Optimized Analysis of Semi-Volatile Organic Compounds

Optimized analysis of semi-volatile organic compounds (SVOC) in environmental samples in compliance with U.S. EPA Method 8270 utilizing GC-MS Authors Amit Gujar1, Kenneth M Free1, Tim Anderson1, and Adam Ladak2 1Thermo Fisher Scientific, USA 2Thermo Fisher Scientific, UK Keywords ISQ 7610 mass spectrometer, TRACE 1610 GC, GC-MS, EPA Method 8270, trace analysis, gas chromatography, single quadrupole mass spectrometry, phthalates, semi-volatile organic compound, SVOC, SVOA, base neutral acids, BNA, organic contaminants Introduction Semi-volatile organic compounds (SVOCs) are ubiquitous in our environment and raise concerns regarding health for humans and wildlife. They are released in various everyday processes, including manufacturing and agriculture. Thus, the analysis of SVOCs in extracts of many matrices, such as solid waste, soil, air, and water, is commonly performed by environmental testing laboratories. Regulations are in place worldwide to monitor the presence of SVOCs in environmental samples to protect the environment and human exposure. The United States Environmental Protection Agency (EPA) released the first SVOC method by gas chromatography/mass spectrometry (Method 8270) at the end of 1980.1 EPA Method 8270D and derivative methods are now used in environmental labs globally to monitor SVOCs. Analytical testing laboratories that follow EPA 8270 methodology for the analysis of SVOCs must comply with several requirements before starting the analysis. These include the ability for the MS instrument to pass decafluorotriphenyl phosphine (DFTPP) tuning criteria, relative retention time (RRT) of target analytes criteria, linearity of calibration curve criteria, and suggested minimum response factors. This application note shows how the Thermo Scientific™ ISQ™ 7610 single quadrupole GC-MS system can meet EPA Method 8270D requirements. One of the unique features of the ISQ 7610 single quadrupole MS systems is NeverVent™ technology, which allows laboratories to minimize instrument downtime with fast removal of the ion source for maintenance and to change the analytical column without venting the system. The ISQ 7610 MS also introduces a new detector, the XLXR™ detector system, with a wider linear dynamic range and longer lifetime compared to previous generation detectors. Experimental For these experiments, an ISQ 7610 single quadrupole MS system was equipped with the Thermo Scientific™ ExtractaBrite™ ion source and coupled to a Thermo Scientific™ TRACE™ 1610 GC. The Thermo Scientific™ iConnect™ Split-Splitless (SSL) Injector module (P/N 19070010) was used as the GC inlet. Thermo Scientific™ Chromeleon™ Chromatography Data System (CDS) software was used to acquire, process, and report data. The instrument method parameters are shown in Table 1. Tuning The default ISQ 7610 “EI Full Tune” is optimized for maximum sensitivity, allowing the user to achieve low ppb levels of analyte detection. The concentration of SVOC for most analyses using the EPA Method 8270 is in the ppm range; hence, the default EI Full Tune was modified using the “Advanced AutoTune” option to lower the overall sensitivity of the MS system. The tuning emission current was reduced to 10 µA and the detector sensitivity was adjusted to deliver 5 million counts for m/z 219 for perfluorotributylamine (PFTBA). Adjusting the detector sensitivity changes the gain on the detector (and hence the electron multiplier voltage) to achieve the required sensitivity. An added benefit of this AutoTune procedure is that it extends the life of the electron multiplier because the gain, in most cases, is lower than the default EI Full Tune option. EPA Method 8270 uses a dynamic tuning procedure for checking the MS tuning performance. This is done by using decafluorotriphenyl phosphine (DFTPP) and checking various m/z ions and their relative intensities. Figure 1 shows the total ion chromatogram (TIC) of the GC-MS tuning mixture (Restek Cat. No. 31615) containing DFTPP, and Figure 2 shows the mass spectrum for the DFTPP. Chromeleon CDS software has a dedicated reporting package for environmental laboratories and automatically reports tune evaluation performance with a Pass/Fail indicator. Table 2 shows the DFTPP ion abundance spectrum check criteria according to EPA Method 8270D