The depletion of mineable gold reserves, paired with the increase in demand for electronics, underlines the need for sustainable gold recycling methods. Owing to its high precious metal content, electronic waste (e-waste) is a promising source for gold recovery. Conventional approaches, such as pyro- and hydrometallurgy, remain environmentally taxing, producing harmful emissions and toxic byproducts. This study advances a recently reported ultrasound-based, green technology for recovering gold from discarded printed circuit boards (PCBs). The method uses localized cavitation in water, driven by high-intensity focused ultrasound (HIFU), to mechanically remove gold from PCB edge connectors. In this work, the influence of ultrasound frequency on removal efficiency is investigated using three custom-built HIFU transducers operating at 4.2, 7.3, and 11.8 MHz. Gold removal at 4.2 MHz was found to be 4.6 and 3.8 times more efficient than at 11.8 MHz and 7.3 MHz, respectively. Direct comparison of the erosion marks to the pressure fields revealed that complex frequency-dependent cavitation cloud dynamics are likely responsible for the increase in removal efficiency at the lowest frequency employed. The improved efficiency indicates potential for scale-up, although industrial viability will require further optimization of throughput and thermal management.

An ion source concept is described where the sample flow is stopped in a confined volume of an ion mobility spectrometer creating time-dependent patterns of ion patterns of signal intensities for ions from mixtures of volatile organic compounds and improved signal-to-noise rate compared to conventional unidirectional drift gas flow. Hydrated protons from a corona discharge were introduced continuously into the confined volume with the sample in air at ambient pressure, and product ions were extracted continuously using an electric field for subsequent mobility analysis. Ion signal intensities for protonated monomers and proton bound dimers were measured and computationally extracted using mobilities from mobility spectra and exhibited distinct times of appearance over 30 s or more after sample injection. Models, and experimental findings with a ternary mixture, suggest that the separation of vapors as ions over time was consistent with differences in the reaction rate for reactions between primary ions from hydrated protons and constituents and from cross-reactions that follow the initial step of ionization. The findings suggest that the concept of stopped flow, introduced here for the first time, may provide a method for the temporal separation of atmospheric pressure ions. This separation relies on ion kinetics and does not require chromatographic technology.

Rate coefficients (k) for the reactions of hydrated protons and a sample vapor (M) to form protonated monomers (MH+(H2O)n) and proton bound dimers (M2H+) were determined simultaneously by using ion mobility spectrometry with a tandem drift tube at ambient pressure. In this method, sample vapors were introduced to a first drift region with stepwise reactions: M + H+(H2O)n→k1 MH+ (H2O)y + (n - y) H2O and M + MH+ (H2O)y→k2 M2H+ + yH2O. Ions with a drift time between 9 and 18 ms in the first drift region were subsequently mobility analyzed in purified air with the second drift region using a synchronized second ion gate with boxcar averaging. Slope for plots of ion abundance against drift time was fitted by successive approximation between peaks of H+(H2O)n and MH+(H2O)y to obtain k2 until computed and experimental slopes matched within a maximal deviation of 0.01. Values for k1 were obtained from the experimental baseline slope when adjusted for k2. Rate coefficients for triethyl phosphate and phenylacetate were determined using this method with k1 values of 1.14 × 10-9 ± 1.87 × 10-10 cm3/s and 0.81 × 10-9 ± 9.26 × 10-11 cm3/s and k2 values of 1.05 × 10-9 ± 4.13 × 10-10 cm3/s and 1.07 × 10-9 ± 1.86 × 10-10 cm3/s, respectively. Relative error for this method was determined using mobility spectra generated with a COMSOL model and artificial rate coefficients. Rate coefficients were then extracted from the modeled mobility spectra and compared to the original artificial values. Relative error of this method was 10% and should be generally applicable for individual substances with reactions forming protonated monomers and proton bound dimers.

