Nicolas H. Bings

Microfluidic devices connected to fused-silica capillaries with minimal dead volume.

Fused-silica capillaries have been connected to microfluidic devices for capillary electrophoresis by drilling into the edge of the device using 200-μm tungsten carbide drills. The standard pointed drill bits create a hole with a conical-shaped bottom that leads to a geometric dead volume of 0.7 nL at the junction, and significant band broadening when used with 0.2-nL sample plugs. The plate numbers obtained on the fused-silica capillary connected to the chip were about 16-25% of the predicted numbers. The conical area was removed with a flat-tipped drill bit and the band broadening was substantially eliminated (on average 98% of the predicted plate numbers were observed). All measurements were made while the device was operating with an electrospray from the end of the capillary. The effective dead volume of the flat-bottom connection is minimal and allows microfluidic devices to be connected to a wide variety of external detectors.

Atomic Spectroscopy: A Review

Atomic Absorption Spectrometry 4653 Flame Atomic Absorption Spectrometry 4653 Electrothermal Atomic Absorption Spectrometry 4654 Volatile Species Generation Atomic Absorption Spectrometry 4654 Direct Solids Atomic Absorption Spectrometry 4655 Continuum Source Atomic Absorption Spectrometry 4655 Atomic Fluorescence Spectrometry 4655 Atomic Emission Spectrometry 4656 DC Arc and Low-Power RF Radiation Sources 4656 Inductively Coupled Plasmas 4656 Microwave Induced Plasmas 4658 Microplasmas 4658 Laser Induced Breakdown Spectroscopy 4658 Glow Discharge Optical Emission and Mass Spectrometry 4660 Fundamental Studies 4660 Methodological Studies and Applications of GD-OES and GDMS 4661 New GD Sources for Novel Applications and Combined GD-LA Systems 4663 Inductively Coupled Plasma Mass Spectrometry 4664 Fundamental Studies 4665 Instrumental Developments and Applications 4667 Literature Cited 4677

An improved microstrip plasma for optical emission spectrometry of gaseous species

Abstract A modified compact 2.45 GHz microstrip plasma (MSP) operated with Ar as working gas at atmospheric pressure has been characterized and examined for its suitability for the determination of Hg as gaseous species by optical emission spectrometry. As a formerly described MSP the new device is provided on a sapphire substrate. The areas of plasma stability in terms of gas flow rates and microwave power for both MSPs with respect to plasma form and reflected power were investigated. Power levels of 5–40 W and Ar flow rates of 15–60 l/h were used. The modified MSP, which extends out of the channel in the sapphire substrate, was used for the recording of emission spectra for Hg vapor at different working conditions. Using optimized parameters a detection limit for Hg of less than 10 ng Hg/l Ar is obtained. The attainable excitation temperatures in the modified MSP at different microwave power were determined under the use of Fe as thermometric species and introducing ferrocene into the plasma. They were found to be at the order of 6000–7000 K for a power of 10–40 W and a gas flow of 15 l/h. It was shown that the modified MSP source can be combined with both a conventional monochromator with photomultiplier detection and a miniaturized spectrometer with CCD detection, whereby space–angle limitations are not stringent.

Direct determination of metals in lubricating oils by laser ablation coupled to inductively coupled plasma time-of-flight mass spectrometry

Rapid simultaneous multielemental determination of Na, Mg, Al, Ti, Cr, Fe, Ni, Co, Cu, Ag and Pb in lubricating oil samples was carried out by combining direct laser ablation (LA) of the oils with inductively coupled plasma time-of-flight mass spectrometry (ICP-TOFMS). This method offers the advantage of a simplified sample preparation technique without the need for sample decomposition or sample dilution with organic solvents, although dealing with a relatively complex matrix. Because of the high data acquisition speed of the ICP-TOFMS an enormous amount of sample-information can be collected within a short period of time. The used system can acquire complete mass spectra at 20 kHz, a rate leading to data resulting from the average of 20000 individual spectra, considering a short integration interval of only 1 s. Consequently, analysis time is reduced drastically, although the multielemental capabilities are improved, compared to conventional quadrupole mass spectrometers. Two different calibration strategies were investigated and showed good agreement: external calibration based on the use of different standard oils and aqueous solution-based calibration. The analysis of a certified reference material SRM 1634b showed good accuracy for all the investigated elements. Detection limits were in the range of 0.5 ng g−1 (Pb) to 28 ng g−1 (Cr) and the precision was typically around 6% RSD. The good agreement obtained on fresh and used lubricating oil samples using conventional ICP-TOFMS after sample decomposition demonstrates that direct LA-ICP-TOFMS is a rapid and powerful tool for the analysis of trace and wear metals in lubricating oil.

