Product
Review
Electrospray in Flight Orthogonal acceleration bringstheadvantages of time of flight to electrospray Atfirstglance, electrospray ionization (ESI) and time-of-flight (TOF) mass analysis seem an unlikely pair. After all, electrospray produces a continuous stream of ions, and TOF requires pulsed operation. According to Kenneth Standing of the University of Manitoba (Canada) physics department, electrospray and TOFMS can be interfaced axially, but sensitivity in this geometry is very low, on the order of 0.1% or less. However, orthogonal acceleration TOFMS eliminates such problems. Rather than being interfaced axially, the ion source and flight tube are positioned at right angles, and ions are pulsed into the flight tube by the application of voltages. "With orthogonal injection, you effectively have a storage region. You're putting this very low energy beam in, and it's drifting along like a long sausage. You can inject a fairly reasonable proportion of that sausage into the flight tube," says Standing. The instruments that are commercially available for ESI-TOFMS can be divided into two types—the single MS instruments from Analytica of Branford, Bruker Daltonics, Micromass, PerSeptive Biosystems, and Sensar Larson Davis (available in North and South America from Jeol USA) and the tandem MS instruments from Micromass and PE SCIEX. Some of the specifications for these instruments sre listed in Table 1. The single MS instruments consist of electrospray sources interfaced to rf-only ion guides (quadrupoles in some cases, hexapoles in others). The ion guides serve two purposes. They focus the ion Celia M. Henry
beam so that it has forward velocity but little sideways velocity, and they deliver the ions to the TOF analyzer, which is perpendicular to the ion guide. For example, a packet of positive ions is pulsed into the TOF analyzer by applying a positive voltage to grids—the ions separate in the flight region according to their m/z values, and they are detected when they strike a microchannel plate and anode detector assembly. The signal from the detector is digitized with either a time-to-digital converter (TDC) or an analog-to-digital cori-
verter (ADC) The digitization rate and the tvoe of digitizer affect the performance characteristics of the instrument With the exception of the Sensar instrument the systems include reflectron TOF analyzers The instruments which can
be ODerated i
struments because of the addition of a mass-resolving quadrupole. Why ESI-TOF?
TOF mass analysis brings several advantages to ESI—primarily mass range, speed, mass accuracy, and mass resolution. TOF has a theoretically unlimited mass range. In some ways, this might seem unnecessary for ESI, which produces ions in highcharge states. Many people have asserted that ESI does not produce ions beyond m/z 4000, which is within the range of modern quadrupoles. Standing agrees that the larger mass range is often unnecessary. However, he adds, "If you decide you want to look at noncovalent complexes, that argument doesn't hold. The accessible sites for protonation may be buried in the interior of a noncovalent complex. You tend to get a higher m/z.
TV T S
or MS/MS '
mnHp differ fmm the sintrle Analytical MS T O F inChemistry News & Features, March 1, 1999 197 A
Product
Review
Product
Enterprise
BioTOF
LCT
Company
Analytica of Branford
Bruker Daltonics
Micromass
29 Business Park Dr.
Manning Park
100 Cummings Center, Ste. 407N
Branford, CT 06405
19 Fortune Dr.
Beverly, MA 01915-0061
Billerica, MA 01821
800-390-4660
203-488-8899
978-667-9580 URL
www.aob.com
www.daltonics.bruker.com
www.micromass.co.uk
Price (U.S. dollars)
INA
$295,000
-$200,000
Dimensions Footprint (cm)
69 W x 62 H x 56 D
180 W x 81 D
90 W x 76 D
Weight (kg)
91
350
130
MS type
MS
MS
MS
Ion source
Electrospray (5-1500 uL/min); APCI
High- and low-flow-rate electrospray; Electrospray (5-1000 uL/min) or at-
(100-2000 uL/min)
microspray and nanospray; dual
mospheric pressure chemical ioniza-
spray for quasi-internal calibration;
tion (200-2000 uL/min); nanoflow
negative or positive ions
electrospray (10-1000 nL/min) samples may be directly infused in solution or the system may be interfaced to an HPLC system
Mass analyzer
1 -m effective path length with single- 3-m effective path length with
Reflectron time-of-flight mass ana-
stage reflectron
lyzer with a two-stage orthogonal
reflectron
extraction region and linear reflectron
Detectors
Dual microchannel plate with post-
Dual microchannel plate detector
Dual microchannel plate and anode
acceleration enhancement
assembly
detector assembly
Mass range
20-20000 mlz
>10,000 m/z
13,000 mlz at full acquisition rate
Mass resolution (ml\m)
5000 FWHM at mlz 1500
>10,000 FWHM
5000 FWHM at mlz 1000
Mass accuracy
10 ppm (with quasi-internal
5 ppm (with quasi-internal
Better than 5 ppm RMS at 1 giga-
(with internal calibration)
calibration)
calibration)
byte/s acquisition rate
Pulse repetition rate (Hz)
Up to 20,000
Not applicable
Up to 20,000
Spectral storage rate
100 spectra/s
2 - 1 0 spectra/s
10 spectra/s
Computer system
Pentium-based PC
INA
Pentium II 450 MHz
Software
Data system operating under
Data system operating under
Microsoft NT 4.0 operating system;
Windows NT
Windows NT
MassLynx NT MS
Low-flow ESI probe (50-1000 nl_/
Atmospheric pressure chemical ion-
Atmospheric pressure chemical ion-
min); dual ESI probes; CE/MS probe
ization; nanospray; low-frequency ion ization; nanoflow electrospray; CE guide for high -m/z ions electrospray; OpenLynx, open-ac-
Options
cess, walk-up, exact mass and combinatorial chemistry software; protein/ peptide-sequencing software
Special features
Reader service number
Multistage hexapole ion guide can
Demonstrated high m/z capabilities;
accumulate ions between pulses for
low pressure minimizes collisions in
mass measurement on the fly; inte-
very high sensitivity analyses; fast
flight tube (operating pressure
