Rapid Screening For Semivolatile Compounds – 144 Compounds in Less than 9 minutes

Last week, I attended Enviro Analysis 2013 in Toronto, Canada with Michelle. She presented a poster highlighting her BFR column trimming work, and gave an oral presentation on some results from a Spring Creek sediment study (a local fly-fisherman’s paradise) done in conjunction with Penn State, featuring the new Rxi-PAH column.

I presented a poster featuring the very low detection limits achieved for the Combination EPA Methods 521 (nitrosamines) and 522 (1,4-dioxane) by Concurrent Solvent Recondensation – Large Volume Splitless Injection (CSR-LVSI) that I’ve been working on. I will link to a .pdf of the poster at the end of the post (be forewarned, it is very large at 1.2 m × 1.8 m).

However, what I want to focus on today is the 9 minute semivolatiles screening run  I presented at the end of the Mass Spectrometry: Techniques & Applications session (figure 1).

Figure 1. Semivolatiles analysis including US EPA Appendix IX compounds by Method 8270D

The goal of this project was to come up with a way of rapidly characterizing heavily contaminated extracts, so we opted for a short, narrow column and split injection. The split injection and narrow split liner (2 mm ID) enables us to begin our chromatographic run with a very narrow analyte band, yielding excellent early eluting peak shapes (tall narrow peaks also improve method sensitivity) and helps preserve later eluting critical separations (see figure 2).

Figure 2. 2 mm ID vs. 4 mm ID split precision liner injection band comparison

Figure 2. 2 mm ID vs. 4 mm ID split precision liner injection band comparison

Going with split injection also helps us in our second goal, which is protecting the column from nonvolatile co-extracted material. The chromatograms shown here were collected with a split ratio of 10:1. This is not sufficient for heavily contaminated samples; you will need to use your own judgment to balance chromatographic performance with client needs. However, keep in mind that dark extracts should not be injected on your semivolatiles system.

heavily contaminated extract

Figure 3. A heavily contaminated sample run at varying split ratios

Analyzing the heavily contaminated extract at a split ratio of 10:1 (figure 3.a) contaminated the sample pathway enough that the elution time of benz[a]anthracene shifted 2 minutes. This two minute shift remained when a follow-up laboratory control sample (LCS) was run. The extra material in the 10:1 split analytical run also contributed to the loss of resolution of benz[a]anthracene and chrysene, an isobaric pair sharing quant ion m/z=228. When the sample was analyzed with a 50:1 split ratio (figure 3.b), the benz[a]anthracene and chrysene separation was preserved. Figure 4 shows the extracted ion chromatograms (m/z=228) for the LCS and sample runs with split ratios of 10:1 and 50:1, collected after the initial contamination of the analytical system (and subsequent retention time shift).

10 vs 50 split

Figure 4. Extracted ion chromatogram (m/z=228) overlay of LCS and heavily contaminated sample extract runs collected with split ratios of 10:1 and 50:1

Inlet and column contamination is always a possibility when you are dealing with hazardous waste samples. That is why we went with the 12 m 0.18 Rxi-5ms column. The column is really a composite of a 10 m segment and a 2 meter segment joined with a press-fit connection. I ordered a 20m × 0.18 × 0.18 and had it cut into 2 10m segments (this is approximately 17.5 loops). The 2nd 10 meter segment can be cut into five 2 meter guard columns.

The 2 m segment is intended to act as a true guard column. Normally, deactivated pre-columns are used as guards, but they don’t trap all the non-volatile residue. This results in the “guard” and analytical column requiring trimming, since some of the non-volatile residues are not trapped until they encounter the stationary phase.

We have verified that the critical separations are maintained with at least a meter of guard removed. You do not need to alter the oven ramp rates (they are already maxed out), but you will need to calibrate the column length in the software to maintain the correct column flow (0.9 mL/min). You may have noticed that this screening run requires a relatively fast scanning rate (11.5 Hz); consequently, I don’t think this analysis will work well on older instrumentation (I would guess a 5973 with the fast electronics package would be the bare minimum).

Figure 5 is an 11×17 .pdf file with complete instrument acquisition parameters and peak identification, and as promised, the CSR-LVSI poster is Figure 6. Michelle’s Rtx-1614 Column Trimming Poster is Figure 7.

gc_ev1328 Cgram Layout

Figure 5. Labeled chromatogram with complete acquisition parameters

EnviroAnalysis 2013 EPA 521 522 Poster CSR-LVSI revised CMR

Figure 6. Low to sub PPT detection limits are achievable for 1,4-dioxane and nitrosamines when using CSR-LVSI

Figure 7. Same Separation with Half the Column: Extending the Lifetime of your GC Column with Column Trimming Maintenance and Method Translation

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