Critical evaluation of the potential of radiofrequency pulsed glow discharge–time-of-flight mass spectrometry for depth-profile analysis of innovative materials

The combination of radiofrequency pulsed glow discharge (RF-PGD) analytical plasmas with time-of-flight mass spectrometry (TOFMS) has promoted the applicability of this ion source to direct analysis of innovative materials. In this sense, this emerging technique enables multi-elemental depth profiling with high depth resolution and sensitivity, and simultaneous production of elemental, structural, and molecular information. The analytical potential and trends of this technique are critically presented, including comparison with other complementary and well-established techniques (e.g. SIMS, GD–OES, etc.). An overview of recent applications of RF-PGD–TOFMS is given, including analysis of nano-structured materials, coated-glasses, photovoltaic materials, and polymer coatings     

Quantification of bromine in flame-retardant coatings by radiofrequency glow discharge–optical emission spectrometry

There is an increasing concern regarding the toxicity and environmental distribution and impact of brominated organic compounds employed as flame retardants. Thus, present interest in searching for new analytical techniques and methods allowing a rapid, simple and reliable detection of those compounds in materials and wastes potentially containing such flame retardants is not surprising. The feasibility of using radiofrequency glow discharge plasma spectrometry coupled with optical emission spectrometry (rf-GD-OES) as a rapid and simple tool to directly analyse bromine-containing flame-retardant polymeric layers is investigated here. Polymeric layers for calibration were made by mixing appropriate amounts of tetrabromobisphenol A, bisphenol A, phloroglucinol and diphenylmethane-4,4′-diisocyanate in tetrahydrofuran. The corresponding blanks (polymers without tetrabromobisphenol A) were also prepared. Detection of bromine was investigated both in the visible (at 470.48 nm) and in the near-infrared (at 827.24 nm) regions, using a charge-coupled device for detection. Discharge parameters affecting the emission intensity of bromine were first optimized (in argon and helium as possible plasma gases) and the analytical performance characteristics were then evaluated. The best detection limit (0.044% Br) was achieved measuring Br I 827.24 nm in a He discharge, using a forward power of 70 W and a pressure of 45 Torr. The linearity range extended up to 27% Br. Finally, the applicability of the rf-GD-OES method proposed to the quantitative analysis of bromine in solid materials coated with flame-retardant commercial paints was successfully demonstrated. Figure Flame Retardants     

Arsenic and antimony determination by on-line flow hydride generation–glow discharge–optical emission detection

Hollow cathode (HC) and conventional flat cathode (FC) glow discharge (GD) optical emission spectrometry (OES) were used as detectors for the determination of arsenic and antimony by on-line hydride generation (HG) in a flow system. Both radiofrequency (rf) and direct current (dc) sources were investigated to produce the discharge. The design of the HC and FC and also the parameters governing the discharge (pressure, He flow rate, voltage, current and delivered power) and the HG (sodium borohydride concentration and reagent flow rates) were investigated using both cathodes. The analytical performance characteristics of HG–GD–OES with HC and FC were evaluated for some emission lines of arsenic (193.7, 200.3, 228.8 and 234.9 nm). The best detection limit (0.2 μg l⁻¹) was obtained when the emission line of 228.8 nm was used with FC. Under the same arsenic optimized experimental conditions, the system was evaluated to determine antimony at 259.7, 252.7 and 231.1 nm, 252.7 nm being the emission line which produced the best detection limit (0.7 μg l⁻¹). The rf-HC–GD–OES system was applied successfully to the determination of arsenic in freeze-dried urine in the standard reference material 2670 from NIST. Finally, a flow injection system was assayed to determine arsenic at 228.8 nm, using a dc-GD with both FC and HC. The results indicated that for low volumes of sample, the HC discharge allows better analytical signals than the FC.     

Development of a miniature dielectric barrier discharge–optical emission spectrometric system for bromide and bromate screening in environmental water samples

