Single particle inductively coupled plasma mass spectrometry and its variations for the analysis of nanoparticles.

Single particle inductively coupled plasma mass spectrometry (spICPMS) can count and weigh metal-containing nanoparticles (NPs), enabling their sizing if their geometry, density, and composition are known. With a nebulizer and a spray chamber for sample introduction, both the sample uptake rate and the transport efficiency must be determined when calibrating with solutions. In contrast, flow injection (FI) and mono-segmented flow analysis (MSFA) coupled to spICPMS do not need determination of the transport efficiency and sample uptake rate for accurate NP mass measurement. Correcting for the significant settling time on some instruments is also discussed, as well as calibration through signal integration instead of averaging, which eliminates the need to measure the transport efficiency when seeking NP mass. Nitrogen added to the outer plasma gas can reduce the background for the determination of P, S, Ca and Fe. Infrared heating of the sample introduction system provides 100% transport efficiency, enabling accurate particle mass and concentration measurements without measurement of transport efficiency.

Forensic analysis by solid sampling electrothermal vaporization coupled to inductively coupled plasma optical emission spectrometry.

To analyze trace evidence found at crime scenes, non-destructive analysis techniques or analysis techniques requiring minute amounts of sample are preferred. One such technique is solid sampling electrothermal vaporization (ETV) coupled to inductively coupled plasma optical emission spectrometry (ICPOES), which requires only 0.1-5 mg of sample. As a result, it has been utilized in several applications of forensic research. This article discusses the capabilities of ETV-ICPOES among current analytical methods and introduces its value as a tool for the analysis of forensic evidence. The latest advancements of ETV-ICPOES demonstrate the diverse opportunities for the identification, determination, and discrimination of evidence. Methods of ETV-ICPOES for the direct analysis of various physical evidence, including trace evidence, are reviewed. Some methods involve quantification of multiple elements using, commonly, matrix-matched external calibration with certified reference materials. Other methods combine qualitative multi-element analysis, based on the area of each analyte peak produced during the vaporization step of the ETV temperature program, and multivariate analysis using principal component analysis or linear discriminant analysis. In all cases, internal standardization with an argon emission line first compensates for sample loading effects on the plasma. Perspectives for utilizing ETV-ICPOES in future forensic settings are also offered.

Sex determination of mummies through multi-elemental analysis of head hair using electrothermal vaporization coupled to inductively coupled plasma optical emission spectrometry.

Sex determination of human remains is of great archaeological significance, as it provides a more complete picture of social and familial structures within ancient societies. Typically performed through examination of bones in the pelvic region, accurate sex determination can be exceedingly challenging in the absence of a sufficiently preserved skeleton. Here, a method for sex determination in living humans, involving measurement of magnesium, strontium, sulfur, and zinc in head hair along with multivariate statistics, was applied for the first time to hair collected from 500 year-old mummies originating from Peru. Hair samples were washed in doubly deionized water, dried, and ground prior to analysis via electrothermal vaporization coupled to inductively coupled plasma optical emission spectrometry; only 2 mg of hair is required for analysis. Point-by-point internal standardization was performed with Ar i 430.010 nm to compensate for sample loading effects on the plasma. Peak areas were integrated and mass corrected before being used in combination with multivariate analysis. Although principal component analysis provided insufficient separation between the sexes, linear discriminant analysis (LDA) was highly effective for sex determination. Using mummy hair as the LDA model enabled accurate sex prediction of the mummies, showing that, despite the age of the hair, the samples still contain the necessary elemental information for sex determination. For accurate sex determination of mummies using hair collected from living humans, magnesium had to be replaced by sodium due to significant differences in dietary habits. With this simple modification, hair from living humans in North America could be used to successfully predict the sex of individuals who lived more than 500 years ago in Peru. This work paves the way for broader use of non-skeletal sex determination methods within the field of archaeology, filling a significant gap.

Literature review and meta-analysis of gastric and intestinal bioaccessibility for nine inorganic elements in soils and soil-like media for use in human health risk assessment.

