Experimental evaluation of a hyperbolic ion trap for fourier transform ion cyclotron resonance mass spectrometry.

The Penning ion trap, consisting of hyperbolically curved electrodes arranged as an unbroken ring electrode capped by two end electrodes whose interelectrode axis lies along the direction of an applied static magnetic field, has long been used for single-ion trapping. More recently, it has been used in "parametric" mode for ion cyclotron resonance (lCR) detection of off-axis ions. In this article, we describe and test a Penning trap whose ring electrode has been cut into four equal quadrants for conventional dipolar ICR excitation (on one pair of opposed ring quadrants) and dipolar ICR detection (on the other pair). In direct comparisons to a cubic trap, the present hyperbolic trap offers somewhat improved ICR mass spectral peak shape, higher mass resolving power, and comparable frequency shift as a function of trapping voltage. Mass measurement accuracy over a wide mass range is improved twofold and mass discrimination is somewhat worse than for a cubic trap. The relative advantages of parametric, dipolar, and quadrupole modes are briefly discussed in comparison to screened and unscreened cubic traps.

Hemoglobin function in stored blood. XIII. A citrate-adenine preservative with optimal pH to maintain red cell 2,3-DPG (function) and ATP (viability).

Increasing pH by a 0.5 increment over the commonly used preservative, acid-citrate-dextrose with adenine (ACD-Ad), results in a significant improvement in 2,3-DPG, with no significant loss in concentrations of ATP. The intermediate pH preservative, 6.0, also had ATP concentrations which equaled those of the low pH preservatives, 5.0 and 5.5, from the 21st to the 42nd day of storage. A citrate-adenine preservative, with a pH between 5.5 and 6.0, would seem to be optimal for maintenance of hemoglobin function and red cell viability, as determined by measurements of 2,3-DPG and ATP concentrations.