Polycyclic aromatic hydrocarbons (PAHs) are a group of organic compounds with two or more fused aromatic rings. They are found in fossil fuels and are produced by the incomplete combustion of organic matter, making them ubiquitous in the environment. Due to their potential toxic effects, including carcinogenicity and endocrine disruption, PAHs are closely monitored in the environment, especially in soil and water samples. However, the analysis of PAHs in environmental samples presents several challenges, particularly when adhering to stringent regulatory requirements such as the U.S. EPA Method 8270E1. In this blog, we will explore these challenges and how advanced GC-MS technology can be utilized to address and overcome these challenges.
Challenges in PAH Analysis
1. Regulatory Compliance
Compliance with EPA Method 8270E requires specific tuning and calibration procedures. For instance, the method mandates the use of DFTPP (Decafluorotriphenylphosphine) tuning to ensure ion abundances are within acceptable limits. Additionally, maintaining consistent instrument performance over extended runs without maintenance is crucial to meet regulatory standards and ensure results are reported in a timely manner.
2. Complex Sample Matrix
Environmental samples including soil and wastewater are complex matrices and contain interference that can affect the accurate detection and quantification of PAHs. The presence of isobaric compounds necessitates high chromatographic resolution to distinguish between closely eluting PAH compounds, such as benzo[b]fluoranthene and benzo[k]fluoranthene.
3. Wide Range of Detection Levels
PAH analysis must cover a wide range of detection levels across different matrices, from low parts-per-billion (ppb) to high parts-per-million (ppm) concentrations. This diversity necessitates a versatile analytical method capable of maintaining accuracy and precision across a broad dynamic range. Creating and managing multiple calibration curves for different concentration ranges and matrices can be time-consuming and prone to errors.
Overcoming the Challenges of PAH Analysis in Environmental Samples
![Figure 1: Chromatographic separation and peak shape for 19 investigated PAHs, 5 labelled ISTD and 2 Surrogate standards in a solvent standard at 0.1 ppm acquired in SIM. Tracks of the quantification ions are reported for each peak in different colors.
1=Naphthalene-d8, 2=Naphthalene, 3=2-methyl Naphthalene, 4=1-methyl Naphthalene, 5=Acenaphthylene, 6=Acenaphthene, 7=Acenaphtene-d10 , 8=Dibenzofuran, 9=Fluorene, 10=Tribromophenol 2,4,6, 11=Phenantrene-d10 , 12=Phenantrene, 13=Anthracene, 14=Fluoranthene, 15=Terphenyl-d14, 16=Pyrene, 17=Benz[a]anthracene, 18=Chrysene-d12, 19=Chrysene 20=Benzo[b]fluoranthene, 21=Benzo[k]fluoranthene,
22=Benzo[a]pyrene, 23=Perylene-d12, 24=Dibenzo[a,h]anthracene, 25=Indeno[1,2,3-cd] pyrene, 26=Benzo[g,h,i]perylene](https://www.thermofisher.com/blog/analyteguru/wp-content/uploads/sites/25/2024/12/tackling-pah-analysis-blog-figure-1-1024x552.jpg)
Figure 1: Chromatographic separation and peak shape for 19 investigated PAHs, 5 labelled ISTD and 2 Surrogate standards in a solvent standard at 0.1 ppm acquired in SIM. Tracks of the quantification ions are reported for each peak in different colors.
