Agilent announces what it describes as the fastest available chromatographic technique for analysing the purity of fuel-grade ethanol
Agilent Technologies Europe has announced a two-dimensional gas chromatographic (2-D GC) technique for determining the purity of denatured fuel-grade ethanol used as a gasoline additive and for analysing thiophene in benzene.
The system provides the fastest chromatographic analysis of fuel ethanol purity available, nearly ten times faster than the standard American Society for Testing and Materials (ASTM) D5501 method.
For both analyses, the 2-D GC method provides precise qualitative and quantitative results in one run and on one system.
Fuel grade ethanol is an oxygenated additive used in reformulated gasoline (RFG) to improve octane rating and reduce emissions of smog-producing pollutants.
In addition to ethanol, this additive also contains natural gasoline as a denaturant, to render it unsuitable for beverage use, and methanol, a natural impurity.
Since methanol is an oxygen-containing species, its concentration must be determined as it can affect the resulting properties of the RFG.
However, the denaturant complicates analysis because it is difficult to separate ethanol and methanol from the hydrocarbons found in the denaturant.
Standard ASTM analysis can extend to 60 minutes and requires a cryogenic coolant.
Benzene is an important feedstock for producing commodity chemicals.
Many of these processes use expensive catalysts that can be poisoned easily by small amounts of sulphur-containing impurities.
Thiophene is a common sulphur impurity difficult to analyse at trace levels in benzene because its boiling point and molecular weight are similar to benzene. Until now, successful thiophene analyses in benzene have required expensive and complicated detectors.
With the 2-D GC system, however, standard flame ionisation detectors can be used to measure part-per-billion levels of thiophene.
This method has significant advantages over standard methodologies for analysing methanol in denatured fuel ethanol and thiophene in benzene.
This system performs GC analysis of denatured fuel ethanol in seven minutes, nearly ten times faster than the standard ASTM method. Overall run time was also faster since the 2-D method used an initial oven temperature that was much higher than ambient and did not require cryogenic coolants.
For benzene analysis, this method can also measure overall benzene purity and key impurities such as hydrocarbons, toluene, and 1,4-dioxane in the same run as the thiophene determination.
The 2-D technique uses a primary column for performing an initial separation of the target compound from the sample matrix.
As the target compound and any interferences elute from this column, they are diverted to a secondary column that contains a stationary phase with different selectivity.
The chromatographic separation finishes on the secondary column.
A simplified fluidic Dean's switch couples the two columns and performs the transfer of compounds from the first to the second column.
Agilent chemists used an Agilent 6890N GC, a split/splitless injector, a pneumatics control module, two flame ionisation detectors, an automatic liquid sampler and two columns with different selectivities to test the 2-D technique.
The system was precise and stable over extended periods of time, with results nearly identical to those obtained using more expensive and complex GC systems.
Further information is available by requesting Agilent application notes 'Analysis of trace (mg/kg) thiophene in benzene using two-dimensional gas chromatography and flame ionisation detection', Agilent publication 5988-9455EN, and 'Fast determination of denatured fuel ethanol purity by two-dimensional gas chromatography', Agilent publication number 5988-9460EN. These notes are available without charge from any Agilent sales office or its website.
