis coupled to gas chromatography-mass spectrometry (TA-GC-MS). The continuously evolving gases of the TA are modulated by a liquid CO₂ modulator. Because of the rapid cycling of the fast-GC module, it is possible to obtain the best separation while maintaining the online character of the TA. Restrictions in separation and retention time shifting, known from isothermal and normal ramped fast-GC systems, are overcome

Single Photon Ionization Orthogonal Acceleration Time-of-Flight Mass Spectrometry and Resonance Enhanced Multiphoton Ionization Time-of-Flight Mass Spectrometry for Evolved Gas Analysis in Thermogravimetry: Comparative Analysis of Crude Oils

Coupling thermal analysis (TA) with a subsequent analytical method in order to investigate evolved gaseous products from the thermal analysis is a well established method. A popular practice to analyze the gaseous products evolving from thermal analysis is mass spectrometry using electron impact ionization (EI).(1-4) As the kinetic energy of the electrons thereby is typically far beyond the ionization energies of the assayed samples, the electron impact effects fragmentation particularly of organic compounds, hampering the correlation of the ion signals to the gaseous compounds. This applies for complex mixtures in particular. Fragmentation can be reduced using so-called soft ionization techniques. In the course of the presented setup, single photon ionization (SPI) using electron beam pumped excimer lamps (EBEL) emitting vacuum ultraviolet (VUV) light (lambda = 126 nm) is employed. For the instrumentation, a TA system has been coupled to an EBEL-SPI-oaTOFMS (oaTOFMS: orthogonal acceleration time-of-flight mass spectrometry) system using a heated transfer capillary in order to detect semivolatile organic substances from the gas flow of a thermobalance with high temporal resolution. Presented measurements focus on crude oils of different origins. In-depth analysis demonstrates that it is possible to tell apart different crude oil samples on the basis of temperature resolved mass spectra gained from the described setup. TA allows for the assay of crude oils without sample preparation via a distillation process which precedes the thermal decomposition of nonvolatile oil components, i.e., resins and asphaltenes. The gases that evolve during thermal analysis are a complex mixture of organic compounds. These can be analyzed without losing molecular information using mass spectrometry with a soft ionization technique, such as SPI