Gulf Coast Conference 2011

Many think that GC is an adult technology, but many improvements are still being worked on. For practical applications, that means that analysis can be done more accurately, faster, and more reliably by choosing optimal settings and by using the right products and conditions. We will touch here on the most recent developments at Restek for trace and normal sulfur analysis, then zoom in on light hydrocarbons, CFCs, and high temperature separations. We also will show several smart suggestions to help you to secure correctness of your data, looking at sample introduction, column installation/operation, and detector effects. Most challenges can be solved by analyzing the chromatogram. In this seminar, we will be using many chromatograms to help you recognize problems and be able to fix them.

Alumina PLOT columns have a long history of being used for the analysis of volatile hydrocarbons. Due to the highly selective retention mechanisms at work in Alumina PLOT columns, saturated and unsaturated hydrocarbons can be fully resolved in a variety of applications. To enhance the performance of Alumina PLOT columns when performing quantitative work at trace level concentrations, Alumina adsorbents must be deactivated with salts like KCl and Na2SO4. The practical separation behavior of Alumina PLOT columns is highly dependent on a number of factors. Alumina PLOT columns are susceptible to water contamination and may need periodic thermal conditioning to restore performance. Repeated cycling to high temperatures can alter the selectivity of the adsorbent material coated in Alumina PLOT columns. Instrument conditions can also strongly affect the separation characteristics of Alumina PLOT columns. Variations in carrier gas flow rate, initial oven temperatures, initial oven hold times, and oven ramp rates can significantly shift retention times and elution orders for volatile hydrocarbons. The type of salt used for deactivation and the concentration at which it is applied can also influence the response for active compounds like 1,2-butadiene and chlorofluorocarbons. This paper will investigate new Alumina PLOT column adsorbents with respect to thermal stability, inertness, and selective retention. Applications will be shown, illustrating their performance in the analysis of chlorofluorocarbons and difficult-to-analyze reactive hydrocarbons.

In 1990, the Oil Pollution Act (OPA) was promulgated under the direction of the National Oceanic and Atmospheric Administration (NOAA) following the Exxon Valdez oil spill in March of 1989. These regulations require a Natural Resource Damage Assessment (NRDA) following a release of oil into the nation’s waterways. Currently NOAA is conducting an NRDA to determine the impact of the Deepwater Horizon oil spill. There are several NRDA technical working groups (TWGs) assembled to determine: baseline conditions before the oil spill, impacts to plants and animals following the spill, and the current conditions of the marine ecosystem. The trustees are also evaluating impacts from the response to include use of dispersants. Aquatic toxicity of crude oil is critical to providing estimates of damage following a spill. Determinations of acute toxicity of crude oils require an understanding of the total composition of the source material. Measurements of the water-accommodated fractions (WAF) for semi-volatiles focus mostly on polycyclic aromatic hydrocarbons (PAHs). While this approach is effective in making chronic toxicity determinations, it falls short of measuring the initial exposure to the marine ecosystem. Less emphasis has been placed on the forensic chemistry of light distillates since the time of exposure to marine life is significantly less than middle-distillate products. Toxicity of crude oil WAFs varies with oil type and animal species tested. Results of GC/MS testing PAHs, BTEX, total volatile petroleum hydrocarbons (VPH), and total extractable petroleum hydrocarbons (EPH) found that the toxicity was greatest for PAHs and BTEX. This paper will address techniques for the analysis of crude oil by EPA Method 8260 purge-and-trap GC/MS to determine purging efficiencies of matrix including affects of dispersant compounds on crude recoveries and speciation of 8260 aromatics in three different sources of petroleum distillates.

On April 20, 2010, the offshore drilling rig Deepwater Horizon exploded and caught fire in the Gulf of Mexico near the Louisiana coast. The rig sank and, until capped, spewed almost 5,000,000 barrels of oil into the Gulf. Although chemical dispersants and containment booms were used to mitigate the leak, oil spread over a large area, and the event could be one of the biggest environmental and economical disasters ever in the United States. The impact includes sensitive wetlands with large bird and animal populations, the Gulf fishing industries, and tourism. As it regards commercial fishing, a large area of the Gulf was closed because of possible contamination of seafood from the oil. FDA has issued a protocol to reopen closed fishing waters that includes sensory and chemical testing of seafood (for polycyclic aromatic hydrocarbons, or PAHs, and their alkylated congeners). Unfortunately, the NOAA sample preparation method that the FDA proposes to use for chemical testing is extremely tedious and time-consuming, requires expensive pressurized fluid extraction and gel permeation chromatography equipment, and uses large volumes of environmentally unfriendly methylene chloride. Turnaround time for 30 samples is estimated to be 5 to 7 days employing up to 5 lab staff. An alternate approach is to use QuEChERS, the Quick – Easy – Cheap – Effective – Rugged – Safe extraction method that was invented for pesticides in fruits and vegetables. In this work, a QuEChERS approach was used to generate seafood sample extracts for GC- and GCxGC-TOFMS determination of PAHs, PCBs, and organochlorine pesticides. Numerous samples can be prepared in batch fashion for analysis in a very short period of time (approximately 2 hours) to allow increased throughput. Good recoveries were achieved for spiked fresh seafood, including shrimp, oysters, scallops, and crabs. A NIST SRM (Standard Reference Materials®) of mussel tissue also showed high recoveries with the QuEChERS approach. GCxGC-TOFMS was necessary for the complex mussel tissue sample and allowed for improved detection limits of PAHs.

