One standard - several methods

One to rule them all!
Lord of the rounds

With our Nano-Pellets it is possible to use the same reference material across three different analytical techniques.

To exemplify the applicability only one of many analysed elements is shown, Strontium (Sr).

10 mm Apatite-NP in front of our aluminium mount.
10 mm Apatite-NP in front of our aluminium mount.

1. Laser ablation inductively coupled mass spectrometry - LA-ICP-MS

The data shown in Table 1 (Tab.1) come from a homogeneity test performed on 10 different 10 mm diameter Apatite-NP Nano-Pellets. The spot size was set to 50 µm. The analytical pattern is shown in Figure 1 (Fig.1).

Tab.1: Results [µg/g] from the homogeneity test from 10 Apatite-NP Nano-Pellets. Data shown were measured on m/z 88.
Tab.1: Results [µg/g] from the homogeneity test from 10 Apatite-NP Nano-Pellets. Data shown were measured on m/z 88.

The results in Tab. 1 show each average, standard deviation, and relative standard deviation (RSD) from the 21 analyses. The data show excellent within- and between-unit homogeneity, the RSD is always around 1 %.

Data provided by Dr. Axel Sjöquist of Axray Scientific AB and Dr. Thomas Zack from the University of Gothenburg using a 213 nm NWR laser and an Agilent 8800 mass spectrometer.

Fig.1: Analytical pattern for the homogeneity test. 3 sequences of 7 randomly chosen spots are analysed, resulting in a total of 21 analyses.
Fig.1: Analytical pattern for the homogeneity test. 3 sequences of 7 randomly chosen spots are analysed, resulting in a total of 21 analyses.

2. Micro x-ray fluorescence – Micro-XRF

A similar homogeneity test was run using micro-XRF (Tab.2). 50 random spots were scattered inside a defined area on the pellet surface, using the instrument’s software to 20 µm. Fig.3 shows an elemental distribution map of Strontium.

Fig.2: Camera image of 10 Apatite-NP from inside the Bruker M4 Tornado µXRF instrument.
Fig.2: Camera image of 10 Apatite-NP from inside the Bruker M4 Tornado µXRF instrument.
Fig.3: Micro-XRF elemental distribution map of Sr in 10 Apatite-NP Nano-Pellets.
Fig.3: Micro-XRF elemental distribution map of Sr in 10 Apatite-NP Nano-Pellets.

To make the Nano-Pellets infinitely thick and to avoid issues with x-ray beam geometry, 13 mm diameter NPs with a thickness of approx. 5-6 mm were used.

Tab.2: Results [cps] from the homogeneity test on 10 different Apatite-NP Nano-Pellets. Strontium was measured on the K-alpha 1 emission line.
Tab.2: Results [cps] from the homogeneity test on 10 different Apatite-NP Nano-Pellets. Strontium was measured on the K-alpha 1 emission line.

These data also show excellent within- and between-unit homogeneity. The exception is Nano-Pellet 6 where the RSD is highest at 3,4 %, most likely due to surface contamination, not instrument stability.

Since the signal from detectors in XRF instruments follows a Poisson distribution an expected standard deviation can be calculated by taking the square root of the total counts per second (cps).

Comparing the measured relative standard deviation to the Poisson relative standard deviation shows, with exception of Nano-Pellet 6, that the measured RSD is below the expected RSD from Poisson counting statistics.

Data provided by Dr. Roald Tagle, Senior Application Scientist at Bruker Nano GmbH, Berlin using the M4 Tornado instrument.

3. Laser-induced breakdown spectroscopy - LIBS

The homogeneity test using LIBS was performed on a single, 20 mm diameter Apatite-NP Nano-Pellet. The ablation pattern can be found in Fig. 4.

Fig.4: Ablation pattern on the 20 mm diameter Apatite-NP Nano-Pellet. The red rectangle shows 4 bursts. These 4 bursts form a so-called position (P). There are a total of 9 positions, yielding a total of 36 analyses.
Fig.4: Ablation pattern on the 20 mm diameter Apatite-NP Nano-Pellet. The red rectangle shows 4 bursts. These 4 bursts form a so-called position (P). There are a total of 9 positions, yielding a total of 36 analyses.

A total of 36 spots (300 µm) were analysed. Tab. 3 shows the average of 4 measurements in 9 so-called positions (P). The data are peak-normalised, meaning the peak intensity of the analysed emission-line is normalised to the average intensity of the spectrum.

Tab.3. Peak normalised results from the LIBS homogeneity test. Strontium was measured at 422 nm wavelength.
Tab.3. Peak normalised results from the LIBS homogeneity test. Strontium was measured at 422 nm wavelength.

These data again show very good within-pellet homogeneity, the RSD does not exceed 6 %.

Data provided by Applied Photonics Ltd using their benchtop modular system inside an Ar-purged sample chamber coupled to Quantel Q-Smart 450 laser (1064 nm, 6 ns) and a Spectro-Module-6-Multi-channel spectrometer.

All in all, these three homogeneity tests show, that Nano-Pellets can yield excellent within- and between-unit repeatability across three different analytical techniques.
myStandards GmbH & Analytical Partners