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Here, we describe a digital-waveform dual-quadrupole mass spectrometer that enhances the performance of our drift tube FT-IMS high-resolution Orbitrap mass spectrometer (MS). The dual-quadrupole analyzer enhances the instrument capabilities for studies of large protein and protein complexes. The first quadrupole (q) provides a means for performing low-energy collisional activation of ions to reduce or eliminate noncovalent adducts, viz., salts, buffers, detergents, and/or endogenous ligands. The second quadrupole (Q) is used to mass-select ions of interest for further interrogation by ion mobility spectrometry and/or collision-induced dissociation (CID). Q is operated using digital-waveform technology (DWT) to improve the mass selection compared to that achieved using traditional sinusoidal waveforms at floated DC potentials (>500 V DC). DWT allows for increased precision of the waveform for a fraction of the cost of conventional RF drivers and with readily programmable operation and precision (Hoffman, N. M. . A comparison-based digital-waveform generator for high-resolution duty cycle. Review of Scientific Instruments 2018, 89, 084101).

Here, we describe a digital-waveform dual-quadrupole mass spectrometer that enhances the performance of our drift tube FT-IMS high-resolution Orbitrap mass spectrometer (MS). The dual-quadrupole analyzer enhances the instrument capabilities for studies of large protein and protein complexes. The first quadrupole (q) provides a means for performing low-energy collisional activation of ions to reduce or eliminate noncovalent adducts, viz., salts, buffers, detergents, and/or endogenous ligands. The second quadrupole (Q) is used to mass-select ions of interest for further interrogation by ion mobility spectrometry and/or collision-induced dissociation (CID). Q is operated using digital-waveform technology (DWT) to improve the mass selection compared to that achieved using traditional sinusoidal waveforms at floated DC potentials (>500 V DC). DWT allows for increased precision of the waveform for a fraction of the cost of conventional RF drivers and with readily programmable operation and precision (Hoffman, N. M. et al.. A comparison-based digital-waveform generator for high-resolution duty cycle.

Digital Waveform Technology (DWT) has recently evolved to provide sufficient duty cycle resolution necessary to create a purely digital waveform-based mass filter. Digital operation provides a number of options that remain extremely challenging for sinusoidal waveform technology (SWT) driven systems. One of those options is collecting ions in a gas-filled digital ion guide/trap and subsequently axially injecting the collected ions in a temporally-short and spatially-focused packet into the digital mass filter (DMF). This work explores the effects of trapping ions before mass analysis. In particular, it focusses on the measured response of the ion distribution as a function of axial ejection conditions while maintaining identical trapping conditions. The ejection energy was varied showing changes in the ion distribution that corresponded to desolvation, multimeric dissociation and small molecule from the higher charge states. This study shows that duty cycle-base ion ejection from into an axial potential well and out of the same well of a gas-filled linear quadrupole is essentially equivalent in terms of energy imparted to the ion. However, the energizing mechanism of the ejection process is radial rather than axial. Sampling issues of the trapped ions from the gas-filled quadrupole were analyzed and discussed.

With advances in the precision of digital electronics, waveform generation technology has progressed to a state that enables the creation of m/z filters that are purely digitally driven. These advances present new methods of performing mass analyses that provide information from a chemical system that are inherently difficult to achieve by other means. One notable characteristic of digitally driven mass filters is the capacity to transmit ions at m/z ratios that vastly exceed the capabilities of traditional resonant systems. However, the capacity to probe ion m/z ratios that span multiple orders of magnitudes across multiple orders of magnitude presents a new set of issues requiring a solution. In the present work, when probing multiply charged protein species beyond m/z 2000 using a gentle atmospheric pressure interface, the presence of solvent adducts and poorly resolved multimers can severely degrade spectral fidelity. Increasing energy imparted into a target ion population is one approach minimizing these clusters; however, the use of digital waveform technology provides an alternative that maximizes ion transport efficiency and simultaneously minimizes solvent clustering. In addition to the frequency of the applied waveform, digital manipulation also provides control over the duty cycle of the target waveform. This work examines the conditions and approach leading to optimal digital waveform operation to minimize solvent clustering. Graphical Abstract ᅟ.

