Exploring quantitative cellular bioimaging and assessment of CdSe/ZnS quantum dots cellular uptake in single cells, using ns-LA-ICP-SFMS.

Quantitative bioimaging of Quantum Dots (QDs) uptake in single cells by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) is a challenging task due to the high sensitivity and high spatial resolution required, and to the lack of matrix-matched reference materials. In this work, high spatially resolved quantitative bioimaging of CdSe/ZnS QDs uptake in single HT22 mouse hippocampal neuronal cells and in single HeLa human cervical carcinoma cells is novelty investigated combining: (a) the use of a ns-LA-ICP-Sector Field (SF)MS unit with mono-elemental fast and sensitive single pulse response for 114Cd+; and (b) the spatially resolved analysis of dried pL-droplets from a solution with a known concentration of these QDs to obtain a response factor that allows quantification of elemental bioimages. Single cells and dried pL-droplets are morphologically characterized by Atomic Force Microscopy (AFM) to determine their volume and thickness distribution. Moreover, operating conditions (e.g. spot size, energy per laser pulse, etc.) are optimized to completely ablate the cells and pL droplets at high spatial resolution. Constant operating conditions for the analysis of the single cells and calibrating samples is employed to reduce potential fractionation effects related to mass load effects in the ICP. A number concentration of CdSe/ZnS QDs between 3.5 104 and 48 104 is estimated to be uptaken by several selected single HT22 and HeLa cells, after being incubated in the presence of a QDs suspension added to a standard cell culture medium. Mono-elemental bioimaging at subcellular resolution seems to show a higher number concentration of the CdSe/ZnS QDs in the cytosol around the cell nucleus.

A novel gas sampling introduction interface for fast analysis of volatile organic compounds using radiofrequency pulsed glow discharge time of flight mass spectrometry.

An improved gas sample introduction interface is developed and characterized for gas chromatography coupling and for direct injection of volatile organic compounds (VOCs), in a pulsed glow discharge (pulsed-GD) ion source coupled to a time of flight mass spectrometer (TOFMS) that is typically used for direct solid analysis. The novel interface allows the introduction of the analytes in the flowing afterglow region of the GD (a few mm away from the negative glow region) to reduce plasma quenching effects. Analyte ion signals are acquired in the temporal afterglow region, where low fragmentation of the molecular species is produced, providing useful qualitative and quantitative molecular information (e.g. molecular ion). Analytical capabilities of the pulsed-GD ion source with the novel gas sampling interface provides improved performance compared to previous designs. In particular, limits of detection for the analysis of VOCs in air were below (better) that legally established limits according to Directive 2008/50/EC of the European Parliament.

Pulsed rf-GD-TOFMS for depth profile analysis of ultrathin layers using the analyte prepeak region.

Direct solid analysis of ultrathin layers is investigated using pulsed radiofrequency (rf) glow discharge (GD) time-of-flight mass spectrometry (TOFMS). In particular, previous studies have always integrated the detected ion signals in the afterglow region of the rf-GD pulse, which is known to be the most sensitive one. Nevertheless, the analytical capabilities of other pulse time regions have not been evaluated in detail. Therefore, in this work, we investigate the analyte prepeak region, which is the pulse region where the analyte ions peak after the initial sputtering process of each GD pulse, aiming at obtaining improved depth profile analysis with high depth resolution and with minimum polyatomic spectral interferences. To perform these studies, challenging ultrathin Si-Co bilayers deposited on a Si substrate were investigated. The thickness of the external Si layer was 30 nm for all the samples, whilst the internal Co layer thicknesses were 30, 10, 5, 2 and 1 nm, respectively. It should be remarked that the top layer and the substrate have the same matrix composition (Si > 99.99%). Therefore, the selected samples are suitable to evaluate the response of the Si ion signal in the presence of an ultrathin Co layer as well as the possible oxygen contaminations or its reactions. Additionally, these samples have been evaluated using time-of-flight secondary ion mass spectrometry, and the results compare well to those obtained by our pulsed rf-GD time-of-flight mass spectrometry results.

