Simultaneous Analysis of PAHs Across Multiple Matrices

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 Authors Chiara Calaprice1, Brian Pike2, Giulia Riccardino3, Adam Ladak4, and Paul Silcock4 1Thermo Fisher Scientific, Bremen, DE 2PACE Analytical IDEA Laboratory, Minneapolis, MN, USA 3Thermo Fisher Scientific, Milan, IT 4Thermo Fisher Scientific, Hemel Hempstead, UK Keywords Polycyclic aromatic hydrocarbons (PAHs), EPA Method 8270E, ISQ 7610 mass spectrometer, extended dynamic range, gas chromatography-mass spectrometry (GC-MS), ExtractaBrite, Chromeleon, Environmental Analysis Pack Goal The aim of this application note is to demonstrate the wide dynamic range and the robustness of the Thermo Scientific™ ISQ™ 7610 single quadrupole mass spectrometer, using the new Thermo Scientific™ XLXR™ detector, coupled to a Thermo Scientific™ 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.1One 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 first challenge is that isobaric compounds must have sufficient chromatographic resolution, in particular benzo[b]fluoranthene and benzo[k] fluoranthene. 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 optimization 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 final 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 utilization is affected and results to clients are delayed. In this application note, the ISQ 7610 single quadrupole GC-MS system was utilized 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 five orders of magnitude was utilized to analyze 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 analyzed 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 significantly reduced due to the ability to exchange the column and clean the ionization 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), labeled 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, labeled 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 35104 and 35115 for water, and EPA Method 35466 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 analysis Liquid injections of the sample extracts were performed using a Thermo Scientific™ TriPlus™ RSH SMART autosampler. Chromatographic separation was achieved using a Thermo Scientific™ 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 film thickness and the high working temperature (up to 360 ˚C). For the analysis, the ISQ 7610 single quadrupole GC-MS, coupled with a TRACE 1610 GC gas chromatograph and equipped with the ExtractaBrite™ ion source, was used. The method conditions are shown in Table 1. The system was operated in Selected Ion Monitoring (SIM) mode to monitor the PAHs, and in full scan (from 50 to 500 m/z, dwell time 0.20 s) for the tuning solution. 2Table 1. GC-MS acquisition method parameters for the determination of 19 PAHs in water and soil samples Injection parameters Inlet module and mode SSL, split Liner P/N 453A1925-UI Liner type and size Thermo Scientific™ LinerGOLD™, 4 mm i.d. × 78.5 mm Injection volume (µL) 1 Inlet temperature (˚C) 300 Split flow (mL/min) 15 Carrier gas, carrier flow (mL/min), carrier mode He, 1.5, constant flow Split ratio 10:1 Purge flow (mL/min) 5 Pre-injection needle wash 5 times, with DCM Post-injection needle wash 10 times with DCM, 10 times with MeOH Chromatographic column Thermo Scientific™ TraceGOLD™ TG-PAH P/N 26055-0470 Column dimensions 30 m × 0.25 mm i.d. × 0.10 μm Oven temperature program Temperature 1 (˚C) 40 Hold time (min) 1 Temperature 2 (˚C) 285 Rate (˚C/min) 35 Temperature 3 (˚C) 295 Rate (˚C/min) 3 Temperature 4 (˚C) 350 Rate (˚C/min) 30 Hold time (min) 2 Total GC run time (min): 15.2 MS parameters Ion source ExtractaBrite Transfer line temperature (˚C) 350 Ion source temperature (˚C) 350 Ionization type EI Electron energy (eV) 70 Emission current (µA) 10 Acquisition mode SIM, 2 ions/compound Dwell time (s) 0.02 Table 2. List of target PAH compounds, with their retention time and SIM quantification and confirmatory ions Compound name Rt (min) MS quantifier ion (m/z) MS confirmatory ion (m/z) Naphthalene-d8 4.7 136 108 Naphthalene 4.8 128 129 2 - methyl Naphthalene 5.2 142 141 1 - methyl Naphthalene 5.3 142 141 Acenaphthylene 5.9 152 151 Acenaphthene 6.0 153 154 Acenaphthene-d10 6.0 162 164 Dibenzofuran 6.1 168 139 Fluorene 6.4 165 166 Phenanthrene-d10 7.2 188 184 Phenanthrene 7.2 178 176 Anthracene 7.2 178 176 Fluoranthene 8.1 202 200 Terphenyl-d14 8.3 244 122 Pyrene 8.4 202 200 Benz[a]anthracene 9.5 228 226 Chrysene-d12 9.7 240 236 Chrysene 9.7 228 226 Benzo[b]fluoranthene 11.3 252 250 Benzo[k]fluoranthene 11.4 252 250 Benzo[a]pyrene 12.1 252 250 Perylene-d12 12.2 264 260 Dibenzo[a,h]anthracene 13.5 278 139 Indeno[1,2,3-cd]pyrene 13.5 276 138 Benzo[g,h,i]perylene 13.9 276 138 A full list of analytes, as well as quantifier and qualifier ions that were monitored, is listed Table 2. The system was tuned with a built-in EPA Method 8270E specifically designed tune type. Data processing Data were acquired, processed, and reported using Thermo Scientific™ Chromeleon™ 7.3 CDS software, which allows instrument control, method development, quantitative/qualitative analysis, and customizable reporting all within one platform. The GC-MS Environmental Extension Pack includes a suite of report templates, processing methods and eWorkflows™ to facilitate environmental analysis by GC-MS using EPA Methods 8270, 3524, 525, and 82606. For the analysis of PAHs, monitoring the ratios between the masses of the DFTPP is required and automatically performed by the software System Suitability Check. Chromeleon CDS allows rapid implementation of the PAHs method into any analytical laboratory and ensures the system produces results shortly after installation. Results and discussion Chromatographic separation and resolution of isomers The optimized GC conditions and the high selectivity of the TraceGOLD TG-PAH capillary column allowed for chromatographic resolution of isobaric compounds in a total run time of 15.2 minutes, meeting the EPA Method 8270E requirements. Gaussian peak shapes were obtained for all the compounds, including the ones with high boiling points. 1 2 11 7 3 15 An example chromatogram obtained for a solvent standard at 0.1 ppm is shown in Figures 1 and 2. Peaks of naphthalene and benzo[g,h,i]pyrene, the first and the last eluting PAHs, show gaussian and sharp peak shape from the beginning to the end of the method; baseline peak width for benzo[g,h,i]pyrene was 0.034 min. Phenanthrene and anthracene compounds are almost baseline resolved; benzo[b]fluoranthene and benzo[k]fluoranthene have a resolution of 20% (calculated as the ratio between the height of the valley and the smaller height of the apex of the two compounds); dibenzo[a,h]anthracene and indeno[1,2,3-cd]pyrene coelute and rely on mass separation. 18 5 4 6 12 13 8 9 10 14 16 17 19 23 20 21 22 24 25 26 1 = Naphthalene‐d8 , 2 = Naphthalene, 3 = 2‐methyl Naphthalene, 4 = 1‐methyl Naphthalene, 5 = Acenaphthylene, 6 = Acenaphthene, 7 = Acenaphthene‐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 Figure 1. Chromatographic separation and peak shape for 19 investigated PAHs, 5 labeled 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. 4Calibration and linearity A calibration curve ranging from 2.5 ng/mL to 20,000 ng/mL was prepared to assess linearity with the average relative response factor (AvRF) calibration fit type and the %RSD <15% criterion required in the EPA Method 8270E. Calculated %RSDs were <10% for all the compounds across the entire calibration range. The extended dyna