When soils become contaminated, a human health risk assessment (HHRA) is beneficial for determining whether identified contaminants of potential concern (COPCs) pose a risk to human health. In certain jurisdictions, when calculating doses from soil ingestion during the exposure assessment step of a HHRA, validated bioaccessibility methods may be used to accurately represent a contaminant's relative absorption factor (RAF). Where validated methods do not exist, risk assessors must either a) conduct their own literature search (which can be time consuming), b) create their own validation study (also a time consuming process), or c) use default assumptions (i.e., a RAF of 1). This literature search and meta-analysis characterizes the past 28 years of published analysis for aluminum (Al), antimony (Sb), arsenic (As), cadmium (Cd), chromium (Cr), iron (Fe), lead (Pb), manganese (Mn), and mercury (Hg) from 13 different gastric and intestinal bioaccessibility methodologies. These elements were selected as they are often risk drivers in HHRAs and are sometimes identified as COPCs in HHRAs at contaminated sites. Results were compiled from soil deriving from a variety of sources and varying in physicochemical properties. The mean percent bioaccessibility and 95 percent upper confidence limit on the mean (95 UCL) were calculated to better inform further study and validation of methods for elements additional to Pb, As, and Cd, which may be applicable to future HHRAs. Although there has been plenty of study into effects of various soil and method parameters on elemental bioaccessibility, meta-analysis found limited evidence that these findings are generalizable. Meta-analysis was also limited by little variability in certain parameters, but a more targeted analysis identified some correlative influences of pH and particle size for well-studied elements within the dataset. High bioaccessibility variability indicates that moving away from default parameters to use percent bioaccessibility to represent contaminant RAF must still be completed on a site-specific basis. The study has identified that more bioaccessibility studies for Al, Cr, Sb, Fe, Mn, and Hg, particularly studies that seek to validate bioaccessibility testing of these elements, will be beneficial for more robust and informative future risk assessments.

Biosynthesis of the Fungal Organophosphonate Fosfonochlorin Involves an Iron(II) and 2-(Oxo)glutarate Dependent Oxacyclase.

The fungal metabolite Fosfonochlorin features a chloroacetyl moiety that is unusual within known phosphonate natural product biochemistry. Putative biosynthetic genes encoding Fosfonochlorin in Fusarium and Talaromyces spp. were investigated through reactions of encoded enzymes with synthetic substrates and isotope labelling studies. We show that the early biosynthetic steps for Fosfonochlorin involve the reduction of phosphonoacetaldehyde to form 2-hydroxyethylphosphonic acid, followed by oxidative intramolecular cyclization of the resulting alcohol to form (S)-epoxyethylphosphonic acid. The latter reaction is catalyzed by FfnD, a rare example of a non-heme iron/2-(oxo)glutarate dependent oxacyclase. In contrast, FfnD behaves as a more typical oxygenase with ethylphosphonic acid, producing (S)-1-hydroxyethylphosphonic acid. FfnD thus represents a new example of a ferryl generating enzyme that can suppress the typical oxygen rebound reaction that follows abstraction of a substrate hydrogen by a ferryl oxygen, thereby directing the substrate radical towards a fate other than hydroxylation.

Source apportionment of bioaccessible lead in soil reference materials using the continuous on-line leaching method and inductively coupled plasma mass spectrometry.

Bioaccessibility (the amount of a contaminant extracted by the gastrointestinal fluids during digestion) is often incorporated in the assessment of contaminated soils and foods. Current methods, including those published by the United States Environmental Protection Agency (US EPA) and United States Pharmacopoeia (USP), use a batch method of analysis which requires hours of extraction prior to instrumental analysis with inductively coupled plasma mass spectrometry (ICPMS). The continuous on-line leaching method (COLM) uses a more direct method of analysis as extracts are sent directly to the ICPMS instrument, which can reduce extraction time and give real-time elution kinetics. For this study, four reference soils (NIST 2710, NIST 2710a, NIST 2711a, and BGS 102) that are typically used with bioaccessibility methods were extracted using the COLM and US EPA and USP gastrointestinal fluids. With the transient time-resolved data from the COLM, differential elution indicating multiple Pb sources was observed in NIST 2710a, NIST 2711a, and BGS 102. Two methods for calculating the Pb isotope ratios to identify these sources included a point-by-point ratio average method and a more precise regression slope method. There was no statistically significant difference between the ratios obtained by these methods of calculation. Furthermore, NIST 2710a and NIST 2711a did not have any statistically significant difference between the Pb isotope ratios of two observed sources. BGS 102 had a significantly different secondary source of Pb, which was identified to be from Pb historically added to gasoline. Investigation into the regions these soil reference materials were sourced from supported this finding as BGS 102 comes from a more densely populated, industrialized area where soil contamination with Pb from gasoline is likely to be more prevalent. This type of bioaccessibility investigation is only possible with the COLM as it gives real time elution information. Incorporation of the COLM into future bioaccessibility studies (and inclusion of other elements for isotopic analysis, like Sr) will lead to more thorough and comprehensive bioaccessibility studies in the future.

