Rapidly Analyze a Wide Range of Glycol Ethers by GC-MS Using the New Rxi-1301Sil MS Column
Chromatographic conditions were developed for a fast GC-MS glycol ether analysis on the Rxi-1301Sil MS column. This cyano-based thin film column provides better resolution and faster run times than the thick film cyanopropylphenyl-type columns commonly used for speciation of the glycol ethers. The glycol ethers are high production volume industrial chemicals that often occur as complex mixtures of isomers. The Rxi-1301Sil MS column is uniquely matched for the separation of these isomers while still producing narrow and symmetric peaks for the low molecular weight ethylene glycol ethers.
The Glycol Ethers
Glycol ethers are a broad class of commodity chemicals that find use in numerous applications. They are commonly used as ingredients in paints and coatings, cleaning products, and personal care products. This class of compounds is characterized by repeating ethylene (E-series) or propylene (P-series) glycol units terminated on one or both ends by alkyl ethers, phenyl ethers, or acetates (Figure 1). Glycol ethers are produced and used in enormous quantities, primarily in Western Europe, China, and the United States.
Their unique amphiphilic structure gives the glycol ethers favorable properties such as low volatility, strong solvent strength, high water solubility, and the ability to serve as coupling agents that promote the miscibility of aqueous and organic phases. These properties make glycol ethers a popular alternative to traditional oxygenated solvents such as ketones, ethers, and alcohols.
Toxicological studies indicate that the lower molecular weight E-series glycol ethers, such as ethylene glycol methyl ether (EGME), ethylene glycol ethyl ether (EGEE), and their acetates, may pose a more serious health hazard to humans and animals than their higher molecular weight counterparts.
The European Union and Canada have both adopted regulations limiting the use of glycol ethers in consumer products. In the EU, several of the glycol ethers are banned entirely while others are regulated to a specific concentration level. In 2010, Environment Canada (EC) published a reference method  for analysis of glycol ethers in consumer products including cleaners, degreasers, and coatings. This method addresses the most commonly used glycol ethers and describes an analytical approach for achieving the reporting limits set by Canadian regulation.
Glycol Ethers of Regulatory Importance are Well Resolved in Minimal Time
The Environment Canada reference method recommends a standard 624-type column in a 60 m x 0.32 mm x 1.80 µm format and a temperature program that spans 30 minutes for glycol ether analysis. The Rxi-1301Sil MS column has very similar selectivity to that of 624-type columns as both are based on cyanopropylphenyl stationary phases; however, the thinner film and higher thermal stability of the Rxi-1301Sil MS column provide good separations in a fraction of the time.
The Rxi-1301Sil MS column in a 30 m x 0.25 mm x 0.25 µm format with optimized run conditions results in an analysis time of just 8 minutes. Using a fast temperature program, baseline resolution of the DPGME isomer group is possible and is comparable to, if not better than, the original method (Figure 2). The 0.25 µm film results in higher efficiency, narrow peaks, and, in turn, improved resolution with less retention. The Rxi-1301Sil MS column also has a temperature limit of 320 °C, allowing for a high-temperature isothermal hold to remove any low-volatility sample components from the column. If these low-volatility contaminants are not removed during the analytical run they may elute in subsequent analyses as broad “ghost” peaks, possibly interfering with analytes of interest.
Faster run times can also be achieved using narrow-bore 30 meter 624-type columns with the same phase ratio, such as a 30 m x 0.25 mm x 1.4 µm format, which will maintain the same elution order. However, as shown in Figures 3 and 4, chromatographic resolution is reduced in exchange for speed in this situation, and coelution of the DPGME III isomer with DEGEE occurs. Poor resolution of the TPGME isomer group is also apparent. In contrast to 624-type columns, the Rxi-1301Sil MS column provides better resolution of critical compounds for glycol ether analysis in a much faster analysis time.
Chromatograms were collected using a 200 amu scan range beginning at 20 amu in order to capture the low mass fragments generated by electron ionization of the glycol ethers. The glycol units fragment readily and even the higher molecular weight P-series compounds do not produce abundant ions greater than 150 amu. A high scan speed was employed to achieve enough points across the narrow peaks.
Rapid Analysis is Achieved Using a Thin Film Column Alternative
The Rxi-1301Sil MS column is based on the same stationary phase chemistry as the Rxi-624Sil MS column, but it is made in a thin film format (0.25 µm). This combination of selectivity and film thickness provides an ideal solution for fast GC-MS analysis of a wide range of glycol ethers, making the Rxi-1301Sil MS column ideal for the analysis of comprehensive lists of glycol ether compounds.
Figure 5 shows the optimized separation of 24 glycol ethers and two internal standards on the Rxi-1301Sil MS column. Perfluorinated glycol ethers, such as fluorinated triethylene glycol methyl ether (perfluoro-TEGME), are commercially available and represent candidates for functionally similar surrogates or internal standards for applications where isotope-labeled standards are not practical or are unnecessary.
While column bleed can be a concern with some stationary phases, the Rxi-1301Sil MS column can be used with confidence. At the maximum method temperature of 300 °C, column bleed is minimal and does not interfere with mass spectral compound identification. Low column bleed is critical to the operation of sensitive mass selective detectors and allows full scan spectra to be collected without interference from bleed ions.
The new Rxi-1301Sil MS column from Restek provides a significant opportunity to improve glycol ether analysis. While 624-type columns are often used for this work, the Rxi-1301Sil MS column allow separations to be achieved in much faster analysis times. Glycol ethers of regulatory concern can be analyzed in just 8 minutes while still achieving good separations of key isomers. Labs interested in reducing analysis times for current methods based on 624-type columns should consider adoption of the Rxi-1301Sil MS column into their testing programs. The Rxi-1301Sil MS column offers high thermal stability and very low bleed, ensuring optimal performance for glycol ether analysis.