Abstract: In some embodiments, a tandem (MS/MS) mass spectrometry method includes selecting a collision-induced dissociation (CID) voltage amplitude and a q-parameter value for a quadrupole ion trap to optimize a daughter ion fragmentation process for a given parent ion mass-to-charge (m/z) ratio. The q and CID voltage values may be selected according to a look-up table and/or using approximate analytical expressions. The correspondence between m/z values and (q, CID) value pairs may be established by pre-measurement calibration. A fragmentation-optimized q value may be computed according to m/z, and a CID voltage value may be determined according to the computed q value. A user may also force q to another value, for example in order to facilitate trapping of a desired daughter ion mass range, and the controller computes a CID voltage value according to the forced q value.

Abstract: According to one aspect, the low-frequency (e.g. lock channel) performance of a nuclear magnetic resonance (NMR) saddle-shaped, distributed-capacitance radio-frequency (RF) coil is improved by connecting a pair of auxiliary inductors across a plurality of leads extending upward from the coil upper ring. The upward-extending leads can be formed from the same foil as a main coil structure. The auxiliary inductors are separated from the coil window, so that magnetic susceptibility discontinuities introduced by the auxiliary inductors can be compensated for. In one embodiment, two half-toroid auxiliary inductors are positioned to form a full toroid shape. Some lost high-frequency performance can be recovered by using a split capacitance band positioned over the lower coil ring. The split capacitance band allows capacitance tuning while maintaining an RF current path close to the coil window.

Abstract: Nuclear magnetic resonance (NMR) systems and methods employing squashed (transversely-elongated) sample vessels (sample tubes or flow cells) for holding liquid NMR samples, and matching squashed saddle-shaped RF coils allow reducing sample and/or coil losses and increasing the RF circuit quality factors (Q). In a present implementation, the RF coils and sample vessels have rectangular cross-sections. Rounded (e.g. ellipsoidal) or other squashed cross-sections may also be used. The coil corresponding to the highest sample losses is positioned such that the magnetic field generated by the coil is along the major axis of the sample vessel. Squashed sample vessels may also be used with conventional circular coils, particularly for low-temperature measurements where sample losses dominate.

Abstract: An NMR sample tube assembly for holding a sample comprises a sample tube, a sealing plug for sealing the sample within the sample tube, and a rotor for spinning the assembly. The plug is clamped to the sample tube by an axial force. Preferably, the sample tube has a sealing flange protruding from the sample tube exterior along an inlet region of the sample tube. A filling part of the plug is sized to maintain an air escape clearance between the filling part and the sample tube for allowing air to escape out of the sample tube as the filling part is inserted therein. The rotor is secured to a protruding sealing part of the plug and clamps the sealing part to the sealing flange. The designs allow the use of wide sample tube mouths, and reduce the amount of air bubbles present in the samples during measurements.

Abstract: Test tubes with different dielectric properties are used for holding different samples/solvents within a nuclear magnetic resonance (NMR) probe of an NMR spectrometer. The test tube dielectric properties are chosen such that the overall capacitance seen by the NMR probe coils remains constant as different samples and test tubes are inserted into the probe. Samples having different solvents introduce substantially equal frequency shifts into the measurement circuitry. The disclosed systems and methods facilitate automated NMR measurements, and do not require specialized electronic or moving mechanical components for tuning compensation.

Abstract: An electrodynamic ion guide for a mass spectrometer comprises multiple sections having different guiding field central axes. At least one of the guiding fields can be an asymmetric guiding field having a quadrupole component and a dipole component. The ion guide can be positioned in a guide chamber with the first field central axis facing an inlet aperture and the second field central axis facing an outlet aperture. The ion guide allows the efficient use of a guide chamber with no line of sight from the inlet aperture to the outlet aperture, such that undesired liquid droplets entering the guide chamber through the inlet aperture do not exit through the outlet aperture. In the preferred embodiment, the ion guide comprises a plurality of longitudinally-concatenated, progressively narrowing segments, each segment including four flat plates arranged symmetrically about a central geometric axis.

