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Breath analysis has attracted increasing attention in recent years due to its great potential for disease diagnostics at early stages and for clinical drug monitoring. There are several recent examples of successful development of real-time, in vivo quantitative analysis of exhaled breath metabolites via mass spectrometry. On the other hand, current mass spectrometer accessibility limitations restrict point-of-care applications. Here now, an offline method is developed for quantitative analysis of exhaled breath collected on inexpensive filter substrates for direct desorption and ionization by using low-temperature plasma-mass spectrometry (LTP-MS). In particular, different operating conditions of the ionization source were systematically studied to optimize desorption/ionization by using glycerol, a low volatility compound. Applications with respect to propofol, γ-valprolactone, and nicotine analysis in exhaled breath are demonstrated in this study. The effects of several filter substrate properties, including filter material and pore size, on the analyte signal were characterized. Cellulose filter papers performed best with the present analytes. In addition, filters with smaller pores enabled a more efficient sample collection. Furthermore, sample-collection flow rate was determined to have a very significant effect, with slower flow rates yielding the best results. It was also found that filters loaded with sample can be successfully stored in glass vials with no observable sample loss even after 3 days. Limits of detection under optimized conditions are shown to be competitive or significantly better compared with relevant techniques and with additional benefits of cost-efficiency and sample storage capabilities.

Compressed sensing improves sample throughput by orders of magnitude of GDOES elemental mapping via single-pixel spectral imaging.

Nanoparticle (NP) characterization is critical in many fields due to the use of NPs in numerous applications. Traditional NP characterization techniques, however, are limited by low sample throughput, and few can measure the size and elemental composition. Furthermore, sample throughput limitations are compounded in elemental mapping (EM) techniques for obtaining NP spatial distribution. Glow discharge optical emission spectroscopy (GDOES) EM can provide large area maps directly and cost-effectively from solid samples within tens of seconds. Here, GDOES EM is demonstrated for the first time for NP characterization in terms of mass, elemental composition, and size/structure dimensions. The effects of GD pulsed power, pressure, and sample substrate were studied, and optimized conditions resulted in limits of detection at single pg levels. While this is not at the level of single nanoparticle sensitivity, size differentiation of Ag and Au nanoparticles was successfully demonstrated between 5 and 100 nm, while the internal dimensions of complex core-shell NPs were also identified through the optical emission changes as a function of time.

In this work, a field-switching (FS) technique is employed with a flowing atmospheric pressure afterglow (FAPA) source in drift tube ion mobility spectrometry (DTIMS). The premise is to incorporate a tip-repeller electrode as a substitute for the Bradbury-Nielsen gate (BNG) so as to overcome corresponding disadvantages of the BNG, including the gate depletion effect (GDE). The DTIMS spectra were optimized in terms of peak shape and full width by inserting an aperture at the DTIMS inlet that was used to control the neutral molecules' penetration into the separation region, thus preventing neutral-ion reactions inside. The FAPA and repeller's experimental operating conditions including drift and plasma gas flow rates, pulse injection times, repeller positioning and voltage, FAPA current, and effluent angle were optimized. Ion mobility spectra of selected compounds were captured, and the corresponding reduced mobility values were calculated and compared with the literature. The 6-fold improvements in limit of detection (LOD) compared with previous work were obtained for 2,6-DTBP and acetaminophen. The enhanced performance of the FS-FAPA-DTIMS was also investigated as a function of the GDE when compared with FAPA-DTIMS containing BNG.

Herein, a novel diode laser-assisted micro-pyrolysis program (LAMP) technique is demonstrated and coupled with flowing atmospheric-pressure afterglow ambient mass spectrometry for instantaneously profiling polymers and polymer additives. Laser power modulation allows thermal separation of additives and different pyrolysis products, as shown through positive- and negative-mode high-resolution mass spectra and Kendrick mass defect plots of homopolymers, copolymers, polymer blends, and complex polymer samples. LAMP allows much faster temperature control through real-time duty cycle changes and gives significantly better spatial confinement compared to typical resistive heating pyrolysis approaches. Finally, MS imaging, with lateral and depth resolution, is demonstrated for a complex polymer pressure-sensitive adhesive tape sample.

A wide variety of plasma geometries and modalities have been utilized for chemical analysis to date, however, there is much left to be understood in terms of the underlying mechanisms. Plasma diagnostics have been used for many years to elucidate these mechanisms, with one of the most powerful techniques being laser scattering approaches. Laser scattering provides information about the energetic species distributions, in terms of kinetic energy and densities, which can provide invaluable insights into the fundamental processes of chemical analysis plasmas with minimal perturbation. Thomson scattering (TS) from free electrons is the most difficult to implement due to the extremely stringent instrumental requirements for discerning the signal from competing scatterers in low-density plasmas, such as those seen in analytical chemistry applications. Nonetheless, relatively few instruments have been developed to satisfy these stringent requirements. In this paper, the design and characterization of a transmission-type triple grating spectrograph (TGS), with high numerical aperture (0.25)/contrast (≤10−6 at 532 ± 0.5 nm)/stray light rejection (∼1.8 × 10−8 at 532 ± 22–32 nm) required for TS, will be presented. In addition, proof-of-principle measurements on glow discharges operated under typical optical emission spectroscopy (OES) conditions demonstrate the high light throughput and low limits-of-detection (∼109 cm−3 at ∼1 eV Te) afforded by the new instrument.

Optical emission spectroscopy (OES) imaging is often used for diagnostics for better understanding of the underlying mechanisms of plasmas. Typical spectral images, however, contain intensity maps that are integrated along the line-of-sight. A widespread method to extract the radial information is Abel's inversion, but most approaches result in accumulation of error toward the plasma axial position, which is often the region of most interest. Here, a Fourier-transform based Abel's inversion algorithm, which spreads the error evenly across the radial profile, is optimized for OES images collected on a push-broom hyperspectral imaging system (PbHSI). Furthermore, a sub-pixel shifting (SPS) sampling protocol is employed on the PbHSI in the direction of the radial reconstruction to allow improved fidelity from the increased number of data points. The accuracy and fidelity of the protocol are characterized and optimized with a software-based 3-dimensional hyperspectral model datacube. A systematic study of the effects of varying levels of representative added noise, different noise filters, number of data points and cosine expansions used in the inversion, as well as the spatial intensity distribution shapes of the radial profile are presented. A 3D median noise filter with 3-pixel radius, a minimum of 50 points and 8 cosine expansions is needed to keep the relative root mean squared error (rRMSE)

