Agilent’s GC WAX Column Technology Developments Greatly Advance Performance of Polar Compound Analyses

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Globally, Agilent is the world’s leading developer and vendor of fused-silica capillary columns for gas chromatography. These columns were invented in 1978 by a team headed by Ray Dandeneau, then working in Hewlett-Packard’s Chemical Analysis Group, as described by Mike McMullen. The interview below is an example of how Agilent continues to work to improve specific features of products to maintain technical and market leadership.

Gary Lee was product marketing lead involved in a several-year program focused on improving Agilent’s WAX columns. Now a product specialist in Northern California, Gary has decades of experience spanning many roles, most notably focused on fused-silica capillaries.

RLS: What are WAX columns used for?

GL: WAX columns have been very important for laboratories around the world since the early days of gas chromatography. The polyethylene glycol (PEG) stationary phase is highly polar with separation characteristics driven on the basis of hydrogen bonding sites, which makes them useful for a wide range of polar compound applications for quality control and raw material analyses in the food and flavors, petroleum, pharmaceutical, and industrial chemical industries.

RLS: What are the main performance metrics?

GL: There are three main column performance attributes for WAX columns that are key for successful GC analyses: stationary phase stability, chemical inertness, and column-to-column reproducibility.

1. Stability: Low bleed, stable retention, longevity. Lifetime is related to bleed, since high bleed shows up by loss of stationary phase, retention time shifting, and detector fouling. Nonvolatile matrix material can also foul the column over time, resulting in shorter lifetime and increased frequency of inlet maintenance.
2. Chemical performance for polar compounds: Column inertness is especially important to provide sharp peaks for improved detection limits. Most WAX column analyses are for applications with matrices containing a wide range of polar compound functionalities such as acids, aldehydes, amines, alcohols, glycols, etc.
3. Column-to-column reproducibility: Reliably consistent performance is of utmost importance, particularly with labs having long-established methods and compound libraries based on a particular WAX column configuration.

RLS: What is the state-of-the-art today?

GL: Since 2012, Agilent has had a dedicated R&D focus on WAX column research and development that has resulted with the introduction of three new WAX phases as well as performance improvements on classic WAX columns in the Agilent J&W columns portfolio. The latest new product is DB-HeavyWAX, which has a T_max of 280 °C isothermal/290 °C temperature programmed.

For years, chromatographers have asked for higher-temperature-range WAX columns to enable extended range of analysis to address carryover, extended analysis times, short column life, and compatibility for multidimensional analyses. The added 30 °C in T_max of the DB-HeavyWAX extends the application range that will be useful for any lab using WAX columns for its work—GC and GC/MS. Carryover or extended analysis times can be significantly reduced while column longevity is increased. A few examples include:

• Cold-pressed citrus essential oil samples typically have higher boiling compounds not present in steam distilled samples. DB-HeavyWAX provides extended analysis and eliminates carryover of the heavier compounds.
• In the hydrocarbon processing industry, analysis of pyrolysis gasoline can be challenging due to the presence of higher-molecular-weight aromatic compounds, and similarly, extended analysis without ghost peaks (or baseline lumps) associated with carryover of the heavier aromatics.
• Analysis of fatty acid methyl esters (FAMES) in jet fuel per Energy Institute Method IP 585 (GCMS) is improved with ultralow bleed for improved response, especially with late-eluting compounds and less column bleed contamination into the mass detector, which reduces instrument downtime with less MS source cleaning frequency.

RLS: These are significant. Can you explain the chemistry responsible for HeavyWAX?

GL: Much of this is proprietary so I cannot provide details, but I’ll say that with our dedicated pure research emphasis on WAX GC column phases, our scientists and production team developed a completely new and novel approach with the phase design, manufacturing optimization, and scaleup.

RLS: The DB-WAX Ultra Inert capillaries are also quite interesting. What can you tell us about them and when to use them?

GL: The R&D emphasis with the DB-WAX Ultra Inert (UI) was focused on improved peak shape for analysis of challenging polar compounds, with the highest level of column-to-column inertness performance and thermal stability.

Chromatographers and analysts, particularly in the food and flavors industry, have been vocal about the need for WAX column technology improvement. Our benchmark studies indicated that WAX column inertness performance for all the top brands of GC columns was limited, especially for challenging compounds important to the food and flavors industry, such as decanal, proprionic acid, 2-ethylhexanoic acid, and ethyl maltol.

As with all UI column development efforts, this was a considerable project involving a multidisciplined approach to design and engineer a clearly differentiated level of inertness performance. Every DB-WAX UI column is tested with these specific compounds included in the mix, which eliminates the need to prescreen columns. With the same selectivity (retention index) specifications of the popular DB-WAX, the DB-WAX UI is an easy upgrade for laboratories that have developed extensive compound libraries based on DB-WAX. The DB-WAX Ultra Inert is recommended to all labs looking to improve results for their most difficult polar compound analyses.

RLS: I’m intrigued with the DB-FATWAX. How was it designed? What are its features and enabled applications?

GL: The DB-FATWAX Ultra Inert is an extension of our WAX column development work and is designed specifically for reliable separation of FAMES, fatty acid ethyl esters (FAEEs), and free fatty acids. DB-FATWAX UI columns are individually tested with a FAME mixture to ensure reproducible FAME equivalent chain length (ECL) values; proper identification of important FAMES such as EPA, DPA, and DHA; and column-to-column separation reproducibility of key pairs of FAMES. For labs running analyses of short- and medium-chain FAMES and polyunsaturated fatty acid (PUFA) samples, the Ultra Inert performance and thermal stability will provide enhanced longevity.

RLS: Is the work continuing?

GL: Much has been learned from our ongoing R&D and production development engineering that feeds constant improvement initiatives. The team has improved the family of “classic” WAX columns. For example, INNOWAX and CP-Wax 52 CB columns have tighter specifications for inertness performance and QC testing while maintaining stationary phase selectivity. Another example is from the development of the DB-FATWAX columns, where the broader discussion about fast cis/trans FAMES analysis resulted in the introduction of DB-FastFAME columns.

There is definitely more to come from the Agilent J&W GC columns team.

Robert L. Stevenson, Ph.D., is Editor Emeritus, American Laboratory/Labcompare; e-mail: [email protected]