We developed a single cell amine analysis approach utilizing isobarically multiplexed samples of 6 individual cells along with analyte abundant carrier. This methodology was applied for absolute quantitation of amino acids and untargeted relative quantitation of amines in a total of 108 individual cells using nanoflow LC with high-resolution mass spectrometry. Together with individually determined cell sizes, this provides accessible quantification of intracellular amino acid concentrations within individual cells. The targeted method was partially validated for 10 amino acids with limits of detection in low attomoles, linear calibration range covering analyte amounts typically from 30 amol to 120 fmol, and correlation coefficients (R) above 0.99. This was applied with cell sizes recorded during dispensing to determine millimolar intracellular amino acid concentrations. The untargeted approach yielded 249 features that were detected in at least 25 % of the single cells, providing modest cell type separation on principal component analysis. Using Greedy forward selection with regularized least squares, a sub-selection of 100 features explaining most of the difference was determined. These features were annotated using MS2 from analyte standards and accurate mass with library search. The approach provides accessible, sensitive, and high-throughput method with the potential to be expanded also to other forms of ultrasensitive analysis.

The demand for rare and precious metals (RPMs), e.g. gold, is increasing, as these are used in the ever-increasing amount of electronics needed for technological development and digitalization. Due to their rarity, virgin mining of RPMs is becoming more difficult and expensive. At the same time, over 62Mt of e-waste is created globally each year. The high concentration of gold and other RPMs in e-waste makes it an excellent source for recycling. Unfortunately, current recycling methods need to separate the different metals and the current pyrometallurgical and hydrometallurgical processes also create toxic pollutants, large amounts of wastewater and require highly corrosive substances. Here we present a new method for gold removal for the purpose of recycling, using only water and high-intensity focused ultrasound to induce material erosion through cavitation. An 11.8MHz ultrasonic transducer is used to first image the sample to locate gold-coated pads on discarded printed circuit boards (PCBs) and subsequently to remove only the gold layer. We demonstrate that the gold removal can be controlled by the number of transmitted ultrasonic bursts and that the energy efficiency is optimal when only minute amounts of the nickel layer beneath are also removed. Removing solely the gold layer also decreases the need for further processing steps. This greener gold removal method for e-waste is therefore well aligned with, and contributing to, the United Nations Sustainable Development Goal 12: Ensure sustainable consumption and production patterns.

Post-translational modifications (PTMs) alter the function and fate of proteins and cells in almost every conceivable way. Protein modifications can occur as a result of specific regulating actions of enzymes, such as tyrosine kinases phosphorylating tyrosine residues or by nonenzymatic reactions, such as oxidation related to oxidative stress and diseases. While many studies have addressed the multisite, dynamic, and network-like properties of PTMs, only little is known of the interplay of the same site modifications. In this work, we studied the enzymatic phosphorylation of oxidized tyrosine (l-DOPA) residues using synthetic insulin receptor peptides, in which tyrosine residues were replaced with l-DOPA. The phosphorylated peptides were identified by liquid chromatography-high-resolution mass spectrometry and the site of phosphorylation by tandem mass spectrometry. The results clearly show that the oxidized tyrosine residues are phosphorylated, displaying a specific immonium ion peak in the MS2 spectra. Furthermore, we detected this modification in our reanalysis (MassIVE ID: MSV000090106) of published bottom-up phosphoproteomics data. The modification, where both oxidation and phosphorylation take place at the same amino acid, has not yet been published in PTM databases. Our data indicate that there can be multiple PTMs that do not exclude each other at the same modification site.

We present a surface sampling method for the chemical analysis of liquid-immersed solid samples. Liquid immersion allows samples to be kept in a hydrated state. We employed cavitation generated by high-intensity focused ultrasound for localized material removal. The appropriate transducer–sample distance was determined using the actuating ultrasound transducer prior to sampling, allowing sonication in focus despite surface height variation. We demonstrate the proposed surface sampling method on water-submerged glass cover slides painted with permanent markers, achieving sampling with tunable spot size down to 500 μm. The removed and collected material was transferred for chemical analysis by electrospray ionization mass spectrometry, which showed mass peaks characteristic to the permanent markers.

