Single Particle ICP-MS Research Articles

Single Particle Inductively Coupled Plasma Time-of-Flight Mass Spectrometry—A Powerful Tool for the Analysis of Nanoparticles in the Environment

Single-particle inductively coupled plasma-mass spectrometry (SP-ICP-MS) has emerged as an important tool for the characterization of inorganic nanoparticles (NPs) in the environment. Although most SP-ICP-MS applications rely on the quadrupole ICP-MS (ICP-QMS), it is limited by the slow scanning speed of the quadrupole. Recent advancements in instrumentation have led to the development of inductively coupled plasma time-of-flight mass spectrometry (ICP-TOF-MS) which offers a viable solution. In this review, we discuss the recent advances in instrumentation and methodology of ICP-TOF-MS, followed by a detailed discussion of the applications of SP-ICP-TOFMS in analyzing NPs in the environment. SP-ICP-TOFMS has the potential to identify and quantify both anthropogenic and natural NPs in the environment, providing valuable insights into their occurrence, fate, behavior, and potential environmental risks.

Vertical distribution of inorganic nanoparticles in a Norwegian fjord

Due to the analytical challenges of detecting and quantifying nanoparticles in seawater, the data on distributions of NPs in the marine environment is limited to qualitative studies or by ensemble measurements subject to various analytical artifacts. Single particle inductively coupled plasma mass spectrometry (SP-ICP-MS) allows determination of individual inorganic NPs at environmentally relevant concentrations, yet only few studies have been conducted on selected elements in surface sea water. Here, a sequential multi-element screening method was developed and implemented to provide a first survey of the horizontal and vertical distributions of inorganic nanoparticles and trace elements in a pristine Norwegian fjord prospect for submarine tailings deposition. Statistical control of false-positive detections while minimizing the size detection limit was ensured using a novel raw signal processing. Scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) gave confirmative and qualitative information regarding particle morphology and composition. Following SP-ICP-MS screening for particles of 16 elements, particulate Al, Fe, Mn, Pb, Si and Ti were found and determined to mass concentrations in ng/L of 1–399, 1–412, below limit of detection (<LOD) - 269, <LOD - 1, <LOD - 1981 and <LOD - 127 ng/L with particle number concentrations up to 108 particles per liter. Total metals concentrations were at least an order of magnitude higher, at concentrations in μg/L of 1–12 for Al, 2–13 for Fe, 0.3–11 Mn, 0.02–0.5 for Pb, 46 to 318 Si and 0.04–0.4 for Ti. A strong depth dependence was observed for both trace elements and particles with concentrations increasing with depth. Our results provide a baseline for the fjord and new data on environmental levels of both total metals and metal containing nanoparticles including the vertical and horizontal distribution of natural nanoparticles.

Effects of brake wear nanoparticles on the protection and repair functions of the airway epithelium

Long term exposure to particulate air pollution is known to increase respiratory morbidity and mortality. In urban areas with dense traffic most of these particles are generated by vehicles, via engine exhaust or wear processes. Non-exhaust particles come from wear processes such as those concerning brakes and their toxicity is little studied. To improve our understanding of the lung toxicity mechanisms of the nanometric fraction of brake wear nanoparticles (BWNPs), we studied whether these particles affect the barrier properties of the respiratory epithelium considering particle translocation, mucus production and repair efficiency. The Calu-3 cell line grown in two-compartment chambers was used to mimic the bronchial epithelial barrier. BWNPs detected by single-particle ICP-MS were shown to cross the epithelial tissue in small amounts without affecting the barrier integrity properties, because the permeability to Lucifer yellow was not increased and there was no cytotoxicity as assessed by the release of lactate-dehydrogenase. The interaction of BWNPs with the barrier did not induce a pro-inflammatory response, but increased the expression and production of MU5AC, a mucin, by a mechanism involving the epidermal growth factor receptor pathway. During a wound healing assay, BWNP-loaded cells exhibited the same ability to migrate, but those at the edge of the wound showed higher 5-ethynyl-2′-deoxyuridine incorporation, suggesting a higher proliferation rate. Altogether these results showed that BW.NPs do not exert overt cytotoxicity and inflammation but can translocate through the epithelial barrier in small amounts and increase mucus production, a key feature of acute inflammatory and chronic obstructive pulmonary diseases. Their loading in epithelial cells may impair the repair process through increased proliferation.