It is commonly known in gas chromatography that many problems can be traced to the injection system (e.g., sample, syringe, inlet), so the injection system is a primary place to look for possible issues. This is a valid statement as 90% of “trouble” is related to injection conditions. One must also be aware that activity may be caused by other contributions. Especially if we look at non-symmetrical peaks, there are more important areas to look at. Not only can the columns used be overloaded or poorly deactivated, but the contribution of the detector also has a huge impact on peak shape and response. Here it is shown that flame tips can adsorb up to 90% of a component and cause tailing on polar as well as basic/acidic components. Though it looks as if columns are not performing, it’s the detector that is the problem.

Natural gas is a complex mixture of low molecular weight hydrocarbons, inert gases, and other impurities including a variety of sulfur-containing compounds. Raw natural gas containing significant amounts of hydrogen sulfide and other organic sulfurs is typically processed to remove these compounds. Odorants are added to the final product to meet safety regulations. Testing of natural gas in its raw and refined states requires the use of chromatography systems that supply sufficient resolution of the hydrocarbons normally found in natural gas from any of the sulfur contaminants or odorants. Wall coated open tubular (WCOT) columns coated with methyl silicone stationary phases have been successfully used for the separation of low molecular weight hydrocarbons. Analyzing low molecular weight sulfur compounds can also be performed on the thick-film Rtx®-1 columns. Peak shape and sensitivity for sulfur gases is highly influenced by the inertness of the column and proper deactivation is required. The thick-film Rtx®-1 column is the best column for sulfur speciation in natural gas. Besides the Rtx®-1 column, we also looked at the application of porous polymers for volatile and heavier sulfur compounds. The separation mechanism for PLOT columns is significantly different than that observed for WCOT columns. The unique selectivity of different porous polymers can influence relative elution order of sulfur-containing compounds versus low molecular weight hydrocarbons. A comparison illustrating elution order patterns and relative inertness of PLOT columns versus WCOT columns for sulfur analysis is shown. Very interesting results were obtained for the Rt®-U-BOND porous polymer. This adsorbent is highly inert, resulting in near perfect H2S and COS peaks. Also, the position of both peaks is very interesting as they elute far away from propane and ethane. On the Rt®-U-BOND porous polymer, the propylene elutes together with propane, and ethylene elutes before the ethane. This selectivity, together with the unique inertness, makes this column a very good candidate for a single-column solution to measure trace sulfur gases in ethylene AND propylene.

To analyze basic compounds at nanogram levels using gas chromatography, a basic surface modification is often required to reduce the impact of the acidic fused silica. Additionally, to separate volatile components, retention and efficiency at lower temperatures is required. Base-modified polyethylene glycols have been available for some time, but they are not very stable and they lose efficiency when used below 60 °C. Siloxanes are more challenging for base modification as the stability of the siloxane polymer should not be compromised. There are some solutions available, but there is room for improvement as present phase technologies are considered not optimal, which translates into short column lifetimes and non-reproducibility in amine response. An advanced base deactivation technology where a new surface deactivation of fused silica was introduced has been made available several years ago by Restek Corporation. Such columns were commercialized under the names Rtx®-5 Amine and Rtx®-35 Amine columns. A similar approach was taken for designing a more stable column for volatile amines, not only by increasing the film thickness, but also by creating a direct link with the (base) surface deactivation. Additionally, the number of cross-links (bridges) between polymer chains was optimized to make the polymer keep efficiency as low as temperatures of 40 ºC. The higher degree of cross-linking was incorporated to make the column more resistant for amine/water mixtures. The column, named the Rtx®-Volatile Amine column, was tested with a series of amine samples and water matrices to demonstrate performance. In this poster, several applications will be presented and discussed.

In light hydrocarbon analysis, the separation and detection of traces of polar hydrocarbons like acetylene, propadiene, and methylacetylene is very important. Using commercial alumina columns with KCl or Na2SO4 deactivation often results in low response of polar hydrocarbons. Additionally, challenges are observed in response-in time stability. Solutions have been proposed to maximize response for components like methylacetylene and propadiene using alumina columns that were specially deactivated. Operating such columns showed still several challenges: Due to different deactivations, the retention and loadability of such alumina columns have been drastically reduced. A new alumina deactivation technology was developed that combined the high response for polar hydrocarbon with maintaining the loadability. This allows the high response for components like methylacetylene, acetylene, and propadiene also to be used for impurity analysis as well as TCD-type applications. Such columns also showed excellent stability of response-in time, which was superior to existing solutions. Additionally, it was observed that such alumina columns could be used up to 250 °C, extending the Tmax by 50 °C. This allows higher hydrocarbon elution, faster stabilization, and also widens application scope of any GC where multiple columns are used. In this poster, the data is presented showing the improvements made in this important application field.