Optical emission spectrometry helps identify nanoparticles

In an open access article published in the journal MoleculesAnd the The researchers provided an accurate model that correctly estimated the number of nanoparticles in water from the molar concentration and mass of gold nanoparticles (AuNPs). Ultraviolet visible spectroscopy (UV-vis) and transmission electron microscopy (TEM) were used in this paper to generate and analyze citrate-coated gold nanoparticles.

Stady: A simple model for quantifying the number of metallic nanoparticles in samples using inductively coupled plasma optical emission spectrometry. Image Credit: Yurchanka Siarhei / Shutterstock.com

Many environmental studies of nanomaterials, including their fate, toxicity, and general appearance, depend on accurate estimation of the number and size of nanoparticles.

Environmental matrix simulations were generated by adding gold nanoparticles to the sediment, extracting them with the leachate, and separating them from the bulk matrix using centrifugal separation and phase transfer methods. Inductively coupled plasma optical emission spectrometry (ICP-OES) was used to measure the molar concentration of gold nanoparticles on the extracted residues.

Determining the number of nanoparticles in the separated residues is made possible by the molar concentration, average diameter of 27 nm, and the colloidal suspension sizes of the gold nanoparticles. In addition, ICP-OES was used to determine the number of nanoparticles in samples based on the plot of the number of gold nanoparticles versus the mass of gold nanoparticles.

The present study was the first application of the gravitational approach to ICP-OES to count the number of nanoparticles after phase transfer separation.

The growth of engineered metallic nanomaterials (ENMs) in recent decades

Recent decades have witnessed an exponential increase in the study and development of metal-engineered nanomaterials (ENMs), which has led to extensive commercialization of items using metal-engineered nanomaterials.

Because of the increase in their use, engineered metallic nanomaterials have been released into the environment and have potentially harmful effects on human and animal health.

However, more research is needed to understand their ecological spread, fate and behavior in the environment to provide suggestions for policy makers.

The environmental impact of metal-engineered nanomaterials is not well understood due to a lack of data regarding their diffusion in the natural environment. The complete lack of robust extraction techniques and analytical methods for studying metallic nanomaterials contributes to poor knowledge regarding the environmental effects of engineered nanomaterials.

Concentrations of metallic nanoparticles (ENPs) were observed in different shapes, such as mass. However, accurate calculation of the molar concentration, and thus the number of nanoparticles, may be the most important feature for studying the fate, environmental impact, toxicity and behavior of modified nanoparticles.

Various analytical models are created to solve these problems. However, since they depend on the composition and dimensions of metal-made nanoparticles, most of these models are only applicable to certain types of metal-engineered nanoparticles.

Based on these technologies, other models have been created, including:

  • gravity measurements
  • light absorption
  • turbidity measurement
  • dynamic light disintegration
  • Laser-induced avalanche detection
  • Counting individual particles
  • Induced plasma related spectrometry
  • optical sensor.

However, the most popular methodology for measuring metal-synthesized nanoparticles in a natural environment is the single-particle counting method based on inductively coupled mass spectrometry (SP-ICP-MS) technology. Calculate the molar concentration of metallic nanoparticles in the sample using the transit efficiency.

It is necessary to create universal designs that are straightforward to use especially for metallic engineered nanoparticle sizes and shapes due to the rapid rate of their manufacture and utilization.

A bottom-up approach that began with metal-engineered nanoparticle production, characterization, elevation, extraction, separation, and quantification was proposed to meet the requirements of an accurate method for determining the number of nanoparticles in a sample.

Finally, the gravimetric approach was adapted to show the relationship between the mass of gold nanoparticles obtained from molar concentration and the number of gold nanoparticles. It has been predicted that this relationship model is applicable to different types of nanoparticles that can be characterized and studied by ICP-OES.