Ambient mass spectrometry (AMS) allows direct desorption and ionization of analytes in real time with minimal-to-no sample preparation. However, it may present inadequate capabilities for differentiating isomers. Here, a reactive flowing atmospheric-pressure afterglow (reactive-FAPA) AMS source is developed for rapid isomer differentiation by derivatization of analytes in real time. The effects of the reactive-FAPA operating conditions on the reagent and product ions were studied and optimized for highly volatile and non-volatile model compounds with different carbonyl functional groups. In addition, two functional isomers of valproic acid (VPA) metabolites, 4-ene VPA and γ-valprolactone, are successfully differentiated for the first time by incorporating methylamine (MA) reagent vapor into the plasma effluent used for desorption/ionization. Reactive-FAPAMS for 4-ene VPA shows only detectable peaks of the protonated acylation product [M + MA-H2O + H]+, while for γ-valprolactone, it shows detectable peaks for both protonated acylation product [M + MA-H2O + H]+ and protonated intermediate [M + MA + H]+. A method for quantitative characterization of mixtures of 4-ene VPA and γ-valprolactone is also developed and validated. In addition, reactive-FAPAMS also shows better detection sensitivity compared to nonreactive-FAPAMS for some larger analyte types, such as UV filters and steroids. The limit of detection (LOD) of pregnenolone acetate in reactive-FAPAMS is 310 ng/mL, which is about 10 times better than its LOD in nonreactive-FAPA.

Thin-layer chromatography (TLC) is a widespread technique because it allows fast, simple, and inexpensive analyte separations. In addition, direct analysis of the compounds separated on TLC plates via mass spectrometry (MS) has been shown to provide high sensitivity and selectivity while avoiding time-consuming sample extraction protocols. Here, direct desorption low-temperature plasma-mass spectrometry (LTP-MS) as well as diode laser assisted desorption (LD) LTP-MS are studied for direct spatially resolved analysis of compounds from TLC plates. Qualitative and quantitative characterization of amino acids, pharmaceuticals, and structural isomers were performed. The nature of the TLC plate stationary phase was found to have a significant influence, together with the analyte's characteristics, on the desorption efficiency. Tandem MS is shown to greatly improve the limits of detection (LODs). Direct desorption LTP-MS, without external thermal assisted desorption, demonstrates its best performance with cellulose TLC plates (LODs, 0.01 ng/mm2 to 2.55 ng/mm2) and restricted performance with normal-phase (NP) TLC plates (several analytes without observable signal). LD LTP-MS, with systematic optimization of irradiance and focal point diameter, is shown to overcome the direct-desorption limitations and reach significantly improved LODs with NP TLC plates (up to ×1000 better). In addition, a wide-ranging characterization of amino acid analytical figures of merit with LD LTP-MS shows that LODs from 84 pg/mm2 down to 0.3 pg/mm2 are achieved on NP TLC plates.

Glow discharge atomic spectrometry has been very popular for direct solid, quantitative, conductive and non-conductive materials characterization. Lateral resolution capabilities, however, have been very limited. Described in this review are the advantages and current limitations of glow discharge surface elemental mapping, coupled with optical emission or mass spectrometry, along with recent advances in measurement strategies to overcome many of the conventional limitations. Recent applications, including glow discharge optical emission spectroscopy (GDOES) ultra-high throughput elemental mapping of thin films and combinatorial libraries utilizing glow discharge as an excitation source are presented. Also, current advances for extending the lateral and depth resolution capabilities of GDOES elemental mapping to larger samples by adapting the discharge chamber design are discussed. In addition, the realization of glow discharge mass spectrometry (GDMS) elemental mapping through a pixel-by-pixel rastering method is reviewed, along with the potential advantages. Furthermore, the three-dimensional elemental mapping capabilities recently displayed by GDOES are considered to show the future trends, which include the potential of allowing elemental mapping protocols previously reserved for fundamental studies to be implemented for routine diagnostic mapping of high sample numbers.

Push-broom hyperspectral imaging (Pb-HSI) is a powerful technique for obtaining the spectral information along with the spatial information simultaneously for various applications, from remote sensing to chemical imaging. Spatial resolution improvement is beneficial in many instances; however, typical solutions suffer from the limitation of geometric extent, lowered light throughput, or reduced field-of-view (FOV). Sub-pixel shifting (SPS) acquires higher-resolution images, compared to typical imaging approaches, from the deconvolution of low-resolution images acquired with a higher sampling rate. Furthermore, SPS is particularly suited for Pb-HSI due to its scanning nature. In this study, an SPS approach is developed and implemented on a Pb-HSI system for plasma optical emission spectroscopy. The preliminary results showed that a periodic deconvolution error was generated in the final SPS Pb-HSI images. The periodic error was traced back to random noise present in the raw/convoluted SPS data and its frequency displays an inverse relationship with the number of sub-pixel samples acquired. Computer modelled data allows studying the effect of varying the relative standard deviation (RSD) in the raw/convoluted SPS data on the final reconstructed SPS images and optimization of noise filtering. The optimized SPS Pb-HSI technique was used to acquire the line-of-sight integrated optical emission maps from an atmospheric pressure micro-capillary dielectric barrier discharge (μDBD). The selected plasma species of interest (He, I, N2, N2+, and O) yield some insight into the underlying mechanisms. The SPS Pb-HSI technique developed here will allow implementing geometric super-resolution in many applications, for example, it will be used for extracting radially resolved information from Abel's inversion protocols, where improved fitting is expected due to the increase in resolution/data points.