Abstract: A radio-frequency (RF) coil for a nuclear magnetic resonance (NMR) probe includes rounded longitudinal conductors connecting end rings formed by sheets. The rounded conductors can be formed by curled sheets or wires. The rounded conductors allow reduced RF losses at the coil window edges, and thus allow increased coil sensitivities. The rounded conductors also allow increased coil sensitivities for an orthogonal coil, by allowing increased transparency to the magnetic field generated by the orthogonal coil. A curled-sheet RF coil can be generated from a single etched sheet by curling longitudinal sections of the sheet into tubular longitudinal conductors. To make such a coil, each longitudinal section is inserted into a longitudinal slot of a sheet-curling member, and the member is rotated about its longitudinal axis. As the curling member is rotated, the longitudinal sheet section wraps around the curling member and becomes curled.

Abstract: Low-temperature (cryogenic) radio-frequency (RF) coils for nuclear magnetic resonance (NMR) applications include composite multi-layered structures including an internal normal metal layer clad on both sides by external high-purity annealed aluminum layers. The magnetic susceptibilities of the internal and external layers are opposite in sign, and the thicknesses of the layers are chosen such that the composite structure has a net magnetic susceptibility equal to that of its surroundings (vacuum or support material). The internal layer can have a higher resistivity and magnetoresistance than the external layers. The use of high-purity, annealed aluminum for the external layers allows relatively high Q-factors for the cryogenic coils.

Abstract: Flow cells and stationary-sample vessels (test tubes) are used sequentially in the same dual-function nuclear magnetic resonance (NMR) probe. The user can easily convert the probe between flow and stationary-sample configurations without removing the probe housing. Tapered guiding surfaces are provided for guiding stationary-sample vessels from above and flow cells from below to respective measurement positions. Sample flow connection tubing used during flow measurements is accommodated within the probe during stationary-sample measurements. The dual-function NMR probe is useful in continuous flow-through, stop-flow, and fixed-sample analysis applications, including applications that couple high-pressure liquid chromatography (HPLC) with nuclear magnetic resonance spectroscopy and applications for analyzing small quantities of stationary organic samples.

Abstract: A bypass valve allows fast and reliable sequential transfer of samples from a 96-well plate to a flow-through nuclear magnetic resonance (NMR) probe of an NMR spectrometer. The bypass valve has three ports: an inject port connected to a first input of the flow-through probe; a load port connected to a needle capable of drawing the samples from the 96-well plate; and a hold port connected to a holding loop. The syringe pump draws a sample from the 96-well plate through the needle and the bypass valve into the holding loop. The position of the bypass valve is switched, and the sample and a dose of push solvent are pushed into the flow-through probe through the bypass valve. After NMR measurements are performed on the sample, the sample is drawn into the holding loop through the bypass valve, at the same time as air is flushed through the probe. The position of the bypass valve is again switched, and the sample is pushed out through the needle.

Abstract: A re-entrant radio-frequency (RF) TE11-mode cavity resonator allows generating a spatially homogeneous RF magnetic field for magnetic resonance (NMR, MRI) applications. The azimuthal current distribution is truly (continuously) sinusoidal. Moreover, the geometry allows tuning the cavity resonance frequency over a wide range. The resonator includes an outer cylindrical shell, and an inner re-entrant shell extending only along the ends of the outer shell. The magnetic resonance target of interest is placed in the middle region of the outer cylindrical shell. Multiple re-entrant inner shells can be used, particularly if multiple resonances are desirable. The resonator can be driven capacitively or inductively, for example by placing excitation loops in the space between the outer and inner shell. Multiple excitation loops are used to drive the resonator in quadrature. The resonance frequency of the cavity can be tuned by rotating tuning paddles placed between the inner and outer shells.

Abstract: Radio-frequency (RF) heating is used to accelerate the thermal equilibration of dielectrically lossy nuclear magnetic resonance (NMR) samples. High-power heating RF pulses are applied to the sample before lower-power measurement RF pulses, using any of the NMR probe coils. The heating pulses are offset in frequency relative to the measurement pulses, such that the heating pulses do not magnetically affect the spins of interest. Heating pulse sequences of decreasing power can be used to prevent the sample temperature from overshooting the desired equilibrium temperature. Heating RF pulses can pre-establish the thermal effects of both measurement-independent and measurement-dependent heating. For pre-establishing the thermal effects of measurement-dependent heating, the heating pulse transients are chosen to be proportional to subsequent measurement pulse transients.