A model to quantitatively predict ion abundances from atmospheric pressure chemical ionization (APCI) between hydrated protons and a volatile organic compound (VOC) was extended to binary mixtures of VOCs. The model includes differences in vapor concentrations, rate coefficients, and reaction times and is enhanced with cross reactions between neutral vapors and protonated monomers. In this model, two specific VOCs were considered, a ketone, 6-methyl-5-hepten-2-one (M, and an amine, 2,6-di-tert-butyl-pyridine (N), with measured "conditional rate coefficients" (in cm3·s-1) of kM = 1.11 × 10-9 and kN = 9.17 × 10-10, respectively. The cross reaction of MH+(H2O)x to NH+(H2O)y was measured as kcr = 1.31 × 10-12 at 60 °C. Cross reactions showed an impact on ion abundances at t > 30 ms for equal vapor concentrations of 100 ppb for M and N. In contrast, this impact was negligible for vapor concentrations of 1 ppb and did not exceed 5% change in product ion abundance up to 1000 ms reaction times. The model was validated with laboratory measurements to within ∼10% using an ion mobility spectrometer and effective reaction time obtained from computational fitting of experimental findings. This was necessitated by complex flow patterns in the ion source volume and was determined as ∼10.5 ms. The model has interpretative and predictive value for quantitative analysis of responses with ambient pressure ion sources for mass spectrometry and ion mobility spectrometry.

Concentrations of volatile organic compounds (VOCs) in air can be reduced in electrostatic separators where VOCs are ionized using ion-molecule reactions, extracted using electric fields, and eliminated in a waste flow. Embodiments for such separator technology have been explored in only a few studies, despite the possible advantage of purification without adsorbent filters. In one design, based on ionization of VOCs in positive polarity with hydrated protons as reactant ions, efficiencies for removal were measured as 30-40% . The results were fitted to a one-dimensional convective diffusion model requiring an unexpectedly high production rate of reactant ions to match both the model and data. A realistic rate of reactant ion production was used in finite element method simulations (COMSOL) and demonstrated that low removal efficiency could be attributed to non-uniform patterns of sample flow and to incomplete mixing of VOCs with reactant ions. In analysis of complex systems, such as this model, even limited computational modeling can outperform a pure analytical approach and bring insights into limiting factors or system bottlenecks.Implications: In this work, we applied modern computational methods to understand the performance of an air purifier based on electrostatics and ionized volatile organic compounds (VOCs). These were described in the publication early 2000s. The model presented was one-dimensional and did not account for the effects of flow. In our multiphysics finite element models, the efficiency and operation of the filter is better explained by the patterns of flow and flow influences on ion distributions in electric fields. In general, this work helps using and applying computational modelling to understand and improve the performance bottlenecks in air purification system designs.

Cavitation-induced surface erosion has been studied for decades. High-intensity focused ultrasound (HIFU) enables localized erosion, with applications in many fields. However, no research has been published on machining solely with HIFU. Compared to existing micro-machining technologies, HIFU exhibits a unique set of benefits: inexpensive, minimal maintenance due to non-contact machining without slurry, mitigated chemical load, and monitoring capability. We demonstrate controlled surface machining of mirror-polished aluminium (AW-5754) using high-frequency (12 MHz) HIFU-induced cavitation erosion. Optimal sonication parameters (transducer-sample distance, amplitude, cycles per burst, number of bursts, and pulse repetition frequency) for stationary surface erosion were first identified experimentally. These parameters served as a basis for studying the effect of sonication parameters during on-the-fly erosion, i.e., engraving lines. The effect of stage translation velocity and the number of repeated passes across the engraved line were also studied. Subsequently, the acronym of our laboratory, “ETLA”, was engraved, with a 500 µm letter height and an average line width of 53 µm.

We have developed an ultrasound-based surface sampling method permitting surface studies for liquid immersed samples. The method employs high-intensity focused ultrasound, which can remove material from predetermined areas and induce acoustic streaming that causes the immersion liquid to flow. In this study, we studied several conditions of acoustic streaming, which can affect particle transport away from the sampled surface. First, we explored suitable acoustic streaming conditions by finite element modelling. Next, we measured the induced streaming fields by particle image velocimetry. This study comprised cases, when a high-intensity focused ultrasound beam encountered a solid surface at different transducer-surface distances. A change in direction of streaming occurred when a focusing transducer was moved from −2λ defocus to -4λ defocus (towards the surface). Thus, we found suitable conditions for an upwards directing acoustic streaming field. This kind of defocus condition can be coupled to the surface sampling process allowing efficient particle transport for subsequent chemical analysis.