Determination of the Particle Number Concentration, Size Distribution, and Species of Dominant Silver-Containing Nanoparticles in Soils by Single-Particle ICP-MS.

The potential risk of various silver-containing nanoparticles (AgCNPs) in soils is related to the concentration, size, and speciation, but their determination remains a great challenge. Herein, we developed an effective method for determining the particle number, size, and species of dominant AgCNPs in soils, including nanoparticles of silver (Ag NPs), silver chloride (AgCl NPs), and silver sulfide (Ag2S NPs). By ultrasonication wand-assisted tetrasodium pyrophosphate extraction, these AgCNPs were extracted efficiently from soils. Then, multistep selective dissolution of Ag NPs, AgCl NPs, and whole Ag NPs/AgCl NPs/Ag2S NPs was achieved by 1% (v/v) H2O2, 5% (v/v) NH3·H2O, and 10 mM thiourea in 2% (v/v) acetic acid, respectively. Finally, the particle number concentration and size distribution of AgCNPs in the extracts and the remaining AgCNP particle number concentration after each dissolution were determined by single-particle inductively coupled plasma mass spectroscopy for speciation of the dominant AgCNPs. AgCNPs were detected in all five soil samples with the concentrations of 0.23-8.00 × 107 particles/g and sizes of 16-110 nm. Ag2S NPs were the main form of AgCNPs in the examined soils with the percentage range of 53.98-69.19%, followed by AgCl NPs (11.42-23.31%) and Ag NPs (7.78-16.19%). Our method offers a new approach for evaluating the occurrence and potential risk of AgCNPs in environmental soils.

Risk assessment of silver and microplastics release from antibacterial food containers under conventional use and microwave heating

The evaluation of the migration of ionic silver and nanoparticulated silver (AgNPs) from antimicrobial plastic packaging to food is crucial to ensure its safety. Migration assays were performed on reusable silver-containing polypropylene (PP) food containers and a silicone baby bottle, using food simulants, under conventional or microwave heating and repeated use. The PP containers released significant amounts of silver, increasing with temperature, contact time, acidity and lower crystallinity. Silver migration in the silicone bottle was much lower. Risk assessment of released silver was done considering European authorities safety recommendations, with some containers far exceeding these levels. No significant AgNPs release was detected in the simulants by single particle-ICPMS. Silver-containing microplastics and silicone microparticles were detected by SEM in the food simulants after the migration assays. Consumers may be continuously exposed to the harmful effects of ionic silver and microplastics, which can potentially lead to health issues.

Determination of Titanium (IV) Oxide Nanoparticles Released from Textiles by Single Particle – Inductively Coupled Plasma – Mass Spectrometry (SP-ICP-MS)

Monitoring TiO2 nanoparticles (NPs) that are released from functional textiles is significant for assessing the potential risk to consumers. However, determining the size distribution of TiO2 NPs is still a challenge due to agglomeration. The present study employed single particle–inductively coupled plasma–mass spectrometry (SP-ICP-MS) to quantify TiO2 NPs released from functional textiles. Through screening dispersants and validating the standard samples, an accurate method for determining the size and number of TiO2 NPs was developed. The validated procedure was successfully used to determine the release of TiO2 NPs from yarn in sweat and water media throughout the day. The result revealed that the yarn decorated with TiO2 NPs released approximately the same particle size distribution from 60 to 260 nm in both media. The released particle concentration was 0.094 µg/mL with a mean size of 136 nm in water and a particle concentration of 0.120 µg/mL with a mean size of 133 nm in sweat. Additionally, based upon transmission electron microscopy, anatase TiO2 NPs were identified. It is expected that this work is significant in the evaluation of the toxicological effects of multifunctional textiles modified by TiO2 NPs on human health.

