Abstract: Eddy current compensation for magnetic field transients arising from electric current transients is obtained by digital computation of the time dependence of the eddy current magnetic effect, reversing the sense thereof to obtain a corrective signal portion, converting both the corrective portion and the basic signal profile to analogue form, summing same and directing the pre-compensated electric current through an inductive element.

Abstract: A spectral interval excited by ICP-ES containing expected lines is modeled from wavelength calibration information and from spectra of model components. A sample is then excited and fit to the data with concurrent observation of wavelength calibration and a linear least squares fit obtained with analysis of residuals to determine presence of unexpected spectral features which, if present, provide additional model components for an iterative fitting.

Abstract: A birdcage coil is operated in a balanced mode through connection of signal ground to a shield surrounding the coil. The driven leg of the coil includes tune capacitors, through which balance is maintained.

Abstract: A double resonance NMR apparatus in accordance with the present invention comprises a first resonator, a slotted resonator, and a slotted Rf shield. The axial shield slots on the Rf shield are aligned with the axial resonator slots on the slotted resonator to provide increased penetration of the Rf field from the first resonator into the sample, thereby increasing the total magnetic energy deposited into the sample.

Abstract: A spectrophotometer including a light source (1) operative to emit a beam of light (15), an optical system for directing the light beam (15) to a sample (8) to be analyzed, and a detector (9) which detects the intensity of the light beam after the beam interacts with the sample (8). The light source (1) is operative to emit bursts of light separated by an interval during which no light is emitted. By way of example, a xenon tube may be used for that purpose. The spectrophotometer measures the intensity of the light beam generated by each burst of light after that beam interacts with the sample. Each such light beam may be divided into first and second parts (5 and 4) prior to interaction with the sample (8), and the optical system is arranged to direct the first part (5) to the sample (8) and to direct the second part (4) to a second detector (7) for conducting a reference measurement. A dark signal measurement may be conducted immediately before or after each burst of light.

Abstract: A method and apparatus which utilizes the hysteritic behavior of type II superconductors is provided for reducing the effective magnetic susceptibility of such high temperature superconducting materials being used close to the sample region in nuclear magnetic resonance system probes by providing decaying AC changes in the magnetic field parallel to said superconductive material. The method is particularly applicable to receiver coils. Reducing the effective magnetic susceptibility of superconducting receiver coils enables the improved sensitivity they inherently provide to be realized without loss of resolution resulting from line broadening caused by susceptibility discontinuities of materials near the sample region of the probe.

Abstract: Angular and current distributions for an elliptical birdcage resonator are realized in a design that achieves constant electrical phase between adjacent legs of the coil. Equal peak currents in the driven legs of the orthogonal modes yields exact quadrature operation.

Abstract: A 1/4 wave circuit switch for use in an NMR probe has a housing with a stepped cavity for precisely locating switch components inside. The 1/4 wave circuit switch cooperates with a 1/4 wave tube and is designed to receive either an external capacitor on a capacitor stick for single tune operations or a 1/4 wave center conductor with a threaded tip on a 1/4 wave stick for double tune operations. For single tune operations, the external capacitor comes into contact at one end with a resiliently supported, movable electrical contact and at the other end with a spring clip inside the housing cavity to orient the external capacitor in parallel with the NMR coil. The movable electrical contact is resiliently biased by a pair of crescent washers supported by an insert plug which serves as a positive stop for the travel of the electrical contact.

Abstract: The use of audio signals from rotating samples in an NMR probe in a polarizing magnetic field as part of a nuclear magnetic resonance spectrometer for monitoring and remediating sample spinning speeds is presented.

Abstract: A peristaltic pump comprises a rotatable drum 2 having rollers 5 or cams 5' for squashing a flexible tube 9 against a profiled surface 10 of a presser plate 7. Tube 9 is mounted between supports 14 and 15 on presser plate 7 and is automatically movable between an inoperative and operative (pumping) position by pivotal movement of plate 7 about axis 8 produced by an electro mechanical actuator. A flexible membrane 33 is sandwiched between rollers 5 or cams 5' for eliminating shear forces on the tube 9. The construction of the pump and shape of profile 10 are such as to mimimise pulsations in the output flow. Systems for supplying a sample for analysis to spectroscopic apparatus using the peristaltic pump are also described.

Abstract: A sample delivery system for a flow-through NMR analysis is provided, which utilizes pressurized gas as a means for conveying a sample into and out of an NMR spectrometer. Two sources of gas pressure, a forward pressure and back pressure, oppose the sample within the tubing of the sample delivery system and the tubing of the flow-through system which are operatively coupled together. Conveyance of the sample in any direction within the tubing is achieved by adjusting the pressure differential. Precise positioning of the sample in the magnetic field center and complete removal of the sample from the NMR spectrometer when analysis is complete are achieved by using a signal processor which receives signals from the NMR detector or other detectors positioned along the length of the tubing. These signals provide an indication of the position of the sample in the tubing. The signal processor uses this information to adjust the forward and back pressure, thereby achieving the desired positioning of the sample.

