TXRF Analysis for Ultratrace Element Analysis of Nanoparticles

Advanced materials such as nanoparticles are widely used for the manufacture of industrial and consumer products. Continuous advance in product development along with increasing concerns about the effect on human health and the environment has led to a rising demand for versatile analytical technologies. This report describes the use of total reflection X-ray fluorescence (TXRF) analysis for nanoparticles in different fields.

Instrumentation

All measurements were conducted using the benchtop TXRF spectrometer S2 PICOFOX. This instrument is fitted with an air-cooled low power X-ray tube (Mo target), a multilayer monochromator with 80% reflectivity and the liquid nitrogen-free XFlash Silicon Drift Detector (SDD) with an energy resolution of less than 150 eV (Mn Ka).

Nanoparticle Characterization

The sample amount required for TXRF analysis is extremely small and is therefore most suitable for R&D projects. For semi-quantitative analysis such as the determination of element ratios, TXRF is non-destructive and enables almost complete sample recovery.

The example given below describes the analysis of element ratios in CdSe nanoparticles coated with ZnS. The sample was prepared using a cotton bud by transferring a few particles to a quartz sample carrier and TXRF measurement was then applied. Figure 1 shows the results for three samples with comparable compositions and good concordance to the target values.

Figure 1. Element ratios of coated nanoparticles. The black frame (〈) shows the target values

Detection Limits of Nanoparticles in Solution

Monitoring of nanoparticles released in the environment requires extremely sensitive analytical technologies for precise detection of these particles. The example given describes the detection of TiO₂ nanoparticles after dilution. 10 μl Ga standard solution (100 mg/l) was added to 1 ml of nanoparticle solution comprising approximately 1 mg/l TiO₂. Various dilution stages up to a factor of 100 were applied. 10 μl of each solution were transferred to a quartz carrier and measured for 1000 s. Table 1 shows the concentrations of TiO₂ in all solutions. Under these conditions, the detection limit for the nanoparticles was calculated to 3.7 μg/l.

Table 1. Measurement of the concentration of TiO₂ nanoparticles after dilution

Analysis of Nanoparticle Coating

In a subsequent experiment, the amount of a Ru coating of TiO₂ nanoparticles was determined. About 40 mg (exact weight required) were resuspended in 2.5 ml Triton X-100. 10 μl internal Ga standard (1 g/l) was added and then the careful homogenization 10 μl suspension was transferred to a quartz carrier and measured for 120 s. Figure 2 shows a spectrum of this sample measurement. The amount of Ru was calculated to 72 μg/l, which was in accordance with ICP results (65 μg/l).

Figure 2. Spectrum of TiO₂ nanoparticles coated with Ru

Conclusions

The examples in this report clearly show that TXRF analysis is an appropriate method for ultratrace element analysis of nanoparticles. Due to its versatility, TXRF can be applied to R&D, quality control or environmental monitoring.

This information has been sourced, reviewed and adapted from materials provided by Bruker X-Ray Analysis.

For more information on this source, please visit Bruker X-Ray Analysis.