Investigation of the afterglow time regime in pulsed radiofrequency glow discharge time-of-flight mass spectrometry.

The pulsed power operation mode of a radiofrequency (rf) glow discharge time-of-flight mass spectrometer was investigated, for several ions, in terms of intensity profiles along each pulse period. Particular attention was paid to the plateau and transient afterglow regions. An rf pulse period of 4 ms and a duty cycle of 50% was selected to evaluate the influence of discharge parameters in the afterglow delay and shape of Ar(+), Ar(2)(+) and several analytes (Br, Cl, Cu) contained in polymeric layers. Pulse shapes of Ar(+) and Ar(2)(+) ions vary with pressure and power. At low pressures the highest intensity is observed in the plateau while at higher pressures (>600 Pa) the afterpeak is the dominant region. Although the influence of the applied power is less noticeable, a widening of the afterglow time regime occurs for Ar(+) when increasing the power. Maximum intensity of the argon signal is measured in the afterglow at 30 W, while the area of such afterpeak increases with power. The maximum intensity of Ar(2)(+) is obtained at the highest power employed (60 W) and the ratio maximum intensity/afterglow area remains approximately constant with power. Analytes with ionization potentials below (Cu) or just above (Br) the argon metastable energy show maxima intensities after argon ions decay, indicating they could be ionized by collisions with metastable Ar atoms. Chlorine signals are observed in the afterglow despite their ionization potential is well above the energy of argon metastable levels. Moreover, they follow a similar pattern to that observed for Ar(2)(+) , indicating that charge-transfer process with Ar(2)(+) could play a significant role.

Polymer screening by radiofrequency glow discharge time-of-flight mass spectrometry.

The aim of this work is to optimise and evaluate radiofrequency glow discharge (RF GD) time-of-flight mass spectrometry (TOFMS) for identification of organic polymers. For this purpose, different polymers including poly[methylmethacrylate], poly[styrene], polyethylene terephthalate-co-isophthalate and poly[alpha-methylstyrene] have been deposited on silicon wafers and the RF GD-TOFMS capabilities for qualitative identification of these polymeric layers by molecular depth profiling have been investigated. Although some molecular information using the RF continuous mode is available, the pulsed mode offers a greater analytical potential to characterise such organic coatings. Some formed polyatomic ions have proved to be useful to identify the different polymer layers, confirming that layers having similar elemental composition but different polymer structure could be also differentiated and identified.

Direct chemical in-depth profile analysis and thickness quantification of nanometer multilayers using pulsed-rf-GD-TOFMS.

Nanometer depth resolution is investigated using an innovative pulsed-radiofrequency glow discharge time-of-flight mass spectrometer (pulsed-rf-GD-TOFMS). A series of ultra-thin (in nanometers approximately) Al/Nb bilayers, deposited on Si wafers by dc-magnetron sputtering, is analyzed. An Al layer is first deposited on the Si substrate with controlled and different values of the layer thickness, t(Al). Samples with t(Al) = 50, 20, 5, 2, and 1 nm have been prepared. Then, a Nb layer is deposited on top of the Al one, with a thickness t(Nb) = 50 nm that is kept constant along the whole series. Qualitative depth profiles of those layered sandwich-type samples are determined using our pulsed-rf-GD-TOFMS set-up, which demonstrated to be able to detect and measure ultra-thin layers (even of 1 nm). Moreover, Gaussian fitting of the internal Al layer depth profile is used here to obtain a calibration curve, allowing thickness estimation of such nanometer layers. In addition, the useful yield (estimation of the number of detected ions per sputtered atom) of the employed pulsed-rf-GD-TOFMS system is evaluated for Al at the selected operating conditions, which are optimized for the in-depth profile analysis with high depth resolution.

In-depth profile analysis of filled alumina and titania nanostructured templates by radiofrequency glow discharge coupled to optical emission spectrometry.