Increased digitalization and technological development raises the demand for rare and precious metals (RPM). Due to their rarity, mining RPMs from the earth is becoming increasingly difficult. Traditional urban mining methods to recover RPMs from printed circuit boards (PCB) need to separate the RPMs from non-metallic substances, e.g. plastic. This separation requires toxic substances and causes unwanted and toxic by-products and emissions. The ability to identify regions-of-interest on PCBs, i.e. the gold pads, and to extract RPMs from only the desired areas would reduce the need for toxic substances. In this study, a single 12 MHz high-intensity focused-ultrasound transducer was used to 1) image a PCB to locate the gold pads, and 2) to subsequently induce inertial cavitation to remove gold from three extraction areas on the selected gold pad. The sonication was performed in water without additional chemicals. Gold removal was verified by imaging the pad with a coded-excitation scanning acoustic microscope ( $f_{c} = 375$ MHz). Average areas and volumes of the three extraction regions were $A= (12.2 \pm 0.5).10^{3}$ µm 2 and $V=(18 \pm 2).10^{3}$ µm 3 , respectively. The total amount of removed gold and nickel (from beneath the gold plating) from all three extraction areas was estimated to $m_{Au, tot}= (570 \pm 20)$ ng and $m_{Ni, tot}= (440 \pm 30)$ ng. This study constitutes a first step towards more environmentally friendly, non-toxic urban mining of RPMs.

Most HIFU-induced cavitation applications use low frequencies (< 5 MHz), limiting the spatial precision of material erosion. Here, high-frequency (12 MHz) HIFU-induced cavitation was used to locally remove material from aluminium and thin film samples. Control over pit volume and surface area (pits with 20 - 200 µm diameter) was demonstrated by varying sonication parameters. Pit surface areas and volumes were quantified with a scanning acoustic microscope. Increasing the number of bursts increased the eroded volume but also caused a greater variation in pit area, owing to the stochasticity of inertial cavitation. Increasing the sonication amplitude increased the erosion area, as a larger area of the beam exceeded the local cavitation threshold. These results will be used to find suitable sonication parameters for localized HIFU surface-sampling.

Gas phase reactions between hydrated protons H+(H2O)n and a substance M, as seen in atmospheric pressure chemical ionization (APCI) with mass spectrometry (MS) and ion mobility spectrometry (IMS), were modeled computationally using initial amounts of [M] and [H+(H2O)n], rate constants k1 to form protonated monomer (MH+(H2O)x) and k2 to form proton bound dimer (M2H+(H2O)z), and diffusion constants. At 1 × 1010 cm-3 (0.4 ppb) for [H+(H2O)n] and vapor concentrations for M from 10 ppb to 10 ppm, a maximum signal was reached at 4.5 μs to 4.6 ms for MH+(H2O)x and 7.8 μs to 46 ms for M2H+(H2O)z. Maximum yield for protonated monomer for a reaction time of 1 ms was ∼40% for k1 from 10-11 to 10-8 cm3·s-1, for k2/k1 = 0.8, and specific values of [M]. This model demonstrates that ion distributions could be shifted from [M2H+(H2O)z] to [MH+(H2O)x] using excessive levels of [H+(H2O)n], even for [M] > 10 ppb, as commonly found in APCI MS and IMS measurements. Ion losses by collisions on surfaces were insignificant with losses of <0.5% for protonated monomer and <0.1% for proton bound dimer of dimethyl methylphosphonate (DMMP) at 5 ms. In this model, ion production in an APCI environment is treated over ranges of parameters important in mass spectrometric measurements. The models establish a foundation for detailed computations on response with mixtures of neutral substances.