Characterization of platinum nanoparticles for fuel cell applications by single particle inductively coupled plasma mass spectrometry.

The most effective utilization of platinum (Pt) in fuel cells is achieved through the use of nanoparticles (NPs) that offer a large electrochemically active surface area. Because the stability of NPs decreases as they become smaller, their size and size distribution must be known in order to optimize the catalysts' durability, while offering high catalytic activity. Single particle inductively coupled plasma mass spectrometry (spICPMS) can quantify the mass of metallic NPs suspended in aqueous medium, which can then be converted into a size if the NPs' shape, density and composition are known. In this study, for the first time, spICPMS was compared to transmission electron microscopy (TEM) for the characterization of 10 nm Pt NPs. After verifying the accurate sizing of commercial Pt NPs with diameters of 30, 50 and 70 nm, spICPMS with solution calibration was applied to laboratory-synthesized 10 nm Pt NPs possessing a near spherical shape and 10 ± 2 nm diameter according to TEM. The same NPs were also analyzed by spICPMS with Pt size calibration using Pt NPs standards. Irrespectively of the calibration strategy, spICPMS measured the entire population of 659 Pt NPs (6-65 nm), while TEM analyzed the 500 Pt NPs that appeared isolated in the field of view (6-18 nm). Analysis of the size distribution histograms revealed that the modal and mean diameters were respectively 10 and 11 ± 2 nm using solution calibration, and 12 and 13 ± 2 nm using particle size calibration. Both of these mean diameters are in agreement with the TEM measurements according to a Student's t-test at the 95% confidence level, demonstrating that spICPMS, with a size detection limit of 6 nm, can accurately quantify 10-nm Pt NPs while at the same time analyzing the entire sample.

Preconcentration of noble metals on alumina prior to analysis by inductively coupled plasma mass spectrometry: Application to geological samples.

A preconcentration method for the determination of noble metals (Ag, Au, Ir, Os, Pd, Pt, Re, Rh, Ru) was developed using alumina as a sorbent. The method involves an off-line preconcentration analytical procedure: the formation of chloro-complexes of these elements with HCl, loading of the chloro-complexes on alumina followed by elution of analytes and analysis by inductively coupled plasma mass spectrometry. The effects of HCl/HNO3 concentration in the sample digest, mass of alumina, and concentration of eluents (HCl and HNO3)/thiourea were studied using multivariate experimental designs. Using 2 M HCl as eluent, detection limits were improved by a factor of 10-20 for Ag, Ir, Os, Pd, Pt, and Ru, and 3-5 for Re and Rh compared to those achieved by direct nebulization (i.e. without preconcentration). Accuracy was verified through analysis of CDN-PGMS-19 ore reference material. Using 2 M HCl for elution, the results for Ag, Pd and Pt agreed with the reference values obtained based on aqua regia digestion (which does not achieve total dissolution). For the determination of Au, evaporation of HNO3 and elution with thiourea were required.

Integrating Instead of Averaging Signal Intensity to Simplify Nanoparticle Mass Measurement by Single Particle Inductively Coupled Plasma Mass Spectrometry.

The use of single particle inductively coupled plasma mass spectrometry has been rapidly expanding for the analysis of nanoparticles (NPs). When external calibration with standard solutions is done to find the mass of NPs, the average signal intensity for each standard solution is typically used, which requires measurement of the transport efficiency of solutions through the spray chamber. However, if the signal is integrated over a constant time period for all standards and samples, then there is no need to determine the transport efficiency to measure NP mass, as the mass of analyte aspirated can be directly found by multiplying the analyte concentration in each standard by the sample uptake rate and the integration time. The line of best fit through the calibration curve of integrated signal versus mass is then used to find the total mass of NPs nebulized during the integration time, the mass of each NP then corresponding to the fraction of the total integrated signal caused by the NP. Measurement of the transport efficiency is only required if the concentration of NPs is desired.