Characteristics of Picoliter Droplet Dried Residues as Standards for Direct Analysis Techniques

The characteristics of dried residues of picodroplets of single-, two-, and three-element aqueous solutions, which qualify these as reference materials in the direct analysis of single particles, single cells, and other microscopic objects using, e.g., laser ablation inductively coupled plasma time-of-flight mass spectrometry (LA-ICP-TOF-MS) and micro-X-ray fluorescence (MXRF), were evaluated. Different single-, two-, and three-element solutions (0.01-1 g/L) were prepared in picoliter volume (around 130 pL) with a thermal inkjet printing technique. An achievable dosing precision of 4-15% was calculated by total reflection X-ray fluorescence (TXRF) determination of the transferred elemental mass of an array of 100 droplets. The size of the dried residues was determined by optical microscopy to be 5-20 microm in diameter depending on the concentration and the surface material. The elemental distribution of the dried residues was determined with synchrotron micro-X-ray fluorescence (SR-MXRF) analyses. The MXRF results show high uniformity for element deposition of every single droplet with an RSTD of 4-6% depending on the concentration of spotted solution. The shape and height profile of dried residues from picoliter droplets were studied using atomic force microscopy (AFM). It was found that these dry to give symmetrical spherical segments with maximum heights of 1.7 microm. The potential of this technique for direct LA-ICP-TOF-MS analysis is shown.

Time-of-flight mass spectrometry as a tool for speciation analysis

Abstract Time-of-flight mass spectrometry (TOFMS) has recently been introduced as an alternative to scanning-based mass analyzers for use in elemental analysis. Coupled with an inductively coupled plasma or alternative ion source, TOFMS can produce a complete atomic mass spectrum in less than 50 μs. Because of this high spectral-generation rate, even very brief transient signals can be recorded with high fidelity. Furthermore, each mass spectrum is derived from the same sub-microsecond pulse of ions, so high precision can be achieved by using either isotope-ratioing or internal standardization techniques. All these features make TOFMS attractive for the measurement of transient signals, such as those commonly encountered in speciation analysis. In this paper, the capabilities of TOFMS in speciation will be demonstrated through the coupling of gas chromatography and capillary electrophoresis with an inductively coupled plasma-TOFMS. Additionally, the development of novel switched gas sampling glow discharge (GSGD) ionization sources will be described and their role in chemical speciation will be evaluated. The switched GSGD has the ability to collect both atomic and molecular mass spectra in rapid succession, to provide additional information about chemical species. The coupling of various sample introduction systems (flow-cell, exponential dilutor, capillary gas chromatography and electrothermal vaporization) to the GSGD is outlined.

Receptor-mediated uptake of boron-rich neuropeptide y analogues for boron neutron capture therapy.

Peptidic ligands selectively targeting distinct G protein‐coupled receptors that are highly expressed in tumor tissue represent a promising approach in drug delivery. Receptor‐preferring analogues of neuropeptide Y (NPY) bind and activate the human Y1 receptor subtype (hY1 receptor), which is found in 90 % of breast cancer tissue and in all breast‐cancer‐derived metastases. Herein, novel highly boron‐loaded Y1‐receptor‐preferring peptide analogues are described as smart shuttle systems for carbaboranes as 10B‐containing moieties. Various positions in the peptide were screened for their susceptibility to carbaborane modification, and the most promising positions were chosen to create a multi‐carbaborane peptide containing 30 boron atoms per peptide with excellent activation and internalization patterns at the hY1 receptor. Boron uptake studies by inductively coupled plasma mass spectrometry revealed successful uptake of the multi‐carbaborane peptide into hY1‐receptor‐expressing cells, exceeding the required amount of 109 boron atoms per cell. This result demonstrates that the NPY/hY receptor system can act as an effective transport system for boron‐containing moieties.