Quantitative analysis and characterization of PtNPs in road dust based on ultrasonic probe assisted extraction and single particle inductively coupled plasma mass spectrometry

As a result of their growing use, platinum nanoparticles (PtNPs) can pollute different environmental compartments, especially road dust due to their application in vehicle catalytic converters. Their presence in these matrices should be controlled to achieve adequate environmental risk assessment, but there is a lack of standardized analytical methods for this purpose. Therefore, this study describes the development and analytical characterization of a rapid sample preparation strategy for the analysis of PtNPs in road dust by single particle inductively coupled plasma mass spectrometry (SP-ICP-MS). Parameters within the critical steps of the extraction (such as the type of energy, sample-to-reagent ratio, intensity, or time), and subsequent phase separation have been optimized using a road dust reference material (BCR-723, certified for total Pt), and spiked road dust samples. The final method consists of a sonication probe assisted extraction, using water as extractant, followed by a separation based on centrifugation, and dilution prior to SP-ICP-MS. Information about size and both mass- and particle-based concentration is provided in <11 min. A recovery rate of 100 ± 1% is achieved in the spiked road dust samples, and a 12 ± 1% (n = 6) of the total Pt was found to be as PtNPs in the certified reference material. The applicability of this methodology has been proven performing the analysis of PtNPs in real road dust samples, with sizes between 15 and 75 nm, and concentrations (6.0–20.0 ng g−1) that represents from 11 to 27% of the Pt content.

Occupational Exposure to Metal Engineered Nanoparticles: A Human Biomonitoring Pilot Study Involving Italian Nanomaterial Workers

Advances in nanotechnology have led to an increased use of engineered nanoparticles (ENPs) and the likelihood for occupational exposures. However, how to assess such exposure remains a challenge. In this study, a methodology for human biomonitoring, based on Single Particle Inductively Coupled Plasma Mass Spectrometry (SP-ICP-MS), was developed as a tool to assess the ENPs exposure of workers involved in nanomaterial activities in two Italian Companies. The method was validated for size and number concentration determination of Ag, Au, In2O3, Ir, Pd, Pt, and TiO2 NPs in urine and blood samples. The results showed the presence of In2O3 NPs in blood of exposed workers (mean, 38 nm and 10,371 particles/mL), but not in blood of controls. Silver, Au, and TiO2 NPs were found in urine (mean, Ag 29 nm and 16,568 particles/mL) or blood (mean, Au 15 nm and 126,635 particles/mL; TiO2 84 nm and 27,705 particles/mL) of workers, though these NPs were found also in controls. The presence of ENPs in both workers and controls suggested that the extra-professional exposure is a source of ENPs that cannot be disregarded. Iridium, Pd, and Pt NPs were not detected neither in blood nor in urine. Overall, the findings provided a rational basis to evaluate the exposure assessment to ENPs in cohorts of workers as part of risk assessment and risk management processes in workplaces.

Quantification of monodisperse and biocompatible gold nanoparticles by single-particle ICP-MS.

Bioanalytical and biomedical applications often require nanoparticles that exhibit narrow size distributions and biocompatibility. Here, we demonstrate how different synthesis methods affect gold nanoparticle (AuNPs) monodispersity and cytotoxicity. Using single particle inductively coupled plasma mass spectrometry (SP-ICP-MS), we found that the size distribution of AuNPs synthesized with a cetyltrimethylammonium chloride (CTAC) cap was significantly improved compared to AuNPs synthesized with citrate capping agents. We determined an up to 4× decrease in the full width at half maximum (FWHM) value of the normal distributions of AuNP diameter and up to a 12% decrease in relative standard deviation (RSD). While the CTAC-capped AuNPs exhibit narrow nanoparticle size distributions, they are cytotoxic, which limits safe and effective bioanalytical and biomedical applications. We sought to impart biocompatibility to CTAC-capped AuNPs through a PEGylation-based surface ligand exchange. We developed a unique ligand exchange method driven by physical force. We demonstrated the successful PEGylation using various PEG derivatives and used these PEGylated nanoparticles to further bioconjugate nucleic acids and peptides. Using cell viability quantification, we confirmed that the monodisperse PEGylated AuNPs were biocompatible. Our monodisperse and biocompatible nanoparticles may advance safe and effective bioanalytical and biomedical applications of nanomaterials.