Single particle inductively coupled plasma mass spectrometry with and without flow injection for the characterization of nickel nanoparticles.

This work compares the performance of transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD), single particle inductively coupled plasma mass spectrometry (spICPMS) and flow injection (FI) coupled to spICPMS for the characterization of synthetic ferromagnetic Ni nanoparticles (NPs) prepared with and without polyvinylpyrrolidone (PVP) stabilizer. Whereas single NPs measurement by XRD yielded nominal diameters of 13.7 and 16.6 nm with and without PVP respectively, a diameter of 100-130 nm was obtained by TEM and SEM with or without PVP, indicating extensive agglomeration during preparation for microscopy. In contrast, without PVP stabilization, mean and mode sizes of respectively 35 ± 18 and 21 nm by spICPMS and 33 ± 15 and 20 nm by FI-spICPMS were obtained for suspensions of Ni NPs using external calibration with Ni standard solutions. With PVP stabilization, the mean and mode sizes respectively decreased to 27 ± 12 and 18 nm by spICPMS and 25 ± 10 and 16 nm by FI-spICPMS. Mass balance taking into account the amount of dissolved Ni was verified in all cases. No degradation in performance resulted from using FI-spICPMS instead of spICPMS, even though measurement of NPs mass by FI-spICPMS is done without knowledge of the transport efficiency and the sample uptake rate. This is the first time that spICPMS and FI-spICPMS are demonstrated to be suitable for the characterization of ferromagnetic NPs.

Stabilization and Solvent Driven Crystal-to-Crystal Transition between New Bismuth Halides.

The investigations of bismuth halide chemistry in DMSO/MeOH solutions led to the discovery of a new solvent-stabilized compound with a chemical formula of Cs3BiBr6·3DMSO. In addition, a new phase of Cs3BiBr6 was generated as a result of a crystal-to-crystal transition driven by the change in the solvent composition. The solvent stabilized Cs3BiBr6·3DMSO adopts an orthorhombic P212121 type crystal structure with unit cell dimension of a = 13.6160(6) Å, b = 14.4359(8) Å, and c = 14.6487(7) Å. Bulk single crystals of Cs3BiBr6·3DMSO with average size of 4.5 × 3.5 × 3.5 mm3 were grown by the antisolvent crystal growth method. With the change of the solvent composition from 2:1 DMSO: MeOH to 1:1 DMSO: MeOH, the single crystals of Cs3BiBr6·3DMSO underwent a crystal-to-crystal transition yielding another structurally distinct Cs3BiBr6 phase, with a tetragonal P42/m type structure and unit cell dimensions of a = 9.8394(5) Å, b = 9.8394(5) Å, and c = 8.0950(6) Å. Both compounds exhibit isolated BiBr6 octahedral resembling the structures of the zero-dimensional (0D) perovskites.

Enhancement of the Capabilities of Inductively Coupled Plasma Mass Spectrometry Using Monosegmented Flow Analysis.

Flow injection (FI) in combination with inductively coupled plasma mass spectrometry (ICPMS) is advantageous for the analysis of volume-limited samples and is invaluable for the analysis of corrosive samples that would prematurely degrade ICPMS components. However, the dispersion process with 50-µL injections in FI degrades ICPMS sensitivity. Monosegmented flow analysis (MSFA), where the sample plug is in the middle of 1 mL of air, eliminates dispersion while preserving the rinsing effect of the carrier. More reproducible as well as sharper, narrower, and more symmetrical peaks result with MSFA than FI, leading to a 2-fold improvement in detection limit and a 5-fold increase in sample throughput versus FI. Furthermore, by facilitating the formation of small droplets during nebulization, the air surrounding the sample even enhances sensitivity by 20-40%, depending on the element, compared to that obtained with direct sample aspiration. Coupling MSFA to ICPMS, which does not degrade analytical performance, is advantageous for the determination of Pt in 0.50 M H2SO4 electrolyte from a simulated fuel cell. It also enables the multielement analysis of a 150-µL buffer sample containing as little as 60 µg of plant protein, thus further extending the range of applications of ICPMS.