The development of highly ordered and self-assembled magnetic nanostructures such as arrays of Fe or Ni nanowires and their alloys is arousing increasing interest due to the peculiar magnetic properties of such materials at the nanoscale. These nanostructures can be fabricated using nanoporous anodic alumina membranes or self-assembled nanotubular titanium dioxide as templates. The chemical characterization of the nanostructured layers is of great importance to assist the optimization of the filling procedure or to determine their manufacturing quality. Radiofrequency glow discharge (RF-GD) coupled to optical emission spectrometry (OES) is a powerful tool for the direct analysis of either conducting or insulating materials and to carry out depth profile analysis of thin layers by multi-matrix calibration procedures. Thus, the capability of RF-GD-OES is investigated here for the in-depth quantitative analysis of self-aligned titania nanotubes and self-ordered nanoporous alumina filled with arrays of metallic and magnetic nanowires obtained using the template-assisted filling method. The samples analysed in this work consisted of arrays of Ni nanowires with different lengths (from 1.2 up to 5 microm) and multilayer nanowires of alternating layers with different thicknesses (of 1-2 microm) of Ni and Au, or Au and FeNi alloy, deposited inside the alumina and titania membranes. Results, compared with other techniques such as scanning electron microscopy and energy-dispersive X-ray spectroscopy, show that the RF-GD-OES surface analysis technique proves to be adequate and promising for this challenging application.

Analysis of small bubbles in glass by glow discharge--time-of-flight mass spectrometry.

The chemical reactions occurring during the glass manufacturing processes can give rise to small bubbles, damaging the required glass properties. To avoid eventual bubbles formation, the chemical composition of the bubbles should be known to trace back the gas sources and take appropriate corrective actions. Mass spectrometry is a most adequate detection technique for such purpose due to its ability to provide the required information in a short time. Analysis of these small bubbles in glass requires a system incorporating a very small volume (for a fast evacuation of the entire line and low dilution of the analytes) and a fast mass analyser allowing the quasi-simultaneous detection of the whole spectral interval of interest, such as a time-of-flight mass spectrometer (TOFMS). In this work, the analytical potential of a radiofrequency glow discharge (rf-GD) coupled to a TOFMS was evaluated for the first time for the analysis of bubbles in glasses. The operating conditions of the rf-GD (pressure and applied power) were optimized by introducing into the system known volumes of air. Detection limits in the order of nL were obtained for molecular nitrogen, oxygen and carbon dioxide. Finally, a stainless steel bellows valve was modified to serve as glass breaker for the sampling process. This valve was connected on-line to the mass spectrometer inlet line and proved to be most appropriate for the analysis of the gaseous content of bubbles (with diameters below 0.5mm) entrapped in industrial glasses.

Spectroscopic evaluation of a compact magnetically boosted radiofrequency glow discharge for time-of-flight mass spectrometry.

A compact magnetically boosted radiofrequency glow discharge (GD) has been designed, constructed and its analytical potential evaluated by its coupling to a mass spectrometer (MS). Simple modifications to the original source configuration permitted the insertion of permanent magnets. Small cylindrical Nd-Fe-B magnets (diameter = 4 mm, h = 10 mm) were placed in an in-house-modified GD holder disc that allows easy and fast exchange of the magnets. The different processes taking place within the GD plasma under the influence of a magnetic field, such as sputtering, ionisation processes and ion transport into the MS, were studied using different GD operating conditions. Changes to the ionisation and ion transport efficiency caused by the magnetic field were studied using an rf-GD-TOFMS setup. A magnetic field of 60-75 gauss (G) was found not to affect the sputtering rates but to enhance the analyte ion signal intensities while decreasing the Ar species ion signals. Moreover, magnetic fields in this range were shown not to modify the crater shapes, enabling the fast and sensitive high depth resolved analysis of relatively thick coated samples (micrometre) by using the designed compact magnetically boosted rf-GD-TOFMS.

Modifying argon glow discharges by hydrogen addition: effects on analytical characteristics of optical emission and mass spectrometry detection modes.

