Group-Type Analysis of Oxygenated Compounds with a Silica Gel Porous Layer Open Tubular Column and Comprehensive Two-Dimensional Supercritical Fluid and Gas Chromatography

Dual-Column Stopped-Flow GC Method for Quantification of Permanent Gases, Water, and Organic Acids from a Single Injection

Analysis of permanent gases and organic acids is typically performed with separate methods due to challenges in achieving sufficient resolution when using GC columns that are chemically compatible with acids. We developed a method to analyze samples containing high levels of water, organic acids, oxygenates, and permanent gases (CO, CO2, and C2H4) using a single injection. Resolution is achieved using two columns: (1) an HP-FFAP column resistant to water and acids, which separates compounds based on hydrogen-bonding affinity, and (2) a GS-CarbonPLOT column capable of separating permanent gases. We employed a column isolation methodology using rotary valves to allow a heart cut of permanent gases, which coelute off the HP-FFAP column, to be trapped on the CarbonPLOT column. After separation and analysis of water, organic acids, and oxygenates via the HP-FFAP column, flow is resumed on the CarbonPLOT column, and the permanent gases are separated independently. By utilizing the unique combination of columns and the stopped-flow sequence, we achieved separation and quantification of the wide array of compounds occurring during lactic acid dehydration to acrylic acid from a single injection without the need for a sophisticated flow modulator or multiple GCs or detector arrays. This GC apparatus serves as an economical in-line analysis method for our catalytic studies and is applicable to a wide array of samples relevant to biobased fuels and chemicals.

A high-repetition-rate, fast temperature-programmed gas chromatograph and its online coupling to a supercritical fluid chromatograph (SFC × GC)

We present a fast gas chromatographic system that can be used as a second dimension in comprehensive two-dimensional (supercritical fluid × gas) chromatography (SFC × GC). The temperature of the short (1 m long) capillary column is controlled by a resistively heated coaxial stainless-steel tube. The electrical resistance and, therefore, temperature of the stainless-steel tube are measured by continuous monitoring of the current/voltage ratio. Highly repeatable heating rates of up to 2100 °C min^-1 (35 °C s^-1) are obtained, which should be high enough for the most demanding fast chromatograms. To reduce the cooling time between temperature programs, the column is cooled by injecting evaporating carbon dioxide into the space between the coaxial heater and the column. This gives cooling rates of 5100 °C min^-1 (85 °C s^-1), which allows quick succession of temperature programs. More repeatable heating profiles with stable GC retention times together with faster cooling are significant improvements on previous SFC × GC systems. Cycle times of four gas chromatograms per minute could readily be achieved, which allows efficient coupling to high-resolution stop-flow SFC in the first dimension. We demonstrate the fast chromatograph by separating fatty acid methyl esters, yielding information that would be useful in the food and biodiesel industries.

The pre-separation of oxygen containing compounds in oxidised heavy paraffinic fractions and their identification by GC-MS with supersonic molecular beams

The heavy petroleum fractions produced during refining processes need to be upgraded to useable products to increase their value. Hydrogenated heavy paraffinic fractions can be oxidised to produce high value products that contain a variety of oxygenates. These heavy oxygenated paraffinic fractions need to be characterised to enable the control of oxidation processes and to understand product properties. The accurate identification of the oxygenates present in these fractions by electron ionisation (EI) mass spectrometry is challenging due to the complexity of these heavy fractions. Adding to this challenge is the limited applicability of EI mass spectral libraries due to the absence of molecular ions from the EI mass spectra of many oxygenates. The separation of oxygenates from the complex hydrocarbon matrix prior to high temperature GC-MS (HT-GC-MS) analysis reduces the complexity of these fractions and assists in the accurate identification of these oxygenates. Solid phase extraction (SPE) and supercritical fluid chromatography (SFC) were employed as prefractionation techniques. GC-MS with supersonic molecular beams (SMBs) (also named GC-MS with cold-EI) utilises a SMB interface with which EI is done with vibrationally cold sample compounds in a fly-through ion source (cold-EI) resulting in a substantial increase in the molecular ion signal intensity in the mass spectrum. This greatly enhances the accurate identification of the oxygenates in these fractions. This study investigated the ionisation behaviour of oxygenated compounds using cold-EI. The prefractionation by SPE and SFC and the subsequent analysis with GC-MS with cold-EI were applied to an oxygenated heavy paraffinic fraction.