Conducting experimental investigations

A wet chemical technique, a bottom-up strategy, was used to create the engineered nanoparticles. Ultraviolet spectrophotometric characterization of the metal-synthesized nanoparticles was performed. This spectroscopy technique helped to investigate the optical properties of metallic nanoparticles.

High-resolution transmission electron microscopy (HRTEM) has helped determine the sizes and configurations of gold nanoparticles. For the characterization of HRTEM, new nanoparticles were produced and sonicated prior to analysis. Such a measure was necessary to prevent precipitation which could alter the shape of the nanoparticles and make it difficult to determine the effect of each reducing agent on size and shape.

The filtrate, which simulates appropriate environmental processes to extract sediments into supernatants, was used to extract nanomaterials from bulk matrices. The total molar concentration of gold that created specific nanomaterials in solution was then evaluated using centrifugal and phase transfer procedures.

The ability to extract nanomaterials from bulk matrices using a phase transfer separation technique has been established. However, the presence of nanomaterials in the intermediate phases caused significant phase transfer problems. 20 ml of the supernatant diluted from 0.5 g of sediment was lifted with 100 L of gold nanoparticles and separated into 6 ml of toluene to test the phase transfer procedure.

ICP-OES analysis of aqueous, intermediate and organic phases confirmed the fraction of the separated sample containing gold nanoparticles. As mentioned earlier, toluene and the intermediate phase contained significantly more gold nanoparticles than the aqueous phase. Therefore, toluene and intermediate phase residues were mixed and subjected to ICP-OES analysis.

Traces of gold detected in the aqueous phase after ICP-OES analysis were traced back to unreacted gold during reductions. Finally, the phase transfer separation method can accurately and effectively separate gold nanoparticles from dissolved gold metal ions because the gold salt has not been completely converted into gold nanoparticles.

A centrifugal separation technique evaluated the separation of gold nanoparticles from the supernatants. In the centrifugation procedure, 1 g and 0.5 g of the sediment were lifted in triplicate with different amounts of gold nanoparticles, extracted and separated, then digested and subsequently analyzed by ICP-OES. After centrifugation, the gold nanoparticle residues were digested and subjected to ICP-OES analysis.

Leachate systems were placed in 50 mL centrifuge tubes. They were then centrifuged for 20 min at 2000 rpm to separate the supernatant from the sediment during centrifugal separation of gold nanoparticles. As the system was equipped with spherical gold nanoparticles, the centrifugal extraction method extracted the spherical nanoparticles in the supernatant phase as it assumed that the suspended nanomaterials were spherical and behave according to Stokes’ law. Finally, the supernatants were poured into a 50 ml beaker after centrifugation was completed.

For the phase transfer separation of gold nanoparticles, 0.3354 g of octadecylamine (OCTDA) was measured and diluted in 100 ml of toluene to create a 0.01 M concentration solution. In addition, the efficacy of the phase transfer technique was confirmed by digesting the known molar concentration of gold nanoparticles without extracting them with OCTDA toluene solution.

Study results and their importance

The molar concentration and number of nanoparticles are essential for quantitative analysis. Thus, the results of this work will help ecologists to investigate the occurrence of nanoparticles with useful modeling information.

Filtration, centrifugation and phase transfer procedures were used to separate the gold nanoparticles from the bulk matrix. The authors measured the molar volume and concentration using HRTEM and ICP-OES, respectively.

The concentration and molar volume parameters were then fitted to the gravimetric formulas modified to determine the number of nanoparticles in the sample. The results revealed a relationship between the mass of AuNPs and the number of nanoparticles in the sample. This relationship can estimate the number of nanoparticles in the environment.

The authors believe that the proposed approach will make it easier to use HRTEM and ICP-OES, two commonly used laboratory techniques, to analyze the number of nanoparticles in the environment.


Hendricks, N.; , Olatunji, or . Gombe, b. (2022). A simple model for quantifying the number of metallic nanoparticles in samples using inductively coupled plasma optical emission spectrometry. Molecules27 (18), 5810.

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