Using application examples, this study shows the benefits of using a high-resolution crystal for certain types of analysis and demonstrates the performance advantages of the new PX8 multilayer compared to the TlAP crystal.
PX8 is a new synthetic multilayer with very similar analysis characteristics to TlAP. However, it has a much longer lifespan and is non-toxic, thereby aiding end-of-life disposal.
For some applications the analysis of light elements (O – Mg) requires a higher resolution than normally provided by the PX1 multilayer. One example is the analysis of Mg in aluminium alloys, where a higher-resolution TlAP crystal is often used instead of PX1. However, the TlAP crystal is toxic and its hygroscopic nature shortens its lifetime compared to other crystals. As environmental legislation becomes stricter with regard to the presence of toxic elements in all types of equipment and in waste, an alternative for the TlAP crystal is desirable.
PX8 is a new synthetic multilayer with very similar analysis characteristics to TlAP. However, it has a much longer lifespan and is non-toxic, thereby aiding end-of-life disposal.
Using application examples, this study shows the benefits of using a high-resolution crystal for certain types of analysis and demonstrates the performance advantages of the new PX8 multilayer compared to the TlAP crystal.
Analysis of low concentrations of Mg in aluminium alloys using a PX1 crystal is affected by the intense Al Kα peak, which increases the background for Mg significantly (Figure 1). This results in a higher detection limit for Mg even though the sensitivity for Mg is high. By using either PX8 or TlAP for this application, the higher resolution eliminates the effect of Al Kα on the Mg background. This gives a better peak: background ratio, which improves the detection limit for Mg even though the sensitivity is much lower compared to the PX1 crystal. Figure 1 compares scan measurements for Mg Kα in aluminium alloys using a TlAP crystal and the PX1 and PX8 multilayers. The PX8 multilayer shows very similar analysis characteristics compared to the TlAP crystal.
Figure 1. Scans of Mg Kα in an aluminum alloy sample, using a TlAP crystal and PX1 and PX8 multilayers
To test the accuracy of the analysis of Mg in aluminium alloys, calibrations were set up using both a TlAP crystal and a PX8 multilayer. A set of certified reference materials (CKD 236 – 246) was used to set up these calibrations. Figures 2 and 3 show the calibration plots for Mg derived using TlAP and PX8, respectively. The calibration plots show excellent correlation between the certified concentrations and the intensities. Detailed calibration results are shown in Table 1, together with the lower limits of detection (LLD).
Figure 2. Calibration plot for Mg in aluminium alloys using a TlAP crystal
Figure 3. Calibration plot for Mg in aluminium alloys using a PX8 multilayer
Table 1. Calibration results and detection limits (LLD) for Mg in aluminum alloys using a TlAP crystal and a PX8 multilayer
The RMS error (1 sigma) for both calibrations is very similar, indicating a similar accuracy of both crystals. The LLD for magnesium is slightly better when using a TlAP crystal because of the slightly lower background compared to the PX8 multilayer.
Another advantage of the PX8 multilayer compared to the TlAP crystal is the absence of higher order lines from major elements in the sample. For example, high calcium concentrations in cement samples produce strong third order lines for Ca Kα and Ca Kβ when using TlAP. These third order lines overlap with magnesium and can disturb the analysis. These higher order lines are virtually eliminated by PX8.
Figure 4 shows scans in the region of Mg Kα for a cement sample using both TlAP and PX8. For TlAP, the third order calcium peaks are clearly visible whereas for PX8 these higher order lines have been suppressed.
Furthermore, the suppression of higher order lines by PX8 will also improve the results for standardless analysis, since spectra will be cleaner with fewer lines causing interference on analyte lines of other elements in the sample.
Figure 4. Compared to TlAP, PX8 successfully suppresses third order lines of calcium in a cement sample.a
Figure 5. Increased sensitivity of PX8 for sodium compared to TlAP
PX8 has a 10% increase in sensitivity for Mg Kα compared to TlAP (compare Figures 2 and 3). The sensitivity gains of PX8 are even more significant for lighter elements, with an increase of ± 20% for Na Kα and ± 30% for F Kα and O Kα. However, because the background also increases slightly for these elements, the LLD values for both the PX8 and TlAP crystals are similar. The increased sensitivity for sodium is graphically illustrated in Figure 5.
The PX8 multilayer is a very good alternative to the TlAP crystal for analyzing elements from oxygen to magnesium. It is non-toxic, has a longer lifetime than TlAP and suppresses higher order interferences. In terms of detection limits, increases in the sensitivity of PX8 are offset by slightly higher backgrounds, resulting in a comparable performance to TlAP.
The analysis of low concentrations of magnesium in aluminum alloys typically requires a high-resolution crystal like TlAP. The analytical performance of PX8 is comparable to TlAP, although the obtainable LLDs are a little higher. Using slightly longer counting times can easily compensate for this small difference.