1=Naphthalene-d8, 2=Naphthalene, 3=2-methyl Naphthalene, 4=1-methyl Naphthalene, 5=Acenaphthylene, 6=Acenaphthene, 7=Acenaphtene-d10 , 8=Dibenzofuran, 9=Fluorene, 10=Tribromophenol 2,4,6, 11=Phenantrene-d10 , 12=Phenantrene, 13=Anthracene, 14=Fluoranthene, 15=Terphenyl-d14, 16=Pyrene, 17=Benz[a]anthracene, 18=Chrysene-d12, 19=Chrysene 20=Benzo[b]fluoranthene, 21=Benzo[k]fluoranthene,
22=Benzo[a]pyrene, 23=Perylene-d12, 24=Dibenzo[a,h]anthracene, 25=Indeno[1,2,3-cd] pyrene, 26=Benzo[g,h,i]perylene
A PAH analysis method was fully optimized on the Thermo Scientific ISQ 7610 single quadrupole GC-MS system, equipped with the XLXR detector to overcome these challenges. For more information on the methods details and extensive data from the analysis you can review the full application note. The highlights of the benefits of using this GC-MS system include:
1. Wide Dynamic Range
The XLXR detector offers an extended linear dynamic range and during this study over four orders of magnitude (2.5 ppb to 20 ppm) were covered for the 19 PAHs analyzed. This wide dynamic range eliminates the need for separate calibration curves for different concentration ranges, simplifying the workflow and reducing the potential for errors.
Using a single calibration curve for multiple matrices, such as soil and water, offers significant advantages:
- Simplified Workflow: A single calibration curve across a wide dynamic range streamlines the analytical process, reducing the time and effort required to prepare and manage multiple curves.
- Increased Throughput: By eliminating the need for separate curves, laboratories can analyze more samples in less time, enhancing productivity and reducing turnaround times.
- Improved Accuracy: Combined calibration curves minimize the potential for calibration errors, ensuring consistent and reliable quantification across different sample types.
- Versatility Across Matrices: The ability to use a single calibration curve for different matrices (e.g., soil and water) enhances the versatility of the analytical method, making it easier to adapt to various environmental sample types without compromising accuracy.
![Figure 2: Examples of Average Response Factor calibration curve for some of the 19 PAHs analyzed, (from left to right: Naphthalene, Dibenzofuran, Phenantrene, Fluoranthene, Benzo[b]fluoranthene), Benzo[g,h,i]perylene, annotated with the %RSD. Linearity spans over 5 orders of magnitudes, from 2.5 to 20000 ng/mL.](https://www.thermofisher.com/blog/analyteguru/wp-content/uploads/sites/25/2024/12/tackling-pah-analysis-blog-figure-2-1024x640.jpg)
Figure 2: Examples of Average Response Factor calibration curve for some of the 19 PAHs analyzed, (from left to right: Naphthalene, Dibenzofuran, Phenantrene, Fluoranthene, Benzo[b]fluoranthene), Benzo[g,h,i]perylene, annotated with the %RSD. Linearity spans over 5 orders of magnitudes, from 2.5 to 20000 ng/mL.
2. Sensitivity
The system demonstrates excellent sensitivity with low instrument detection limits (IDLs) and method detection limits (MDLs) in the low picogram range. These detection limits exceed regulatory requirements, ensuring that even trace levels of PAHs are accurately quantified, providing reliable data for environmental monitoring.
3. Robustness
The GCMS system maintained consistent sensitivity and peak shape over extended runs, with no significant performance degradation after 136 injections or 52 hours of continuous operation. This robustness is crucial for continuous operation of the system, allowing laboratories to run samples over an entire weekend without user intervention. This ensures high throughput and maximizes productivity.
Conclusion
The Thermo Scientific ISQ 7610 GC-MS system provides a comprehensive solution to the challenges of PAH analysis in environmental samples. Its advanced features, including a wide dynamic range, excellent sensitivity, and robust performance, ensure compliance with EPA Method 8270E and improved laboratory efficiency. By leveraging the benefits of combined calibration curves, laboratories can achieve accurate, reliable, and high-throughput PAH analysis.
For more detailed information on the capabilities of this advanced GC-MS system, please visit the ISQ 7610 GC-MS product page.
References
- US EPA Method 8270E: Semivolatile Organic Compounds by Gas Chromatography/ Mass Spectrometry, Revision 6, June 2018
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