The Benefits of Hydrogen Carrier Gas in PCB Analysis

Goal The aim of this application note is to compare the performance of the Thermo Scientific™ TSQ™ 9610 triple quadrupole mass spectrometer coupled to the Thermo Scientific™ TRACE™ 1610 GC with hydrogen versus helium as the carrier gas for the determination of polychlorinated biphenyls. For guidance on the analytical performance of the proposed method, acceptance criteria as per U.S. EPA Method 1668 were considered. Introduction Polychlorinated biphenyls (PCBs) are a group of industrial organic chemicals consisting of carbon, hydrogen, and chlorine atoms. Due to their non-flammability, chemical stability, high boiling point, and electrical insulating properties, PCBs were used in hundreds of industrial and commercial applications including electrical, hydraulic equipment, plasticizers, plastics, rubber products, and dyes. The production of these compounds has been banned in the United States since 19771 because of their persistence in the environment and their tendency to enter the food chain and bioaccumulate in living organisms due to their lipophilicity. Environmental analysis of polychlorinated biphenyls (PCBs) at reduced running costs using hydrogen as carrier gas Application note | 002549 Keywords Polychlorinated biphenyls, PCBs, HeSaver-H2 Safer, GC-MS/MS, H2 carrier gas, U.S. EPA 1668 Environmental Authors Łukasz Rajski, Daniel Kutscher Thermo Fisher Scientific, Bremen, Germany There are currently 209 known PCBs congeners that can be divided into two groups according to their structural and toxicological characteristics: • Non-dioxin-like PCBs (non-DL-PCBs), which represent the majority of the PCB congeners, are characterized by a lower degree of toxicity. • Dioxin-like PCBs (DL-PCBs) include the 12 most toxic congeners (non‐ortho PCBs 77, 81, 126, 169 and mono‐ortho PCBs 105, 114, 118, 123, 156, 157, 167, 189), which have structures and toxicities similar to dioxins. DL-PCBs are classified as persistent organic pollutants (POPs), and they have been regulated under the Stockholm Convention for POPs since 2001.2 Following the Clean Water Act (CWA) in 1972, the United States Environmental Protection Agency (U.S. EPA) developed an analytical method, U.S. EPA Method 1668 and following revisions3 that can be applied for the determination of PCBs in wastewater, surface waters, soil, sediments, biosolids, and tissue matrices using gas chromatography coupled to high-resolution gas chromatography/ high-resolution mass spectrometry (HRGC/HRMS).3 However, recent advances in gas chromatography-triple quadrupole mass spectrometry allow for high sensitivity and selectivity, leading to the consideration of GC-MS/MS as a reliable tool for PCBs analysis. This application note reproduces the experiments described in a previously published application note,4 where polychlorinated biphenyls were analyzed using helium carrier gas. Here, helium was replaced by hydrogen. Additionally, the Thermo Scientific™ HeSaver-H2 Safer™ carrier gas saving technology was applied. HeSaver-H2 Safer technology offers a unique solution for laboratories to minimize carrier gas consumption during both standby and operational modes. When helium is used as carrier gas, the consumption can be drastically reduced without any changes to the analytical method or deterioration of performance. However, the Split-Splitless (SSL) injector modified to work in the HeSaver-H2 Safer mode can be used also in conjunction with hydrogen as a carrier gas, where the limited and fixed carrier gas flow allows for safe usage without the need to install additional sensors. At the same time, the hydrogen gas consumption is equally reduced and will lead to further cost savings, allowing laboratories to run their instrumentation longer on a single gas tank or using gas generators. Experimental The analytical method used for this study is described in a previous application note,4 however, minor modifications to the method were made and are summarized in Table 1. The use of