Investigation of programmable temperature vaporisation as a sample introduction method for ambient ionisation MS Bryan McCullough, Camilla Liscio, Christopher Hopley Queens Road, Teddington, Middlesex, TW11 0LY, UK [email protected] Introduction Recent work in our group has focussed on the use and development of ambient ionisation techniques for real-world applications. One such application is the detection of biodiesel (fatty acid methyl ester; FAME) contamination in jet fuels. The current approach for testing jet fuels involves off-site measurement of FAME content, typically by GC/MS methods with run times often in excess of 40 minutes. Given the potential for major incidents should contamination occur there is a desire to develop fast, at-site methods for the measurement of FAME in jet fuel with one approach being the combination of ambient ionisation with miniaturised mass spectrometry. Here, we describe our investigation of atmospheric solids analysis probe (ASAP) and subsequent development of a programmable temperature vaporisation (PTV)-based method for sample introduction. Initial Study PTV-CDI-MS PTV Sample Introduction The legal limit for total FAME in jet fuel is 5 mg/kg. Samples were prepared for this study by spiking a FAME CRM (IRMM, ERM-EF001) into Jet A1 fuel at levels between 1 and 250 mg/kg. The samples were then analysed from a glass rod dipstick by ASAP-MS using a modified APCI source on a Quattro Ultima QqQ MS (Micromass, Manchester, UK). The full range of standards was analysed in both full-scan and SIM modes (monitoring for C14 to C18 FAME). Figure 1 shows a typical mass spectrum obtained for the 250 ppm sample. The set of FAME in jet fuel standards was analysed by PTV corona discharge ionisation MS as follows: Injection volume: 10 µL Injection temperature: 70 °C Vent time: 30 s Temperature ramp: 16 °C/s Hold temperature: 320 °C Hold time: 180 s PTV is routinely used in GC/MS to allow temperature discrimination during the injection stage. We modified our APCI probe in order to interface the MS with an ATAS Optic 2 PTV as shown in Figure 2. 134.2 C18 120.1 297.6 134.1 100 121.2 147.1 161.1 165.1 137.3 % 187.3 189.2 201.3 187.3 105.1 215.4 265.5 247.5 263.5 255.3 101.2 % 0 80 105.0 217.3 229.4 C14 239.4 241.4 C16 103.2 120 140 160 180 200 220 240 260 280 297.5 298.5 300 120 140 160 180 200 220 240 260 283.3 298.5 299.3 C20 371.4 309.5 313.5 280 CD Needle 300 320 340 360 Using this set-up samples are injected onto the PTV then selectively transferred to the MS or sent to the vent valve across a temperature program. 380 400 420 440 460 480 500 m/z 520 Figure 3: PTV-CDI-MS mass spectrum of 250 ppm FAME in jet fuel. C18 253.4 279.4 100 293.5 229.4 104.8 105.2 100 C16 201.3 105.2 350 °C Figure 2: Schematic of PTV-CDI-MS 295.5 C14 118.8 215.4 107.2 0 80 159.2 173.1 Scan AP+ 1.34e8 151.3 119.1 N2 Flow Scan AP+ 8.29e7 Transfer Line 120.2 100 MS Inlet APCI Probe Jet Fuel ptv test through probe Components BMC_120814_002 578 (10.708) Cm (576:579) 119.2 121.2 Jet Fuel avtur 25ppm 4567 biodiesel asap rods Components BMC_080814_006 78 (1.479) Cm (78:88) PTV w/ focus liner C20 320 340 360 Figure 1: Mass spectrum for 250 ppm FAME in jet fuel by ASAP-MS From the full data set the following was apparent: 380 400 As before samples were analysed by full scan and SIM. Figure 3 shows a typical mass spectrum for 250 ppm FAME in jet fuel demonstrating the clear enhancement in signal for the FAMEs and reduction in jet fuel signal (cf. fig. 1). 420 • The mass spectra are dominated by jet fuel components • The peak widths for ASAP are very narrow with few points across a peak • Repeated analysis of fuel coated glass rods quickly contaminated the source The net result of these observations was a limit of detection (S/N > 3) in SIM mode of 100 ppm. 460 480 12 500 m/z 520 Calibration Curve C18:1 10 Normalised Intensity • Sample loading using the dipstick method is inconsistent 440 8 6 y = 0.0398x + 0.0221 R² = 0.99459 4 2 0 0 50 100 150 200 250 300 Total FAME (mg/kg) Figure 4: Calibration curve for C18:1 The limit of detection using this method was found to be between 5 and 10 mg/kg total FAME. Figure 4 shows the calibration curve obtained for the C18:1 ion showing good linearity in the 5-250 ppm range. Conclusions & further work • ASAP-MS was unable to produce the required sensitivity, primarily due to matrix interference • PTV sample introduction provides temperature discrimination during sample introduction allowing the volatile matrix components to be vented prior to analysis of the less volatile compounds of interest. Using this approach it is possible to reach the required sensitivity limits. • Further work is required to examine the potential for true quantitative analysis in this application e.g. addition of an internal standard • In future we plan to examine how this sample introduction technique can be coupled with the new generation of miniaturised MS instrumentation Acknowledgements: The work described was supported by the UK National Measurement System Chemical and Biological Metrology Programme. 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