Number-based Size Distribution Research Articles

Determination of submicron aerosols effective density using two-stage low-pressure impactor and aerosol electrometer based on pre-measured particle size distribution

A novel methodology was presented for determining the representative effective density of aerosols of a given size distribution, using a lab-made two-stage low-pressure impactor and an aerosol electrometer. Electrical currents upstream (Imeasured, up) and downstream (Imeasured, down) of the 2nd stage of the impactor were measured using a corona charger and the aerosol electrometer. In addition, the electrical currents upstream (Icalculated, up) and downstream (Icalculated, down) of the 2nd stage of the impactor were calculated using the aerosol charging theory. Then, the difference between the ratio of Imeasured,down to Imeasured,up and the ratio of Icalculated,down to Icalculated,up was iterated with varying the presumed effective density until the difference was smaller than 0.001. The methodology was validated using poly-disperse sodium chloride (NaCl) particles. The effective densities of ambient aerosols were then obtained from indoor and outdoor environments and compared with those calculated from a relation between mobility (scanning mobility particle sizer (SMPS) measurement) and aerodynamic (electrical low-pressure impactor (ELPI) measurement) diameters. Compared to the effective densities obtained with SMPS and ELPI measurements, the effective densities obtained using the methodology introduced in this paper differed within 10 % deviation, depending on measurement location. After an averaged effective density for given size distribution is obtained at a measurement location, the number-based size distribution can be easily converted to mass-based size distribution using the representative effective density.

Quantifying Exhaled Particles in Healthy Humans During Various Respiratory Activities Under Realistic Conditions.

Background: Quantitatively collecting and characterizing exhaled aerosols is vital for infection risk assessment, but the entire droplet size spectrum has often been neglected. We analyzed particle number and size distribution of healthy participants in various respiratory activities, considering inter-individual variability, and deployed a simplified far-field model to inform on infection risks. Methods: Participants repeated the same respiratory activities on two visits. Particles were collected using an airtight extraction helmet supplied with High Efficiency Particulate Air (HEPA) filtered air. The sampling volume flow was transported to two particle counters covering the small and large particle spectrum. The applied simple mass balance model included respiratory activity, viral load, room size, and air exchange rates. Results: Thirty participants completed the study. The major fraction of the number-based size distribution was <5 μm in all respiratory activities. In contrast, the major fraction of the volume-based size distribution was 2-12 μm in tidal breathing, but >60 μm in all other activities. Aerosol volume flow was lowest in tidal breathing, 10-fold higher in quiet/normal speaking, deep breathing, coughing, and 100-fold higher in loud speaking/singing. Intra-individual reproducibility was high. Between participants, aerosol volume flow varied by two orders of magnitude in droplets <80 μm, and three orders of magnitude in droplets >80 μm. Simple model calculations not accounting for potential particle size-dependent differences in viral load and infection-related differences were used to model airborne pathogen concentrations. Conclusions: Quantitative analysis of exhaled aerosols for the entire droplet size spectrum as well as the variability in aerosol emission between individuals provides information that can support infection research. Clinical Trial Registration number: NCT04771585.

Instrument with an ultra-wide dynamic detection range for the optical counting and sizing of individual particles in suspensions.

The characterization of dispersions, suspensions, and emulsions is important in a wide range of scientific applications and industries. Samples can consist of different materials and a wide range of particle sizes and concentrations. A single particle sizing and counting instrument with a dynamic detection range of ≥6 decades has been developed to detect single nano- and microparticles in aqueous suspensions based on light scattering measured in two directions. Hydrodynamic focusing is employed for particle separation and to provide stable conditions for light scattering detection. This gives the advantage of size resolution in the nm range, allowing, e.g., number based size distributions, classification of nanomaterials, determination of particle agglomerates, developments for dispersion stability analysis, or cutoff of filter media. In addition, concentration determination is based on sample volume measurement with <20 nl measurement uncertainty. We present results of particle detection in a size range from approximately above 40 nm for gold nanoparticles to 8μm for polystyrene particles using a prototyped instrument of the LUMiSpoc® series produced by LUM GmbH. The data obtained demonstrate the advantages of single-particle detection, particularly for characterizing polydisperse systems, such as precise particle sizing in the nanometer range through light scattering intensity based on Mie scattering theory. In addition, we present particle concentration data based on the integrated measurement of sample volume, which allows particle concentration to be determined with an uncertainty of 2.5% (95% confidence interval). To achieve such small uncertainties, dilution series measurements must be used to correct for coincidence losses and particle adhesion.

