Analysis of Di(2-ethylhexyl)phthalate by GC-MS Using Hydrogen Carrier Gas

Importance of the Topic

Di(2-ethylhexyl)phthalate (DEHP) is a widely used plasticizer with environmental and health concerns. Reliable quantification of DEHP in various matrices is critical for regulatory compliance, quality control, and risk assessment. Traditional GC-MS analyses rely on helium as a carrier gas, but helium shortages and rising costs have driven interest in hydrogen as an alternative. This study evaluates the performance of hydrogen carrier gas on the Shimadzu GCMS-QP2010 Ultra system for DEHP analysis.

Objectives and Overview of the Study

The primary goal was to compare mass spectral integrity, sensitivity, and quantitative performance of DEHP analysis when using hydrogen versus helium carrier gas. Key objectives included:

• Assessing any changes in mass spectral patterns under hydrogen flow.
• Determining the detection limit and signal-to-noise ratio in SIM mode at low concentrations.
• Evaluating repeatability and linearity of calibration curves from 0.05 to 5 mg/L.

Methodology and Instrumentation

A series of DEHP standards (0.05–5 mg/L) with phenanthrene-d10 as an internal standard (0.5 mg/L) were prepared in hexane. Analyses were performed on the Shimadzu GCMS-QP2010 Ultra equipped with a Dual Inlet Turbo Molecular Pump. Chromatographic separation used a Rtx-5MS capillary column (30 m × 0.25 mm I.D., 1 µm film). Key parameters:

• Injection: splitless, 1 µL at 250 °C.
• Oven program: 100 °C (1 min) to 230 °C at 20 °C/min, then to 320 °C at 10 °C/min (3 min).
• Carrier gas: hydrogen linear velocity 65 cm/s
• Mass spectrometer: interface 280 °C, ion source 200 °C; scan m/z 80–300 (0.3 s/event); SIM monitoring m/z 149, 167.

Main Results and Discussion

Mass spectral comparison at 5 mg/L DEHP showed identical fragmentation patterns for hydrogen and helium carriers, confirming spectral integrity. SIM analysis at 0.05 mg/L yielded a signal-to-noise ratio of 94, demonstrating that hydrogen provided high sensitivity even at low levels. Repeatability (n=5) at 0.05 mg/L showed 2.63 %RSD, and calibration linearity across 0.05–5 mg/L achieved an R² of 0.999. These metrics meet typical quantitative requirements in environmental and industrial settings.

Key observations:

• No alteration in mass spectra with hydrogen carrier gas.
• High sensitivity in SIM mode comparable to helium.
• Excellent repeatability and linear calibration over the tested range.

Benefits and Practical Applications

Using hydrogen as a carrier gas offers multiple advantages:

• Cost savings and supply security compared to helium.
• Maintained spectral fidelity and analytical sensitivity for DEHP.
• Applicability to routine environmental monitoring, plasticizer analysis, and QA/QC processes.

Future Trends and Possibilities

As hydrogen adoption grows, future work may explore:

• Extended method validation for diverse phthalate esters and complex matrices.
• Integration of hydrogen usage protocols in regulatory guidelines.
• Automation and safety enhancements for hydrogen handling in high-throughput laboratories.

Conclusion

This study demonstrates that hydrogen carrier gas can successfully replace helium for GC-MS analysis of DEHP on the Shimadzu GCMS-QP2010 Ultra. It maintains mass spectral integrity, sensitivity, and quantitative performance, while offering economic and supply benefits. Proper safety measures for hydrogen handling should be implemented.

References

• Shimadzu Corporation. Analysis of Di(2-ethylhexyl)phthalate by GC-MS Using Hydrogen Carrier Gas, LAAN-J-MS-E082, First Edition July 2013.