21 Tesla Fourier Transform Ion Cyclotron Resonance Mass Spectrometer: A National Resource for Ultrahigh Resolution Mass Analysis

B American Society for Mass Spectrometry, 2015 J. Am. Soc. Mass Spectrom. (2015) 26:1626Y1632 DOI: 10.1007/s13361-015-1182-2 RESEARCH ARTICLE 21 Tesla Fourier Transform Ion Cyclotron Resonance Mass Spectrometer: A National Resource for Ultrahigh Resolution Mass Analysis Christopher L. Hendrickson,1,2 John P. Quinn,1 Nathan K. Kaiser,1 Donald F. Smith,1 Greg T. Blakney,1 Tong Chen,2 Alan G. Marshall,1,2 Chad R. Weisbrod,1 Steven C. Beu3 1 National High Magnetic Field Laboratory, Florida State University, 1800 East Paul Dirac Drive, Tallahassee, FL 32310, USA Department of Chemistry and Biochemistry, Florida State University, 95 Chieftain Way, Tallahassee, FL 32306, USA 3 S. C. Beu Consulting, 12449 Los Indios Trail, Austin, TX 78729, USA 2 Abstract. We describe the design and initial performance of the first 21 tesla Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometer. The 21 tesla magnet is the highest field superconducting magnet ever used for FT-ICR and features high spatial homogeneity, high temporal stability, and negligible liquid helium consumption. The instrument includes a commercial dual linear quadrupole trap front end that features high sensitivity, precise control of trapped ion number, and collisional and electron transfer dissociation. A third linear quadrupole trap offers high ion capacity and ejection efficiency, and rf quadrupole ion injection optics deliver ions to a novel dynamically harmonized ICR cell. Mass resolving power of 150,000 (m/Δm50%) is achieved for bovine serum albumin (66 kDa) for a 0.38 s detection period, and greater than 2,000,000 resolving power is achieved for a 12 s detection period. Externally calibrated broadband mass measurement accuracy is typically less than 150 ppb rms, with resolving power greater than 300,000 at m/z 400 for a 0.76 s detection period. Combined analysis of electron transfer and collisional dissociation spectra results in 68% sequence coverage for carbonic anhydrase. The instrument is part of the NSF High-Field FT-ICR User Facility and is available free of charge to qualified users. Keywords: FT-ICR, FTMS, Fourier transform mass spectrometry Received: 5 March 2015/Revised: 28 April 2015/Accepted: 30 April 2015/Published Online: 20 June 2015 Introduction H igh field Fourier transform ion cyclotron resonance (FTICR) mass spectrometry offers the highest achievable broadband mass resolving power and mass accuracy of any mass analyzer [1, 2]. Resolving power and spectral acquisition rate improve linearly, and mass accuracy and dynamic range improve quadratically with magnetic field [3]. Resolving power greater than 1 million and mass accuracy better than 1 ppm become routine at sufficiently high magnetic field strength, and high resolving power and mass accuracy can be combined with on-line LC separation and MS/MS [4]. Consequently, increased magnetic field has been a persistent goal in FT-ICR instrument development. However, the expense and complexity of superconducting magnets scale with a high power of the Correspondence to: Christopher Hendrickson; e-mail: field strength, so fewer labs are able to acquire and support the highest field systems. We report here the design, construction, and characterization of the first 21 tesla FT-ICR mass spectrometer, which is the highest field system to date. The instrument is part of the National High Field FT-ICR User Facility at the National High Magnetic Field Laboratory (NHMFL), and is available to all qualified users. Experimental Reagents and Sample Preparation Bovine serum albumin (BSA) and carbonic anhydrase (CA) were used as received from Sigma-Aldrich (St. Louis, MO, USA) and diluted to 1 μM in 49:49:1 methanol:water:formic acid. Seven standard peptides (Sigma-Aldrich) were diluted in 49:49:1 acetonitrile:water:formic acid in the following proportion: leu-enkephalin (2 μM), beta-casomorphin (1 μM), angiotensin II (2 μM), angiotensin III (1 μM), C. L. Hendrickson et al.: 21 Tesla FT-ICR Mass Spectrometer bradykinin (1 μM), Substance P (2 μM), and melittin (1.5 μM). All samples were infused at 500 nL/min and ionized by microelectrospray [5]. Fluoranthene was used as received from Sigma-Aldrich for generation of electron transfer dissociation (ETD) reagent ions. 1627 21 Tesla Hybrid FT-ICR Mass Spectrometer NHMFL External Trap 21 T Magnet UHV Isolation Quadrupole Ion Transfer Optics Magnet The 21 tesla magnet (Bruker Daltonics, Billerica, MA, USA) room temperature bore diameter is 123 mm, the distance to field center is 1047 mm, and the overall length is 2272 mm. A set of eight cryoshims was used to achieve magnet spatial inhomogeneity less than 5 ppm over a 60 mm diameter by 100 mm long cylinder, which closely matches the working volume of the ICR cell. After shimming the magnet with only the NMR probe inside the magnet bore, the magnet axial inhomogeneity was rechecked with the ICR vacuum chambers and turbopumps in place. The measured difference was less than 1 ppm across the axial length of the ICR cell, so no effort was made to re-shim. No ferroshims were used but could be incorporated in the future, which would reduce the bore diameter to ~104 mm. The measured magnet drift rate was ~4 ppb/h two months after energization and has settled to less than 2 ppb/h after eight months of operation. The magnet cryostat is divided into two thermally separate regions. The lower section contains the complete set of magnet coils and ~1500 L of liquid helium. The upper section stores ~500 L of liquid helium at 4.2 K. A lambda refrigerator uses vaporization and gas expansion of liquid helium from the upper cryostat to cool liquid helium (and the magnet coils) in the lower cryostat to ~2.17 K, which allows magnet operation at 21 tesla. The magnet features a closed cryogenic system with no liquid nitrogen and negligible loss of liquid helium. Instead, the magnet is cooled by a pair of two-stage cryocoolers. The first stages are used to cool shields within the cryostat to ~50 K and the second stages cool surfaces in the upper cryostat to ~4 K to liquefy the helium gas generated by the lambda refrigerator and any boil-off from the upper bath. The cryocoolers and lambda refrigerator vacuum pump operate on an annual maintenance interval, at which time liquid helium can be added if necessary. FT-ICR Mass Spectrometer A schematic of the instrument is shown in Figure 1. The mass spectrometer combines a modified Velos Pro [6–8] (ThermoFisher Scientific, San Jose, CA, USA) with an NHMFL-designed external linear quadrupole ion trap, quadrupole ion transfer optics, and novel dynamically harmonized ICR ion trap (DHC) [9, 10]. The Velos Pro front end offers high sensitivity, efficient ion isolation, precise control of ion number, and both collisional dissociation and front-end electron transfer dissociation (FETD; we use the simpler term BETD^ here). The instrument was laser-aligned with the magnet bore by use of a set of transparent laser detectors (On-T (...truncated)