A numerical model for the calculation of the minimum ignition energy of pure and mixture dust clouds

A numerical model is developed for the minimum ignition energy (MIE) calculation of pure and mixture dust clouds, considering the influence of particle size distribution. The original particle number based size distribution is approximated with median sizes (number d50) of the subdivisions obtained by dividing the original distribution range. The MIE is calculated for 5 pure dusts, 2 mixtures of combustible dusts and 2 mixtures of combustible & inert dusts. For pure dust clouds, as the number of subdivisions and hence d50s increases, variation trend of the MIE as a function of dust concentration (MIE(conc)) gradually shifts from a “V” to a “U” or “bathtub” shape, along with an increase in the concentration where the dust cloud MIE (minimum MIE(conc) value) is reached. Furthermore, the calculated MIE fluctuates at lower number of d50s but gradually stabilizes as the d50 number further increases. The calculated MIE variation trends correspond well with the experimental data. However, due to uncertainties in the dust cloud formation and spark release in the experimental tests, differences in the definitions of the d50 in different studies and high idealization of the numerical model, there are deviations between the absolute experimental and calculated MIE values.

Towards a generic protocol for measuring the constituent particle size distribution of E171 in food by electron microscopy

Food additive E171 (titanium dioxide, TiO 2 ) is authorized to be used as food colorant in the European Union. E171 is a particulate material, containing a fraction of nanoparticles. A major challenge for food control laboratories is the lack of harmonized, validated analytical methods for measuring the physicochemical properties of nanoparticles in food. This study proposes a generic method for the determination of the number-based size distribution of the constituent particles of E171 in food products based on transmission electron microscopy (TEM). As proof of concept, the protocol was evaluated on 20 food products containing E171 and one personal care product containing titanium dioxide. The total titanium concentration in the products measured by inductively coupled plasma - mass spectrometry (ICP-MS) ranged from 0.1 to 4.0 g/kg, corresponding to 0.2–6.7 g TiO 2 /kg. The required initial mass of starting product needed for TEM analysis was estimated from the ICP-MS concentration. Sample preparation included matrix digestion, a first centrifugation step to remove the remaining food matrix, sonication to reduce agglomeration, and a second centrifugation step to concentrate the sample. Descriptive TEM analysis showed that five food products, labelled to contain E171, contained smaller rutile TiO 2 particles (20–40 nm) coated with mica, which are potassium aluminium silicate-based pearlescent pigments. For 14 other food products and the personal care product, the protocol resulted in a homogenous distribution of the TiO 2 particles over the grid surface. In general, variation between products in the number of particles on the grids was limited; on average, 672 ± 173 particles were measured in 10 images. The median of the minimum Feret diameter distribution varied from 72 ± 7 nm to 135 ± 14 nm. The percentage of nanoparticles (minimum Feret diameter smaller than 100 nm) ranged from 23% to 82%. The corresponding mass percentages of these fractions ranged from 3% to 41%. The percentages of E171 particles smaller than 30 nm was very low (3% or less) while corresponding mass fractions were negligible. For only one food product, the TiO 2 concentration was too low to apply the protocol without adaptations. • A generic protocol for particle size measurement of E 171 in food is proposed. • The protocol is designed for transmission electron microscopy. • The protocol was evaluated on 20 food products and one personal care product. • The median Fmin varied from 72 ± 7 nm to 135 ± 14 nm. • The percentage of nanoparticles (<100 nm) ranged from 23% to 82%.