Dielectric barrier discharge (DBD) at atmospheric pressure provides an efficient radiation source for the excitation of bromine and it is used for the first time for optical emission spectrometric (OES) detection of bromide and bromate. A portable DBD–OES system is developed for screening potential pollution from bromide and bromate in environmental waters. Bromide is on-line oxidized to bromine for in-situ generation of volatile bromine. Meanwhile, a helium stream carries bromine into the DBD micro-plasma for its excitation at a discharging voltage of 3.7 kV and optical emission spectrometric detection with a QE65000 charge-coupled device (CCD) spectrometer in the near-infrared spectral region. Similarly, the quantification of bromate is performed by its pre-reduction into bromide and then oxidized to bromine. The spectral characteristics and configuration of the DBD micro-plasma excitation source in addition to the oxidation vapor generation of bromine have been thoroughly investigated. With a sampling volume of 1 mL, a linear range of 0.05–10.0 mg L⁻¹ is obtained with a detection limit of 0.014 mg L⁻¹ by measuring the emission at 827 nm. A precision of 2.3% is achieved at 3 mg L⁻¹ bromide. The system is validated by bromine detection in certified reference material of laver (GBW10023) at mg L⁻¹ level, giving rise to satisfactory agreement. In addition, it is further demonstrated by screening trace bromide and bromate as well as spiking recoveries in a series of environmental water samples.     

Evaluation of gel electrophoresis techniques and laser ablation–inductively coupled plasma-mass spectrometry for screening analysis of Zn and Cu-binding proteins in plankton

The determination of metal-binding proteins in plankton is important because of their involvement in photosynthesis, which is fundamental to the biogeochemical cycle of the oceans and other ecosystems. We have elaborated a new strategy for screening of Cu and Zn-containing proteins in plankton on the basis of separation of proteins by use of Blue-Native PAGE (BN-PAGE), which entails use of a non-denaturing Tris–tricine system and detection of metals in the proteins by laser ablation inductively coupled plasma mass spectrometry (LA–ICP–MS). For comparison, denaturing PAGE based on Tris–glycine and Tris–tricine systems and Anodic-Native PAGE have also been investigated. A large number of protein bands with MW between 20 and 75 kDa were obtained by use of Tris–glycine PAGE but detection of metals by LA–ICP–MS was unsuccessful because of loss of metals from the proteins during the separation process. Different protein extraction, purification, and preconcentration methods were evaluated, focussing on both issues—achieving the best extraction and characterization of the proteins while maintaining the integrity of metal–protein binding in the plankton sample. Use of 25 mmol?L^?1 Tris–HCl and a protease inhibitor as extraction buffer with subsequent ultrafiltration and acetone precipitation was the most efficient means of sample preparation. Two Cu and Zn proteins were detected, a protein band corresponding to a MW of 60 kDa and another poorly resolved band with a MW between 15 and 35 kDa.     

Collisional–radiative model for the sputtered copper atoms and ions in a direct current argon glow discharge

A collisional–radiative model is developed for various levels of the sputtered copper (Cu) atoms and their ions in an argon (Ar) direct current glow discharge, used as an analytical source for optical emission spectrometry. In this application, attention is paid to the photons emitted by sputtered atoms and ions, and hence to the behavior of excited levels of these species. 8 Cu atomic and 7 Cu⁺ ionic levels are considered in the model, as well as the Cu²⁺ ions. Typical results of the model are the level populations (in two dimensions) of the various levels, and the relative contributions of the different populating and depopulating processes. This model is not only of interest for analytical glow discharge optical emission spectrometry, but also for plasma diagnostic tools and for copper–vapor lasers.     

In-depth profile analysis of thin films deposited on non-conducting glasses by radiofrequency glow-discharge–optical emission spectrometry

The potential of radiofrequency glow-discharge–optical emission spectrometry (rf-GD–OES) for quantification of thin films on non-conducting materials has been investigated. A commercial rf-GD chamber from Jobin Yvon operated at 13.56 MHz with Ar as discharge gas was used. The signal integration time was 0.1 s. The effect on emission yields of thin conducting layers on glasses of different thickness was studied in detail, using the rf-GD in the common operating mode “constant pressure–constant forward power”. Calibration curves were obtained for two types of material—conducting reference materials and a set of non-conductors comprising homogeneous glass of known composition and three different thicknesses coated (or not) with thin layers of gold. Qualitative and quantitative in-depth profile analyses of different coated non-conducting samples were investigated. A variety of samples, including different thick glass substrates (from 1.8 to 5.8 mm), different thin films deposited on homogeneous glasses (from 6 nm to 35 nm), and different kinds of coating (conductors such as Fe, Ni, Cr, Al, and Nb and non-conductors such as Si₃N₄) were studied at 450 Pa pressure and 20 W forward power. The quantitative in-depth profiles proved satisfactory and results for depths and concentrations were similar to nominal values.     