An overview of the effects produced by the presence of hydrogen in a glow discharge (GD), generated either in argon or in neon, is given. Extensive work related to the addition of hydrogen to GDs, coupled with optical emission spectrometry (OES) and mass spectrometry (MS), has been published in the last few years in an attempt to explain the processes involved in the discharge of mixed gases. Although numerous experimental results have already been explained theoretically, a complete understanding of the effects brought about by mixing hydrogen with argon (or another discharge inert gas) has not been reported yet. The use of theoretical models implemented using a computer has allowed the importance of some collisional and radiative processes in the inert gas plasma when hydrogen is present to be evaluated. This review shows, however, that both experimental work and theoretical work are still needed. The influence of small quantities of hydrogen on discharge parameters, such as electrical current or dc bias voltage, on crater shapes and on sputtering rates is thoroughly reviewed along with the effect on the analytical signals measured by OES and MS. Also, hydrogen-effect corrections needed to carry out proper calibrations for direct solid quantitative analyses are discussed.

Fluorescence optosensors based on different transducers for the determination of polycyclic aromatic hydrocarbons in water.

This paper presents the development of two optosensors for the determination of four polycyclic aromatic hydrocarbons (anthracene, benzo[a]pyrene, fluoranthene and benzo[b]fluoranthene) using a photomultiplier device and an intensified coupled charge device (ICCD) as optical transducers, respectively. These optosensors are based on the on-line immobilization of the analytes onto a non-ionic resin solid support (Amberlite XAD-4) in a continuous flow system, followed by the measurement of their native fluorescence. The determinations were performed using 15 mM H(2)PO(4)(-)/HPO(4)(2-) buffer solution at pH 7 and 25% 1,4-dioxane. Detection limits were 6.4 and 9.3 for ANT, 3.3 and 2.5 for BbF, 1.4 and 13.2 for FLT, and 1.7 and 7.8 for BaP using optosensor 1 or 2, respectively. Relative standard deviations were 7.9 and 6.7 for ANT at 50 ng mL(-1), 3.5 and 7.4 for BbF at 60 ng mL(-1), 3.6 and 8.9 for FLT at 50 ng mL(-1), and 6.7 and 11.6 for BaP at 50 ng mL(-1) using optosensor 1 or 2, respectively. Finally, a critical comparison between the two configurations based on different transducers (photomultiplier and ICCD) for resolving and simultaneously determining mixtures of the polycyclic aromatic hydrocarbons under study in water samples (tap and mineral waters) were carried out.

Mercury speciation by HPLC--cold-vapour radiofrequency glow-discharge optical-emission spectrometry with on-line microwave oxidation.

Hollow-cathode (HC) radiofrequency glow-discharge (rf-GD) optical-emission spectrometry (OES) has been used as detector for the determination of inorganic mercury by cold-vapour (CV) generation in a flow-injection (FI) system. Both NaBH4 and SnCl2 were evaluated as reducing reagents for production of mercury CV. The conditions governing the discharge (pressure, He flow rate, and delivered power) and Hg CV generation (NaBH4 or SnCl2 concentration and reagent flow rate) were optimized using both reducing agents. The analytical performance characteristics of FI-CV-rf-GD-OES for mercury detection were evaluated at the 253.6 nm emission mercury line. Detection limits (DL) of 0.2 ng mL(-1) using SnCl2 and 1.8 ng mL(-1) using NaBH4 were obtained (100 microliter sample injections were used). When the optimized experimental conditions using SnCl2 had been determined, the analytical potential of this CV-rf-GD-OES method was investigated as on-line detector for high-performance liquid chromatographic (HPLC) speciation of mercury (Hg(II) and methylmercury). The HPLC-CV-rf-GD-OES detection limits for 100 microliter sample injections were found to be 1.2 and 1.8 ng mL(-1) (as mercury) of inorganic mercury and methylmercury, respectively. The reproducibility observed was below +/- 8% for both species. Finally, the HPLC-CV-rf-GD-OES system developed was successfully applied to the determination of methylmercury (speciation) in two certified reference materials, Dorm-2 and Dolt-2.