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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.

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.

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.

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.

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.

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.

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.

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.

Flowing afterglow atmospheric pressure glow discharge mass spectrometry (FA-APGD-MS) was used to interrogate different polymer species such as biopolymers, synthetic homo- and co-polymers. The main advantages of FA-APGD-MS for polymer samples include speed (

Analytical and Bioanalytical Chemistry, 396 (1), ISSN:1618-2650, ISSN:1618-2642

A novel method based on ultrasound-assisted EESI-MS has been developed and applied to rapidly detect the presence of melamine in raw milk, wheat gluten and milk powder with no or minor sample pre-treatment; the high sample throughput and figures of merit make it specially useful for screening melamine levels well below the current safety limit in various food matrices.

A novel method based on ultrasound-assisted EESI-MS has been developed and applied to rapidly detect the presence of melamine in raw milk, wheat gluten and milk powder with no or minor sample pre-treatment; the high sample throughput and figures of merit make it specially useful for screening melamine levels well below the current safety limit in various food matrices.

Recent findings suggest that long-term exposure to diethyl phthalate (DEP), one of the widely used phthalate esters, can lead to serious health problems. Most perfumes contain non-negligible amounts of DEP. Rapid and sensitive detection of DEP in perfumes is thus of increasing importance. A novel procedure based on extractive electrospray ionization mass spectrometry (EESI-MS) has been developed for fast detection and identification of DEP in perfumes without the need for any sample pretreatment. The limit of determination for DEP in perfume was less than 100 ppb using tandem mass spectrometry on a commercial quadrupole time-of-flight mass spectrometer. The dynamic range of this method was about 4 orders of magnitude. A single sample analysis was completed within a few seconds, providing a rapid way to obtain semiquantitative information on the DEP content in perfumes. This study shows that both volatile and nonvolatile analytes (e.g., amino acids) in liquids can be directly sampled by neutral desorption, providing a convenient way for high-throughput screening of target compounds using EESI-MS.

Electron impact ionization has several known advantages; however, heated filament electron sources have pressure limitations and their power consumption can be significant for certain applications, such as in field-portable instruments. Herein, we evaluate a VUV krypton lamp as an alternative source for ionization inside the ion trap of a mass spectrometer. The observed fragmentation patterns are more characteristic of electron impact ionization than photoionization. In addition, mass spectra of analytes with ionization potentials higher than the lamp's photon energy (10.6 eV) can be easily obtained. A photoelectron impact ionization mechanism is suggested by the observed data allowed by the work function of the ion trap electrodes (4.5 eV), which is well within the lamp's photon energy. In this case, the photoelectrons emitted at the surface of the ion trap end-cap electrode are accelerated by the applied rf field to the ring electrode. This allows the photoelectrons to gain sufficient energy to ionize compounds with high ionization potentials to yield mass spectra characteristic of electron impact. In this manner, electron impact ionization can be used in ion trap mass spectrometers at low powers and without the limitations imposed by elevated pressures on heated filaments.

An instrument that combines near-field laser ablation at atmospheric pressure with an ion trap/time-of-flight mass spectrometer was developed. By coupling a UV laser into a fiber tip of a scanning near-field optical microscope, ablation craters much smaller than achievable with conventional laser optics can in principle be obtained. Laser ablation was performed on samples such as DHB, anthracene, and pyrene. Desorbed neutral analytes are transferred from atmospheric pressure to an ion trap, ionized, and stored. After 10 ms, the ions are extracted into a sensitive time-of-flight spectrometer. We demonstrate the feasibility of this unique SNOM-MS instrument for chemical analysis with unprecedented lateral resolution at atmospheric pressure. Spatially resolved molecular analysis with a lateral resolution of 5 microm (fwhm) and a sensitivity of approximately 60 fmol of solid anthracene is demonstrated, along with topographical analysis with the same instrument. No other technique available today offers this lateral resolution in combination with soft mass spectrometry and the capability of sampling fragile specimens at atmospheric pressure.