Tracking Silver Nanoparticles during Their Synthesis by Inductively Coupled Plasma Mass Spectrometry: Implications for Colorimetric Sensing of Mercury Ions

Silver nanoplates have been used in the colorimetric sensing of analytes through various mechanisms. Herein, we proposed the use of single-particle inductively coupled plasma mass spectrometry (SP-ICP-MS) for providing additional information on changes in nanoparticles during the colorimetric sensing of analytes. The information on equivalent spherical diameter and the number of particles obtained from SP-ICP-MS was employed for tracking the changes in silver nanoparticles during their synthesis process under various synthesis conditions and also during the colorimetric sensing of mercury. By comparing the edge size of triangular nanoplates observed by transmission electron microscopy, the information on the plate thickness of triangular silver nanoplates was also estimated by the size information from SP-ICP-MS. Four types of silver nanoplates were examined including bare silver nanoplates, silver nanoplates capped with glutathione, silver nanoplates capped with glutathione mixed with 0.05 mg L–1 mercury and bromide ions, and silver nanoplates capped with glutathione mixed with 1 mg L–1 mercury and bromide ions. The information on equivalent spherical diameter and the number of particles was used for understanding the sensing mechanism of the silver nanoplates toward mercury ions. The information from SP-ICP-MS was combinedly used with plasmon absorption data, as well as the information from field-flow fractionation-ICP-MS (FFF-ICP-MS), in order to study the changes in silver nanoparticles at various concentrations of mercury ions. A linear increase in particle concentrations was observed by SP-ICP-MS for the concentration range of 0.001–0.01 mg L–1 mercury ions. The particle concentrations were highest at 0.01 mg L–1 mercury ions and decreased to the same numbers as for the bare silver nanoplates without bromide etching. This study shows the potential use of SP-ICP-MS to provide additional information for tracking silver nanoparticles during their synthesis and colorimetric sensing of mercury ions. In addition, for SP-ICP-MS analysis of particle concentrations for the diluted silver nanoplates in contact with mercury ions before etching with diluted bromide ions, the limit of detection for mercury was pushed down to approximately 0.01 μg L–1, which would be very useful for the analysis of real samples under environmentally relevant conditions.

A Novel Method for the Background Signal Correction in SP-ICP-MS Analysis of the Sizes of Titanium Dioxide Nanoparticles in Cosmetic Samples.

We discuss the features involved in determining the titanium dioxide nanoparticle (TiO2NP) sizes in cosmetic samples via single particle inductively coupled plasma mass spectrometry (SP-ICP-MS) in the millisecond-time resolution mode, and methods for considering the background signal. In the SP-ICP-MS determination of TiO2NPs in cosmetics, the background signal was recorded in each dwell time interval due to the signal of the Ti dissolved form in deionized water, and the background signal of the cosmetic matrix was compensated by dilution. A correction procedure for the frequency and intensity of the background signal is proposed, which differs from the known procedures due to its correction by the standard deviation above the background signal. Background signals were removed from the sample signal distribution using the deionized water signal distribution. Data processing was carried out using Microsoft Office Excel and SPCal software. The distributions of NP signals in cosmetic product samples were studied in the dwell time range of 4-20 ms. The limit of detection of the NP size (LODsize) with the proposed background signal correction procedure was 71 nm. For the studied samples, the LODsize did not depend on the threshold of the background signal and was determined by the sensitivity of the mass spectrometer.

Contribution to optimization and standardization of antibacterial assays with silver nanoparticles: the culture medium and their aggregation

