Experimental Applied Biosystems Voyager DE-STR+ MALDI-TOF MS N2 laser (3 nsec pulse, λ = 337 nm) Laser intensity 2104, 96% grid voltage, 100 nsec delay extraction (unless otherwise noted on individual spectra) Linear mode Technics Hummer VI Sputter Instrument MALDI Plates Applied Biosystems Gold and Stainless Steel 100 well MALDI plates Multiple washings with tetrahydrofuran (THF), 6M nitric acid, DI water, and acetone Metal sheets Aluminum, brass, and copper metal sheets Cut into ~ 1cm 2 squares and mounted onto 4 well MALDI plate Multiple washings with THF, 6M nitric acid, DI water, and acetone ZnO nanorods and SiO 2 nanoparticles, suspended in methanol Polymers Cationizing salts Silver trifluoroacetate (AgTFA), sodium trifluoroacetate (NaTFA) Polymer/salt mixtures dissolved in THF and vortexed. 0.5 μL spotted on MALDI plates or metal sheets and allowed to air dry. Spectra analyzed by Polymerix ® and Data Analysis ® Nontraditional Matrices for Polymer Analysis by MALDI-TOF Mass Spectrometry Justin R. Engle, J. Ray Runyon, and S. Kim R. Williams Department of Chemistry and Geochemistry, Colorado School of Mines, Golden, CO 80401, email@example.com Abstract Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) has been used for the analysis of polymers. Organic matrices such as dithranol, trans-retinoic acid, and 2,5-dihydroxybenzoic acid (DHB) are commonly used to facilitate desorption and ionization of polymers. However, the use of these organic matrices leads to matrix signals at m/z values below ~1000 Daltons. Consequently, the usefulness of this low m/z region is severely compromised (Figure 1). MALDI-TOF MS of biological samples and 200 Daltons poly(ethylene glycol) has been done with nanosized inorganic particles (instead of organic matrices) [1,2]. Various metal substrates (no matrix) have also been used for protein analysis with an infrared laser . Our study extends these concepts of inorganic particles and matrixless MALDI-TOF MS to low molecular weight organosoluble polymers. References:  Q. Zhang, H. Zou, Z. Guo, Q. Zhang, X. Chen, J. Ni. Rapid Commun. Mass Spectrom. 15, 217-223 (2001).  T. Kinumi, T. Saiso, M. Takayama, H. Niwa, J. Mass Spectrom. 35, 417-422 (2000).  D. Rousell, S. Dutta, M. Little, K. Murray, J. Mass Spectrom. 39, 1182-1189 (2004). AnalyteSupplier*Nominal MWPolydispersity Polystyrene 800 (PS 800) APSCM w 826 M n 726 1.14 Polystyrene 2200 (PS 2200) PEM w 2200 Poly(ethylene glycol) 700 (PEG 700) APSCM w 700 M n 645 1.09 Poly(ethylene glycol) 1690 (PEG 1690) APSCM w 1690 M n 1615 1.05 Objectives Decrease matrix mass signals below ~1000 Dalton and perform MALDI-TOF MS analysis of low molecular weight polymers. Use inorganic particles (SiO 2 nanoparticles, ZnO nanorods, and gold sputter) in lieu of organic matrices. Eliminate matrix altogether and evaluate the feasibility of MALDI-TOF MS analysis of low molecular weight polymers directly off MALDI plates (gold and stainless steel) and metallic substrates (aluminum, brass, and copper). Figure 1: 2,5-DHB (9.85 mg/mL in THF); PS 800 (1.12 mg/mL in THF); AgTFA (4.88 mg/mL in THF). Polymer:Matrix:Salt :: 1:9:4. Laser intensity 1926. Figure 1 shows significant matrix interferences below ~1000 Daltons. Two PS 800 adduct series can be discerned. The 104 m/z difference is indicative of PS oligomer. Figure 2: PS 800 (4.99 mg/mL) with AgTFA (5.10 mg/mL) in 1:1 (v/v) on clean aluminum sheet. At peak 892 m/z: resolution - 195; S/N - 237.9:1. Calculated M w 939 and M n 822 Figure 4: PS 800 (4.99 mg/mL) with AgTFA (5.10 mg/mL) in 1:1 (v/v) on brass metal sheet. At peak 996 m/z: resolution - 182; S/N - 347.4:1 Calculated M w 866 and M n 746. Figure 3: PS 800 (4.99 