hydrogen as carrier gas often leads to shorter retention times, if the analytical conditions, such as column, carrier gas flow rate, and oven program, remain unchanged. The retention times obtained using hydrogen as carrier gas can be found in Appendix 1. Table 1. GC-MS parameters modified in comparison to AN000561 SSL parameters Inlet module and mode SSL, HeSaver-H2 Safer, Splitless Split flow (mL/min) 50 (Nitrogen) Carrier gas, flow (mL/min) H2 ; 1.2 Pressurizing gas Nitrogen Oven Column Thermo Scientific™ TRACE™ TR-PCB 8 MS; 50 m, 0.25 mm, 0.25 μm (P/N 26AJ148P) TSQ 9610 mass spectrometer parameters Transfer line temperature (°C) 330 Ion source type and temperature (°C) AEI, 350 Emission current (μA) 10 Results and discussion Separation Maintaining chromatographic resolution is critical when analyzing PCBs. In the analyzed set of PCBs, the pentachlorobiphenyls, commonly referred to as PCB-123 and PCB-118, were monitored. These two compounds have similar retention times and identical transitions. Therefore, a good chromatographic method is necessary to avoid interference. With the TRACE TR-PCB 8 MS column, baseline separation of these two congeners was achieved (Figure 1) with no modification or amends to the chromatographic method. Instrumental detection limits One of the main concerns when changing the carrier gas from helium to hydrogen is a potential sensitivity drop. The instrumental detection limits (IDLs) were determined for the individual congeners by diluting the CS0.2 standard four times, so that a final concentration of 0.05 ng/mL was achieved. This solution was repeatedly injected (n=10). IDLs were calculated considering the one-tailed Student’s t-test values for the corresponding n-1 degrees of freedom at 99% confidence, the injected on-column (OC) concentration, and the absolute peak area %RSD (<15%) for each analyte. Figure 2 shows that the IDLs obtained with hydrogen were nearly identical to those with helium. All compounds had an IDL under 20 fg except PCB-209. 2 Figure 1. Quantifying peaks of all analyzed PCBs (A) and separation of the critical pair of PCB congeners 123/118 (B) 0 5 10 15 20 25 30 PCB-1 PCB-3 PCB-4 PCB-19 PCB-15 PCB-54 PCB-104 PCB-37 PCB-155 PCB-77 PCB-81 PCB-188 PCB-123 PCB-118 PCB-114 PCB-105 PCB-126 PCB-202 PCB-167 PCB-156 PCB-157 PCB-169 PCB-208 PCB-189 PCB-205 PCB-206 PCB-209 fg OC Instrumental detection limits H2 He Figure 2. Instrumental detection limits expressed as the mass of PCB injected on column 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 0.0e0 2.5e8 5.0e8 7.5e8 1.0e9 1.3e9 1.5e9 1.8e9 2.0e9 12.600 12.625 12.650 12.675 12.700 12.725 12.750 12.775 12.800 12.825 12.850 12.872 0.0e0 5.0e7 1.0e8 1.5e8 2.0e8 2.5e8 3.0e8 3.5e8 4.0e8 4.5e8 5.0e8 5.5e8 A) B) PCB-123 PCB-118 Counts Minutes Minutes Counts 3 ratio of 10 injections at 0.05 ppb. The reference values for the data in Figure 3B were the average ion ratios from the calibration curve. Linearity All investigated PCBs showed excellent linearity. All analytes achieved a coefficient of determination equal to or higher than 0.9998 (Figure 4A), and the relative standard deviation of the average response factor did not exceed 3% (Figure 4B). Ion ratio The correct ion ratio is very important for the unambiguous identification of the analytes. However, at low concentration levels it can deviate from the expected value and subsequently generate a false negative result. The reproducibility of the ion ratio was thus investigated across a wide concentration range. Figure 3A presents the ion ratio values of PCB-114 as an example, whereas Figure 3B depicts a deviation of the average Figure 3. Ion ratio of PCB 114 at various concentration levels (A) and ion ratio deviation of all analytes at 0.05 ppb (B) Figure 4. Evaluation of the linearity in the range 0.1–2000 ppb: coefficient of determination (A) and relative standard deviation of the average response factor (B) 0% 20% 40% 60% 80% 100% 120% 140% PCB 114 Ion ratio Average ratio + 20% Average ratio - 20% 0% 2% 4% 6% 8% 10% 