The abundance of ions is an essential parameter for ion mobility and mass spectrometry instrument design and for the control or optimization of chemical reactions with reactant ions. This information also advances the study of atmospheric pressure ion kinetics under continuous ionization, which has a role in developing trace level chemical analyzers. In this study, an ionization chamber is described to measure the abundance of ions produced by a 4.9 keV, model L12535, soft x-ray source from Hamamatsu Corporation. Ions of positive and negative polarity were measured independently in an 8 × 30 mm2 cross section at distances of 12-136 mm at ambient air from an uncollimated beam. Ions were collected using electric fields and 16 sets of plates. The ion current decreased exponentially with distance from the source, and the calculated ion concentration varied between 1.0 × 108 and 3.8 × 105 ions cm-3 on plates. A 2D-COMSOL model including losses by recombination and diffusion was favorably matched to changes in ion current intensity in the ionization chamber. Although the ionization chamber was built to characterize a commercial ion source, the design may be considered generally applicable to other x-ray sources.

We developed a new multiplexed reversed phase liquid chromatography-high resolution tandem mass spectrometric (LC-MS/MS) method. The method is based on isobaric labeling with a tandem mass tag (TMT10-plex) and stable isotope-labeled internal standards, and was used to analyze amino acids in mouse brain microdialysis samples. The TMT10-plex labeling of amino acids allowed analysis of ten samples in one LC-MS/MS run, significantly increasing the sample throughput. The method provides good chromatographic performance (peak half-width between 0.04–0.12 min), allowing separation of all TMT-labeled amino acids with acceptable resolution and high sensitivity (limits of detection typically around 10 nM). The use of stable isotope-labeled internal standards, together with TMT10-plex labeling, ensured good repeatability (relative standard deviation ≤ 12.1 %) and linearity (correlation coefficient > 0.994), indicating good quantitative performance of the multiplexed method. The method was applied to study the effect of d-amphetamine microdialysis perfusion on amino acid concentrations in the mouse brain. All amino acids were reliably detected and quantified, indicating that the method is sensitive enough to detect low concentrations of amino acids in brain microdialysis samples.

Additive manufacturing (3D printing) is a disruptive technology that is changing production systems globally.

Significant enantioselective recognition has been achieved through the introduction of long range ordered and highly interconnected 300 nm diameter pores in molecularly imprinted polymer matrices.

In this study, the feasibility of direct infusion electrospray ionization microchip mass spectrometry (chip-MS) was compared to the commonly used liquid chromatography-mass spectrometry (LC-MS) in non-targeted metabolomics analysis of human foreskin fibroblasts (HFF) and human induced pluripotent stem cells (hiPSC) reprogrammed from HFF. The total number of the detected features with chip-MS and LC-MS were 619 and 1959, respectively. Approximately 25% of detected features showed statistically significant changes between the cell lines with both analytical methods. The results show that chip-MS is a rapid and simple method that allows high sample throughput from small sample volumes and can detect the main metabolites and classify cells based on their metabolic profiles. However, the selectivity of chip-MS is limited compared to LC-MS and chip-MS may suffer from ion suppression.

Studies in optics and acoustics have employed metamaterial lenses to achieve sub-wavelength localization, e.g. a recently introduced concept called 'acoustojet' which in simulations localizes acoustic energy to a spot smaller than λ/2. However previous experimental results on the acoustojet have barely reached λ/2-wide localization. Here we show, by simulations and experiments, that a sub-λ/2 wide localization can be achieved by translating the concept of a photonic jet into the acoustic realm. We performed nano- to macroscale molecular dynamics (MD) and finite element method (FEM) simulations as well as macroscale experiments. We demonstrated that by choosing a suitable size cylindrical lens, and by selecting the speed-of-sound ratio between the lens material(s) and the surrounding medium, an acoustic jet ('acoustic sheet') is formed with a full width at half maximum (FWHM) less than λ/2. The results show, that the acoustojet approach can be experimentally realized with easy-to-manufacture acoustic lenses at the macroscale. MD simulations demonstrate that the concept can be extended to coherent phonons at nanoscale. Finally, our FEM simulations identify some micrometer size structures that could be realized in practice. Our results may contribute to starting a new era of super resolution acoustic imaging: We foresee that jet generating constructs can be readily manufactured, since suitable material combinations can be found from nanoscale to macroscale. Tight focusing of mechanical energy is highly desirable in e.g. electronics, materials science, medicine, biosciences, and energy harvesting.