A simple method of target preparation for the bulk analysis of powder samples by laser ablation inductively coupled plasma mass spectrometry (LA–ICP–MS)

A simple and rapid procedure using a glue technique has been developed for the preparation of stable targets from powder samples for bulk analysis by LA– ICP–MS. The procedure was evaluated for the analysis of trace elements in SiC, of rare-earth elements in different types of silicate (rocks, sediments, and soils), and of Au and platinum-group elements in geological silicates. The test analysis was conducted using an IR laser in combination with a quadrupole mass spectrometer. The recommended preparation procedure offers the possibility of different types of calibration, for example application of certified reference samples in combination with prepared spiked samples on a base of a natural or synthetic matrix, or addition calibration. The resulting calibration functions are linear over a range of several decades. The trueness of the results was evaluated by use of certified reference samples. Analytical concentration ranges, detection limits, and the relative standard deviations are reported. Received: 20 November 2000 / Revised: 13 March 2001 / Accepted: 17 March 2001     

Assessing the suitability of a green solvent for gel permeation chromatography–mass spectrometry analysis

The study presents the possibility of performing the analysis of oligomeric structures and polymer additives by gel permeation chromatography (GPC) with atmospheric pressure chemical ionization (APCI) mass spectrometry (MS) in dibuthoxymethane (DBM, butylal), a halogen-free and less hazardous solvent than typically used chloroform and tetrahydrofuran. Polystyrene oligomers and Irganox® additives were analyzed in DBM using 2.1?mm internal diameter GPC columns, allowing to decrease the flow rate down to 50?µL/min, compatible with APCI–MS interface. The ionization was controlled by adding 1% chloroform in DBM to obtain (M+Cl)^? adducts, allowing a fast optimization of method parameters.     

Analytical performance of three commonly used extraction methods for the gas chromatography–mass spectrometry analysis of wine volatile compounds

The analytical performance of three extraction procedures based on cold liquid–liquid extraction using dicloromethane (LLE), solid phase extraction (SPE) using a styrene–divinylbenzene copolymer and headspace solid phase microextraction (SPME) using a carboxen–polydimethylsiloxane coated fibre has been evaluated based on the analysis of 30 representative wine volatile compounds. From the comparison of the three procedures, LLE and SPE showed very good linearity covering a wide range of concentrations of wine volatile compounds, low detection limits, high recovery for most of the volatile compounds under study and higher sensitivity compared to the headspace-SPME procedure. The latter showed in general, poor recovery for polar volatile compounds. Despite some drawbacks associated with the LLE and SPE procedures such as the more tedious sampling treatment and the use of organic solvents, the analytical performance of both procedures showed that they are more adequate for the analysis of wine volatiles.     

Study of near infra red femtosecond laser induced particles using transmission electron microscopy and low pressure impaction: Implications for laser ablation–inductively coupled plasma-mass spectrometry analysis of natural monazite

The characteristics of infra red femtosecond laser-induced aerosols are studied for monazite (LREE, Th(PO₄)) ablation and correlations are established with inductively coupled plasma-mass spectrometry (ICP-MS) signals. Critical parameters are tested within wide ranges of values in order to cover the usual laser ablation -ICP-MS analysis conditions: pulse energy (0.15 < E₀ < 1 mJ/pulse), pulse width (60 < τ < 3000 fs), ablation time (t ≤ 10 min) and transport length (l ≤ 6.3 m). Transmission electron microscopy reveals that aerosols are made of agglomerates of ~ 10 nm particles and 20–300 nm phosphorus depleted condensed spherical particles. These structures are not affected by any laser ablation parameter. Particle counting is performed using electronic low pressure impaction. Small changes on particle size distribution are noticed. They may be induced either by a peak of ablation rate in the first 15 s at high fluence (larger particles) or the loss of small particles during transport. We found a positive correlation between I (ICP-MS mean signal intensity in cps) and N (particle density in cm^? 3) when varying E₀ and t, suggesting that N is controlled by the irradiance (P₀ in W·cm^? 2). Elemental ratio measurements show a steady state signal after the initial high ablation rate (mass load effect in the plasma torch) and before a late chemical fractionation, induced by poor extraction of bigger, early condensed spherical particles from the deepening crater. Such chemical fractionation effects remain within uncertainties, however. These effects can be limited by monitoring E₀ to shorten the initial transient state and delay the attainment of an unfavorable crater aspect ratio. Most adopted settings are for the first time deduced from aerosol characteristics, for infra red femtosecond laser ablation. A short transport (l < 4.0 m) limits the agglomeration of particles by collision process along the tube. Short τ is preferred because of higher P₀, yet no benefit is found on ICP-MS signal intensity under 200 fs. Under such pulse widths the increased particle production induces more agglomeration during transport, thereby resulting in higher mass load effects that reduce the ionization efficiency of the plasma torch. Thus, pulse energy must be set to get an optimal balance between the need for a high signal/background ratio and limitation of mass load effects in the plasma torch.     

