C. Derrick Quarles

Liquid Sampling-Atmospheric Pressure Glow Discharge Ionization Source for Elemental Mass Spectrometry

A new, low power ionization source for elemental MS analysis of aqueous solutions is described. The liquid sampling-atmospheric pressure glow discharge (LS-APGD) operates by a process wherein the surface of the liquid emanating from a 75 μm i.d. glass capillary acts as the cathode of the direct current glow discharge. Analyte-containing solutions at a flow rate of 100 μL min(-1) are vaporized by the passage of current, yielding gas phase solutes that are subsequently ionized in the <5 W (maximum of 60 mA and 500 V), ~1 mm(3) volume, plasma. The LS-APGD is mounted in place of the normal electrospray ionization source of a Thermo Scientific Exactive Orbitrap mass spectrometer system without any other modifications. Basic operating characteristics are described, including the role of discharge power on mass spectral composition, the ability to obtain ultrahigh resolution elemental isotopic patterns, and demonstration of potential limits of detection based on the injection of aliquots of multielement standards (S/N > 1000 for 5 ng mL(-1) Cs). While much optimization remains, it is believed that the LS-APGD ion source may present a practical alternative to high-powered (>1 kW) plasma sources typically employed in elemental mass spectrometry, particularly for those cases where costs, operational overhead, simplicity, or integrated elemental/molecular analysis considerations are important.

Elemental mapping of biological samples by the combined use of LIBS and LA-ICP-MS

In this study a combination of Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) and Laser Induced Breakdown Spectroscopy (LIBS) was used for laterally resolved elemental analysis of biological samples. In general LA-ICP-MS is an excellent technique for the analysis of many trace elements. However, bulk components such as H or O are not accessible using this technique. In addition to those elements, also some other elements that are difficult or impossible to investigate using LA-ICP-MS (i.e., F, N, Cl, etc.), could be detected by LIBS. In this work, the simultaneous use of LIBS and LA-ICP-MS (tandem LA/LIBS) for the analysis of biological samples is presented, opening the door for the possibility of complete analysis of the elemental composition of a human tumor sample. Results show good correlation with the histological stainings. The obtained distribution images provide a valuable basis for further medical interpretation.

Femtosecond laser ablation particle introduction to a liquid sampling-atmospheric pressure glow discharge ionization source

This work describes the use of a compact, liquid sampling–atmospheric pressure glow discharge (LS-APGD) ionization source to ionize metal particles within a laser ablation aerosol. Mass analysis was performed with a Thermo Scientific Exactive Mass Spectrometer which utilizes an orbitrap mass analyzer capable of producing mass resolution exceeding m/Δm > 160,000. The LS-APGD source generates a low-power plasma between the surface of an electrolytic solution flowing at several μl min−1 through a fused silica capillary and a counter electrode consisting of a stainless steel capillary employed to deliver the laser ablation particles into the plasma. Sample particles of approximately 100 nm were generated with an Applied Spectra femtosecond laser located remotely and transported through 25 meters of polyurethane tubing by means of argon carrier gas. Samples consisted of an oxygen free copper shard, a disk of solder, and a one-cent U.S. coin. Analyte signal onset was readily detectable relative to the background signal produced by the carrier gas alone. The high mass resolution capability of the orbitrap mass spectrometer was demonstrated on the solder sample with resolution exceeding 90,000 for Pb and 160,000 for Cu. In addition, results from a laser ablation depth-profiling experiment of a one cent coin revealed retention of the relative locations of the ∼10 μm copper cladding and zinc rich bulk layers.