A novel chemical ionization source for organic mass spectrometry is introduced. This new source uses a glow discharge in the flowing afterglow mode for the generation of excited species and ions. The direct-current gas discharge is operated in helium at atmospheric pressure; typical operating voltages and currents are around 500 V and 25 mA, respectively. The species generated by this atmospheric pressure glow discharge are mixed with ambient air to generate reagent ions (mostly ionized water clusters and NO+), which are then used for the ionization of gaseous organic compounds. A wide variety of substances, both polar and nonpolar, can be ionized. The resulting mass spectra generally show the parent molecular ion (M+ or MH+) with little or no fragmentation. Proton transfer from ionized water clusters has been identified as the main ionization pathway. However, the presence of radical molecular ions (M+) for some compounds indicates that other ionization mechanisms are also involved. The analytical capabilities of this source were evaluated with a time-of-flight mass spectrometer, and preliminary characterization shows very good stability, linearity, and sensitivity. Limits of detection in the single to tens of femtomole range are reported for selected compounds.

Glow discharge optical emission spectrometry has cemented itself as an important surface elemental analysis technique in part because of its superb depth resolution (on the order of single nanometers). However, very few studies have explored the ability of the glow discharge to provide laterally resolved elemental information. In the present study, an end-on-viewed pulsed radio frequency glow discharge is coupled to a monochromatic imaging spectrometer to provide lateral surface imaging. The performance of the technique is demonstrated with etched copper circuits on fiber-glass substrates, and it is shown how several operating parameters including pressure, pulsed mode operation, and time-resolved detection affect the lateral surface resolution. In addition, because a pulsed radio frequency glow discharge offers elemental information on nonconducting samples, the technique is applied to the three-dimensional elemental analysis of proteins on blotting substrates. Several alternative sample types are also examined, including photographic film and glass.

Although inductively coupled plasma emission and mass spectrometry have been in widespread use for a long time, there is still a gap in our knowledge concerning how atoms are formed in the ICP, by which mechanisms they are excited, how ionization occurs, and how these factors are influenced by operating parameters of the ICP such as gas flow rates, radiofrequency power, and viewing or sampling position. Furthermore it is still not clear how or whether the sampling cone of the mass-spectrometer interface affects the ICP itself. Although many measurements have been made downstream from the sampling orifice, less is clear about the influence of the interface upstream of the sampling process. In our laboratory is available a suite of measurement tools and techniques that are being exploited to address these questions. These techniques permit us to map, on a spatially resolved basis, such critical features as electron-energy distributions, gas-kinetic temperatures, ground-state analyte atom and ion number densities, electron concentrations, and densities of excited-state argon species. In turn, these parameters can be measured in the presence and absence of suspected interferents and in the presence and absence of an ICP-MS sampling cone. Here, the basis of these measurements will be described. Also, based on recent results, mechanisms of excitation of analyte atoms and ions will be proposed and the influence of the ICP-MS sampling cone will be examined.

Chromium contamination of the environment has become an important issue due to the potential health threat it poses. Conventional technologies to clean up heavy metal ions from contaminated waters have been utilized, but these technologies are not cost-effective. However, the use of agricultural waste byproducts for the removal of Cr(VI) from contaminated waters may be a new cost-effective alternative. Oat byproducts from the Juarez Valley in Mexico were studied for the ability to bind Cr(VI) under different temperature and time conditions. The metal binding ability of oat byproducts was calculated from experimental data collected at temperatures of 8, 26, and 54°C, and time exposures of 1, 6, 24, 48, and 72 h at each temperature. These results showed that the binding of Cr(VI) to oat biomass increased as time and temperature increased. The bound chromium was recovered from the oat biomass by treatment with 0.2 M HCl. Through the use of X-ray absorption spectroscopy, the reduction of Cr(VI) to Cr(III) was determined to occur by the oat byproducts. These results indicate that the use of agricultural waste byproducts could be a better alternative for the removal and subsequent reduction of Cr(VI) to Cr(III) from contaminated waters.

