Tandem Ion Trap Design with Enhanced Mass Analysis Capabilities for Large Populations of Ions

Novel control modes to improve the performance of rectilinear ion trap mass spectrometer with dual pressure chambers

The rectilinear ion trap (RIT) has gradually become one of the preferred mass analyzers for portable mass spectrometers because of its simple configuration. In order to enhance the performance, including sensitivity, quantitation capability, throughput, and resolution, a novel RIT mass spectrometer with dual pressure chambers was designed and characterized. The studied system constituted a quadrupole linear ion trap (QLIT) in the first chamber and a RIT in the second chamber. Two control modes are hereby proposed: Storage Quadrupole Linear Ion Trap-Rectilinear Ion Trap (SQLIT-RIT) mode, in which the QLIT was used at high pressure for ion storage and isolation, and the RIT was used for analysis; and Analysis Quadrupole Linear Ion Trap-Rectilinear Ion Trap (AQLIT-RIT) mode, in which the QLIT was used for ion storage and cooling. Subsequently, synchronous scanning and analysis were carried out by QLIT and RIT. In SQLIT-RIT mode, signal intensity was improved by a factor of 30; the limit of quantitation was reduced more than tenfold to 50 ng mL^-1, and an optimal duty cycle of 96.4% was achieved. In AQLIT-RIT mode, the number of ions coexisting in the RIT was reduced, which weakened the space-charge effect and reduced the mass shift. Furthermore, the mass resolution was enhanced by a factor of 3. The results indicate that the novel control modes achieve satisfactory performance without adding any system complexity, which provides a viable pathway to guarantee good analytical performance in miniaturization of the mass spectrometer.

Extending the Ion Capacity of a Linear Ion Trap Using Nonlinear Radio Frequency Fields

Mass selective axial ejection (MSAE) from a low pressure linear ion trap (LIT) is investigated in the presence of added auxiliary nonlinear radio frequency (rf) fields. Nonlinear rf fields allow ions to be ejected with high sensitivity at large excitation amplitudes and reduced deleterious effects of space charge. These permit the operation of the LIT at ion populations considerably larger than the space charge limit usually observed in the absence of the nonlinear fields while maintaining good spectral resolution and mass accuracy. Experimental data show that the greater the strength of the nonlinear field, the less the effects of space charge on mass assignment and peak width. The only deleterious effect is a slight broadening of the mass spectral peaks at the highest values of added nonlinear fields used. Graphical Abstract ᅟ.

High efficiency tandem mass spectrometry analysis using dual linear ion traps

Tandem mass spectrometry (MS/MS) plays an essential role in modern chemical analysis. It is used for differentiating isomers and isobars and suppressing chemical noise, which allows high precision quantitation. The MS/MS analysis has been typically applied by isolating the target precursor ions, while disregarding other ions, followed by a fragmentation process that produces the product ions. In this study, configurations of dual linear ion traps were explored to develop high efficiency MS/MS analysis. The ions trapped in the first linear ion trap were axially, mass-selectively transferred to the second linear ion trap for MS/MS analysis. Ions from multiple compounds simultaneously introduced into the mass spectrometer could be sequentially analyzed. This development enables highly efficient use of the sample. For miniature ion trap mass spectrometers with discontinuous atmospheric pressure interfaces, the analysis speed and the quantitation precision can be significantly improved.

Study of the efficiency for ion transfer through bent capillaries

Discontinuous atmospheric pressure interfaces (DAPIs) with bent capillaries represent a highly simplified and flexible means for introducing ions into a vacuum manifold for mass analysis or gas phase ion reactions. In this work, a series of capillaries of different radians and curvatures were used with DAPI for studying the impact of the capillary bending on the ion transfer. The variation of transfer efficiency was systematically characterized for dry and solvated ions. The efficiency loss for dry ions was less than one order of magnitude, even with a three-turn bent capillary. The transfer of solvated ions generated by electrospray was found to be minimally impacted by the bending of the transfer capillary. For multiply protonated ions, the transfer efficiency for ions at lower charge states could be relatively well retained, presumably due to the lower reactivity associated with proton transfer reaction and the compensation in intensity by conversion of ions at higher charge states.

Accelerated simulation study of space charge effects in quadrupole ion traps using GPU techniques

Space charge effects play important roles in the performance of various types of mass analyzers. Simulation of space charge effects is often limited by the computation capability. In this study, we evaluate the method of using graphics processing unit (GPU) to accelerate ion trajectory simulation. Simulation using GPU has been compared with multi-core central processing unit (CPU), and an acceleration of about 390 times have been obtained using a single computer for simulation of up to 10(5) ions in quadrupole ion traps. Characteristics of trapped ions can be investigated at detailed levels within a reasonable simulation time. Space charge effects on the trapping capacities of linear and 3D ion traps, ion cloud shapes, ion motion frequency shift, mass spectrum peak coalescence effects between two ion clouds of close m/z are studied with the ion trajectory simulation using GPU.

A system consisting of cation-exchange chromatography, combined surface-activated chemical and electrospray ionization, and ion-trap analysis for the analysis of 8-oxo-7,8-dihydro-2'-deoxyguanosine in urine

RATIONALE

8-Hydroxy-2'-deoxyguanosine has served as a biomarker for oxidative damage to DNA from different types of biological samples, and various techniques have been used to analyze it. In particular, liquid chromatography coupled to mass spectrometry has been used to identify 8-hydroxy-2'-deoxyguanosine in urine samples. Usually, a triple quadrupole analyzer and multiple reaction monitoring have been employed for its detection. Only a few studies have used a less expensive ion-trap analyzer instead.

METHODS

We have developed a new liquid chromatography/mass spectrometry procedure that incorporates cation-exchange chromatography in conjunction with surface-activated and electrospray ionization with an ion trap analyzer for the mass spectral step.

RESULTS

The combination of two ionization sources reduced the matrix effect arising from in-source reactions, thus increasing the sensitivity to levels comparable with those obtained by triple quadrupole analyzers.

CONCLUSIONS

This new method for 8-hydroxy-2'-deoxyguanosine detection provided increased sensitivity and reduced chemical noise, using a less expensive, stable and accurate mass spectrometric technology.