Trace elemental analysis of automotive paints by laser ablation–inductively coupled plasma–mass spectrometry (LA–ICP–MS)

Paints and coatings are frequently encountered as types of materials that are submitted to forensic science laboratories as a result of trace evidence transfers. The aim of this study was to develop a method to complement the commonly used techniques in a forensic laboratory in order to better characterize these samples for forensic purposes. A laser ablation method has been used to simultaneously sample several layers directly prior to introduction into an inductively coupled plasma-mass spectrometer for the detection and quantification of the trace metals present in the layer(s). Time-resolved analysis plots displaying the elemental response and quantification of selected metals are compared to associate/discriminate paint samples. Matrix-matched standards were successfully incorporated into the analysis scheme for quantification of lead in the solid paint samples. Preparation of new matrix-matched standards for quantification of additional elements developed for this study are also presented. A sample set of eighteen (18) survey automotive paint samples have been analyzed with the developed method in order to determine the utility of LA-ICP-MS for trace element analysis of paints.     

Classification of singly ionized iron emission lines in the 160–250 nm wavelength region from Grimm-type glow discharge plasma

In order to investigate the emission behavior of singly ionized iron lines excited by a Grimm-type glow discharge plasma, we have compiled a wavelength table of the lines in the 160–250 nm region. Three different plasma gases (argon, neon, and argon-helium mixed gas) have been employed to compare the relative intensities of the ionic iron lines. It is found that the emission intensities of some line groups which appear in the wavelength range of less than 190 nm are especially dependent on the nature of the plasma gas employed. These excitations can be principally explained from charge transfer collisions between iron atoms and plasma gas ions.     

Liquid sampling–atmospheric pressure glow discharge (LS-APGD) ionization source for elemental mass spectrometry: preliminary parametric evaluation and figures of merit

A new, low-power ionization source for the elemental analysis of aqueous solutions has recently been described. The liquid sampling–atmospheric pressure glow discharge (LS-APGD) source operates at relatively low currents (<20 mA) and solution flow rates (<50 μL min⁻¹), yielding a relatively simple alternative for atomic mass spectrometry applications. The LS-APGD has been interfaced to what is otherwise an organic, LC-MS mass analyzer, the Thermo Scientific Exactive Orbitrap without any modifications, other than removing the electrospray ionization source supplied with that instrument. A glow discharge is initiated between the surface of the test solution exiting a glass capillary and a metallic counter electrode mounted at a 90° angle and separated by a distance of ~5 mm. As with any plasma-based ionization source, there are key discharge operation and ion sampling parameters that affect the intensity and composition of the derived mass spectra, including signal-to-background ratios. We describe here a preliminary parametric evaluation of the roles of discharge current, solution flow rate, argon sheath gas flow rate, and ion sampling distance as they apply on this mass analyzer system. A cursive evaluation of potential matrix effects due to the presence of easily ionized elements indicate that sodium concentrations of up to 50 μg mL⁻¹ generally cause suppressions of less than 50%, dependant upon the analyte species. Based on the results of this series of studies, preliminary limits of detection (LOD) have been established through the generation of calibration functions. While solution-based concentration LOD levels of 0.02–2 μg mL⁻¹ are not impressive on the surface, the fact that they are determined via discrete 5 μL injections leads to mass-based detection limits at picogram to single-nanogram levels. The overhead costs associated with source operation (10 W d.c. power, solution flow rates of <50 μL min⁻¹, and gas flow rates <10 mL min⁻¹) are very attractive. While further optimization in the source design is suggested here, it is believed that the LS-APGD ion source may present a practical alternative to inductively coupled plasma sources typically employed in elemental mass spectrometry.     

Use of pneumatic nebulization and laser ablation–inductively coupled plasma–mass spectrometry to study the distribution and bioavailability of an intraperitoneally administered Pt-containing chemotherapeutic drug

Quadrupole-based inductively coupled–mass spectrometry (ICP-MS) with pneumatic nebulization as a means of sample introduction was employed for quantification of platinum in blood and tissue samples of rats with peritoneal carcinomatosis, receiving intraperitoneal treatment with the Pt-containing chemotherapeutic drug oxaliplatin, and in the perfusate solution used for this purpose. The Pt levels were measured for various treatment conditions, i.e., with and without supporting treatment with the drug bevacizumab and at two different temperatures. Limits of detection obtained for platinum in blood and tissue samples were 0.3 and 2.0 pg g_,⁻¹ respectively. Evaluation of drug penetration into the tumor, under different conditions of treatment, was carried out via laser ablation–ICP-MS. Quantitative mapping of the Pt distribution in tissue sections of rat was attempted relying on gelatin standards. The results show an influence of the temperature at which the treatment is carried out, while supporting administration of the drug bevacizumab did not seem to affect the results.     