and passing evaluation result for the injection. The other components of the GC-MS tuning mix include pentachlorophenol, benzidine, and 4,4’-DDT, which are primarily used to check for inlet inertness and column performance. Peak tailing for pentachlorophenol and benzidine is an indication of basic and acidic active sites in the inlet and/or column, possibly requiring inlet maintenance including trimming the front end of the column. EPA Method 8270D requires that the tailing factor for these two compounds be not more than 2. The injection of the GC-MS tuning mix gave tailing factors of 1.22 and 1.18 for pentachlorophenol and benzidine, respectively. 4,4’-DDT is used to assess inlet performance with the criteria that the breakdown products DDD and DDE be no more than 20%. No degradation of DDT was observed, thus indicating pristine inlet conditions. Table 1. Autosampler, GC, and MS instrument method parameters Parameter AS 1610 Autosampler Syringe Injection volume Pre-injection solvent and cycle Sample rinses Value 10 µL, 25 gauge, 50 mm length, cone tip (P/N 36500525) 1 µL Acetone, 2 cycles 3 Post-injection solvent and cycles Dichloromethane, 2 cycles Injector draw speed Fill Strokes Air volume Pre-injection delay time Post-injection delay time TRACE 1610 GC system Column Liner SSL mode Inlet temperature Split flow Septum purge flow Carrier flow Oven program ISQ 7610 MS system MS transfer line temperature Ion source temperature Source type Slow 3 1 µL 0.0 min 3.0 min Thermo Scientific™ TraceGOLD™ TG-5ms, 30 m × 0.25 mm × 0.5 µm (P/N 26098-2230) Splitless liner single taper with wool, 4 mm i.d., 78.5 mm length (P/N 453A1925-UI) Split 300 °C 15 mL/min (split ratio = 10) Constant flow of 5.0 mL/min Constant He flow of 1.5 mL/min 37 °C (2.0 min) 25 °C/min to 100 °C (0.1 min) 30 °C/min to 280 °C (0.1 min) 10 °C/min to 320 °C (5.0 min) Total run time = 19.9 min 300 °C 320 °C ExtractaBrite with EI ion volume Ionization mode, Electron energy EI, 70 eV Emission current 10 µA Scan range Dwell time Detector gain 2 35–500 Da 0.1 s Last saved AutoTuneFigure 1. TIC of the GC-MS tuning mixture Figure 2. Mass spectrum of the DFTPP peak Table 2. DFTPP ion abundance spectrum check criteria results according to EPA Method 8270D Evaluated mass, m/z 51 68 70 127 197 198 199 275 365 441 442 Ion abundance criteria 10–80% of base peak <2% of m/z 69 <2% of m/z 69 10–80% of base peak <2% of m/z 198 Base peak, or >50% of m/z 442 5–9% of m/z 198 10–60% of base peak >1% of m/z 198 Measured % relative abundance 14.2 1.7 0.4 Criteria evaluation result, Pass/Fail Pass Pass Pass 26.1 0.0 59.3 6.2 18.4 4.2 Present but <24% of m/z 442 Base Peak, or >50% of m/z 198 443 15–42% of m/z 442 15.6 Base peak 18.6 Pass Pass Pass Pass Pass Pass Pass Pass Pass 3Standard and sample preparation Standards (Restek 8270 MegaMix Cat. No. 31850, AccuStandard Internal Standard Cat. No. Z-014J, AccuStandard Surrogate Cat No. M-8270-SS) were prepared in methylene chloride. Target compound concentration ranged from 1 to 400 ppm with internal and surrogate standards spiked at a constant concentration level of 4 ppm over 11 calibration levels. A wider target concentration range, compared to that presented in a previous application note (AN10522), was investigated, and this was made possible due to the extended dynamic range of the new XLXR detector system in the ISQ 7610 MS. A chromatogram for the 40 ppm calibration standard is shown in Figure 3 with the investigated calibration levels outlined in Table 3. Table 4 provides retention time and quantification ion information for all analytes, internal standards, and surrogates standards. Identities of all compounds were confirmed by comparison with the NIST library match with a total of 76 target analytes, 6 surrogates, and 6 internal standards. The associated internal standard for each analyte is provided in the table and is in accordance with EPA 8270D methodology. Table 3. Analyte, internal standard, and surrogate concentration levels used for this study Level Cal 1 Cal 2 Cal 3 Cal 4 Cal 5 Cal 6 Cal 7 Cal 8 Cal 9 Cal 10 Target analyte concentration ppm 1 2 5 10 20 40 50 75 100 Internal standard concentration, ppm 4 4 4 4 4 4 4 4 4 Surrogate concentration, ppm 4 4 4 4 4 4 4 4 4 200 Cal 11 400 4 4 4 4 Figure 3. TIC of the 40 ppm semivolatile mix spiked with internal standards and surrogates