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Best of both worlds When it comes to MS", basically two choices are available—the Paul trap (the "quadrupole ion trap") and the Penning trap (used in FT ion cyclotron resonance)—each with its advantages and disadvantages. The Penning trap offers extraordinary mass accuracy and mass range but requires much lower pressures than the Paul trap. How about a hybrid that offers the best of both ion traps? Alan Marshall and his co-workers at Florida State University do just that with a "combined linear ion trap". The new ion trap consists of three sections, each formed from four circular parallel rods. The middle section is held at ground bias voltage, and ions along or opposed to the magnetic field direction are confined by applying the same static bias potential to both sets of endcap rods.
The configuration of a linear combined ion trap. (Adapted with permission. Copyright 1997 American Society for Mass Spectrometry)
Relative to the conventional Penning trap, the combined linear ion trap can better tolerate ion-neutral collisions without destabilizing the trajectories of the ions. Also, the new trap has no theoretical upper mass limit, so the effective upper llmit is simply that mass at which the cyclotron radius of the ion approaches the radius of the trap. Compared with the Paul trap, the combined trap has a strong magnetic field, which allows the application of FT-ICR techniques for mass determinations with ultrahigh accuracy and resolution. The authors point out that one disadvantage relative to a conventional Penning trap is the need for an additional rf voltage generator and the concomitant need tofilterthe signal at the rf driving frequencv (/. Am Soc Mass Sbectrom 1997 8 962-69) S0003-2700(97)09043-4 CCC: $14.00 © 1997 American Chemical Societv
Electrically controlled fluids Electric fields have been successful in manipulating the flow of aqueous solvents within microchip systems, eliminating the need to manually open and close valves. D. Jed Harrison and co-workers at the University of Alberta (Canada) have extended the ability of such systems to incorporate organic solvents, opening up new possibilities for on-chip synthesis of organic molecules. The reaction between /niitrobenzenediazonium tetrafluoroborate (AZO) and iVjiV-ddmethylaniline (DMA) was performed in a microfabricated glass chip, with the fluid delivery controlled by electroosmotic flow (EOF). For comparison, the reaction was also carried out by mixing the reagents off-chip and allowing them to react for 10 min. The relative onchip reaction efficiency was 22% in acetonitrile and 37% in methanol. The authors correlate these reduced on-chip efficiencies with insufficient reaction times. Reaction products often alter the pH of the solutions; therefore, reservoirs of buffer solutions may be necessary. For this reaction, because an acidic mixture of tetraethylammonium (TEA) acetate/ acetic acid caused a steady decomposition
A boost for glow discharge Want to get more data from your glow-discharge (GD) source? Pengyuan Yang and colleagues at Xiamen University (China) demonstrate that microsecond-pulse (uspulse) GD boosted by a microwave--nduced plasma (MIP) can increase the signal from surface and other solid samples. The researchers analyzed copper and zinc from a brass sample and compared the results from MlP-boosted us-pulse GD with us-pulse GD alone. Peaks were detected by optical emission spectrometry. The results show that MIP couples well with us-pulse GD when the discharge pressure is