Flowing atmospheric pressure afterglow (FAPA) mass spectrometry (MS) is an easy-to-use, cost-effective, and potentially portable technique that allows direct desorption/ionization from samples with little-to-no sample preparation for real-time chemical analysis. However, it has limitations regarding analytes with low desorption efficiency, such as polymers. Here, laser assisted sampling (LAS) is developed and coupled to FAPA MS to allow access to a wider range of chemical information from polymer samples. This is achieved through laser-induced pyrolysis conditions that provide a much higher degree of spatio-temporal control compared to typical pyrolysis techniques. LAS FAPA MS, together with direct desorption FAPA MS, is implemented on pressure sensitive adhesive (PSA) tape samples, which are often found at crime scenes and recovered as forensic evidence. Comparative PSA tape examination is typically performed to assess any differences in the comparison of unknown and known samples and provide an evidentiary association between suspects and crime scenes in forensic applications. PSA tape samples from several manufacturers of duct, masking, and electrical tape were analyzed from the adhesive and backing side. Direct desorption FAPA provides top-surface selectivity and the tape mass spectra are dominated by more peaks at lower m/z, many of which correspond to polymer additives. LAS gives access to sampling from all of the tape layers and the FAPA mass spectra is extended to higher m/z, while polymer fragmentation patterns are evident. Principal components analysis (PCA) was implemented to assess the ability of each technique to distinguish and categorize identified tape classes within the sampled population. The complementary nature of the resulting mass spectra from direct desorption vs LAS FAPA was evident from the PCA as different tape brands sub-sets were discriminated by each technique. The differentiation obtained by combining both methods is already competitive, or better, than conventional techniques, with the additional benefits of AMS.

In this work, the flowing atmospheric-pressure afterglow (FAPA) ambient desorption/ionization source has been coupled with stand-alone Drift Tube Ion Mobility Spectrometry (DTIMS) for the first time. A tip repeller electrode, modified to allow higher bias potential still below the Townsend’s breakdown, was implemented at the FAPA/DTIMS interface to overcome the opposing potentials and facilitate ion transmission. The effect of the lab-built DTIMS and FAPA’s operating conditions (such as plasma voltage, current, gas flow rate, repeller’s potential and positioning, FAPA orientation, etc.) on the signal of selected analytes was studied, for both gas-phase injection and desorption. The FAPA reactant ion peak (RIP) reduced mobility coefficient (K0) corresponds to protonated water clusters (H2O)nH+. The FAPA-DTIMS spectra of several selected compounds showed that their K0 agrees with literature values. Moreover, quantitative characterization of acetaminophen and 2,6-di-tert-butylpyridine (2,6-DTBP) based on desorption or gas-phase injection yield limits of detection (LODs) of 0.03 μg and 18 ppb, respectively.

Real-time analysis of exhaled human breath is a rapidly growing field in analytical science and has great potential for rapid and noninvasive clinical diagnosis and drug monitoring. In the present study, an LTP-MS method was developed for real-time, in-vivo and quantitative analysis of γ-valprolactone, a metabolite of valproic acid (VPA), in exhaled breath without any sample pretreatment. In particular, the effect of working conditions and geometry of the LTP source on the ions of interest, protonated molecular ion at m/z 143 and ammonium adduct ion at m/z 160, were systematically characterized. Tandem mass spectrometry (MS/MS) with collision-induced dissociation (CID) was carried out in order to identify γ-valprolactone molecular ions (m/z 143), and the key fragment ion (m/z 97) was used for quantitation. In addition, the fragmentation of ammonium adduct ions to protonated molecular ions was performed in-source to improve the signal-to-noise ratio. At optimum conditions, signal reproducibility with an RSD of 8% was achieved. The concentration of γ-valprolactone in exhaled breath was determined for the first time to be 4.83 (±0.32) ng/L by using standard addition method. Also, a calibration curve was obtained with a linear range from 0.7 to 22.5 ng/L, and the limit of detection was 0.18 ng/L for γ-valprolactone in standard gas samples. Our results show that LTP-MS is a powerful analytical platform with high sensitivity for quantitative analysis of volatile organic compounds in human breath, and can have potential applications in pharmacokinetics or for patient monitoring and treatment. Graphical Abstract ᅟ.

The use of plasmas for chemical analysis is prevalent and new sorts are continually being explored for potential applications in this field. However, the underlying mechanisms of characteristic processes that occur in plasmas are not completely understood. Free electrons drive chemical reactions, are essential to many plasma inherent processes, and are responsible for sustaining the discharge while governing the kinetic energy transfer between other species. Thomson scattering (TS) is a powerful plasma diagnostic technique for elucidating the fundamental electron parameters of number density, kinetic temperature, and energy distribution function. TS advantages include providing the direct, radially and temporally resolved probing of free electrons, with little-to-no perturbation of the plasma, with no prior assumptions of local thermodynamic equilibrium conditions, and simultaneous electron density/temperature measurements. The aim of this review is to provide a brief explanation of the TS theory and the experimental requirements, as well as highlight selected novel instrumentation advances and insights about chemical analysis plasmas discovered in the most recent TS publications, not previously covered in other reviews.

Plasma optical emission spectral imaging is critical for the development of chemical analysis applications and plasma diagnostics. Nevertheless, typical techniques require array detectors that can be very expensive or pixel-to-pixel rastering approaches that are highly time-consuming. Further, the acquired image files are compressed to keep data manageable, which can be achieved without loss of critical information, thus showing the sparsity of the data. A fairly recent paradigm in sampling, compressed sensing (CS), allows performing compression during acquisition which results in a more efficient use of experimental resources. As such, CS systems can be much faster, cost-effective, or even provide better resolution or throughput. In this study, a CS spectral imaging system, featuring a single-sensor and a variable encoding mask, is designed and implemented for plasma optical emission spectroscopy. The performance, based on PSNR and spatial resolution, is characterized as a function of experimental and image processing parameters such as sensing matrix selection, recovery algorithm choice, and sparsifying basis. Spectral images of optical emissions from plasma species of interest (He I, N2, N2+) were collected from an atmospheric pressure plasma jet. The use of a CS spectral imaging system for plasma diagnostics (Tvib) is reported for the first time.

Analytical chemists are instilled with the Shannon–Nyquist theorem for measuring practices: the sampling frequency must be greater than two times the frequency of the signal of interest to avoid misrepresentation. Furthermore, chemical analysis techniques keep evolving to yield increasing amounts of information resulting in greater demands in data collection, data analysis and computer memory. This leads to typical practices of performing software data compression. In addition, techniques that require increases in spatial frequency of array detectors typically lead to expensive hardware solutions. Over the past ten years, compressed sensing has presented a sampling paradigm shift. The main idea is to perform compression during data acquisition which leads to several advantages, including faster analysis time and availability of cost effective alternatives to array detectors. In this short review, a summary of the main concepts of compressed sensing are presented. In addition, selected examples of compressed sensing applications in spectrochemical analysis are used to showcase its advantages and potential.