Realistic risk assessment of arsenic in rice.

Over 3 billion people share a diet consisting mainly of rice, which may contain significant amounts of arsenic. Because the toxicity of arsenic is dependent on its chemical form and that it may be in a form that is not bio-accessible (i.e. dissolved in the gastrointestinal tract) and can thus not become bio-available (i.e. end up in the blood stream, where it may exert its toxic effect), the bio-accessibility of arsenic was determined in thirteen different types of rice. The effects of washing and cooking were also studied. The total concentration of arsenic ranged from 93 to 989 µg kg-1 and its bio-accessibility ranged from 16 to 93%. Cooking only changed arsenic speciation in a few cases. However, simply washing rice with arsenic-free water before cooking removed 3-43% of the arsenic, resulting in all the rice tested except the most contaminated one being safe to consume by adults.

Simultaneous Speciation Analysis of Arsenic, Chromium, and Selenium in the Bioaccessible Fraction for Realistic Risk Assessment of Food Safety.

A simple and fast method was developed for risk assessment of As, Cr, and Se in food, which is demonstrated here using three cooked and uncooked rice samples (basmati as well as organic white and brown rice). The bioaccessible fraction was first determined through online leaching of rice minicolumns (maintained at 37 °C) sequentially with artificial saliva, gastric juice, and intestinal juice while continuously monitoring potentially toxic elements (As, Cr, and Se) by inductively coupled plasma mass spectrometry (ICPMS). Then, a new ion chromatography method with online detection by ICPMS was developed for the simultaneous speciation analysis of As, Cr, and Se in the bioaccessible fraction to determine the portion of these elements that was actually toxic. Using gradient elution, four As species [As(III), As(V), monomethylarsonic acid, and dimethylarsinic acid], two Cr species [Cr(III) and Cr(VI)], and two Se species [Se(IV) and Se(VI)] were separated within 12 min. The simultaneous speciation analysis of As, Cr, and Se revealed that the simple act of cooking can convert all of the carcinogenic Cr(VI) to the safer Cr(III).

Solid sampling ETV-ICPOES coupled to a nebulization/pre-evaporation system for direct elemental analysis of glutinous rice by external calibration with standard solutions.

Because glutinous rice flour is consumed by millions of individuals around the world, its analysis is essential to ensure its safety. Solid sampling electrothermal vaporization (ETV) coupled to inductively coupled plasma optical emission spectrometry (ICPOES) allows for a quick analysis, precluding the need for time-consuming acid digestion that may also lead to analyte loss or contamination. However, the amount of sample that can be introduced without extinguishing the plasma is limited to about 4mg. The increase in plasma robustness resulting from the concurrent introduction of pre-evaporated water aerosol allows the introduction of 8mg of solid sample without extinguishing the plasma. This modified set-up was compared to conventional ETV for the determination of several elements in three different brands of glutinous rice flour. Not only are detection limits improved, but dried aqueous standard solutions can be used for external calibration, thereby significantly increasing the applicability of solid sampling ETV-ICPOES.

Limits of Detection and Quantification of Electrochemical Quartz-Crystal Nanobalance in Platinum Electrochemistry and Electrocatalysis Research.

The electrochemical quartz-crystal nanobalance has been used in electrochemistry research for over three decades. It provides an atomic/molecular level insight into the nature of interfacial electrochemical phenomena by measuring in situ mass changes on the nanogram scale. The sensitivity of this technique remains unknown because there have been no attempts to determine its limits of detection (LOD) or quantification (LOQ). We propose an experimental approach for determining the values of LOD and LOQ for Pt electrodes in aqueous H2SO4 solutions that employs cyclic voltammetry and frequency variation measurements. However, this methodology is also appropriate to other electrode materials and electrolytes. The LOD and LOQ values depend on the electrolyte concentration and decrease (i.e., the sensitivity increases) as the concentration decreases. Knowledge of the LOD and LOQ values determines the applicability of this technique in research on the oxidation and degradation of Pt catalysts employed in fuel cells.