Assessment of strategies for the formation of stable suspensions of titanium dioxide nanoparticles in aqueous media suitable for the analysis of biological fluids.

Due to their omnipresence in consumer products, there is a growing concern about the potential effects of nanoparticles on human health. Toxicological assessment and NP end-product studies require proper quantification of these materials in biological fluids. However, their quantifications in these media require stable predispersed NP solutions in aqueous media to enable the fortification in the matrices of interest or the preparation of calibration standards. In this study, a sample preparation scheme was developed by studying various dispersion media (polyvinylpyrrolidone and polyethylene glycol) and sonication strategies (bath and ultrasonic probe) to ensure homogeneous dispersion of titanium dioxide nanoparticles. Optimization of the various parameters was performed using SRM NIST 1898 NP reference material, composed of rutile and anatase phases. Number-based size distribution for titanium dioxide NPs was determined by dynamic light scattering and single-particle inductively coupled plasma mass spectrometry to evaluate the procedure efficiency. Changes in mean size and most frequent size distribution were also studied to determine if the agglomeration of nanoparticles occurs at the various dispersion conditions tested. Among the different dispersion parameters tested herein, the use of polyvinylpyrrolidone combined with a sonication process generated by a probe leads to a significant improvement in terms of suspension efficiency and stability over 72h. The dispersion efficiency of the proposed methodology was assessed by single-particle inductively coupled plasma mass spectrometry with spiked biological fluids such as urine and blood. Graphical abstract.

Characterization of the Volume-based or Number-based Size Distribution for Silica Nanoparticles Using a Unique Combination of Online Dynamic Light Scattering Having a Uni-tau Multi-bit Correlator and High-resolution Centrifugal Field-Flow Fractionation Separator.

This paper presents a study of the size distributions of colloidal nanoparticles using an online dynamic light scattering (DLS) unit with a uni-tau multi-bit correlator (UMC) combined with a centrifugal field-flow fractionation (CF3) separator. Conventionally, the FFF-UV-MALS system utilizing field-flow fractionation (FFF) combined with a UV detector and multi-angle light scattering instrument (MALS) could be used to obtain the particle size distribution of colloidal nanoparticles. Lately, DLS as a technique to measure the size distributions of colloid materials has become prevalent. However, the DLS instrument will practically measure only the large particles in a multi-modal particle mixture. Therefore, the CF3-DLS w/UMC system that was developed consisted of a CF3 unit connected to an online DLS instrument with UMC. The system could measure the volume- or number-based size distribution with highly quantitative and accurate histograms for multi-modal samples. The size distributions were validated with size distributions obtained by images of an atomic force microscope (AFM). Two types of colloidal silica nanoparticles with different distribution widths were used in this study.

Improved light scattering measurement with microscopy data for nanoparticle number-based size distribution

Size is the key feature of nanoparticle properties. Nanoparticle size distribution can be measured by microscopy technique and light scattering posterior to a separation technique. Discrepancies can be observed, especially in the case of polydisperse samples. Microscopy is more precise for size and shape measurement, while light scattering provides better information about concentration. An experiment is set up to investigate the feasibility of bringing comparability of Asymmetrical Flow Field-Flow Fractionation followed by Multi-Angle Light Scattering and AFM measurements. A sample made from a mixture of stock samples is built, after detailed characterisation of the stock samples. By obtaining comparability of MALS and AFM measurements, a new way to calibrate MALS instrument without the need for reference material is opened: using aliquots of the sample itself as a reference.