Fluorine analysis using Laser Induced Breakdown Spectroscopy (LIBS)

Laser induced breakdown spectroscopy (LIBS) is evaluated for detecting fluorine using a commercially available J200 Tandem LA/LIBS system from Applied Spectra, Inc. The 685.6 nm fluorine atomic emission line was used to detect and determine the best calibration method for quantifying the amount of fluorine in a set of prepared NIST SRM 120c phosphate rock standards. The multivariate calibration model, based on partial least squares regression (PLS), provided the best accuracy and precision for the sample set analyzed in this study. The detection limit of fluorine using the J200 LIBS system with a 213 nm laser and an ICCD was determined to be 135 ppm from a phosphate rock standard. A rare earth element (REE)-rich mineral high in fluorine content was used to access the potential applications of mapping the fluorine content over a 16 mm2 surface area of the sample.

Instrumental comparison of the determination of Cr3+ uptake by human transferrin

UV-VIS absorbance, inductively coupled plasma-optical emission spectroscopy (ICP-OES), and particle beam/hollow cathode-optical emission spectroscopy (PB/HC-OES) are presented as techniques for determining Cr³+ loading into transferrin (Tf), with and without Fe³+. The methods are compared based on loading percentages (i.e. 100% loading would be equal to 2 M(n+): 1 Tf) determined for Cr³+ loading into apo-transferrin. Spectral interferences and overlapping LMCT bands cause inaccurate chromium (qualitative) and iron (qualitative and quantitative) results for the UV-VIS absorbance method. The ICP-OES and PB/HC-OES methods are in good agreement providing evidence that the PB/HC-OES method is a valid technique for investigating metal-protein complexes. Maximum Cr³+ loading into apo-transferrin over a 24 h period was determined to be 26.8 3.5% by the ICP-OES method and 25.3 2.2% by the PB/HC-OES method. Loading percentages were increased to 49.7 1.9% (ICP-OES) and 55.7 3.2% (PB/HC-OES) when the metal-transferrin solution was allowed to incubate for up to 10 days. Under non-excess carbonate conditions the Cr³+ loading is elevated over a 24 h incubation time, but under physiological conditions the loading is inhibited. Equal loading of Fe³+ and Cr³+ into apo-transferrin was achieved when chromium was at a level more than 5 times in excess of iron. Inhibition of Cr³+ loading was only observed when an excess of Fe³+ was available to bind into apo-transferrin. The ability for Cr³+ to displace Fe3+ from holo-transferrin was observed as small amounts of Cr³+ were loaded into the once occupied metal binding site.

Liquid sampling-atmospheric pressure glow discharge (LS-APGD) microplasmas for diverse spectrochemical analysis applications

Over the last 15 years there has been a great deal of interest in the potential development of spectrochemical sources that come with lower operational overhead than the inductively-coupled plasma (ICP). There are many driving forces for the development of such devices, even with the likely sacrifices in terms of analytical performance. Some of these devices operate in ambient atmospheres in the electrical regime of glow discharge (GD) plasmas, wherein one of the electrodes is an electrolytic solution that serves as the medium for sample introduction. The basic operational space and analytical performance of these devices has been reviewed in the recent past. We focus in this review on the design and operational attributes of the liquid sampling-atmospheric pressure glow discharge (LS-APGD) microplasma. The rationale for the development and basic source designs are first considered, followed by practical contrasts to the other devices provided. A number of studies have been performed to assess the fundamental plasma characteristics including kinetic and excitation temperatures, as well as charged particle densities. Perhaps the greatest difference between the LS-APGD and the other plasmas is the analytical versatility that has been demonstrated. Analytes can be determined by optical emission spectroscopy or mass spectrometry (OES/MS), with sampling regimes consisting of solution phase introduction, particles produced via laser ablation, or through an ambient desorption mechanism directly from the solid state. Finally, the microplasma can be operated in alternative modes wherein either elemental or molecular-form mass spectra are obtained. It is believed that the simplicity of the LS-APGD design, combined with its analytical versatility, suggest that this singular platform could be implemented to address diverse analytical challenges.

