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Analysis of Blood Alcohols on the SUPELCOWAX™ 10

By: Michael D. Buchanan and Robert F. Wallace, Reporter US Vol 25.4


Michael D. Buchanan and Robert F. Wallace
mike.buchanan@sial.com

Introduction

Gas chromatographic analysis of blood alcohols is preceded by one of several sample introduction techniques: direct injection, headspace, or solid phase microextraction (SPME). Each of these techniques has distinct advantages over the others. Regardless of which sample introduction technique is selected, the column choice must result in both sharp peaks and complete resolution of all peaks of interest.

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SUPELCOWAX 10 Column

In this article, the use of a polar SUPELCOWAX 10 capillary column will be evaluated for the GC analysis of blood alcohols. Because this column offers higher polarity than any of the phenylsilicone phases, it is widely used for the separation of many polar compounds, including alcohols. The SUPELCOWAX 10 column will often resolve critical pairs that may not otherwise separate by boiling point alone.

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Experimental

An alcohol sample containing each analyte at 0.08% was prepared in water. The alcohol 2-butanol was included for use as an internal standard. Using a 4 mm I.D. split, cup design liner, a 0.5 μL injection with a split of 100:1 was performed onto a 30 m x 0.25 mm I.D., 0.50 μm SUPELCOWAX 10 column. To achieve good resolution and a short analysis time, a thin film (0.50 μm) was chosen for this analysis.

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Discussion

As shown in Figure 1, an analysis time of less than 8 minutes was achieved with excellent peak shapes and complete separation for all blood alcohol components, their metabolites, and the internal standard. All peaks eluded at less than 80 °C oven temperature. A final oven temperature of 125 °C was used to ensure that any water present in the sample eluted from the column.

Figure 1. Blood Alcohols on the SUPELCOWAX 10 (24284)


A distinct advantage of the SUPELCOWAX 10 for this application is its selectivity. This is most evident when looking at the ethanol peak. Ethanol elutes such that it does not have another peak close behind it. This is critical when analyzing ‘real-world’ samples in which the ethanol peak would be expected to be much larger in size, resulting in a wider peak to the right. The selectivity of the SUPELCOWAX 10 column provides ample room, chromatographically, for the analysis of samples with large ethanol concentrations.

An advantage of using an oven temperature programmed analysis over an isothermal analysis is that the system tends to be kept clean. That is, non-target compounds are forced through the system during each analytical run as the oven temperature rises. With an isothermal analysis, these compounds tend to accumulate in the system, seen in subsequent analyses as carry over and/or ghost peaks. Depending on the sample preparation and sample introduction techniques being employed, the amount of non-target compounds being transferred to the GC column may be sizeable.

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Conclusion

With the SUPELCOWAX 10 column, ethanol, methanol, n-propanol, 2-propanol, and their metabolites acetaldehyde and acetone can be analyzed in less than 8 minutes. This column has distinct advantages for this application over other commercially available columns. In particular, its applicability for samples that contain high concentrations of ethanol.

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Materials

     
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