Determination of number-based size distribution of silica particles using centrifugal field-flow fractionation

Determination of the number-based size distribution of silica particles using the centrifugal field-flow fractionation (CF3) method was investigated. Since the accurate determination of the number-based size distribution of materials is essential in the fields of nanotechnology and biotechnology, the establishment of a robust evaluation method is attractive. We explored optimization of the fractionation conditions for CF3 using silica particles. Using pure water media as the eluent, a band broadening effect was clearly found, and this effect became stronger with higher initial centrifugal field strengths. After addition of 0.05 wt% aqueous FL-70 as a dispersant in the eluent, size fractionation could be performed effectively at higher centrifugal field strengths, providing excellent size separation results. After optimization of the CF3 separation condition, we determined the number-based size distribution of silica particles using three methods: FE-SEM only, CF3 with multi-angle light scattering (CF3-MALS), and a combined CF3 with FE-SEM method (CF3-FE-SEM). To meaningfully compare the CF3-MALS results with the other two methods, we transformed the light scattering intensity to particle numbers using Mie theory. The determined number-based mean sizes of silica particles by the three methods agreed well; however, the evaluated standard deviation of the number-based size distribution of silica particles by the CF3-MALS method was slightly different. This was attributed to the unreliable sizing by MALS of smaller sized particles or low particle concentrations. The combined CF3-FE-SEM method provided near equal accuracy as the costly FE-SEM only and allowed for a significantly faster methodology because CF3 separation reduced the number of silica particles required for an accurate sizing down to just 50 particles per fraction.

Complex of polyethyleneimine and anionic surfactant with functional chain: a versatile surface modifier applicable to various particles, solvents, and surface modification processes

An anionic surfactant (AS) comprising a phosphate ester head group and a functional organic chain branched into a hydrophilic polyethylene glycol-based chain and a hydrophobic alkyl-based chain was complexed with polyethyleneimine (PEI) and applied as universal surface modifier for the fabrication of nanoparticles dispersible in various solvents. The complex formation could be achieved by simply mixing PEI with the AS in solvents such as toluene. While PEI was insoluble in toluene due to its hydrophilic nature, addition of the AS assisted its dissolution due to complex formation between the amine group of PEI and the phosphate group of the AS. The designed PEI-AS complex effectively adsorbed on numerous particles including metal oxides (Al2O3, Y2O3, and SiO2), metal nitrides (AlN), and metal species (Si and Ni), and was applicable to various surface modification processes. For simultaneous bead milling pulverization and surface modification of gas-phase synthesized SiO2 nanoparticles with 2.6 mg/m2 of PEI-AS, the number-based size distribution of the SiO2 nanoparticles reduced to several tens of nanometers after milling, and the resultant pulverized/surface-modified nanoparticles were dispersible in a wide range of organic solvents such as methanol, MEK, IPA, THF, MMA, EtOAc, and toluene. The ligand-exchange process of oleylamine-capped Ag nanoparticles in toluene with 2.0 mg/m2 of PEI-AS was also effective in dispersing Ag nanoparticles in various organic solvents without forming severe aggregation.

Design and Performance Evaluation of a Laboratory-made 200 nm Precut Electrical Cascade Impactor

Increasing public concern regarding air quality has led to the development of efficient aerosol-monitoring techniques. Among the various aerosol measurement instruments based on electrical methods, in this study, an electrical cascade impactor (ECI) was designed and fabricated in our laboratory and was used to measure the real-time size distribution of submicron-sized aerosols. In the study by Park et al. (2007), it was assumed that the size distribution of incoming particles follows a unimodal lognormal distribution. However, in this study, the distribution of particles captured at each stage (including the Faraday cage) was assumed to be a unimodal lognormal distribution; hence, the incoming particles may follow any size distribution. After the particle charging characteristics were obtained for different particle sizes, experiments were performed with monodisperse test particles to determine the collection efficiency of each stage. The current measured in each stage was converted into a number based size distribution of aerosols by using the data inversion algorithm, which utilized the experimentally obtained collection efficiency. Then, a performance evaluation was performed, both in the laboratory and in the field. The results obtained by our ECI were in agreement with the scanning mobility particle sizer (SMPS) data.

