EAS 2011

The performance of a gas chromatograph (GC), a sophisticated piece of expensive analytical instrumentation, can be compromised by a small, low-cost piece of glass housed in the GC’s inlet. Though small and relatively inexpensive, the glass inlet liner plays a crucial role in the complex process of sample vaporization that occurs inside the GC. It can therefore define data’s accuracy, precision, or representation of the sample. So, it is important to have the right inlet liner. However, there are so many to choose from. Part 1 of this talk explored the differences that exist in the myriad split liners for split applications. Part 2 will discuss the effect of liner geometry and packing material on the different demands of splitless and direct injection methods. The presentation will focus on a quantitative demonstration of the effect of varying liner geometries on the analysis of samples spanning a relatively wide range of molecular weights. The interaction between splitless and direct injection method parameters and liner configuration will be discussed. Additionally, the role of wool or other packing materials will be discussed, and we will challenge the belief that relatively slow flow rates during splitless injections eliminate the need for a packing material. Finally, a comparison will be made between the degree of sample transfer during properly configured splitless injections and direct injections. Liner deactivation will specifically not be discussed in this presentation in an attempt to provide information that spans liner manufacturer, since many of the same or similar geometries are offered by a variety of vendors, but each vendor’s deactivation is likely to be different. The best deactivation can still be rendered moot if the wrong liner configuration is chosen for a particular task.

Previous work has suggested that the selection of “orthogonal” columns can be predicted using values determined from the hydrophobic-subtraction model. This presentation will briefly review the model and calculations while relating them to phase selectivity in reversed-phase liquid separations. Empirical results of the hydrophobic-subtraction model will be used in selecting appropriate stationary phases for specific phase-solute interactions, ultimately defining a simplified process for column selection. Additionally, selected terms and their respective contributions to solute retention will be explored for substituted alkyl and non-alkyl phases. This presentation will demonstrate how knowledge of reversed-phase liquid chromatography (RPLC) column phases and phase-solute interactions can aid in choosing the most selective columns for column screening, solute confirmation, and methods development.

Splitless injections are typically employed for EPA Method 8270, Semivolatile Organic Compounds by Gas Chromatography/Mass Spectrometry (GC/MS). A splitless injection provides a greater transfer of analytes onto the head of the column until the split vent is finally opened after a set period of time. While this injection technique is preferred for trace level analyses, it also has its disadvantages. The flow through the injection port is much slower with a splitless injection, which can result in degradation of thermally labile compounds and adsorption of active analytes such as 2,4-dinitrophenol. Peak widths are also typically broader with a splitless injection due to the comparatively slow transfer of analytes onto the head of the column without employing any “focusing” techniques.

Increasing the initial oven temperature was the first goal of this work. By starting at a higher oven temperature, analysis time and instrument cycle time are reduced. The split injection allows a higher initial oven temperature because of the sharper initial injection bands produced by split injection. The second goal was to evaluate additional benefits of employing a split injection. A repeatability study was performed using both split and splitless optimized conditions. Increased injection–to–injection repeatability was achieved by using a 10:1 split injection onto a split liner packed with semivolatiles wool. A 6-point calibration curve from 5 µg/mL to 160 µg/mL was evaluated for instrument sensitivity, linearity, and peak shape. Method ruggedness was evaluated by comparing both injection techniques with EPA Method 8270 generated extracts. This evaluation included continuing calibration checks and frequency of liner and column maintenance.

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.

Analysis of organochlorine pesticides, PCBs, and phenoxy-acid herbicides has long been a routine assay in the environmental sector. Although many of these agents were phased out decades ago, they can still be found in the environment. Environmental laboratories are expected to rapidly analyze extracts of samples with very complicated sample matrices without sacrificing target compound identification. There is also a constant desire for even faster and faster analysis times to help increase sample throughput and, thereby, increase laboratory productivity. Fast GC is a good solution to this need; however, the reduced internal diameter and thinner phase coatings associated with the fast GC movement have been a deterrent to the environmental sector due to concerns of the column’s ability to handle the oftentimes harsh sample matrices encountered in environmental samples.

These analyses require a gas chromatographic stationary phase with proper selectivity and high thermal stability that still maintains a fair degree of column capacity for sample matrix. A specially tuned column pair with the configuration of 30 m x 0.32 mm ID, using a 5-meter 0.32mm ID guard column with a Y-connector, allows one to achieve a greatly reduced analysis time without the repercussions usually encountered when using small bore columns with difficult samples. This poster will focus on the use of two such unique stationary phases in a standard 0.32 mm ID to perform a variety of EPA methods, including 8081, 8151, 505, and others.

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, including the 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 semivolatiles 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 effects of dispersant compounds on crude recoveries and speciation of 8260 aromatics in three different sources of petroleum distillates.

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 methyl silicone WCOT columns, but peak shape and sensitivity can be highly influenced by the inertness of the column. A comparison of three different column deactivation strategies was evaluated for their impact on sulfur separation and low level analysis.

Porous layer open tubular (PLOT) columns have also been used for light hydrocarbon analysis. 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 will be shown.