Aluminium doped ZnO (AZO) alloy films produced by atomic layer deposition (ALD) are analysed by glow discharge optical emission spectrometry (GD-OES). A measurement procedure is established, to determine simultaneously thickness, mean chemical composition and refractive index of homogeneous films using GD-OES and profilometry measurements. The GD-OES measured Al contents of the AZO films lie below those expected for the realised ALD cycles. Determined refractive indices are of the same accuracy as ellipsometry measurements and are dependent on the film composition as well as on the wavelength of the spectral lines used for analysis. The findings support the use of GD-OES as an analysis technique in the development of photovoltaic thin films.

Extractive electrospray ionization mass spectrometry is shown to allow real-time, in vivo drug monitoring and pharmacokinetic measurement in a non-invasive, pain-free manner as demonstrated by the mass spectral measurement of a novel exhaled breath biomarker for valproic acid, a medication used to control epilepsy.

A previously described instrument was used to obtain axial profiles of the gas-kinetic temperature (Tg) in a ms-pulsed glow discharge via Rayleigh scattering. In addition, the electron number density (ne) and the electron temperature (Te) were observed via Thomson scattering. For these measurements, the detection optics of the original instrument were modified and a photon-counting imaging technique was employed to allow the simultaneous observation of Thomson scattering from multiple spatial positions. It was found that the cell pressure and electrical characteristics of the glow-discharge pulse have an effect on the temporal behavior of all fundamental parameters. As with a dc glow discharge, there were two distinct classes of electrons, a high-energy group and a lower-energy (thermalized) group. The thermalized electrons showed greater energies during the prepeak than at the plateau. Following the power pulse, during the afterglow, ne and Te declined monotonically at the temporal and spatial positions observed. The spatial differences in ne during the afterglow are discussed with regards to the spatial variations in argon metastable population.

The ion and electron populations of a glow discharge that uses an electrolytic solution as the cathode (an electrolyte-cathode discharge or ELCAD) were investigated. This paper presents the first determinations of electron number density, ionization temperature, and degrees of ionization in the ELCAD. Spectroscopic techniques were used to keep from perturbing the plasma, a range of conditions was explored, and two regions (the negative glow and the positive column) were observed. By using the Stark broadening of the hydrogen beta line, electron number densities near 8.5 × 1014 cm−3 for the negative glow and 2.5 × 1014 cm−3 for the positive column were found. From those results and measurements of the relative strengths of Mg neutral and ionic lines, ionization temperatures of 5000 K for the negative glow and 4600 K for the positive column were calculated. From these results, the degrees of ionization and norm temperatures were estimated for a variety of elements. Analytical implications of the study are discussed.

A novel direct current glow discharge sustained in helium at atmospheric pressure has been developed. Current–voltage behavior and spectroscopic characteristics strongly suggest that the system operates in the glow regime, in spite of the high pressure. The diffuse and extremely stable discharge is typically operated within a voltage range of 300–900 volts (in the current-controlled mode) and at currents ranging over tens to hundreds of milliamps. Spatially resolved spectroscopic measurements of some selected species are presented. Rotational temperature profiles were calculated using the OH emission spectrum, yielding values in the positive column ranging from 1300 to 1600 K.

A glow discharge using a solution as the cathode was investigated to add to the understanding of the operating mechanism and characteristics of such systems. The intensities and vertical distributions of emission from several analytes and background species were observed and compared with the vertical distribution of Fe excitation and OH rotational temperatures, as well as to electrical characteristics. The effects of the discharge gap size, the pH and conductivity of the solution, the applied current and the solution flow rate on these distributions were also studied. Detection limits for this system were found to be comparable to those of similar systems and mostly in range of tens of parts per billion.

An instrument is described to perform laser-scattering fundamental studies on an analytical planar-cathode glow discharge. Electron properties such as electron number-density, electron temperature and the shape of the electron energy distribution function were successfully obtained via Thomson scattering. It is observed that several groups of electrons contribute to the Thomson scattering spectrum and the existence of a non-Maxwellian electron energy distribution was confirmed. The measured temperature for slow electrons is comparable to that found in previous studies performed with alternative methods. In addition, Rayleigh scattering was used to acquire argon gas-kinetic temperatures. The performance of the instrument as well as the significance of the results will be discussed.