Development and characterization of a thermal inkjet-based aerosol generator for micro-volume sample introduction in analytical atomic spectrometry

A novel system for the introduction of liquid samples into analytical plasmas for atomic spectrometric analysis is presented in this manuscript for the first time. The proposed “drop-on-demand” (DOD) aerosol generator is based on the use of a modified thermal inkjet cartridge. This system employs a lab-built microcontroller, which allows accessing all parameters important for driving the dosing cartridge for the generation of pL-droplets from sample volumes in the μL range. The droplet generation frequency, thus the resulting liquid flow rate, is variable over a wide range from the generation of isolated droplets up to a theoretical flow rate of approximately 2 mL min−1, with parallel operation of all 300 nozzles available on the employed device. The flow rate was investigated in the range from 20 nL min−1 to 6.3 μL min−1 and a new calibration strategy based on the droplet generation frequency instead of on the use of standard solutions of different concentrations is introduced. The new system is characterized and the achievable analytical figures of merit of such a DOD aerosol generator coupled to a quadrupole ICP-MS are outlined and compared to a commercially available pneumatic low-flow nebulizer, the MicroMist™. The new system offers a superior sensitivity by a factor of 8–18, improved limits of detection and better background equivalent concentrations for the investigated elements (Li, Cr, Mn, Co, Ga, Sr, Ag, Cd, In, Ba, Tl and Bi). The achievable precision in multi-elemental DOD-ICP-MS analysis was found to be comparable to the data gained with the corresponding commercial system.

Microstrip microwave induced plasma on a chip for atomic emission spectral analysis

A stable microstrip microwave plasma (MSP) operated at atmospheric pressure with a power of some 10-20 W and at a gas flow of 0.2-0.8 L/min of argon in a resonant structure produced with the aid of microstructuring technology on a 5/spl times/5 cm/sup 2/ quartz wafer provided with a 0.6-mm diameter plasma channel is described. The device is shown to be useful for the excitation of atomic and molecular species and for the atomic emission spectrometric determination of metals and of nonmetals in gases at the trace level, down to the ng/L-level, as shown for the case of sulfur.

Halo-shaped flowing atmospheric pressure afterglow: a heavenly design for simplified sample introduction and improved ionization in ambient mass spectrometry.

The flowing atmospheric-pressure afterglow (FAPA) is a promising new source for atmospheric-pressure, ambient desorption/ionization mass spectrometry. However, problems exist with reproducible sample introduction into the FAPA source. To overcome this limitation, a new FAPA geometry has been developed in which concentric tubular electrodes are utilized to form a halo-shaped discharge; this geometry has been termed the halo-FAPA or h-FAPA. With this new geometry, it is still possible to achieve direct desorption and ionization from a surface; however, sample introduction through the inner capillary is also possible and improves interaction between the sample material (solution, vapor, or aerosol) and the plasma to promote desorption and ionization. The h-FAPA operates with a helium gas flow of 0.60 L/min outer, 0.30 L/min inner, and applied current of 30 mA at 200 V for 6 W of power. In addition, separation of the discharge proper and sample material prevents perturbations to the plasma. Optical-emission characterization and gas rotational temperatures reveal that the temperature of the discharge is not significantly affected (<3% change at 450 K) by water vapor during solution-aerosol sample introduction. The primary mass-spectral background species are protonated water clusters, and the primary analyte ions are protonated molecular ions (M + H(+)). Flexibility of the new ambient sampling source is demonstrated by coupling it with a laser ablation unit, a concentric nebulizer, and a droplet-on-demand system for sample introduction. A novel arrangement is also presented in which the central channel of the h-FAPA is used as the inlet to a mass spectrometer.