Food pesticide residue monitoring has traditionally been performed using gas chromatography (GC), but there is increasing use of liquid chromatography (LC) with tandem mass spectrometry (MS/MS). LC is favored for polar, less thermally stable, less volatile compounds. GC/MS is preferred for volatile, thermally stable species and pesticides that do not ionize well in electrospray or atmospheric pressure chemical ionization LC sources. With MS, complete chromatographic resolution of compounds is not essential, as selected ions or selected reaction monitoring (SRM) transitions are used for pesticide identification and quantification. However, data quality can be improved through better retention and separation of components, especially for structurally similar pesticides. In GC, this better separation can come from comprehensive two-dimensional GC (GCxGC), an approach involving two separations on an orthogonal column set in one analytical run. A fast time-of-flight (TOF) MS is records data from the 100 ms wide peaks produced from GCxGC.

In this work, the QuEChERS extraction approach was used for red bell pepper, cucumber, lemon, raisins, spinach, hazelnuts, and red grapes with subsequent pesticide determinations by LC/MS/MS and GCxGC-TOFMS. Samples spiked with carbamate, organophosphorus, aniline, conazole, macrocyclic lactone, phenylurea, benzoylphenylurea, and strobilurin pesticides at 10 ppb and then QuEChERS extracted showed good recoveries. While GCxGC-TOFMS was limited in the number of pesticides determined due to the compound classes involved, versus LC/MS/MS, selectivity and sensitivity was enhanced by GCxGC. The full mass-range capability of TOFMS allowed non-target compound identification (e.g., in the pepper: endosulfans, endosulfan sulfate, nicotine, and permethrins). LC/MS/MS was extremely sensitive and selective for the targeted compounds. Dilution of QuEChERS extracts prior to LC/MS/MS may allow analysts to avoid extract cleanups.

Blumberg said, “…in spite of more than 15 years of claims… of GCxGC to resolve an overwhelmingly larger number of peaks than 1D-GC… the peak capacity of currently practiced GCxGC does not generally exceed the peak capacity attainable from 1D-GC…”. Blumberg’s point was 1D column operation is suboptimal to increase peak widths for modulation.

We used 120 m 1D columns that “efficiently” generate 15 sec peaks and matched 2D accordingly for 3 modulation cycles per 1D peak to analyze diesel, biodiesel, jet fuel, fog oil, and gasoline. We observed true peak capacity increases versus 1D separations on longer columns.

Since synthetic cannabinoids are relatively new, limited research has been performed to determine the exact urine metabolite profile for any given parent compound. Adding to the complexity of the analysis, many of the metabolites for a given parent are mono-hydroxylated isomers of that parent compound. These metabolites are isobaric compounds that share a very similar fragmentation pattern. These isomers are sometimes analyzed as one group, with little to no chromatographic resolution between the isomers; however, this makes identification of specific metabolites impossible. The objective of this project was to determine the significant metabolites of JWH-018 and JWH-073 in authentic samples and to develop an analysis method for these specific metabolites.

The method presented here involves resolving 12 metabolites for JWH-018 and JWH-073. This method was used along with a straightforward SPE extraction to identify major metabolites in authentic samples. The metabolites identified in the authentic samples were the carboxylic acid metabolites of JWH-018 and the 5-hydroxypentyl metabolite of JWH-018. After the significant metabolites were identified, a new LC method was developed specific to those metabolites, cutting total analysis time from 8.5 minutes to 5 minutes. Samples were then re-analyzed with this faster method. The levels of JWH-018 5-hydroxypentyl metabolite in the authentic samples ranged from 1.9 ng/mL to 86.7 ng/mL, and the levels of JWH-018 N-pentanoic acid metabolite ranged from less than 1 ng/mL to greater than 20 ng/mL.

This poster will outline the extraction and analysis method for the determination of synthetic cannabinoid metabolites in urine.

In the past few years, incense blends such as “K2” or “spice” have gained in popularity. Although these incense blends are not marketed for human consumption, they contain synthetic cannabinoid compounds, that, when smoked, produce a cannabis-like high.

In March 2011, the DEA scheduled JWH-018 and JWH-073, along with other synthetic cannabinoids on an emergency basis. Although these compounds are federally regulated, there are dozens of synthetic cannabinoid compounds available that are not yet regulated. In response to the scheduling of JWH-018 and JWH-073, new “ban-compliant” herbal incense blends are now being marketed.

LC/MS/MS and GC/MS methods were previously developed to determine a range of synthetic cannabinoids in herbal incense. Analysis of incense blends before the ban went into effect showed significant content of JWH-018, JWH-073, JWH-200, and CP 47, 497. These methods were developed to be adaptable for new synthetic cannabinoids as they come on the market. The use of LC/MS/MS allows for fast confirmation of the presence of a synthetic cannabinoid, as well as some structural information. GC/MS aids in structural elucidation of new compounds, due to the larger number of fragments generated from GC/MS ionization.

Several new “ban-compliant” incense blends were analyzed using the previously developed method to determine synthetic cannabinoid content for each blend. This poster will outline both the LC/MS/MS and the GC/MS methods used to determine synthetic cannabinoids in herbal incense blends. Quantitative analytical results for recent ban-compliant blends, as well as pre-ban blends will be presented.