Ion traps and guides are integral parts of current commercial mass spectrometers. They are currently operated with sinusoidal waveform technology that has been developed over many years. Recently, digital waveform technology has begun to emerge and promises to supplant its older cousin because it presents new capabilities that result from the ability to instantaneously switch the frequency and duty cycle of the waveforms. This manuscript examines these capabilities and reveals their uses and effects on instrumentation. Graphical Abstract ᅟ.

This publication demonstrates the use of digital waveform manipulation in linear ion guides to trap isolated ions and fragment them before mass analysis by time-of-flight mass spectrometry (TOF-MS). Ion trapping and collection was performed by waveform duty cycle manipulation to create a negative axial potential between the rods and the end-cap electrodes. Ion isolation can be performed by duty cycle manipulation to narrow the range of stable masses while continuing to axially trap the ions. Further ion isolation can then be performed by jumping the quadrupole frequency to each side of the stability zone to eliminate ions above and below the isolated ion mass. Collision-induced dissociation was demonstrated by duty cycle manipulation to either axially or radially excite the ions. The methods for performing these types of excitations are discussed and demonstrated. These techniques can be combined or used separately for MS(n) analysis. The use of frequency and duty cycle manipulation of the applied waveforms simplifies the hardware while greatly increasing the capabilities of linear ion guides and quadrupole time-of-flight mass spectrometers (Q-TOF-MS). Linear quadrupoles can now be used as high efficiency ion traps for collection, isolation, and tandem mass spectrometry at any value of m/z when operated digitally.

A comparison-based digital waveform generator has been developed that directly enables purely duty cycle controlled digital mass filters. This waveform generator operates by the comparison of a periodic waveform and a DC level to produce a digital waveform. The improved duty cycle realized by this method of waveform generation is demonstrated by producing a mass spectrum of electrosprayed lysozyme by varying the duty cycle of a digital waveform applied to a quadrupole rod set. Operation and control of the waveform generator using an inexpensive open-source microcontroller is discussed.

An inexpensive frequency variable square waveform generator (WFG) was developed to use with existing sinusoidal waveform driven ion funnels. The developed WFG was constructed using readily available low voltage DC power supplies and discrete components placed in printed circuit boards. As applied to ion funnels, this WFG represents considerable cost savings over commercially available products without sacrificing performance. Operation of the constructed pulse generator has been demonstrated for a 1 nF ion funnel at an operating frequency of 1 MHz while switching 48 Vp-p.

Many reported CuIn1-xGaxSe2 (CIGS) thin films for high-efficiency solar cells have been prepared via a two-stage process that consists of a high-vacuum film deposition step followed by selenization with excess H2Se gas or Se vapor. Removing toxic gas and high-vacuum requirements from this process would greatly simplify it and make it less hazardous. We report the formation of CuIn1-xGaxSe2 (x = 0, 0.25, 0.50, 0.75, 1.0) thin films achieved by rapid thermal annealing of spray-deposited CuIn1-xGaxS2 and Se in the absence of an additional selenium source. To prepare the Se layer, commercial Se powder was dissolved by refluxing in ethylenediamine/2,2-dimethylimidizolidine. After cooling to room temperature, this mixture was combined with 2-propanol and the resulting colloidal Se suspension was sprayed by airbrush onto a heated glass substrate. The resulting film was coated with nanocrystalline CuIn1-xGaxS2 via spray deposition of a toluene-based “nanoink” suspension. The two-layer sample was annealed at 550 oC in an argon atmosphere for 60 minutes to form the final CIGS product. Scanning electron microscopy images reveal that film grains are 200-300 nm in diameter and comparable to sizes of the reactant CuIn1-xGaxS2 nanoparticles. XRD patterns are consistent with the chalcopyrite unit cell and calculated lattice parameters and A1 phonon frequencies change nearly linearly between those for CuInSe2 and CuGaSe2.