Large-area surface elemental mapping is highly beneficial for a multitude of applications in fields from materials science to biology. Current typical methods, however, suffer from long acquisition times. Glow Discharge Optical Emission Spectrometry (GDOES), under pulsed-power and higher pressure operation, exhibits a great potential for ultrahigh throughput chemical imaging of large surface area samples. Up until now, various proof-of-principle studies of GDOES elemental mapping have only been applied to smaller surface area samples. Thus, there is a need for development of GDOES systems that allow for analysis of large area samples. Here, the design of different GD configurations for large area sample (10 cm diameter) analysis is investigated as a function of operating conditions such as pressure (133–4000 Pa), applied power (up to 5 kW), and pulsing. An open face electrode (OFE) design generated undesirable heterogeneous plasma at the higher pressures required for achieving spatial resolution. On the other hand, a restrictive anode array mask (RAAM) design provided notable homogeneity within the same pressure range and enabled the lateral resolution of 1 mm diameter silver inclusions embedded in copper. RAAMS were designed varying thickness (3 mm and 12 mm), aperture size (4, 6, 8 mm), geometry, and grounding. Also, as the section sputtered is restricted to the area covered by the apertures, the RAAM provides the opportunity for subsequent analysis of the unsputtered regions via alternative methods. In addition, the RAAM permits higher power densities to be achieved within the limitations of the power supply. These findings help to pave the way for exploiting the full potential of GDOES and its ultrahigh throughput elemental mapping of large surface area samples.

Journal of the American Society for Mass Spectrometry, 20 (11), ISSN:1879-1123, ISSN:1044-0305

Combinatorial chemistry and high-throughput techniques are an efficient way of exploring optimal values of elemental composition. Optimal composition can result in high performance in a sequence of material synthesis and characterization. Materials combinatorial libraries are typically encountered in the form of a thin film composition gradient which is produced by simultaneous material deposition on a substrate from two or more sources that are spatially separated and chemically different. Fast spatially resolved techniques are needed to characterize structure, composition, and relevant properties of these combinatorial screening samples. In this work, the capability of a glow discharge optical emission spectroscopy (GD-OES) elemental mapping system is extended to nitrogen-based combinatorial libraries with nonconductive components through the use of pulsed radiofrequency power. The effects of operating parameters of the glow discharge and detection system on the achievable spatial resolution were investigated as it is the first time that an rf source is coupled to a setup featuring a push-broom hyperspectral imaging system and a restrictive anode tube GD source. Spatial-resolution optimized conditions were then used to characterize an aluminum nitride/chromium nitride thin-film composition spread. Qualitative elemental maps could be obtained within 16.8 s, orders of magnitude faster than typical techniques. The use of certified reference materials allowed quantitative elemental analysis maps to be extracted from the emission intensity images. Moreover, the quantitative procedure allowed correcting for the inherent emission intensity inhomogeneity in GD-OES. The results are compared to quantitative depth profiles obtained with a commercial GD-OES instrument.

The resistance to breakage of sapphire samples of different crystallographic orientations and produced by the Kyropoulos and Verneuil processes was investigated. The fracture strength was determined by using four-point bending tests, whereas the single-edge V-notch beam method was used to measure the fracture toughness. For both mechanical properties, it was found that (i) Verneuil sapphire has values up to two times higher than Kyropoulos sapphire and (ii) the data scatter is also generally higher for Verneuil sapphire. The main factor responsible for this behavior is believed to be the presence of mosaicity in Verneuil and its absence in Kyropoulos sapphire. By using the Read–Shockley model to estimate the energy of low-angle grain boundaries, together with the Griffith energy criterion for intergranular crack propagation, it is demonstrated that intergranular fracture along the mosaic block boundaries is energetically more favorable than transgranular fracture for crack-to-boundary orientations smaller than a critical deflection angle. Nevertheless, both the location of the crack in respect to the boundary, as well as the 3-D nature of these features, must be taken into consideration for a complete description of the intergranular deflection toughening mechanism.

Glow discharge optical emission spectroscopy (GDOES) is becoming a mature technique for depth profiling analysis. The advantages it affords, including fast, quantitative, and multi-elemental analysis, as well as allowing very high depth-resolution, have attracted the attention of the thin film community. Recently, the use of GDOES under pulsed-mode operation and coupled to hyper-spectral imaging techniques has been proposed to perform surface elemental mapping. Several manuscripts have reported on the underlying mechanisms in GDOES pertaining to the spatial resolution, while other manuscripts have reported on elemental mapping applications, for example, regarding separated proteins or thin film combinatorial libraries. Only a couple of studies have reported image processing techniques applied to GDOES elemental mapping and none having to do with image denoising purposes. Herein, image denoising techniques are compared in several scenarios: (a) mapping of homogeneous samples; (b) mapping of heterogeneous samples in two dimensions; (c) mapping of heterogeneous samples in three dimensions. Denoising techniques compared include averaging, median filtering, principal component analysis (PCA), and local pixel grouping-PCA. The peak signal-to-noise ratio is used to show the efficiency of noise removal, while the full-with-half-maximum of emission from sharp features is used to demonstrate the resolution degradation effects of each denoising technique. In general, it is observed that PCA outperforms other techniques albeit with a higher cost of image processing time. Also, it becomes evident that having multiple image slices (a 3rd dimension) affords more efficient noise removal while minimizing losses in spatial resolution.

Previously performed studies have shown that alfalfa shoot biomass can bind an appreciable amount of nickel(II) and chromium(III) ions from aqueous solution. Direct and indirect approaches were applied to study the possible mechanis ms involved in metal binding by the alfalfa biomass. The direct approach involves investigations of the metal-bound alfal fa shoot biomass by X-ray absorption spectroscopic analysis (XANES and EXAFS). Results from these studies suggest that ni ckel(II) and chromium(III) binding mostly occurs through coordination with oxygen ligands. Indirect approaches consist of chemical modification of carboxylate groups that have been shown to play an important role in metal binding to the alfal fa biomass. An appreciable decrease in metal binding resulted after acidic methanol esterification of the biomass, indica ting that carboxyl groups are entailed in the metal binding by the alfalfa biomass. In addition, base hydrolysis of the a lfalfa biomass increased the binding of these metals, which further indicates that carboxyl groups play an important role in the binding of these metal ions from solution. Therefore, by combining two different techniques, our results indicate that carboxylate groups are the major ligands responsible for the binding of nickel(II) and chromium(III) by alfalfa bio mass.