The antimicrobial activity of silver nanoparticles is determined by their size and specific properties, as well as by the chemical composition of the exposure medium in which the nanoparticles are suspended. When the antibacterial tests are carried out in a culture medium, aggregation of the nanoparticles is produced, decreasing their effectiveness. This study proposes the addition of surfactants to the culture medium to prevent the aggregation of silver nanoparticles and optimizes the concentrations of these surfactants. The aggregation of silver nanoparticles was studied by dynamic light scattering (DLS) after dispersion in three liquid culture media (Mueller-Hinton (MH), Luria-Bertani (LB) and Brain Heart Infusion) in which four different surfactants (SDS, Triton X100, Tween 80 and CTAB) were added at concentrations of 0, 0.1, 0.5, 1, 1.5 and 2%. Results showed that, the optimal culture media to prevent aggregation of silver nanoparticles were MH and LB with higher concentrations of Tween 80 and Triton X100 surfactants; being MH + 2% of Tween 80 and MH + 1% Triton X100 the best combinations obtained because the results obtained were closest to the sizes of nanoparticles in ultrapure water. In addition, it has been verified that the optimal medium + surfactant combinations chosen did not affect the viability of Escherichia coli bacteria. Nanoparticle aggregation was not observed by single particle inductively coupled plasma mass spectrometry (SP-ICP-MS) when nanoparticles were incubated for long incubations periods (24 h) in the optimal medium chosen.

Single Nanoparticle Counting-Based Liquid Biopsy for Cancer Diagnosis.

Liquid biopsy has become a sought-after technique for disease diagnosis because it provides real-time, dynamic, and comprehensive information that can alleviate the dilemmas faced by tissue biopsy. Multiplexed microRNAs (miRNAs) have been demonstrated to be promising biomarkers in liquid biopsy but fall short in providing simple and sensitive analytical methods. In this work, we established a novel nanoparticle counting strategy to accomplish simultaneous analysis of three breast cancer-associated miRNAs for breast cancer diagnosis. The frequency of nanoparticles not involved in the formation of sandwich structures was detected by single-particle inductively coupled plasma mass spectrometry (SP-ICPMS) to quantify the targets. The detection limits for miR-21, miR-155, and miR-16 were 49, 51, and 55 amol, respectively. The strategy was applied to clinical samples and successfully achieved the diagnosis between normal individuals and breast cancer patients. The area under the curve (AUC) for the combination of the relative expression of miR-21 and miR-155 was 0.818. The above results indicate that this strategy has potential and holds great promise for playing an essential role in cancer diagnosis.

Characterizing silver nanoparticles in beverages and following their release from silver-containing food containers using sector field single particle inductively coupled plasma mass spectrometry (SP-ICP-MS)

Silver nanoparticles (Ag NPs) are increasingly used in the food industry because of their excellent antibacterial activity. They are integrated into coatings of various food packaging to help ensure longer product shelf life. Nonetheless, the risks associated with Ag NPs are currently not well known and their potential effects on humans are causing growing concern. Furthermore, it is not clear whether NPs have greater or lesser risk than dissolved silver ions or bulk phase Ag. Consequently, it is necessary to characterize the release of silver from silver-enhanced containers into food matrices using sensitive analytical techniques that allow one to distinguish between silver ions and nanoparticles. Single particle ICP-MS is a promising technique to quantify and determine size distributions of very small particles at low concentrations and distinguish between ionic and particulate forms of the analyte. This study focused first on the aging of Ag NPs in three different food simulants (Milli-Q water, 10% ethanol and 3% acetic acid) and in two beverages (orange juice and infant milk formula) in order to validate the technique for low NP concentrations. Acidic media caused significant NP oxidation while the organic macromolecules in the juice appeared to increase the stability of the NPs. Subsequently, a migration study from silver-enhanced containers showed that release was mainly due to ionic forms of the silver. Significant release of dissolved Ag occurred in 3% acetic acid (58% of the total Ag mass of the containers) with lower release being observed in Milli-Q water (33%), 10% ethanol (29%), orange juice (17%) and milk formula (5%). Heating led to a considerable release of silver (again dissolved), likely because of the swelling of the polymer containers. The study suggests that the risks to foods associated with Ag NP in packaging can be determined using existing regulations and guidelines based on (ionic) Ag.

