SLB™-5ms Fast GC Columns for Semivolatile Analysis

By: Michael D. Buchanan, Reporter US Edition 24.4

Introduction

US EPA Method 8270 mandates that the GC-MS instrument be tuned prior to the analysis of any standards or samples. Once an acceptable tune has been achieved, analysis may begin. For an analysis to be considered valid, the injection must occur within twelve hours of the time the tuning solution was injected. This twelve hours of time is often referred to as “tune time.”

In an environmental laboratory that analyzes semivolatiles, there are few options to increase sample throughput. Some of these, such as the purchase of additional instrumentation, requiring a capital expense, or adding a second or third shift, requiring additional payroll, may not be feasible. An alternative is to decrease the actual analysis time on the instrument. This can be done by converting to a shorter, narrower bore column. The shorter analysis time will result in a greater number of injections and thus more billable samples completed during “tune time.”

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Fast GC

Without sacrificing the quality of the analysis, Fast GC uses column and instrument improvements combined with run conditions that give 3- to 10-times faster analyses. It is typically performed using short, 0.10 mm or 0.18 mm I.D. capillary columns with rapid temperature programming rates and high carrier gas linear velocities.

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Analysis on 0.25 mm I.D. Column

An 86-component US EPA Method 8270 standard (72 analytes, 8 surrogates, and 6 internal standards) was analyzed on a 30 m x 0.25 mm I.D., 0.25 μm SLB-5ms column. The resulting chromatogram is shown in Figure 1. Flow rate was programmed to achieve an analysis time of 19.6 minutes.

Figure 1.Semivolatiles on the 0.25 mm I.D. SLB-5ms

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Analysis on 0.18 mm I.D. Column

The principles of Fast GC were applied to analyze the same 86-component US EPA Method 8270 standard on a 20 m x 0.18 mm I.D., 0.18 μm SLB-5ms column. The resulting chromatogram is shown in Figure 2. The analysis time of 8.1 minutes equates to a time savings greater than 11 minutes. A narrow bore injection liner and split injection was used to compensate for the lower sample capacity of the narrow bore column.

Figure 2.Semivolatiles on the 0.18 mm I.D. SLB-5ms

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Conclusion

Switching from the 30 m x 0.25 mm I.D., 0.25 μm SLB- 5ms column to the 20 m x 0.18 mm I.D., 0.18 μm SLB-5ms column resulted in a per run time savings greater than 11 minutes, with all analytes still mass resolved. This translates into approximately fourteen additional runs than can be completed per “tune time.”

If shorter run times are desired, consider converting your semivolatile application to a 0.18 mm I.D. SLB-5ms column.

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