Size Measurement of Radioactive Aerosol Particles in Intense Radiation Fields Using Wire Screens and Imaging Plates

Background: Very fine radiation-induced aerosol particles are produced in intense radiation fields, such as high-intensity accelerator rooms and containment vessels such as those in the Fukushima Daiichi nuclear power plant (FDNPP). Size measurement of the aerosol particles is very important for understanding the behavior of radioactive aerosols released in the FDNPP accident and radiation safety in high-energy accelerators. Materials and Methods: A combined technique using wire screens and imaging plates was developed for size measurement of fine radioactive aerosol particles smaller than 100 nm in diameter. This technique was applied to the radiation field of a proton accelerator room, in which radioactive atoms produced in air during machine operation are incorporated into radiation- induced aerosol particles. The size of 11C-bearing aerosol particles was analyzed using the wire screen technique in distinction from other positron emitters in combination with a radioactive decay analysis. Results and Discussion: The size distribution for 11C-bearing aerosol particles was found to be ca. 70 μm in geometric mean diameter. The size was similar to that for 7Be- bearing particles obtained by a Ge detector measurement, and was slightly larger than the number-based size distribution measured with a scanning mobility particle sizer. Conclusion: The particle size measuring method using wire screens and imaging plates was successfully applied to the fine aerosol particles produced in an intense radiation field of a proton accelerator. This technique is applicable to size measurement of radioactive aerosol particles produced in the intense radiation fields of radiation facilities.

Physicochemical characterization of titanium dioxide pigments using various techniques for size determination and asymmetric flow field flow fractionation hyphenated with inductively coupled plasma mass spectrometry.

Seven commercial titanium dioxide pigments and two other well-defined TiO2 materials (TiMs) were physicochemically characterised using asymmetric flow field flow fractionation (aF4) for separation, various techniques to determine size distribution and inductively coupled plasma mass spectrometry (ICPMS) for chemical characterization. The aF4-ICPMS conditions were optimised and validated for linearity, limit of detection, recovery, repeatability and reproducibility, all indicating good performance. Multi-element detection with aF4-ICPMS showed that some commercial pigments contained zirconium co-eluting with titanium in aF4. The other two TiMs, NM103 and NM104, contained aluminium as integral part of the titanium peak eluting in aF4. The materials were characterised using various size determination techniques: retention time in aF4, aF4 hyphenated with multi-angle laser light spectrometry (MALS), single particle ICPMS (spICPMS), scanning electron microscopy (SEM) and particle tracking analysis (PTA). PTA appeared inappropriate. For the other techniques, size distribution patterns were quite similar, i.e. high polydispersity with diameters from 20 to >700 nm, a modal peak between 200 and 500 nm and a shoulder at 600 nm. Number-based size distribution techniques as spICPMS and SEM showed smaller modal diameters than aF4-UV, from which mass-based diameters are calculated. With aF4-MALS calculated, light-scattering-based “diameters of gyration” (Øg) are similar to hydrodynamic diameters (Øh) from aF4-UV analyses and diameters observed with SEM, but much larger than with spICPMS. A Øg/Øh ratio of about 1 indicates that the TiMs are oblate spheres or fractal aggregates. SEM observations confirm the latter structure. The rationale for differences in modal peak diameter is discussed.

Characterizing Dust from Cutting Corian®, a Solid-Surface Composite Material, in a Laboratory Testing System.