Study on Characterization and Content Determination Method of Silver in Chitosan Antibacterial Gel

To characterize the silver in chitosan antibacterial gel, and to establish a method for the determination of silver content in samples. The silver in the samples was analysed by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and single particle inductively coupled plasma mass spectrometry (SP-ICP-MS). Microwave digestion was adopted to digest the chitosan antibacterial gel, and then the content of silver was determined by flame atomic absorption spectrometry. The analysises showed that the particle size of silver in chitosan antibacterial gel was about 150~ 200 nm. The silver showed good linearity in the concentration range of 25~250 μg/L (y=0.000 35x+0.001 7, r=0.999 9). The recovery rate (n=9) was 98.5%. SEM, EDS and SP-ICP-MS can be used for the characterization of silver particles in chitosan antibacterial gel. Microwave digestion-flame atomic absorption spectrophotometry method is simple, practicable, high precision and high quantitative accuracy, which is suitable for the quantitative analysis of silver in chitosan antibacterial gel.

Extraction and quantification of polystyrene nanoplastics from biological samples

Accurate quantification of nanoplastics (NPs) in complex matrices remains a challenge, especially for biological samples containing high content of organic matters. Herein, a new method extracting and quantifying polystyrene (PS) NPs from biological samples was developed. The extraction included alkaline digestion, centrifugation, and cloud point extraction (CPE), and the quantification included gold nanoparticles formation and labeling on surfaces of the extracted NPs and thereafter measurement with single particle inductively coupled plasma mass spectrometry (SP-ICP-MS). Results show that 25% tetramethylammonium hydroxide solution was an effective alkaline digestion solution for biological matrices, and CPE after centrifugation (3000 rpm, 10 min) was applicable to purify and enrich PS NPs with different sizes (100 and 500 nm) and surface functionalities (-COOH and –NH2 modifications) from the digestion solution. The efficiency of Au labeling on PS NPs surface was improved by about 70% in the presence of 100 μM cetyltrimethylammonium bromide. The performance of the quantification method was examined by extraction and measurement of PS NPs spiked in four representative organism samples including bacteria, algae, nematode, and earthworm, and was further validated by analyzing the accumulated PS NPs in exposed nematodes. Good recovery rates (65 ± 10%–122 ± 22%) were achieved for spiking levels of 5–50 μg g−1; the limit of detection was 3.7 × 107 particles g−1, corresponding to the mass concentration of about 0.02 and 2.5 μg g−1 for the 100 nm and 500 nm PS NPs, respectively. The established extraction and quantification methods are efficient and sensitive, providing a useful approach for further exploring the environmental behavior and toxicity of NPs.

Use of field-flow fractionation and single particle inductively coupled plasma mass spectrometry for the study of silver nanoparticle shape transformation

Field-flow fractionation-inductively coupled plasma mass spectrometry (FFF-ICP-MS) and single particle ICP-MS (SP-ICP-MS) were used for investigation of silver nanoparticle shape transformation. Commercial and laboratory synthesized silver nanoparticles were employed in this study. For laboratory synthesized silver nanoparticles, silver nanosphere seed was first prepared by reducing silver nitrate with sodium borohydride in starch stabilizing agent. The obtained nanosphere exhibited 27.5 nm hydrodynamic diameter from FFF-ICP-MS analysis with equivalent spherical diameter of 26 nm from SP-ICP-MS analysis. This nanosphere underwent shape transformation induced by varying volumes of hydrogen peroxide. Increasing hydrogen peroxide volume resulted in increased particle diameter, and nanoplate formation. These synthesized nanoparticles and commercial silver nanoplates were subjected to shape transformation induced by bromide etching. General trend was observed that bromide addition caused particles to become smaller. Clear trend was found for commercial silver nanoplates that bromide addition caused both hydrodynamic diameter measured by FFF-ICP-MS and equivalent spherical diameter measured by SP-ICP-MS become smaller. Furthermore, the combined information from FFF-ICP-MS and SP-ICP-MS analysis with the use of TEM data were proposed to provide additional information on the edge length and the thickness of silver nanoplates. With the known edge length of commercial silver nanoplates, the thickness was estimated to be 25.4 nm, 7.64 nm, and 4.95 nm for triangular nanoplates with the edge length of 32 nm, 70 nm, and 153.1 nm, respectively. Both FFF-ICP-MS and SP-ICP-MS provided unique information which are useful for nanoparticle characterization.