The presented study gives an integrated overview on the prospects of glow discharge (GD) methods in the chemical analysis of photovoltaic materials. With a focus on recent research and important photovoltaic (PV) materials, the GD coupled analytical methods, high resolution mass spectrometry (MS), time-of-flight-mass spectrometry (TOF-MS) and optical emission spectrometry (OES) are discussed. Each exemplary study carried out will point out the most suitable GD technique for the problem at hand, at the same time showing ways to increase analytical accuracy and to overcome typical instrumental restrictions. Challenging GD-MS analyses of thin and ultra thin films (down to 20 nm) as well as GD-MS and GD-OES studies of ready-to-use modules were carried out, showing the reader the application potential of GD methods in a PV development or production process. For the first time, novel cell concepts based on crystalline silicon on glass and silicon nanowires are analyzed by GD-OES, revealing precise chemical information on the devices. Copyright © 2012 John Wiley & Sons, Ltd.

Glow discharge optical emission spectroscopy (GDOES) has evolved in the last couple of decades from direct bulk solid analysis to a high resolution depth-profiling technique. However, the achievable lateral resolution has been historically restricted to the diameter of the sputtered area, i.e. some millimetres. Recently, there has been a push toward characterizing and improving the GDOES limits of lateral resolution. In consequence, a door has been opened for applications to take advantage of the new information dimensions that the technique affords. It is important to sum what has been accomplished so far to clarify the current possibilities and opportunities for development. It will become evident that the data acquisition requirements of GDOES elemental mapping can only be met via spectral imaging. Accordingly, the studies performed to date will be reviewed with emphasis on the spectral imaging geometry that has been utilized.

In this work, Al2O3–Al2O3 and Al2O3–Ti solder joints intended for space applications were realized by applying metallic multilayers both on Ti and on polycrystalline Al2O3 substrates to ensure wetting during the soldering process. The eutectic Au-12Ge (wt%) alloy with a melting point of 361°C was used as solder material and two different multilayer systems on the ceramic (Cr-Ni/Ti-W/Au,Ti/Pt/Au) were investigated. The influence of different thermal pretreatments of the Al2O3 plates on the multilayer properties, the interface reactions during soldering and the mechanical properties were studied using Glow-Discharge Optical Emission Spectroscopy (GDOES), X-ray Photoelectron Spectroscopy (XPS), Scanning Electron Microscopy (SEM) and a shear test device. It is shown that joints with a good quality can be produced at a soldering temperature of 400°C, whereas their properties and fracture behavior are strongly dependent on the metallization layer properties and the thermal pretreatments.

Glow discharge optical emission spectroscopy (GDOES) has been recognized for allowing direct solid sample elemental analysis with high depth resolution. However, the lateral resolution it affords has been historically restricted to some millimetres or the diameter of the sputtered area. Recently, it was shown that one can obtain laterally resolved information from within the sputtered area by operating the discharge in pulsed power mode. The newly available data dimensions require a new approach to the collection of the GDOES signal with lateral (to recover X and Y positions), spectral (to qualify and quantify elemental information), and temporal resolution (to improve lateral resolution and allow depth profiling). Previous studies have utilized spectral imagers of whisker-broom and staring geometries. In this study we characterize the advantages and disadvantages of using a push-broom geometry hyperspectral imager for GDOES elemental mapping. The results show that the higher light throughput of the push-broom geometry allows faster image acquisition times, compared to other spectral imaging systems with the same components, and thus maintain depth resolutions below 10 nm.

Flowing afterglow atmospheric pressure glow discharge tandem mass spectrometry (APGD-MS/MS) is used for the analysis of trace amounts of pesticides in fruit juices and on fruit peel. The APGD source was rebuilt after Andradeet al. (Andradeetal.,Anal.Chem. 2008; 80: 2646–2653; 2654–2663) and mounted onto a hybrid quadrupole time-of-flight mass spectrometer. Apple, cranberry, grape and orange juices as well as fruit peel and salad leafs were spiked with aqueous solutions containing trace amounts of the pesticides alachlor, atrazine, carbendazim, carbofuran, dinoseb, isoproturon, metolachlor, metolcarb, propoxur and simazine. Best limits of determination (LODs) of pesticides in the fruit juices were achieved for metolcarb (1 mg/L in apple juice), carbofuran and dinoseb (2 mg/L in apple juice); for the analysis of apple skin best LODs were 10 pg/cm 2 of atrazine, metolcarb and propoxur which corresponds to an estimated concentration of 0.01 mg/kg apple, taking into account the surface area and the weight of the apple. The measured LODs were within or below the allowed maximum residue levels (MRLs) decreed by the European Union (1–500 mg/kg for pesticides in fruit juice and 0.01–5 mg/kg for apple skin). No sample pretreatment (extraction, pre-concentration, chromatographic separation) was necessary to analyze these pesticides by direct desorption/ionization using APGD-MS and to identify them using MS/MS. This makes APGD-MS a powerful highthroughput tool for the investigation of very low amounts of pesticides in fruit juices and on fruit peel/vegetable skin. Copyright # 2008 John Wiley & Sons, Ltd.

In order to elucidate the fundamental properties of a low-flow inductively coupled plasma (ICP) operated under total Ar consumption of 0.6 L min − 1 , excitation temperatures, rotational temperatures, ionization temperatures, electron temperatures, and electron number densities were studied with optical emission based methods. The plasma was operated in the SHIP torch ( S tatic H igh Sensitivity I C P ), which was designed for optical emission spectrometric detection. For the first time, this plasma was studied in a laterally resolved manner and at selected observation heights. The Boltzmann plot method was used to obtain excitation and rotational temperatures in the range of 5000–8000 K and 3100–4000 K, respectively. Electron temperatures were determined from the line-to-continuum method to be as high as 9000 K in the analytical channel. The electron number densities were determined with the hydrogen-beta line method and found to be in the range of 5–8 × 10 15 cm − 3 at 1.1 kW radio frequency (rf) power. Ionization temperatures between 6250 and 7750 K were found at different observation heights in the plasma. The influence of applied rf powers between 0.9 and 1.2 kW on selected key parameters was investigated. The low-flow plasma exhibited temperature ranges similar to those prevailing in conventional ICP sources.

Extractive electrospray ionization mass spectrometry (EESI-MS) was applied to rapid fingerprinting of various perfumes for quality classification. Unique EESI-MS fingerprints of ten famous brands were obtained. This technique was shown to be applicable to rapid forgery detection on the example of an authentic and a counterfeit 'Miss Dior' fragrance by Christian Dior. We believe that the high throughput and simplicity of this sample-preparation-free method can be advantageous in the perfume industry, for instance when applied to online quality control.