A metric for evaluation of the image quality of chemical maps derived from LA-ICP-MS experiments

For laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) imaging experiments – as well as other techniques used for elemental or molecular mapping – the accordance of the measured distribution with the actual distribution is of utmost importance to guarantee reliability of the obtained images. In most experiments reported in the past, the experimental conditions have been chosen so that washout effects and signal carry-over are minimized by scanning the sample surface very slowly. Therefore, measurement times become very long and decently resolved images will require acquisition times of several hours up to more than one day. To increase the application range of LA-ICP-MS for imaging it is important to decrease the measurement times, which is best accomplished by increasing the scanning rates. However, depending on the instrumentation, this can lead to blurring and compromised image quality. In this work, we present a metric to compare the measured elemental distribution with their actual distribution based on a sample with visually distinguishable features. This approach allows quantitative determination of the image quality and enables comparison of multiple measurement conditions. This information can be used for method optimization, to get a reasonable tradeoff between image quality and measurement time.

A study on the in vitro percutaneous absorption of silver nanoparticles in combination with aluminum chloride, methyl paraben or di-n-butyl phthalate

Some reports indicate that the silver released from dermally applied products containing silver nanoparticles (AgNP) (e.g. wound dressings or cosmetics) can penetrate the skin, particularly if damaged. AgNP were also shown to have cytotoxic and genotoxic activity. In the present study percutaneous absorption of AgNP of two different nominal sizes (Ag15nm or Ag45nm by STEM) and surface modification, i.e. citrate or PEG stabilized nanoparticles, in combination with cosmetic ingredients, i.e. aluminum chloride (AlCl3), methyl paraben (MPB), or di-n-butyl phthalate (DBPH) was assessed using in vitro model based on dermatomed pig skin. The inductively coupled plasma mass spectrometry (ICP-MS) measurements after 24h in receptor fluid indicated low, but detectable silver absorption and no statistically significant differences in the penetration between the 4 types of AgNP studied at 47, 470 or 750μg/ml. Similarly, no significant differences were observed for silver penetration when the AgNP were used in combinations with AlCl3 (500μM), MPB (1250μM) or DBPH (35μM). The measured highest amount of Ag that penetrated was 0.45ng/cm2 (0.365-0.974ng/cm2) for PEG stabilized Ag15nm+MPB.

Laser ablation – inductively couple plasma – mass spectrometry/laser induced break down spectroscopy: a tandem technique for uranium particle characterization

Laser ablation – inductively coupled plasma – mass spectrometry (LA-ICP-MS) in tandem with laser induced breakdown spectroscopy (LIBS) was employed to chemically map and characterize uranium particles. The uranium particles were doped in various concentrations (0.01, 0.1, 1.0, and 2.0%) to a 50 : 50 Ni : Fe mixture. There was an excellent correlation in regards to concentration and the LA-ICP-MS measurements. In addition, the isotopic composition of the uranium particles was determined within 10% measurement uncertainty. LIBS measurements also showed strong agreement in the particle mapping when compared to the LA-ICP-MS analysis. Moreover, the total analysis time for a 5 × 5 mm area was only 50 minutes. These data suggest that the tandem LA-ICP-MS/LIBS technique can provide rapid and valuable information for nuclear material safeguards and actinide material characterization.

An automated micro-separation system for the chromatographic removal of uranium matrix for trace element analysis by ICP-OES

An automated, miniaturized, off-line separation technique is presented here using an Elemental Scientific Inc. microFAST MC system with UTEVA resin to extract the uranium matrix from its trace element impurities in aqueous media. The collected fractions were analyzed for ~ 30 trace elements using inductively coupled plasma - optical emission spectroscopy. Ten replicate samples were processed with a single column resulting in precision ranging from 3.3% to 6.2% relative standard deviation with regards to the trace element recoveries. Accuracy, with respect to trace element concentrations in the U3O8 Certified Reference Material 124-1, resulted in an average of 13.9% relative deviation while accuracy to the Canadian U3O8 reference material, CUP-2, resulted in an average relative deviation of 8.6%. The total separation time of this automated process was reduced to ~ 30 min per sample while employing a 0.5 mL UTEVA chromatographic resin bed and 2.5 mg of uranium.