Protein corona-induced extraction coupled to Fenton oxidation for selective and non-destructive preconcentration of Ag2S nanoparticles from waters

Sulfidation of silver nanoparticles (AgNPs) to generate silver sulfide nanoparticles (Ag2S-NPs) significantly influences their fate and toxicity in natural environments. However, the correlational research in this field was limited by the lack of methods for speciation analysis of Ag2S-NPs. To address this challenge, a novel protocol for the selective Ag2S-NP extraction from real waters was developed using protein corona-induced extraction coupled to Fenton oxidation of AgNPs with Fe3+/H2O2 reagents. The ability of various concentrations of Fe3+/H2O2 to selectively dissociate AgNPs into ions was first evaluated. Then, selective separation and preconcentration of the remaining Ag2S-NPs was established by optimizing the parameters that may affect the protein corona-induced extraction efficiency, followed by quantification with inductively coupled plasma mass spectrometry (ICP-MS), enabling an ultrahigh enrichment factor of 10,000 and extremely low detection limit (LOD) of 1.8 ng/L. The presence of humic acid (HA), inorganic salts and particles at the environmentally relevant levels had limited effects on Ag2S-NP extraction. As demonstrated by transmission electron microscopy (TEM) analysis and single particle ICP-MS (spICP-MS), the sizes, shapes, and compositions of Ag2S-NPs extracted with the proposed method remain in intact. Good recoveries of 83.7−105% were achieved for the Ag2S-NPs spiked in four natural waters at the level of 97.8 ng/L. Due to the high yields and applicability to Ag2S-NPs at environmentally relevant concentrations, this proposed method is particularly suitable to track the generation and transformation of Ag2S-NPs in various scenarios.

Suppression of spectral interference in dual-elemental analysis of single particles using triple quadrupole ICP-MS

Single particle-inductively coupled plasma-mass spectrometry (SP-ICP-MS) was used in the analysis of single particles/cells. Although quadrupole mass analyzers are widely used, the long settling time restricts measurement to single elements in individual particles. Recently, dual-elemental analysis has successfully been developed with the assistance of oxygen gas in the collision cell. This simple approach greatly expands the capability of quadrupole-based ICP-MS.In this study, we adopted bandpass mode in the first quadrupole (Q1) to improve the limit of detection of single particles against spectral interference. A model was developed to explain the rationale behind the selection of quadrupole voltages. The quadrupole voltages were optimized systematically so that the mass bandwidth of Q1 allowed the transmission of two target analytes while the interference species were rejected. As a result, the signal from the polyatomic interference was reduced by 98% with no significant change in the analyte signal.The bandpass mode was further applied to accurately determine the isotope ratio of 109Ag/107Ag in 80-nm Ag nanoparticles, as well as the Ag content in AgSn alloy particles, under the polyatomic interference of 91Zr16O originating from dissolved ions and particles. This technique was further applied to the determination of two Yb isotopes in algal cells with interference from Gd. Results indicate that this approach has great potential for assessing single particles and biological cells in the presence of severe interference from imaging agents, drugs, or biological fluids.

How to trust size distributions obtained by single particle inductively coupled plasma mass spectrometry analysis

Single particle inductively coupled plasma mass spectrometry (SP-ICP-MS) is a technique widely used to obtain direct information about the number concentration and the size distribution of nanoparticles in liquid suspensions. However, its methods still lack clear quality control strategies to confirm the validity of the information derived from them. Only the detection of the complete size distribution of the nanoparticles in a sample over the size critical value ensures obtaining unbiased quantitative information, otherwise information should be restricted to report the presence of nanoparticles over a certain size and number concentration since their actual total number concentration is underestimated and the size overestimated. Under the latter conditions, data processing produces histograms showing the tails of the incomplete size distributions, although apparently, complete distributions can also be obtained when particle events are recorded as peaks, as reported here for the first time. The occurrence of these misleading situations must be critically evaluated for each SP-ICP-MS analysis. An approach, based on estimation of size critical values and successive dilutions, is proposed for the assessment of the validity of the quantitative information obtained, together with specific criteria for reconsidering the information that can be derived from those measurements. The approach was verified with different case studies and applied to the analysis of complex nanomaterials, confirming the validity of the reported information by comparison with other techniques. A calculation tool is also included to facilitate the estimation of size critical values under experimental conditions.Graphical abstract