Comparison of supercritical fluid chromatography–tandem mass spectrometry and liquid chromatography–tandem mass spectrometry for the stereoselective analysis of chlorfenvinphos and dimethylvinphos in tobacco

This study used reversed-phase liquid chromatography–tandem mass spectrometry and supercritical fluid chromatography–tandem mass spectrometry for determination of the stereoisomers of chlorfenvinphos and dimethylvinphos in tobacco. Tobacco samples were extracted and purified with a modified quick, easy, cheap, effective, rugged, and safe technique using spherical carbon. The performance of both methodologies was comprehensively compared in terms of methods validation parameters (separation efficiency, linearity, selectivity, recovery, repeatability, sensitivity, matrix effect, etc.). Under optimized conditions, the calibration curves of the stereoisomers of chlorfenvinphos and dimethylvinphos in the range of 10–500 ng/mL showed excellent linearity with R² ≥ 0.997 in both methods. The adequate recoveries of analytes from three different spiked tobaccos were obtained using reversed-phase liquid chromatography–tandem mass spectrometry (86.1–95.7%) as well as supercritical fluid chromatography–tandem mass spectrometry (86.5–94.0%). The relative standard deviations for spiked samples were all below 7.0%. Compared with supercritical fluid chromatography–tandem mass spectrometry, lower matrix effects and LODs can be obtained in reversed-phase liquid chromatography–tandem mass spectrometry.     

Analysis of ancient Greco–Roman cosmetic materials using laser desorption ionization and electrospray ionization mass spectrometry

Microsamples of pink cosmetic powders from the Greco–Roman period were analyzed using two complementary analytical approaches for identification of the colouring agents (lake pigments originally manufactured from madder plants with an inert binder, usually a metallic salt) present in the samples. The first technique was a methanolic acidic extraction of the archaeological samples with an additional ethyl acetate extraction of the anthraquinone-type colouring agents which were identified using high performance liquid chromatography coupled to electrospray ionization with high resolution mass spectrometry (LC–ESI–HRMS), and the second was direct analysis of a microsample by laser desorption ionization–mass spectrometry (LDI–MS). The latter technique is well suited when the quantity of samples is very low. This soft ionization technique enables the detection of very small quantities of compounds using the combination of positive and negative-ion modes. It was also successfully applied for the direct analysis of some laboratory-made reference compounds. However, the presence of lead in one of these ancient samples induced a spectral suppression phenomenon. In this case and conditional on a sufficient quantity of available sample, the former method is better adapted for the characterization of these anthraquinone-type molecules. This study also confirmed that purpurin, munjistin, and pseudopurpurin are the principal colouring agents present in these ancient cosmetic powders constituted from madder plants. Presented at the Annual French National Symposium on Mass Spectrometry, Electrophoresis and Proteomics, 20–23 September 2007 in Pau, France.     

Investigation of matrix effects in inductively coupled plasma-atomic emission spectroscopy using laser ablation and solution nebulization — effect of second ionization potential

Plasma-related non-spectroscopic matrix effects of 31 elements in inductively coupled plasma (ICP)-atomic emission spectrometry were investigated using both laser ablation and solution nebulization as sample introduction techniques. Matrix effects were studied by monitoring the excitation conditions of the plasma using the ionic to atomic spectral line intensity ratios of zinc and magnesium. A new kind of matrix interference was found in the ICP that appears to be related to matrices with elements of low second ionization potential. The matrix effects do not correlate with the first ionization potential of the element. Only those matrix elements with low second ionization potential showed severe matrix effects. Increasing the forward power of the ICP or replacing the carrier gas with a 50%/50% argon–helium mixture did not significantly reduce this matrix effect. However, using 100% helium as the carrier gas greatly reduced the extent of this matrix effect, suggesting that argon is involved in the interference mechanism. The interference mechanism may involve interactions between doubly-charged matrix ions and argon species.     

Application of isothermal calorimetry and thermal analysis for the investigation of calcined gypsum–lime–metakaolin–water system

Journal of Thermal Analysis and Calorimetry - The calcined gypsum–lime–metakaolin–water system and its subsystems consisting of two and three components are analyzed using the...