Analysis of Solvents in Industrial Atmospheres by Capillary GC

Reporter EU Volume 14

Similar structures and boiling points among airborne solvents monitored in the workplace often require two GC columns that offer differing selectivities to separate and identify the solvents collected. The highly polar SUPELCOWAX 10 capillary column resolves many industrial solvents based on polarity. In contrast, the nonpolar PTE-5 capillary column resolves solvents by boiling point. The shifts in retention times resulting from the complementary separation mechanisms of the two columns can aid analysts in identifying and quantifying solvents in complex mixtures.

OSHA regulations require the monitoring of solvent concentrations in industrial workplace atmospheres to minimize health risks to workers. The OSHA-specified procedures normally use adsorbent sampling tubes to collect and concentrate the analytes. The analytes are solventdesorbed from the tube and analyzed using gas chromatography. Similar structures and boiling points among the solvents often require two GC columns that offer differing separation mechanisms or selectivities to separate and identify the solvents collected.

Some analysts split the sample injection to the two columns to allow simultaneous detection and analysis with two detectors. This technique can be used when a client of an environmental lab requests a complete analysis of all possible solvents present on the adsorbent tube. Other analysts use one column, confirming the analysis on a second column only when coelutions are suspected, based on the known solvent use at an industrial site.

SUPELCOWAX 10 and PTETM-5 capillary columns provide complementary separations of solvent mixtures. The SUPELCOWAX 10 capillary column offers a highly polar, bonded phase that resolves many industrial solvents based on polarity (Figure A). The PTE- capillary column has a nonpolar, poly(5% diphenyl/95% dimethylsiloxane) phase that resolves solvents approximately by boiling point (Figure B, Table 1). If you know the boiling point of a compound, you can use the chromatogram to estimate its retention time on a PTE-5 column. (Some polar compounds may elute out of boiling point order due to their interaction with the phase.)


Figure A. Industrial Solvents on a SUPELCOWAX 10 Column (25301-U)


Figure B. Industrial Solvents on a SUPELCOWAX 10 Column (24159)


Table 1. Elution Order Comparison

The SUPELCOWAX 10 column provides greater retention of extremely polar compounds (e.g., alcohols) compared to the PTE- column, as shown by the methanol shift (peak 11). Polar compounds, which can tail or be poorly resolved on other phases, are better resolved and display better peak symmetry on the SUPELCOWAX 10 column. The SUPELCOWAX 10 column also provides baseline separation of the o-, p-, and mxylenes, and nearly baseline separation of the p- and m-cresols. We recommend the combined use of the PTE-5 and SUPELCOWAX 10 columns for the most reliable identification and quantitation of solvents in complex mixtures.

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