Mass Spectrometry & Spectroscopy
Analysis of multiple matrices with a single calibration curve for polycyclic aromatic hydrocarbons (PAHs) with the ISQ 7610 GC-MS system following EPA Method 8270E
Chiara Calaprice1 , Brian Pike2 , Giulia Riccardino3 , Adam Ladak4 , and Paul Silcock4
1. Thermo Fisher Scientifi c, Bremen, Germany 2. PACE Analytical IDEA Laboratory, Minneapolis, MN, USA 3. Thermo Fisher Scientifi c, Milan, Italy
4. Thermo Fisher Scientifi c, Hemel Hempstead, UK Goal
The aim of this application note is to demonstrate the wide dynamic range and the robustness of the Thermo Scientifi c™ ISQ™ 7610 single quadrupole mass spectrometer, using the new Thermo Scientifi c™ XLXR™ detector, coupled to a Thermo Scientifi c™ TRACE™ 1610 gas chromatograph, for the analysis of 19 polycyclic aromatic hydrocarbons (PAHs) in soil and water, according to the United States Environmental Protection Agency (EPA) Method 8270E.
Introduction
Polycyclic aromatic hydrocarbons (PAHs) are organic compounds consisting of carbon and hydrogen atoms. Chemically the PAHs comprise two or more aromatic rings bonded in linear, cluster, or angular arrangements, resulting in a wide diversity of physical, chemical, and toxicological properties. PAHs are ubiquitous and can contaminate soil, air, sediments, and water and are resistant to environmental degradation. These compounds are found in fossil fuel sources and manmade chemicals and are derived from the incomplete combustion of organic matter used for human activities (such as vehicle emissions, rubber, plastics, and cigarettes). PAHs have toxic effects because of their chemical structure and act as a carcinogen or endocrine disrupter. Due to their toxicity, they are monitored in the environment with strict regulations [1].
One of the most common regulations followed for the analysis of PAHs is EPA Method 8270E [2]. Analytical laboratories following this method face several challenges. The fi rst challenge is that isobaric compounds must have suffi cient chromatographic resolution, in particular benzo[b]fl uoranthene and benzo[k]fl uoranthene. High boiling compounds, such as benzo[g,h,i]perylene, also pose a challenge as there is a possibility for carryover and peak broadening [3]. Careful optimisation of instrumental conditions must be done to avoid saturation and linearity loss; labs may also need to separate calibration curves for different matrices, for example soil and water, to ensure they do not exceed the linear dynamic range of the system.
Following the regulations for EPA Method 8270E comes with its own challenges. DFTPP tuning must be performed to ensure that the ion abundances are acceptable for the analysis. 8270E requires a tune during the initial full calibration, then the continuing calibration to be run every 12 hours after that for analysis. All previous versions of 8270 before E required a full DFTPP tune every 12 hours. If DFTPP tune fails, the entire of batch of samples must be rerun to be compliant with the method. The fi nal challenge for analytical testing laboratories performing this analysis is to maintain the sample throughput. It is essential that the instrument performs consistently throughout the analysis, and extended runs without maintenance are desirable. If there is any unproductive time on the instrument caused by venting to clean the system or changing the column, the sampler turnaround time and asset utilisation is affected and results to clients are delayed.
In this application note, the ISQ 7610 single quadrupole GC-MS system was utilised for the simultaneous analysis of PAHs in water and soil samples. The XLXR detector comes as standard on the system and offers extended linear dynamic range and lifetime. For this analysis, a single calibration curve over fi ve orders of magnitude was utilised to analyse water and soil samples. This extended dynamic range eliminates the need to run separate curves for different matrices and aids to increase sample throughput. An extended run of soil and water matrices were also analysed on the system to demonstrate the robustness for the analysis of PAHs. The NeverVent™ technology on
the ISQ 7610 GC-MS also allows for instrument downtime to be signifi cantly reduced due to the ability to exchange the column and clean the ionisation source without needing to vent the system. By eliminating unproductive time on the instrument, more injections can be performed on the system.
Experimental Reagents and standards
Native compounds calibration mix containing 18 PAHs listed in the EPA Method 8270 (each component at 2,000 µg/mL, P/N 31995), labelled internal standard mix (2,000 µg/mL, P/N 31206) and GC-MS Tuning mix (1,000 ng/mL, P/N 31615) were purchased from Restek; neat dibenzofuran (10 mg, P/N DRE-C20710000) was obtained from LGC and diluted in dichloromethane (DCM) to a concentration of 10 mg/mL. Surrogate standard mix (4,000 µg/mL, P/N M-8270-SS) was purchased from AccuStandards.
Preparation of solvent calibration curve, instrument detection limit (IDL), and method detection limit (MDL) samples
Thirteen calibration solutions in DCM, containing 19 native PAHs, labelled internal standards and the surrogate standard were prepared, ranging from 2.5 to 20,000 ng/ mL (ppb) (full details in Appendix); the ISTD was at 1,000 ng/mL and the surrogate was at 800 ng/mL. Average response factor calibration was used, and 15% RSD criterion was applied to assess linearity in this wide calibration range. Instrument detection limit (IDL) was calculated by injecting a 2.5 ng/mL calibration solution in DCM. Method detection limit (MDL) was calculated using extracts of water and soil spiked at 2.5 and 5 ng/mL, respectively, after the extraction.
Preparation of samples and QCs Water and soil extracts (n=76) were provided by PACE Analytical®
, USA. Samples were
spiked, extracted following the EPA Methods 3510 [4] and 3511 [5] for water, and EPA Method 3546 [6] for soil. Water and soil samples with low levels of PAHs were spiked to have QCs at low (0.01 ppm), middle (1 ppm), and high (10 ppm) level to check for method accuracy and robustness. All the samples were injected randomly and used to assess instrument robustness over n=150 matrix injections without inlet, column, mass spectrometer maintenance, or re-tuning.
GC-MS/MS analysis
Liquid injections of the sample extracts were performed using a Thermo Scientifi c™ TriPlus™ RSH SMART autosampler. Chromatographic separation was achieved using a Thermo Scientifi c™ TraceGOLD™ TG-PAH 30 m × 0.25 mm i.d. × 0.10 µm column. This column allowed compliance to EPA Method 8270 in terms of resolution, as well as excellent peak shape for all the compounds, including the ones with high boiling point, due to the fi lm thickness and the high working temperature (up to 360˚C).
LAB ASIA - APRIL 2022
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