We conducted a laboratory test to characterize dust from cutting Corian(®), a solid-surface composite material, with a circular saw. Air samples were collected using filters and direct-reading instruments in an automatic laboratory testing system. The average mass concentrations of the total and respirable dusts from the filter samples were 4.78±0.01 and 1.52±0.01mg cm(-3), respectively, suggesting about 31.8% mass of the airborne dust from cutting Corian(®) is respirable. Analysis of the metal elements on the filter samples reveals that aluminum hydroxide is likely the dominant component of the airborne dust from cutting Corian(®), with the total airborne and respirable dusts containing 86.0±6.6 and 82.2±4.1% aluminum hydroxide, respectively. The results from the direct-reading instruments confirm that the airborne dust generated from cutting Corian(®) were mainly from the cutting process with very few particles released from the running circular saw alone. The number-based size distribution of the dusts from cutting Corian(®) had a peak for fine particles at 1.05 µm with an average total concentration of 871.9 particles cm(-3), and another peak for ultrafine particles at 11.8nm with an average total concentration of 1.19×10(6) particles cm(-3) The small size and high concentration of the ultrafine particles suggest additional investigation is needed to study their chemical composition and possible contribution to pulmonary effect.

Two dimensional size–mass distribution function inversion from differential mobility analyzer–aerosol particle mass analyzer (DMA–APM) measurements

We developed and applied a data inversion routine to determine the number based size–mass distribution function (the two dimensional distribution function) from tandem differential mobility analyzer–aerosol particle mass analyzer (DMA–APM) measurements. The two dimensional distribution function is expressed in units of particle number concentration per unit mobility diameter per unit particle mass. It can be used to directly calculate the number based size distribution (commonly determined using DMA measurements) or the mass based size distribution (commonly inferred from impactor measurements). The inversion routine utilizes the Twomey–Markowski algorithm and is applied in this study to DMA–APM measurements of sodium chloride, cesium iodide, and ammonium sulfate particles in the 30–200nm mobility diameter range, as well as acetylene flame generated soot aggregates in the 40–350nm range. To utilize the inversion routine, the APM transfer function must be known a priori. Here it is computed using a modified version of the Ehara (uniform flow) model, with a transmission correction factor inferred from measurements. For the three examined salt particle types, visual representation of the two dimensional distribution function reveals that at a given mobility diameter, particles have very narrow mass distributions, with the peak masses in good agreement with predictions based on bulk salt densities. However, for soot particles, extremely broad distributions are observed. Soot measurements are compared to predictions for quasifractal aggregates in the transition regime; this comparison suggests that aggregates with fractal dimensions ranging from 1.4 to 2.5 are all generated in the same system. Finally, we determine the two-dimensional distribution function for a mixture of ammonium sulfate and soot particles, demonstrating that these two particle populations are separable from one another via mobility-mass analysis.

Nanomaterials in consumer products: a challenging analytical problem.

Many products used in everyday life are made with the assistance of nanotechnologies. Cosmetic, pharmaceuticals, sunscreen, powdered food are only few examples of end products containing nano-sized particles (NPs), generally added to improve the product quality. To evaluate correctly benefits vs. risks of engineered nanomaterials and consequently to legislate in favor of consumer's protection, it is necessary to know the hazards connected with the exposure levels. This information implies transversal studies and a number of different competences. On analytical point of view the identification, quantification and characterization of NPs in food matrices and in cosmetic or personal care products pose significant challenges, because NPs are usually present at low concentration levels and the matrices, in which they are dispersed, are complexes and often incompatible with analytical instruments that would be required for their detection and characterization. This paper focused on some analytical techniques suitable for the detection, characterization and quantification of NPs in food and cosmetics products, reports their recent application in characterizing specific metal and metal-oxide NPs in these two important industrial and market sectors. The need of a characterization of the NPs as much as possible complete, matching complementary information about different metrics, possible achieved through validate procedures, is what clearly emerges from this research. More work should be done to produce standardized materials and to set-up methodologies to determine number-based size distributions and to get quantitative date about the NPs in such a complex matrices.

TEM and SP-ICP-MS analysis of the release of silver nanoparticles from decoration of pastry.