mg/mL) with AgTFA (5.51 mg/mL) in 1:1 (v/v) on clean copper metal sheet. At peak 891 m/z: resolution - 162; S/N - 123.0:1. Calculated M w 744 and M n 625. Figures 2 thru 4 show successful MALDI analysis of PS 800 on aluminum, copper and brass metal sheets. The signal:noise ratios are clearly improved in all cases. The peaks at m/z 107, 214, and 326 are due to silver clusters. The source of the low intensity background signals is unclear. The same metal substrates were also successful for the analysis of PEG 700 and PEG 1690. Figure 5: PS 800 (10.8 mg/mL) with AgTFA (4.89 mg/mL) in 1:1 (v/v) on Clean 100 well Gold MALDI plate. Laser intensity 1926, 200 nsec delay. At peak 794 m/z: resolution 146; signal to noise 89.3 to 1. Calculated M w 692 and M n 647 Figure 6: PS 800 (4.99 mg/mL) with AgTFA (5.42 mg/mL) in 1:1 (v/v) on Clean 100 well Stainless Steel MALDI plate. Laser intensity 1926. At peak 792 m/z: resolution 191; S/N 129.5 to 1. Calculated M w 676 and M n 610 Figure 7: PS 800 (4.99 mg/mL) with AgTFA (5.51 mg/mL) in 1:1 (v/v) on gold sputtered film with aluminum metal sheet backing. At peak 997.83 m/z: resolution - 103; S/N - 91.1:1. Calculated M w 1189 and M n 1030. Figure 8: PS 800 (0.25 mg/mL) with uncoated SiO 2 nanoparticles in 1:1 (v/v) on 100 well stainless steel MALDI plate. Laser intensity 2400, 60% grid voltage, 10 ns delay extraction. At peak 690 m/z: no peak resolution; S/N 50.9:1. Calculated M w 864 and M n 780. Acknowledgements NSF-CHE-0515521 Dr. Dean Lee, Chemistry and Geochemistry Dept., Colorado School of Mines Dr. Frank Osterloh Chemistry Department University of California Davis for ZnO and SiO 2 nanoparticles Conclusions Low molecular weight polymers can be analyzed by MALDI-TOF MS without using traditional organic matrices. Gold sputtering and uncoated SiO 2 nanoparticles worked well for PS800 while ZnO proved successful for PEG. The use of metal substrates and MALDI plates in the absence of matrix allowed analysis of Ps and PEG polymers with molecular weights below 1000 Daltons. PS 800 with 2,5-DHB PS 800 on Various Metal Substrates PS 800 on MALDI Plates PS 800 with Inorganic Particle Matrix Figures 5 and 6 show PS 800 on gold and stainless steel MALDI plates, respectively. In Figure 5, several peaks are attributed to gold (197, 394, and 591 m/z) and silver (107, 214, and 321 m/z) clustering. The stainless steel plate consistently showed good results for PEG 700 and PEG 1690 whereas the MALDI gold plate produced inconsistent results for the analysis of polymers. Figures 7-10 show the use of inorganic particles for MALDI analysis of polymers. Gold sputtering led to successful MALDI of PS 800 and 2200 and PEG 700 and 1690. Possible carbon contamination can be seen below ~500 m/z from the Hummer Technics VI instrument. The uncoated SiO 2 nanoparticles, Figure 8, display multiple mass signals below ~500 m/z not associated with the polymer. The uncoated SiO 2 nanoparticles were also successfully used with PEG 700 and 1690. The ZnO nanorods were unsuccessful in the analysis of PS800 but successful for PEG 700 and PEG 1690 (Figure 10). *APSC – American Polymer Standards Corporation, PE – Perkin Elmer Figure 9: PS 800 (0.25 mg/mL) with ZnO nanorods in 1:1 (v/v) on 100 well stainless steel MALDI plate. Laser intensity 2200, 60% grid voltage, 10 ns delay extraction. Figure 10: PEG 700 (0.53 mg/mL) with ZnO nanorods (in methanol) in 1:1 (v/v) on stainless steel MALDI plate. Laser intensity 1802; 94% grid voltage. At peak 465.67 m/z: resolution - 1160; S/N - 1079.1:1. Calculated M w 560 and M n 509. 4 Well MALDI Plate Aluminum, Brass and Copper substrates
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