product review
Ion Traps Come of Age Software control helps these versatile mass spectrometers mature. Zelda Ziegler
“I
on traps are almost unquestionably the most fascinating mass spectrometers,” argues Graham Cooks of Purdue University, “because they have so much chemistry and so much physics and so much math embedded into one device.” The versatility and productivity of ion traps have made them indispensable for applications as diverse as forensics, pharmacokinetics, and proteomics, with new developments still coming at the request of a broad customer base, say experts. Moreover, manufacturers offer interfaces to couple ion trap mass spectrometers to LC, GC, CE, or gel electrophoresis systems. These interfaces feature alignment rails, hinged chambers, or pins so that sources can be changed, cleaned, and easily realigned, in many cases, without breaking the vacuum, say the manufacturers. In addition, instrument control and data processing have significantly improved, mainly because of advances in software. Ion trap mass spectrometers were last reviewed by Analytical Chemistry four years ago (1998, 70, 533 A–536 A). This Product Review discusses new developments and surveys other improvements since then. Specifications and features of representative ion trapbased instruments with LC and GC capabilities are presented in Tables 1 and 2, respectively. This summary is not meant to be a comprehensive review of all ion trap MS systems; rather, it aims to provide general information on the capabilities and limitations of commercially available ion trap systems.
One less problem The modern three-dimensional quadrupole ion trap had its beginnings in a 1953 patent by the German physicist Wolfgang Paul and his collaborator Helmut Steinwedel. Paul later shared a Nobel Prize for the discovery, and consequently, ions traps are also referred to as Paul traps. Paul’s advance was a technique that
collected ions and maintained them in stable, mathematically predictable trajectories before detection. The total time for accumulation and scan is variable, but on the order of a few hundred milliseconds. Essential to the performance of modern ion traps is a relatively high pressure (1 mTorr) of helium bath gas, which enables collision-induced dis-
S E P T E M B E R 1 , 2 0 0 2 / A N A LY T I C A L C H E M I S T R Y
489 A
product review
Table 1. Selected LC-based ion trap mass spectrometers. esquire3000plus, esquire2000
Model
M-8000 3DQ LC/MS System
Company
Bruker Daltonics 978-663-3660 www.bdal.com or www.bdal.de
Hitachi High Technologies America 800-455-4440 www.hii-hitachi.com
Targeted applications
3000plus: proteomics; 2000: small molecules
Drug discovery, natural products, food analy- DecaXP Plus: proteomics; Advantage: small sis, and proteomics molecules
Chromatography
HPLC, capillary LC, CE
HPLC, CE, CEC, capillary LC
HPLC, CE, capillary LC, direct infusion
ESI, nanoESI, sonic spray ionization, AP-CI, micro-AP-CI
ESI2, AP-CI2, and AP-CI/AP photoionization2; static and dynamic nanospray; AP-MALDI
Stretched
Stretched
Stretched quadrupole
3000plus: 50–3000 standard mode, 100–6000 extended mode; 2000: 50–2200 standard mode, 100–4000 extended mode
10–2000 standard mode, 4000 and 20,000 extended mode
Deca XP Plus: (selectable) 15–200, 50–2000, 100–4000, or 1000–20,000; Advantage: 50–2000
Mass accuracy
±0.1 u across mass range
100 ppm over standard m/z range
±0.1 u
Mass resolution
3000plus: 5000 standard mode, 1300 at 650 u 5600
Scan speed (u/s) 5555
5
MS stages
5
Scan functions
Segmented scan; SIM; MS/MS and MSn; Full-scan MS; selected ion storage simultaneous full-scan MS and MS/MS; automated MSn dependent on base peak or isotopic data; dynamic exclusion
Options
Probes for highly polar, thermally labile, or solid compounds; pulsed positive-ion/negative-ion CI mode; computer-controlled damping gas for increased sensitivity; special kit allows instrument control and data processing from custom-written programs
Probe for solids, liquids, or slurries; turbo molecular or diffusion pump; detection via single-column split-effluent stream or parallel columns; electron-capture, pulsed flame photometric, thermionic specific, or flame ionization detection simultaneous with MS
Special features
S/N of 30:1 for 500 fg octafluoronaphthalene using EI; external ion source; 300 °C source stays clean; change ionization volumes without breaking vacuum; meets U.S. EPA tune requirements
Proprietary valve for instant column/detector switching; switch from EI to CI in
