Mass Spectral Determination of Organo-Metallic Compounds by Very High-Resolution Mass Spectrometry

Robert Swaim1, Kei Murata2, Todd B. Marder2, H. Bernard Linden3, Mathias H. Linden3, Alexander Makarov4, Maciej Bromirski4 1Thermo Fisher Scientific, San Jose, CA, USA, 2Institute for Inorganic Chemistry, Julius-Maximilian-University, Wurzburg, Germany, 3Linden CMS GmbH, Weyhe/Leeste, Germany; 4Thermo Fisher Scientific GmbH, Bremen, Germany

Exactive Plus Orbitrap LC-MS C51H59N2O6P2Rh Isotope pattern of Grubbs Hoveyda Catalyst LIFDI of PEG 1500 Overview with two ion sources on axis

Liquid injection field desorption ionization (LIFDI) is a soft high vacuum ionization technique based on FI/FD.

We present a very high-resolution Thermo Scientific™ Exactive™ Plus Orbitrap mass spectrometer combined with an LIFDI ion source (measured) installed at the back end of the ion path in addition to the ESI source at the front end. This way difficult non-polar compounds such as organo-

metallic catalysts can be characterized which are not accessible by ESI.

(calculated)

LIFDI source at (air sensitive) back end for Introduction non-polar samples

Organo-Metallic compounds are often subject to reaction with air or moisture and do not tolerate protonation or attachment of other ions. Convenient changing of ion sources: working source switched-off, This makes them difficult analytical challenges for assay with mass ESI source at front the other source switched-on, spectrometry. end for LC/MS loading respective tuning, and using respective capillary Field Desorption (FD) has proven an effective way to ionization of these Figure 6. Instrument: Exactive Plus Orbitrap LC-MS with materials resulting in M+• species via a soft ionization process. LIFDI source. Figure 2. Instrument: Exactive Plus Orbitrap LC-MS with Figure 4. Instrument: Exactive Plus Orbitrap LC-MS with LIFDI shares the ionization with FI/FD but transfers the sample by a Figure 1. Instrument: Exactive Plus Orbitrap LC- MS with LIFDI source from Linden CMS, Germany. LIFDI source. LIFDI source. fused silica capillary from ambient pressure to the LIFDI emitter in the LINDEN CMS GmbH Results ion source vacuum. With high-voltage applied, difficult materials desorb as intact M+• ions. • Fig. 2 shows clean spectra of an air sensitive rhodium complex with LIFDI of Grubbs Hoveyda Catalyst Ru4H4(CO)12 intense molecular ion M+• without fragmentation. With the atmospheric source ESI at the front end and the high vacuum source LIFDI at the back end of the ion path, the Exactive Plus LC-MS • Fig. 3 shows the spectra of a reactive ruthenium containing metathesis can be switched back and forth between LIFDI and ESI LC/MS C31H38Cl2N2ORu catalyst. operation without any venting (see Figure 1). Just loading the m/z 626.1405 Methods respective tuning and using the LIFDI or ESI capillary is required. • Fig. 4 shows the measured (above) versus calculated (below) isotope pattern of the catalyst’s intact molecular ion. The sample is placed in a vial. A syringe needle punctures the vial’s septum and the capillary is lowered through the needle into the sample • Fig. 5 shows another Ru species and the loss of CO with a nice match for ca. 2-3 seconds. The vacuum of the LIFDI ion source pulls a plug of between calculated and measured isotope pattern. sample into the capillary and forces it to the emitter filament. This • Fig. 6 provides the spectra of a PEG 1500 mixture dominated by singly process can be done by an autosampler resulting in automated LIFDI. charged ions. (very reactive) Solvent is evaporated from the large whisker surface within a few seconds. The sample is then field-desorbed off the emitter with a Conclusion heating cycle and the ions are drawn into the mass spectrometer and

characterized. Reactive air/moisture sensitive compounds can be accessed with the Exactive Plus Orbitrap instrument equipped with LIFDI-ESI combination

without excessive experimental effort. Changing from one technique to

the other is quick and very convenient.

LIFDI spectra can exhibit intense peaks of intact molecular radical ions M+• from compounds which do not provide meaningful mass spectra by EI or ESI methods.

Figure 3. Instrument: Exactive Plus Orbitrap LC-MS with Figure 5. Instrument: Exactive Plus Orbitrap LC-MS with All trademarks are the property of Thermo Fisher Scientific and its subsidiaries. This information is not intended to encourage use of these products in any manners that might infringe the LIFDI source. LIFDI source. intellectual property rights of others.

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