12% PCB-1 PCB-3 PCB-4 PCB-19 PCB-15 PCB-54 PCB-104 PCB-37 PCB-155 PCB-77 PCB-81 PCB-188 PCB-123 PCB-118 PCB-114 PCB-105 PCB-126 PCB-202 PCB-167 PCB-156 PCB-157 PCB-169 PCB-208 PCB-189 PCB-205 PCB-206 PCB-209 Ion ratio deviation H2 He A) 0.1ppb 0.2 ppb 1 ppb 5 ppb 50 ppb 400 ppb 2000 ppb B) 0.9900 0.9920 0.9940 0.9960 0.9980 1.0000 PCB-1 PCB-3 PCB-4 PCB-19 PCB-15 PCB-54 PCB-104 PCB-37 PCB-155 PCB-77 PCB-81 PCB-188 PCB-123 PCB-118 PCB-114 PCB-105 PCB-126 PCB-202 PCB-167 PCB-156 PCB-157 PCB-169 PCB-208 PCB-189 PCB-205 PCB-206 PCB-209 Coecient of determination R2 H2 He 0.0% 2.0% 4.0% 6.0% 8.0% 10.0% 12.0% 14.0% 16.0% 18.0% 20.0% PCB-1 PCB-3 PCB-4 PCB-19 PCB-15 PCB-54 PCB-104 PCB-37 PCB-155 PCB-77 PCB-81 PCB-188 PCB-123 PCB-118 PCB-114 PCB-105 PCB-126 PCB-202 PCB-167 PCB-156 PCB-157 PCB-169 PCB-208 PCB-189 PCB-205 PCB-206 PCB-209 RSD AvCF H2 He A) B) 4 General Laboratory Equipment – Not For Diagnostic Procedures. © 2023 Thermo Fisher Scientific Inc. All rights reserved. All trademarks are the property of Thermo Fisher Scientific and its subsidiaries unless otherwise specified. This information is presented as an example of the capabilities of Thermo Fisher Scientific products. It is not intended to encourage use of these products in any manner that might infringe the intellectual property rights of others. Specifications, terms and pricing are subject to change. Not all products are available in all countries. Please consult your local sales representative for details. AN002549-EN 1023S Learn more at thermofisher.com/helium-saver Summary The HeSaver-H2 Safer inlet allows laboratories full flexibility to select the carrier gas of choice between helium and hydrogen, while achieving a significant reduction of the consumption. With a simple upgrade to the standard Thermo Scientific™ iConnect SSL injector, the HeSaver-H2 Safer inlet allows for the use of an inert and inexpensive gas for inlet pressurization, whereas the main carrier gas flow is limited to the column flow only. • The use of hydrogen as carrier gas has been demonstrated as an alternative to helium for the analysis of PCBs, reducing the overall cost of running the laboratory. • The use of the HeSaver-H2 Safer inlet reduces the amount of hydrogen going into the gas chromatography system such that safe operation is assured anytime, and no hydrogen sensor is needed inside the GC oven. • Hydrogen did not affect the linearity range; all compounds showed a linear response from 0.1 to 2000 ppb, with avarage R2 >0.999. • The TSQ 9610 triple quadrupole mass spectrometer provided excellent IDLs with hydrogen carrier gas, comparable to those obtained with helium. • The variation of ion ratios was less than 12% for all PCBs at 0.05 ppb. References 1. United States Environmental Protection Agency, U.S. EPA, Learn about Polychlorinated Biphenyls (PCBS), https://www.epa.gov/pcbs/ learn-about-polychlorinated-biphenyls-pcbs 2. Stockholm Convention. http://chm.pops.int/Implementation/IndustrialPOPs/PCBs/ Overview/tabid/273/Default.aspx 3. United States Environmental Protection Agency, U.S. EPA, Method 1668C - Chlorinated Biphenyl Congeners in Water, Soil, Sediment, Biosolids, and Tissue by HRGC/HRMS, April 2010, https://www.epa.gov/sites/default/files/2015-09/documents/ method_1668c_2010.pdf 4. Thermo Fisher Scientific, Application Note 000561: Reproducible trace analysis of PCBs in environmental matrices using triple quadrupole GC-MS/MS. https://assets. thermofisher.com/TFS-Assets/CMD/Application-Notes/an-000561-gc-ms-water-soilpcbs-an000561-en.pdf Appendix 1. List of PCBs retention times Compound Retention time [min] Compound Retention time [min] Compound Retention time [min] PCB-1 7.61 PCB-77 12.04 PCB-167 15.02 PCB-3 8.04 PCB-81 12.34 PCB-156 15.79 PCB-4 8.16 PCB-188 12.53 PCB-157 15.99 PCB-19 8.72 PCB-123 12.69 PCB-169 17.24 PCB-15 9.11 PCB-118 12.79 PCB-208 17.64 PCB-54 9.27 PCB-114 13.03 PCB-189 18.50 PCB-104 9.99 PCB-105 13.56 PCB-205 19.79 PCB-37 10.43 PCB-126 14.60 PCB-206 20.44 PCB-155 10.84 PCB-202 14.70 PCB-209 20.93