Rapid Analysis of Flavors and Fragrances Using High-Efficiency GC Columns

There are many misconceptions about what it means to perform fast gas chromatography (GC) and what the term fast GC implies. Fast GC is often associated with the use of hydrogen as a carrier gas and, although this is certainly a good approach, it is not always necessary to shorten the analysis time. A second misconception is that changing column dimension results in time-consuming method development. Using high-efficiency GC columns can greatly reduce the analysis time and when coupled with the method translation software, the time spent on method development can be greatly minimized.

Efficiency is often related to the number of theoretical plates (N) that a column has and is expressed as plates per meter. It follows that the longer the column, the more plates you have and thus the more efficient the column. Another more effective way to increase column efficiency is to reduce the column i.d. A more efficient, smaller i.d. column can be used to obtain the same number of plates in a shorter length of column. The shorter the column, the less time the analytes take to travel that length of column which equates to shorter analysis times without the loss of efficiency or resolution.

Table I: Method conditions for DB-1 columns

The high-efficiency columns are designed to maintain the same phase ratio as the more commonly used 0.25 mm columns, making for easy method translation. During the chromatographic process, the resulting chromatogram and its associated resolution are the product of the thermodynamics of the system. If the dimensions of the column are changed, then the thermodynamics of the system also change. A new temperature program must be developed to match the new column dimensions. Using the free GC method translation software that is available online at Agilent.com takes the guesswork out of developing a new temperature program. This assumes that the same column phase type and same phase ratio are being used between the two methods. It is not imperative to use the same phase ratio, however if the phase ratio is not maintained, the elution order should be confirmed. An additional option for faster analysis is to use a more efficient carrier gas. When changing carrier gas types from one to another, the method translation software takes into account the efficiencies of the four most commonly used carrier gases (argon, nitrogen, helium and hydrogen) and adjusts the method parameters accordingly.

Figure 1

A generic method was used to analyse spearmint oil on a 30 m × 0.25 mm × 0.25 μm Agilent J&W DB-1 column (Table I). This method was applied to the method translator with the high-efficiency column dimensions and the translated flow-rate and oven parameters were then used (Figure 1). As can be seen from the chromatograms (Figure 2), there is a decrease in run time of approximately 33% (9.7 min) without any loss of resolution, just by using the high-efficiency column. A total speed gain of 16.8 min was realized by using hydrogen as the carrier gas (Figure 2). Again the method was translated using the software which effectively eliminated the time spent on method development.

Figure 2

Conclusion

Using the Agilent J&W High-Efficiency GC column in conjunction with the method translation software makes fast GC method development essentially plug and play. Switching to High-Efficiency GC columns is a quick and easy way to increase productivity in today's high-throughput laboratories while maintaining helium as the carrier gas. Additional speed gains will be obtained by employing hydrogen as the carrier gas.

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