news
Small Paul ion trap big hit Smaller can be better! A. Chutjian and O. J. Orient at the California Institute of Technology introduce a new highresolution Paul ion trap mass spectrometer that’s diminutive in size (r0 = 10 mm) but big on sensitivity and results. With further development, they see such an instrument being used in harsh environments, such as under the sea, on the surface of other planets or asteroids, or in a spacecraft to monitor air during long flights to Mars or beyond. Chutjian and Orient scaled the lenses, trap, and detector of the new instrument to maintain both the required dimensional accuracy for high resolution and the trapping volume for high sensitivity and dynamic range. The instrument has a resolution of m/m = 324, which is limited by the machining accuracy of the trap. It has a demonstrated mass range of 1–300 u and a sensitivity for N2 of 2 1014 counts/Torr s or 500 pptr in a typical vacuum of 10–5 Torr—an improvement of ~100 times over an earlier miniature quadrupole mass spectrometer array. The researchers say that such a trap is potentially useful for harsh environments because it operates in a radio-frequency-only mode; no direct current is
Image not available for use on the Web.
required. Trapping is performed within the well depth of the dynamic radio frequency potential, and no cooling gas is needed. Furthermore, ionization of the
room-temperature gas within the trap is carried out with an electron beam traversing the trapping volume. (Rev. Sci. Instrum. 2002, 73, 2157–2160)
Solid-phase version of ICAT proteomics method Ruedi Aebersold and colleagues at the Insti-
the hydrogen (“light”) tag; a second sam-
tute for Systems Biology update the isotope-
ple uses beads bearing the deuterium
ments using Saccharomyces cerevisiae,
coded affinity tag (ICAT) method for quanti-
(“heavy”) tag. Cysteinyl peptides are cap-
the solid-phase technique identified and
tative proteomics. The new approach uses a
tured on the solid phase. The beads from
quantified more proteins than the standard
solid-phase capture-and-release process, in
both samples are combined, washed, and
ICAT method, the researchers say. In addi-
which a photocleavable linker is attached to
exposed to UV light to cleave the linkers.
tion, the new method permits stringent
aminopropyl-coated glass beads. An isotope
The recovered tagged peptides are then
wash conditions to remove noncysteinyl
tag containing seven hydrogen or deuterium
analyzed by µLC/MS/MS to determine the
peptides and requires less sample han-
atoms is attached to the opposite end of the
sequence, and the relative abundance of
dling, because the cysteinyl peptides are
linker and capped with a sulfhydryl-specific
each peptide is determined by comparing
isolated and the isotopes are incorporated
iodoacetyl group.
the peak intensities for the light- and
in a single step. (Nat. Biotechnol. 2002, 20,
heavy-tagged versions.
512–515)
One protein sample uses beads bearing
In both small- and large-scale experi-
J U LY 1 , 2 0 0 2 / A N A LY T I C A L C H E M I S T R Y
363 A
