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A first inter-laboratory comparison was conducted to demonstrate and document the capability of interested laboratories to measure the fraction of C—OH species on a plasma oxidised poly(propylene) sample by using a chemical derivatisation XPS approach. This report presents the results from that inter-laboratory comparison and includes the data received for the measured values and their associated standard deviations of laboratory means, at a 95% confidence level. The measurements were guided by a protocol developed within the group before and summarised shortly in the paper. Standard deviations that may characterise the state-of-the-art for the nominally simple and rather often practised case of TFAA chemical derivatisation XPS of C—OH species on a plasma oxidised polyolefin surface are calculated following ISO 5725-2:1994. The main conclusion is that the associated degree of equivalence reached by the participating laboratories in this comparison is still low. Further research to improve chemical derivatisation XPS protocols is mandatory.
A case study on the TEM analysis of the size and shape distribution of TiO2 bipyramidal nanoparticles prepared on TEM grids was included in the recently published ISO standard ISO 21363. It was agreed to organize at a later stage a second inter-lab comparison with the nanoparticles distributed to the participants as a liquid suspension. Protocols for uniform nanoparticle deposition on suited supports developed and optimized within the EMPIR nPSize project are also prepared to be distributed. For this, we have chosen the VAMAS platform (www.vamas.org) which offers an excellent international infrastructure of laboratories with high competence in nanoparticle measurement. The VAMAS technical working area dedicated to nanoparticle measurement is TWA 34 ‘Nanoparticle populations’. For this type of nanoparticles, the size and shape distributions are the primary parameters to be reported. Due to the good deposition protocols developed, an automated image analysis is enabled (in contrast to the manual analysis of irregular TiO2 nanoparticles.
In parallel with the TiO2 nanoparticle exercise, two spherical SiO2 nanoparticle samples with bi-modal size distributions (nominal relative number concentrations of 1:1 and 10:1) are prepared for a second VAMAS inter-lab comparison. Here, the nanoparticle concentration is the primary parameter to be measured. For the imaging methods it is targeted to measure the relative nanoparticle concentrations of the two modes. For the absolute nanoparticle concentration to be measured by imaging methods it is necessary to control the volume of the liquid suspension deposited on the substrate and to obtain such a homogeneous nanoparticle deposition on the substrate which allows to count (or extrapolate) all the deposited particles.
ACEnano is an EU-funded project which aims at developing, optimising and validating methods for the detection and characterisation of nanomaterials (NMs) in increasingly complex matrices to improve confidence in the results and support their use in regulation. Within this project, several interlaboratory comparisons (ILCs) for the determination of particle size and concentration have been organised to benchmark existing analytical methods. In this paper the results of a number of these ILCs for the characterisation of NMs are presented and discussed. The results of the analyses of pristine well-defined particles such as 60 nm Au NMs in a simple aqueous suspension showed that laboratories are well capable of determining the sizes of these particles. The analysis of particles in complex matrices or formulations such as consumer products resulted in larger variations in particle sizes within technologies and clear differences in capability between techniques. Sunscreen lotion sample analysis by laboratories using spICP-MS and TEM/SEM identified and confirmed the TiO2 particles as being nanoscale and compliant with the EU definition of an NM for regulatory purposes. In a toothpaste sample orthogonal results by PTA, spICP-MS and TEM/SEM agreed and stated the TiO2 particles as not fitting the EU definition of an NM. In general, from the results of these ILCs we conclude that laboratories are well capable of determining particle sizes of NM, even in fairly complex formulations.
Lateral resolution of secondary ion mass spectrometry - results of an inter-laboratory comparison
(2007)
Recently, BAM organised an inter-laboratory comparison focussed on lateral resolution and accuracy of sub-micron length measurements by secondary ion mass spectrometry (SIMS). Results were submitted by 16 laboratories from 10 countries. The task was to analyse a cross-sectioned semiconductor multilayer stack. The resulting strip pattern in the surface of the sample shows narrow strips, step transitions and gratings of different periods. Imaging analysis of this pattern enables the determination of relevant parameters related to the lateral resolution: (i) The width (FWHM) of the primary ion beam, (ii) the distance between 16% and 84% intensity points in a profile across the image of a step transition and (iii) the modulation of intensity in the images of gratings with different periods. The parameter's data reported by the participants vary in a wide range. A strong variation in the data of primary ion beam width was observed for results measured with the same type of instrument. The distance between two narrow strips was measured with high accuracy. Twelve of sixteen of the submitted values are within the limits of uncertainty of the reference value 964 ± 35 nm. This result shows that the calibration of the length scale of the SIMS instruments is already rather precise in most of the participating laboratories.
First results of an inter-laboratory comparison (27 participants in Europe, Japan and USA) of XPS data obtained with non-conducting samples are presented. Binding energies of Al 2s for alumina, N 1s and imide C 1s for Kapton and Sr 3p3/2 for a strontium titanate film on glass were obtained after static charge referencing with the help of 15 nm gold particles deposited at the surface of the test samples. For the alumina sample C 1s static charge referenced data are also presented. Repeat standard deviations (sr), between standard deviations (sb), reproducibility standard deviations (sR) and total means are evaluated from the experimental data. It can be stated that although the repeat standard deviation is as small as 0.05 eV in the best case, the standard deviation characterizing the reproducibility of the method is obviously not better than 0.15 eV in the best case at the present time. The knowledge of these standard deviations is important for metrology, validations of analytical procedures relying on qualitative photoelectron spectroscopy and XPS databanking.