Metallic silver is an EU approved food additive referred to as E174. It is generally assumed that silver is only present in bulk form in the food chain. This work demonstrates that a simple treatment with water of "silver pearls", meant for decoration of pastry, results in the release of a subfraction of silver nanoparticles. The number-based size and shape distributions of the single, aggregated, and/or agglomerated particles released from the silver pearls were determined by combining conventional bright-field TEM imaging with semiautomatic particle detection and analysis. In addition, the crystal structure of the particles was studied by electron diffraction and chemical information was obtained by combining HAADF-STEM imaging with EDX spectroscopy and mapping. The TEM results were confirmed by SP-ICP-MS. The representative Ag test nanomaterial NM-300 K was used as a positive control to determine the uncertainty on the measurement of the size and shape of the particles.

High resolution particle characterization to expedite development and regulatory acceptance of nanomedicines.

The pharmaceutical industry as well as European and US governing agencies have indicated the need for more accurate, high resolution, characterization of complex drug materials, nanomedicines, to facilitate their development and eventual approval. In particular, accurately measuring the size, zeta-potential, and concentration of nanomedicines is desired. Herein we demonstrate the comprehensive and high resolution analysis capabilities of tunable resistive pulse sensing (TRPS) on the most widely approved nanomedicines to-date, liposomal particles. The number-based size distribution, concentration and volume fraction of liposomes formed by extrusion through a 100 nm or 200 nm Nucleopore filter membrane are shown as well as how freeze-thaw aggregation changes individual liposomes and the overall size distribution. In addition, the simultaneous size and zeta-potential analysis capabilities of TRPS is used to characterize the homogeneity and difference between liposomes made with and without the addition of PEGylated phospholipids.

A reproducible number-based sizing method for pigment-grade titanium dioxide.

A strong demand for reliable characterization methods of particulate materials is triggered by the prospect of forthcoming national and international regulations concerning the classification of nanomaterials. Scientific efforts towards standardized number-based sizing methods have so far been concentrated on model systems, such as spherical gold or silica nanoparticles. However, for industrial particulate materials, which are typically targets of regulatory efforts, characterisation is in most cases complicated by irregular particle shapes, broad size distributions and a strong tendency to agglomeration. Reliable sizing methods that overcome these obstacles, and are practical for industrial use, are still lacking. By using the example of titanium dioxide, this paper shows that both necessities are well met by the sophisticated counting algorithm presented here, which is based on the imaging of polished sections of embedded particles and subsequent automated image analysis. The data presented demonstrate that the typical difficulties of sizing processes are overcome by the proposed method of sample preparation and image analysis. In other words, a robust, reproducible and statistically reliable method is presented, which leads to a number-based size distribution of pigment-grade titanium dioxide, for example, and therefore allows reliable classification of this material according to forthcoming regulations.

Semi-automatic size measurement of primary particles in aggregated nanomaterials by transmission electron microscopy

A combination of transmission electron microscopic imaging and semi-automatic image analysis allows detecting and measuring the primary particles of aggregated nanomaterials. The median primary particle size, the number based size distribution, the percentage of nanoparticles and the volume specific surface area of powdered nanomaterials are determined in the framework of the European Commission's nanomaterial definition.The principle of a semi-automated approach to measure the minimal size in one dimension of primary particles in aggregates by transmission electron microscopy is developed using the model of the powdered, aggregated titanium dioxide representative test nanomaterial NM-100 with a mean primary particle diameter near the 100nm limit. The primary particles are detected based on watershed segmentation and their minimal size and overlap coefficient are measured based on an Euclidean distance map. The primary particles of NM-100 contain 22% nanoparticles, with a size between 1nm and 100nm. The method is evaluated to measure other aggregated TiO2, synthetic amorphous silica and carbon black nanomaterials for which the percentage of nanoparticles is nearly 100%. A high level of automation allows measuring the diameter of the maximal inscribed circle efficiently. The maximal inscribed circle is a measure for the minimal primary particle size in one dimension and is shown to be commutable with Feret min measurements. The standard method to determine the fractal properties and the volume specific surface area of fractal-like aggregates is refined supporting on the diameter of the maximal inscribed circle and the overlap coefficient measurements for each individual primary particle.