Flow Injection Single Particle Inductively Coupled Plasma Mass Spectrometry: An Original Simple Approach for the Characterization of Metal-Based Nanoparticles.

In recent years, single-particle inductively coupled plasma mass spectrometry (spICPMS) has emerged as a reliable tool that can both count metal-containing nanoparticles and measure their mass, thereby allowing sizing if their shape, density, and composition are known. However, the methodology associated with the current spICPMS approach for mass determination requires determination of both the sample uptake rate and the sample introduction efficiency of the nebulization system. In this paper, the proof of concept of a novel approach based on flow injection (FI) analysis coupled to ICPMS, i.e., FI-spICPMS, is presented. Unlike the established technique, this method does not require a determination of the transport efficiency and of the sample uptake rate for the accurate measurement of particle mass. It also only requires a measurement of the transport efficiency for determination of the particle number. Unlike the traditional spICPMS approach, the measurement of transport efficiency by FI-spICPMS is not affected by changes in sample uptake rate. The efficiency of FI-spICPMS is demonstrated through accurate determination of the particle number and size of 60 nm citrate-coated gold nanoparticles suspended in high-purity water. Despite being simpler, the method provides similar results to those obtained by the established spICPMS method. With a 5 ms dwell time and 200 µs settling time, the size detection limit is 20 nm, i.e., the same as with spICPMS.

Estimation of the bio-accessible fraction of Cr, As, Cd and Pb in locally available bread using on-line continuous leaching method coupled to inductively coupled plasma mass spectrometry.

A previously developed, efficient and simple on-line leaching method was used to assess the maximum bio-accessible fraction (assuming no synergistic effect from other food and beverage) of potentially toxic elements (Cr, As, Cd and Pb) in whole wheat brown and white bread samples. Artificial saliva, gastric juice and intestinal juice were successively pumped into a mini-column, packed with bread (maintained at 37 °C) connected on-line to the nebulizer of an inductively coupled plasma mass spectrometry (ICP-MS) instrument equipped with a collision-reaction interface (CRI) using hydrogen as reaction gas to minimize carbon- and chlorine-based polyatomic interferences. In contrast to the conventional batch method to which it was compared, this approach provides real-time monitoring of potentially toxic elements that are continuously released during leaching. Mass balance for both methods was verified at the 95% confidence level. Results obtained from the whole wheat brown and white bread showed that the majority of Cr, Cd and Pb was leached by gastric juice but, in contrast, the majority of As was leached by saliva. While there was higher total content for elements in whole wheat bread than in white bread, a higher percentage of elements were bio-accessible in white bread than in whole wheat bread. Both the on-line and batch methods indicate that 40-98% of toxic elements in bread samples are bio-accessible. While comparison of total analyte concentrations with provisional tolerable daily intake values may indicate some serious health concern for children, when accounting for the bio-accessibility of these elements, bread consumption is found to be safe for all ages.

Optimization of the operating conditions of solid sampling electrothermal vaporization coupled to inductively coupled plasma optical emission spectrometry for the sensitive direct analysis of powdered rice.

Two different approaches were used to improve the capabilities of solid sampling (SS) electrothermal vaporization (ETV) coupled to inductively coupled plasma optical emission spectrometry (ICP-OES) for the direct analysis of powdered rice. Firstly, a cooling step immediately before and after the vaporization step in the ETV temperature program resulted in a much sharper analyte signal peak. Secondly, point-by-point internal standardization with an Ar emission line significantly improved the linearity of calibration curves obtained with an increasing amount of rice flour certified reference material (CRM). Under the optimized conditions, detection limits ranged from 0.01 to 6ngg(-1) in the solid, depending on the element and wavelength selected. The method was validated through the quantitative analysis of corn bran and wheat flour CRMs. Application of the method to the multi-elemental analysis of 4-mg aliquots of real organic long grain rice (white and brown) also gave results for Al, As, Co, Cu, Fe, Mg, Se, Pb and Zn in agreement with those obtained by inductively coupled plasma mass spectrometry following acid digestion of 0.2-g aliquots. As the analysis takes roughly 5min per sample (2.5min for grinding, 0.5-1min for weighing a 4-mg aliquot and 87s for the ETV program), this approach shows great promise for fast screening of food samples.