Abstract: An apparatus is described for carrying out solid phase microextraction and analysis of analytes in a fluid carrier in which a fiber within a housing is vibrated by a vibrating means during microextraction. The housing contains access means so that the carrier and analytes can be brought into contact with the vibrating fiber during the extraction stage. In a preferred embodiment of the present invention, the vibrating means comprises a membrane, a solenoid for vibrating the membrane, a frame, a retainer mounted on the frame for holding the solenoid, a holder for the membrane, and a retainer arm having one end connected to the retainer and the other end attached to the holder. A method for microextraction and analysis is also described in which a vibrating fiber is placed into contact with analytes to be analyzed in a suitable carrier deposited in a container for a sufficient period of time for microextraction to occur.

Abstract: A method for treating M-degree oversampled impulse response data in real time includes generating N initial pseudo-data points derived from an N tap digital filter, processing each datum therewith, down sampling by a factor of r and displacing the processed datum toward the time origin by an appropriate amount. After fourier transform of the data set, the spectral background information bears improved fidelity to the actual spectral noise.

Abstract: A peristaltic pump comprises a rotatable drum 2 having rollers 5 or cams 5' for squashing a flexible tube 9 against a profiled surface 10 of a presser plate 7. Tube 9 is mounted between supports 14 and 15 on presser plate 7 and is automatically movable between an inoperative and operative (pumping) position by pivotal movement of plate 7 about axis 8 produced by an electro mechanical actuator. A flexible membrane 33 is sandwiched between rollers 5 or cams 5' for eliminating shear forces on the tube 9. The construction of the pump and shape of profile 10 are such as to mimimise pulsations in the output flow. Systems for supplying a sample for analysis to spectroscopic apparatus using the peristaltic pump are also described.

Abstract: The use of audio signals from rotating samples in an NMR probe in a polarizing magnetic field as part of a nuclear magnetic spectrometer is presented.

Abstract: An X-ray tube rotating anode is cooled with a liquid metal functioning as a recirculated heat exchange fluid and/or a metal film in a gap between the anode and a stationary structure. The liquid metal is confined to the gap by (a) a labyrinth having a coating that is not wetted by the liquid, (b) a magnetic structure, or (c) a wick. The liquid metal recirculated through the anode is cooled in a heat exchanger located either outside the tube or in the tube so it is surrounded by the anode. The heat exchanger in the tube includes a mass of metal in thermal contact with the recirculating liquid metal and including numerous passages for a cooling fluid, e.g. water. A high thermal conductivity path is provided between an anode region bombarded by electrons and a central region of the tube where heat is extracted.

Abstract: A method of isolating selected ion species in a quadrupole ion trap mass spectrometer is disclosed. One or more ranges of masses to be eliminated from the ion trap are ejected by applying a supplemental dipole excitation waveform, sparsely populated with frequency components, while the trapping field is modulated. The spacing of the frequency components in the supplemental excitation waveform varies across the range of frequencies in the waveform. Preferably, the frequency range is divided into a plurality of subranges, and the spacing of the frequency components in each of the subranges is constant. A method of creating a master set of frequencies used for generating a supplemental excitation waveform is also shown. Likewise, a method of calculating edge frequencies defining a gap in the mass spectrum that is excited by the supplemental waveform is also shown.

Abstract: A method of using a quadrupole ion trap mass spectrometer for high resolution mass spectroscopy is disclosed. In the preferred embodiment, the space charge in the ion trap is controlled to high accuracy. This is done by using a prescan of the trap before each analytical scan, where the ionization parameters used in the prescan are not fixed, but rather are based on the previous analytical scan. The method is especially useful in connection with performance of high resolution MS/MS experiments of the type described in the inventor's prior U.S. Pat. No. 5,198,665.

Abstract: An electrostatic chuck for releasably holding a workpiece comprising a substrate formed by a pair of dielectric elements, each being a single crystal, with at least one electrode embedded therebetween, and a voltage source coupled to each electrode. The chuck is preferably fabricated from two substantially planar dielectric members sandwiched around a brazing compound which become electrodes after the assembly is heated and then cooled.

Abstract: A method of using a quadrupole ion trap mass spectrometer for high resolution mass spectroscopy is disclosed. High resolution of a mass spectrum of a desired species is achieved by first using a slow scanning rate and by first ridding the trap of unwanted ions. Accurate mass calibration is achieved by using a reference compound of known mass and using a second supplemental AC dipole voltage to eject the reference ions at nearly the same time as the sample ions of interest are ejected from the trap. This eliminates the need to scan the trap between the masses of the sample and reference ions. Space charge in the trap is held constant, thereby eliminating a major source of mass axis instability, by using the results of one scan to control the ionization time during the next scan. Preferably, during ionization a broadband supplemental dipole voltage is applied to the ion trap to rid it of unwanted ions.