The flowing afterglow-atmospheric pressure glow discharge (APGD) ionization source described in part 1 of this study (in this issue) is applied to the direct analysis of condensed-phase samples. When either liquids or solids are exposed to the ionizing beam of the APGD, strong signals for the molecular ions of substances present on their surfaces can be detected without compromising the integrity of the solid sample structure or sample substrate. As was observed for gas-phase compounds in part 1 of this study, both polar and nonpolar substances can be ionized and detected by mass spectrometry. The parent molecular ion (or its protonated counterpart) is usually the main spectral feature, with little or no fragmentation in evidence. Preliminary quantitative results show that this approach offers very good sensitivity (detection limits in the picogram regime are reported for several test compounds in part 1 of this study) and linear response to the analyte concentration. Examples of the application of this strategy to the analysis of real-world samples, such as the direct analysis of pharmaceutical compounds or foods is provided. The ability of this source to perform spatially resolved analysis is also demonstrated. Preliminary studies of the mechanisms of the reactions involved are described.

First-order phase transitions are known to be accompanied by hysteresis due to the formation of domains with different order parameters. As the transition is approached, the domain sizes increase to macroscopic dimensions. It is therefore natural to expect that hysteresis will be absent from samples of microscopic size. Here, we explore from a microscopic standpoint the hysteretic behaviour across the spin phase transition that occurs at filling ν=2/3 in the fractional-quantum-Hall regime1,2,3,4,5. Using a single-electron transistor, we follow the evolution of localized states across the spin transition by measuring the local compressibility. Localized-state spectra clearly reveal the hysteretic behaviour accompanying the transition. Using electrostatic gating we continuously vary the size of the sample undergoing the phase transition. For submicrometre dimensions the hysteresis disappears, indicating domain sizes in excess of 500 nm.

The effects of a mass-spectrometer sampling interface on the fundamental parameters of an argon inductively coupled plasma were studied. Laser-scattering techniques were used to obtain radially resolved values for electron number density ( n e ), electron temperature ( T e ), and gas-kinetic temperature ( T g ) of the ICP upstream from the sampler as a function of applied r.f. power while different sample solutions were introduced. In addition, radially resolved calcium ion and atom number densities were determined under the same conditions in order to study the effects of matrix elements upstream from the mass spectrometer interface. It was found that the interface causes changes in the fundamental parameters that are dependent on the ICP applied r.f. power and the pressure at the back of the sampling interface. Furthermore, the changes caused by matrix interferents are different in the presence and in the absence of the sampler.

Current and emerging capabilities of plasma-source mass spectrometry (PS-MS) as it is employed for elemental speciation analysis are reviewed. Fundamental concepts and their advantageous aspects, experimental conditions, and analytical performance are described and illustrated by recent examples from the literature. Novel instrumentation, techniques, and strategies for inductively-coupled plasma mass spectrometry (ICP-MS), microwave-induced plasma (MIP) mass spectrometry, glow-discharge (GD) mass spectrometry, and electrospray ionization (ESI), among others, are described. The use of ionization sources that provide tunable ionization, others that can be modulated between different sets of operating conditions, and others used in parallel is also examined.

We have calculated the gas temperature, electron density, electron energy distribution function, and average electron energy, as a function of distance from the cathode, with a two-dimensional model for an argon direct-current glow discharge. The calculated results are compared with measured values from Rayleigh- and Thomson-scattering experiments, for different values of voltage, pressure and electrical current. The gas-temperature distribution and electron-density profile were found to be in reasonable agreement with experiment. For the electron energy, model and experiment give complementary information, since the experiment is able to detect only the thermal and low-energy electrons, whereas the model focuses mainly on the high-energy electrons.

Radial profiles of Ca and Sr ion number densities in an ICP at 6, 7 and 8 mm above the load coil (ALC) and at 1.25 kW of input rf power were measured by saturated fluorescence induced by an Nd:YAG laser-pumped dye laser at 396.85 nm and 421.55 nm, respectively. The measurements were performed in the presence and in the absence of an ICP-MS sampling interface. When in place, the orifice of the sampling cone was positioned 13 mm ALC on the axis of the plasma torch. The results show that the interface can either raise or lower the ion number densities, depending on the central-gas-flow rate, and can cause a vertical shift of their entire radial profiles with respect to the ICP axis. The introduction of Li, Cu and Zn as matrix elements reduced the ion number densities of the analytes, both in the presence and in the absence of the interface. This effect became more significant at higher central-gas-flow rates. In addition, the peak value of the radial ion number density was found to depend strongly on the central-gas-flow rate maximum occurred at 1.1 l/min for both Ca ion and Sr ion under the ICP operating conditions used in this study. This behavior is very similar to the mass spectrometric signals previously observed downstream and reported in the literature.

Batch laboratory experiments were performed to investigate the effects of pH, chemical modification, time dependency, and interference studies on the binding of trace concentrations of hexachloroplatinate(IV) and tetrachloroplatinate(II) to alfalfa biomass. The pH profiles were measured between pH 2.0 and 6.0. It was found that the binding of trace concentrations of platinum(IV and II) to alfalfa biomass was dependent on pH with a maximum binding occurring at pH 3.0 and a minimum at pH 6.0. When the alfalfa biomass was chemically modified (esterified), maximum binding occurred at pH 6.0 for both oxidation states of platinum. From the batch time dependency experiments, it was found that binding took at least 20 min to level off for both platinum oxidation states. Batch experiments were performed with various concentrations of calcium, magnesium, and sodium (0.1, 1.0, 10, 100 and 1000 ppm) and it was found that calcium affected the binding of platinum(II and IV) to the alfalfa biomass. It was determined that magnesium and sodium did not interfere appreciably with the binding of platinum in either of the oxidation states studied. Finally, batch experiments were performed with Mg 2+ , Ca 2+ and Na + in solutions at various concentrations, and it was observed that the binding was affected similarly to that by calcium alone.

