Supplementary Material
Investigation into Accurate Mass Capability of Matrix-Assisted Laser Desorption/Ionization Time-of-Flight Mass Spectrometry, with respect to Radical Ion Species.
Mark F. Wyatt, Bridget K. Stein and A. Gareth Brenton.
EPSRC National Mass Spectrometry Service Centre, Department of Chemistry, University of WalesSwansea, SwanseaSA2 8PP, U.K.
Further Experimental Details
HPLC grade dichloromethane (DCM) and methanol (MeOH) solvents were purchased from Fischer Scientific (Loughborough, UK). DCTB matrix solution was made to a concentration of 10 mg mL-1 in DCM. Sample solutions were made to a concentration of 1 mg mL-1 in customer-specified solvent, which was DCM for 1-4, 6 and MeOH for 5. However, when it was not possible to weigh an exact amount of sample due to the small amounts submitted, 100 μL of solvent was added to the sample vial, 1 μL of each sample solution vortex-mixed with 49 μL of matrix solution, 0.5 μL of the final mixture spotted onto the gold-plated, deep-welled sample plate and allowed to dry.
The Voyager instrument was operated in positive ion, reflectron mode. The accelerating voltage was 20 kV, while the grid voltage was maintained at 66%. The delay time was 100 ns, but the laser fluence was optimized for each sample, and was attenuated to just above the threshold of ionization. The laser was fired at a frequency of 3 Hz and spectra were accumulated in multiples of 25 or 50 laser shots, with 50 shots in total (50 shots is the minimum number recommended for good peak shape). Voyager Sequence automatic acquisition parameters (in addition to those above): minimum resolution = 12000 (full-width half maximum, FWHM), minimum signal-to-noise ratio = 200, minimum/maximum signal intensity = 1000/40000a and 5000/40000b counts, respectively (aFor the comparison of data acquisition methods, 30 data points were acquired for each variable, from multiple sample spots, over three days. bFor the comparison of potential calibration standard compounds, 30 data points were acquired for each variable, from multiple sample spots, all on the same day). Manual acquisitions of 5 data points in total were acquired from multiple sample spots, all on the same day. Data Explorer automatically accounts for the mass of an electron, so no further correction of the calibrated data is necessary. Statistics were calculated using Microsoft Excel software. All ions measured in this study are either OE+· ion or EE+ ion species formed by dissociation, none are protonated (these are usually not formed with the aprotic matrix used in this study) or other adduct species.
Figure S1. MALDI-TOFMS spectrum of gold-(polyethylene glycol (PEG) carbene)-chloride, 1.
Figure S2. MALDI-TOFMS spectrum of (a)OE+·ion analyte, 2, and EE+ion standard, 1, and (b)OE+· ion analyte, 2, and OE+· ion standards, 3 and 4.
FigureS3. Plot of the errors in mass measurement accuracy (ppm) for OE+·ion analyte, 2, using EE+ ion, 1, and OE+· ion standards, 3 and 4, and automated Method A.
FigureS4. Plot of the errors in mass measurement accuracy (ppm) for OE+·ion analyte, 2,using EE+ ion, 1, and OE+· ion standards, 3 and 4, and manual Method A.
FigureS5. Plot of the errors in mass measurement accuracy (ppm) for EE+ion analyte, 5,usingOE+· ion standards, 2and6, and manual Method A.
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