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Simultaneous Measurement of Water and BTEX in Gasoline using Watercol™ Capillary GC Columns

By: Leonard M. Sidisky, R&D Manager; Katherine K. Stenerson, Michael Halpenny, Michael D. Buchanan, and Gustavo Serrano, Reporter US Volume 34.3

Residual moisture in fuel is very undesirable because it reduces the heat of combustion which increases engine stress. It can also corrode fuel system components, permit gelling of fuel in cold temperatures through ice crystal formation/nucleation, and accelerate the growth of microbial colonies which can clog fuel systems. Monitoring for the BTEX compounds (benzene, toluene, ethylbenzene, and three xylene isomers) is also of great importance to the fuel industry.

Watercol Series Column Chemistries

First introduced at Pittcon 2016, Watercol™ capillary GC columns are manufactured with innovative ionic liquid stationary phases that incorporate a ‘polar imbedded’ linkage. It is this feature (polar imbedded linkage) which results in the ability for these columns to produce a sharp peak shape for water. It is the sharp water peak shape which permits the measurement of water (both qualitatively and quantitatively) with great linearity, sensitivity, and reproducibility. Three column chemistries are currently available.1 Complete column specifications are shown in Table 1.

Narrow peak widths and optimal peak heights are also produced for many organic analytes, making these columns suitable for applications where both water and organic analytes need to be identified and measured. This application shows the separation of both water and the BTEX compounds in a gasoline sample using a Watercol™ 1910 capillary GC column.


Table 1.
Watercol™ Series Column Specifications

Watercol™ 1460
USP Code: None
Phase: Non-bonded; Tri(tripropylphosphoniumhexanamido)triethylamine trifluoromethanesulfonate
Temp. Limits: 30 °C to 260 °C (isothermal or programmed)
Watercol™ 1900
USP Code: None
Phase: Non-bonded; 1,11-Di(3-methylimidazolium)3,6,9-trioxaundecane trifluoromethanesulfonate
Temp. Limits: 30 °C to 180 °C (isothermal or programmed)
Watercol™ 1910
USP Code: None
Phase: Non-bonded; 1,11-Di(3-hydroxyethylimidazolium)3,6,9-trioxaundecane trifluoromethanesulfonate
Temp. Limits: 30 °C to 180 °C (isothermal or programmed)

 

Experimental

Two identical Watercol 1910 columns were installed in separate inlets on the same GC, one going to a FID, and the other going to a TCD. Two detectors were necessary because the FID is able to produce good response for the BTEX compounds, but is unable to detect water. The TCD is able to detect water, but produces a lower response for the BTEX compounds compared to the FID. Throughout the experiment, the same sample mixture was injected onto both columns at the same time.

Two standards, water in ethanol and BTEX in isooctane, were first analyzed to establish run conditions and determine analyte retention times. The chromatogram obtained from the water standard is shown in Figure 1. An unleaded gasoline sample was obtained locally and analyzed. Figure 2 shows the resulting chromatogram with analytes identified. A spiked gasoline sample was also made. The chromatogram obtained from subsequent analysis is displayed in Figure 3.

 

Water Standard

Figure 1. Water Standard

 

Unspiked Gasoline

Figure 2. Unspiked Gasoline

 

Spiked Gasoline

Figure 3. Spiked Gasoline

Results and Discussion

The Watercol™ 1910 column was able to produce sharp peak shapes for all analytes of interest (water and the BTEX compounds). Its selectivity resulted in elution of the water peak free from most of the major constituents present in gasoline. With proper standards, it appears than many of these other compounds could also be identified. Of note is that the timely elution (<19 minutes) of the heaviest gasoline components was possible, even though this chemistry has a maximum temperature limit of 180 °C (isothermal or programmed). An advantage of ionic liquid columns is their ability to elute analytes at lower oven temperatures compared to non-ionic liquid columns. Therefore, they do not need to possess high maximum temperature limits to perform the same applications.

Conclusion

Water can be both an analyte, and a matrix. As such, it is one of the most analyzed compounds in the world. The GC technique is widely used to measure volatile and semivolatile organic compounds for multiple applications in many industries. Utilizing the GC technique to measure both water and organic compounds is a fortunate thing for analytical labs, allowing two measurements to be obtained from a single analysis.

Materials

     

 References

  1. Sidisky, L.M.; Serrano, G.; Desorcie, J.L.; Stenerson, K.K.; Baney, G.; Halpenny, M.; and Buchanan, M.D. Mixing water and gas: the quantitative measurement of water by gas chromatography using ionic liquid capillary columns, Chrom. Today, 2016, 9.1,18.

 

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