The increasing demand for gold has encouraged the development of cost effective and environmentally friendly techniques to recycle and recover this precious metal from waste liquors. Earlier experiments have shown the appreciable ability of alfalfa shoot biomass to accumulate Au(III) from aqueous solutions. Likewise, alfalfa biomass is able to bind other metal ions in noticeable amounts. Thus, experiments with solutions containing multiple metal ions were performed in order to determine the effect of other ions on gold accumulation by alfalfa biomass. Batch laboratory experiments showed that Au(III) binds in a rapid and pH-independent-like manner in the presence of other metal ions, which agrees with experiments using solutions containing only Au(III). In addition, Au(III) was found to have one of the highest metal binding affinities to the alfalfa biomass compared to Pb(II), Cr(III), Cu(II), Zn(II), Ni(II), and Cd(II), even at the optimum binding pH for the other metal ions (pH 5.0). A similar behavior for Au(III) accumulation was observed under flow conditions. Nevertheless, it was determined that the selectivity of the immobilized alfalfa biomass could be shifted towards Au(III) by decreasing the pH of the multi-metal solution to 2.0 (similar to mining and industrial environments where aqueous gold is found). Alfalfa biomass was also found to accumulate Au(III) efficiently even when Ca and Mg ions were added to the multi-metal solutions at concentrations up to 10 000 times higher than Au(III). These results will aid the development of a novel method to recover gold ions from aqueous solutions utilizing alfalfa biomass.

Existing technologies for the extraction and recovery of gold include cyanidation which uses toxic cyanide. Because of the potential health threat created by many of these processes, an increasing need to develop new safer technologies to extract and recover gold from aqueous solution has arisen. Previous experiments have shown that gold(III) is adsorbed by alfalfa biomass at high concentrations in an almost pH-independent manner. However, little data exist for the bio-adsorption of trace levels of gold(III) by alfalfa biomass. Batch laboratory pH profile experiments were performed at trace levels with native alfalfa biomass using a 100 ppb gold(III) aqueous solution. The observed trend in the binding by the alfalfa biomass was highest at pH 2–3 (≈97%) and decreased to approximately 50% at pH 4.0 and 5.0. To explore the effects of hard cations on the trace level gold(III) binding, calcium, magnesium, and sodium cations were added to the gold(III) solutions and binding experiments were repeated to determine how these ions might interfere with the gold(III) bio-adsorption by the biomass. Experiments were also performed using all three cations combined in solution to further explore the effects of hard cations on the trace level gold(III) binding to the alfalfa biomass. All of the interference experiments showed that under optimal conditions the presence of the hard cations in concentrations as high as 3000 times the ppm concentration of gold(III) did not greatly effect binding by the alfalfa biomass.

Previous studies have shown that alfalfa biomass possesses the potential to be a biosorbent for chromium(III) removal from contaminated and industrial wastewaters. However, the mechanism through which chromium(III) binds to alfalfa biomass has not been identified. Therefore, studies were conducted to determine how modification of chemical groups present on the alfalfa biomass affect the chromium(III) binding. Batch pH profile studies were performed on esterified, hydrolyzed and unmodified alfalfa biomasses. A comparison study with ion exchange resins containing carboxyl, thiol, amino, sulfonic, and phosphate groups were also performed. These studies showed that chromium(III) binds predominantly to the alfalfa biomass through carboxyl ligands and follows a binding trend similar to that of the carboxyl resin. In addition, Fourier transform infrared spectroscopy (FTIR) studies were conducted in order to better understand how the chemical modification affects the alfalfa biomass and the mechanism(s) by which chromium(III) binds to alfalfa. From these experiments, it was determined that chromium(III) may be coordinating with carboxyl ligands present on the surface of the alfalfa biomass through a bridging bidentate complex. X-Ray absorption spectroscopy (XAS) studies were also performed, which corroborate with batch modification and ion exchange resin comparison studies, further indicating carboxyl involvement in chromium(III) binding by inactivated alfalfa biomass.

Previous experiments showed that inactivated alfalfa biomass is proficient in the recovery of gold(III) from aqueous solutions. Gold(III) binding to alfalfa biomass is rapid, pH independent, and increases with temperature. Also, X-ray absorption spectroscopy studies showed that alfalfa was able to reduce gold(III) to gold(0), producing nano-particles. This current study was performed to gain a better understanding of the interaction between gold(III) and the alfalfa biomass. Through chloride ion release studies, it was found that three moles of Cl− were released per mole of gold adsorbed. Chemical modification of the alfalfa biomass indicated that both amino and carboxyl functional groups on the alfalfa biomass are involved in the reduction process. Finally, X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) spectroscopy studies suggested that gold(III)is initially reduced to gold(I) and is eventually reduced to gold(0); in addition, the X-ray spectroscopic studies indicated that binding may be occurring through a nitrogen or oxygen ligand.

Traditional methods currently employed to remediate heavy metal contaminated waters prove to be cost prohibitive. Therefore, more cost-effective methods of remediating heavy metals from contaminated waters need to be developed. The use of plant materials as metal adsorbents may be a possible solution. Previously performed experiments have shown that alfalfa shoot biomass can bind an appreciable amount of heavy metal ions, even from multi-contaminate containing solutions. Although the alfalfa biomass has shown to be very effective at removing heavy metal ions from aqueous solution, more research is needed to understand the metal binding mechanism. Carboxyl groups were chemically modified in order to determine their contribution to the metal binding process. Batch experiments were performed with the modified biomass and suggest that carboxyl groups play a significant role in the binding of lead(II). In addition, X-ray absorption spectroscopic analysis (XANES and EXAFS) corroborate these results. These studies are important for determining the ligands that may be involved in the binding of lead ions to alfalfa biomass, thus aiding in our understanding of the mechanisms involved in the removal and recovery of metal ions from contaminated waters through phytofiltration.

Contamination caused by heavy metals as well as their toxic effects on the environment and mankind is well known. However, it has been observed that some native plants have survived within areas polluted with heavy metals. This has been the case with the woody subshrub Solanum elaeagnifolium. It is possible to take advantage of this singular feature by using its inactivated tissues as a biofiltration system. In this work we characterized the mechanism of the binding between the biomass tissues with heavy metals by using chemical modification techniques. These techniques included chemical esterification and hydrolyzation of carboxylic groups and methyl esters, respectively. These studies have shown an overall decrease in metal binding for the esterified biomass, and an overall increase in metal binding for the hydrolyzed biomass as compared with the unmodified biomass. These experiments were performed with Cu(II), Pb(II), Cr(III), Zn(II) and Ni(II). In addition, experiments conducted with modified biomass at different pH conditions were done in order to corroborate the biomass modification results. Also, we used X-ray absorption spectroscopy techniques (XANES and EXAFS) to elucidate the mechanism(s) of metal ion binding.

