Using XRF to Analyze Trace Elements in Polymers

Catalytic substances containing elements such as aluminum, titanium or zinc are required by most polymerization processes in order to create modern plastic materials. Nonetheless, to maintain the desirable properties of the finished product, it is imperative to minimize the presence of catalysts in the final product.

A number of other charges and additives - plasticizers, lubricants, stabilizing agents, neutralizers, antioxidants and pigments - are utilized in the production process in addition to catalysts. These products contain elements like iron (Fe), magnesium (Mg), phosphorous (P), aluminum (Al), chlorine (Cl), calcium (Ca), titanium (Ti) or chromium (Cr).  

Using XRF to Analyze Trace Elements in Polymers

Image Credit: Thermo Fisher Scientific - Elemental Analyzers and Phase Analyzers

To optimize the control over the process, it is therefore vital to conduct elemental analyses on the finished polymer.

Generally, plastics are acid-resistant and electrical insulators and are therefore difficult to put into solution. This means that X-Ray fluorescence is still the best method to obtain precise and rapid analyses for each of the periodic table elements, starting from elements with a Z atomic number as low as boron (Z = 5).

Instrument

To determine the performance of the Thermo Scientific ARL PERFORM'X series spectrometer (Fig. 1) for the analysis of trace elements in polymers, tests were performed on a series of polypropylene (PP) standard samples.

Thermo Scientific ARL PERFORM’X series

Figure 1. Thermo Scientific ARL PERFORM’X series. Image Credit: Thermo Fisher Scientific - Elemental Analyzers and Phase Analyzers

Results

Through optimized coupling between X-Ray tube and sample, as well as with the high-power tube and generator, improved performances are achieved on the ARL PERFORM'X series. This facilitates lower limits of detection and high sensitivity.

Better analysis across the periodic table is enabled by the comprehensive analytical configuration. Thanks to the state-of-the-art Thermo Scientific OXSAS software and its Analytical Assistant, operating the system is extremely simple.

For the calibration of the instrument, chemical analyses were offered and used. The limits of detection achieved for various elements, together with the measurement conditions, are shown in Table 1. 

Table 1. Elements and Analytical conditions. Source: Thermo Fisher Scientific - Elemental Analyzers and Phase Analyzers

Element 4200 W (3 Sigma) [ppm] 2500 W (3 Sigma) [ppm]
Mg 0.77 1.00
Al 0.21 0.27
P 0.12 0.19
Cl 0.27 0.35
Ca 0.13 0.16
Ti 0.09 0.12
Cr 0.10 0.13
Fe 0.06 0.08

 

Precision tests are shown at 4200 W on a polymer sample for trace elements. The analysis was performed by running the sample for ten consecutive investigations with a counting time of 20 seconds per element. Tables 2 and 3 summarize the results.

Table 2. Repeatability for trace analysis in polymers. Source: Thermo Fisher Scientific - Elemental Analyzers and Phase Analyzers

Run Al [ppm] Ca [ppm] Ce [ppm]
1 71.3 104.4 24.2
2 72.0 104.2 24.0
3 71.6 104.1 23.0
4 71.5 105.1 23.5
5 72.5 104.9 23.2
6 73.5 105.2 23.7
7 72.7 105.6 23.6
8 73.4 105.8 22.4
Avg. 72.3 104.9 23.5
SD 1.4 1.0 1.3

 

Table 3. Repeatability for trace analysis in polymers (4200 W). Source: Thermo Fisher Scientific - Elemental Analyzers and Phase Analyzers

Run Fe [ppm] Mg [ppm] Ti [ppm] P [ppm]
1 11.4 60.1 2.1 15.6
2 11.6 59.9 2.0 15.6
3 11.6 60.8 2.0 15.6
4 11.4 60.6 2.1 15.7
5 11.6 61.3 2.0 15.6
6 11.4 61.5 2.0 15.9
7 11.6 61.7 2.2 16.1
8 11.6 60.5 2.1 16.2
Avg. 11.5 60.8 2.0 15.8
SD 0.1 0.28 0.1 0.4

 

Conclusion

High sensitivity and accuracy are required for the analysis of these elements at low concentration levels. As the results show, the ARL PERFORM'X series is ideal for obtaining high-precision results for the detection of Mg, Al, P, Cl, Fe, Ca and Ti in polymer samples.

Though other elements were not present in the standard samples used for this test, they could have been equally identified. The ARL PERFORM'X spectrometers can operate at 2500 W without requiring external water cooling, thanks to their optimum power management. Neither a water cooler nor tap water is required in these cases.

Finally, thanks to intelligent management of the X-Ray tube power at higher power levels (4.2 kW), energy savings and reduced stress on the X-Ray tube are achieved. The state-of-the-art OXSAS analytical software under Windows 7 also offers detailed functions and simplified use.

This information has been sourced, reviewed and adapted from materials provided by Thermo Fisher Scientific - Elemental Analyzers and Phase Analyzers.

For more information on this source, please visit Thermo Fisher Scientific - Elemental Analyzers and Phase Analyzers.

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