We report herein the use of Medicago sativa alfalfa shoot biomass for the removal of gold from aqueous solutions. The accumulation process involves the reduction of Au(III) to colloidal Au(0) and is shown to increase at elevated temperatures and at lower pH. X-ray absorption spectroscopy (XAS) was used to determine that gold(III) was reduced to form gold(0) colloids, which varied in size depending on the pH of the initial solution. The gold cluster radius was 6.2 ± 1 A at pH 5 and 9.0 ± 1 A at pH 2. Our findings indicate that essentially another layer of gold atoms was deposited onto the colloid surface at pH 2. Possible mechanisms of bioreduction and accumulation are discussed.

We present here experimental results that investigate the effects of metal−ion binding on iron−ion sorption to and recovery from alfalfa biomass. Fe(II)− and Fe(III)−ion binding were measured in order to ascertain the differences in binding strengths due to changes in oxidation state. Stronger binding was found for iron(III)−biomass as compared to iron(II)−biomass. The optimal pH for iron uptake was determined to be 5. The results of pH binding profile, iron desorption, and temperature-dependent binding experiments as well as X-ray spectroscopic (XAS) measurements all suggest that binding of iron by alfalfa biomass may be occurring through carboxyl ligands. The XAS experiments further demonstrate that the metal binding proceeds without an oxidation state change, and both iron(II) and iron(III) have similar coordination environments. The information presented will assist in understanding the binding of other metals to alfalfa biomass and in developing methods for their recovery.

Alfalfa shoot biomass has demonstrated the ability to bind an appreciable amount of cadmium(II), chromium(III), copper(II), lead(II), nickel(II), and zinc(II) separately from aqueous solutions. Since most heavy metal contaminated waters contain more than one heavy metal ion, it was necessary to determine the binding abilities of the alfalfa biomass with multi-metal solutions. Batch laboratory experiments were performed with a solution containing 0.1 mM of each of the following metal ions: cadmium(II), chromium(III), copper(II), lead(II), nickel(II), and zinc(II). We determined the pH profile, time dependency, and binding capacity by the alfalfa biomass of each metal ion under multi-elemental conditions. For all the metal ions studied, the alfalfa biomass showed to have a high affinity for metal binding around pH 5.0 within a time period of approximately 5 min. The binding capacity experiments showed that there was a preferential binding of the metal ions from the multi-elemental solution with the following amounts of metal ion bound per gram of biomass: 368.5 micromol/g for copper(II), 215.4 micromol/g for chromium(III), 168.0 micromol/g for lead(II), 56.9 micromol/g for zinc(II), 49.2 micromol/g for nickel(II), and 40.3 micromol/g for cadmium(II). Reacting the biomass from the capacity experiments with 0.1 M HCl resulted in 90% or greater recovery of bound cadmium, copper, lead, nickel, and zinc. However, only 44% of the bound chromium was recovered. These experiments show the ability of Medicago sativa (alfalfa) to bind several metal ions under multi-contaminant conditions. Similar results were obtained when the experiments were performed under flow conditions using silica-immobilized alfalfa biomass. Chromium bound on the silica-immobilized biomass was also difficult to be desorbed with 0. 1 M HCl. The information obtained will be useful for the future development of an innovative technology to remove heavy metal contaminants from polluted ground waters.

The use of metal nanoparticles has shown to be very important in recent industrial applications. Currently gold nanoparticles are being produced by physical methods such as evaporation. Biological processes may be an alternative to physical methods for the production of gold nanoparticles. Alfalfa biomass has shown to be effective at passively binding and reducing gold from solutions containing gold(III) ions and resulting in the formation of gold(0) nanoparticles. High resolution microscopy has shown that five different types of gold particles are present after reaction with gold(III) ions with alfalfa biomass. These particles include: fcc tetrahedral, hexagonal platelet, icosahedral multiple twinned, decahedral multiple twinned, and irregular shaped particles. Further analysis on the frequency of distribution has shown that icosahedral and irregular particles are more frequently formed. In addition, the larger particles observed may be formed through the coalescence of smaller particles. Through modification of the chemical parameters, more uniform particle size distribution may be obtained by the alfalfa bio-reduction of gold(III) from solution.

Previous laboratory batch experiments of Medicago sativa (Alfalfa) indicated that the African shoots population had an appreciable ability to bind copper(II) and nickel(II) ions from aqueous solution. Batch laboratory pH profile, time dependency and capacity experiments were performed to determine the binding ability of the African shoots for cadmium(II), chromium(III), chromium(VI), lead(II), and zinc(II). Batch pH profile experiments for the mentioned ions indicated that the optimum pH for metal binding is approximately 5.0. Time dependency experiments for all the metals studied showed that metal binding to the African alfalfa shoots occurred within 5 min. Binding capacity experiments revealed the following amounts of metal ions bound per gram of biomass: 7.1 mg Cd(II), 7.7 mg Cr(III), 43 mg Pb(II), and 4.9 mg Zn(II). However, no binding occurred for chromium(VI). Nearly all of the metals studied were recoverable by treatment with 0.1 M HCl. Column experiments were performed to study the binding of Cd(II), Cr(III), Cr(VI), Pb(II) and Zn(II) to silica-immobilized African alfalfa shoots under flow conditions. These experiments showed that the silica immobilized African alfalfa shoots were effective for removing metal ions from solution, and over 90% of the bound Pb(II), Cu(II), Ni(II), and Zn(II), and over 70%Cd(II), were recovered after treatment with 10 bed volumes of 0.1 M HCl. The results from these studies will be useful for a novel phytofiltration technology to remove and recover heavy metal ions from aqueous solution.

We report the observation of a fully developed fractional quantum Hall state at $\nu=5/2$ in GaAs/Al$_{x}$Ga$_{1-x}$As quantum wells with mobility well below $10^{7}$\thinspace cm$^{2}$/Vs. This is achieved either by strong illumination or reducing the barrier Al composition without illumination. We explain both results in terms of screening of the ionized remote impurity (RI) potential by nearby neutral shallow donors. Despite the dramatic improvement in the transport features, the energy gap $\Delta_{5/2}$ is limited to a rather small value ($\sim100$ mK), which indicates that once the RI potential is well screened and the $5/2$ state emerges, the size of $\Delta_{5/2}$ is limited by the mobility, i.e., by background impurities.