Stratos is an evolution of PANalytical’s market-leading thin film metrology software used in the analysis of layered samples. This is achieved by calibrating primarily using bulk standards. By doing so, one reduces the dependence on standards that are layered samples, which can be difficult to obtain or certify. Layered standards can be added to improve the calibration and are referred to as TAGS. Stratos is also able to reference specific TAGS for different sample types to optimize the calibration. Apart from bulk and/or in-type standards Stratos can still be calibrated using certified reference materials for ultimate accuracy. Stratos also makes use of a step-by-step setup guide, called the Virtual Analyst, which simplifies and optimises the application setup. It does this by making use of the best possible measurement conditions for a specific sample type. In the past this has been a manual, time- consuming and tedious process.
An application of the Stratos software solution is the analysis of Pb in paint films. Even though lead is a toxic metal, lead-based paint is used in some countries to paint interiors, toys, furniture, playground equipment and other articles with which children can come into contact. Young children are particularly at risk of ingesting lead through normal hand-to-mouth activity. Therefore the Pb content in paint is limited and needs constant screening. An example of such legislation is ‘The Consumer Product Safety Improvement Act of 2008’ in the United States.
This study demonstrates the powerful capabilities of the Epsilon 4 benchtop EDXRF spectrometer - combined with the Stratos software module for determining the mass per unit area of Pb content in paint films using only one bulk standard instead of costly in-type standards.
Instrumentation and measurement conditions
The measurements were performed using an Epsilon 4 EDXRF spectrometer, equipped with a 10 W, 50 kV silver anode X-ray tube, 6 filters, a helium purge facility, a high-resolution SDD silicon drift detector, a spinner and a 10-position removable sample changer. Samples were analyzed using one measurement condition (Table 1). The total measurement time per sample was only 2 minutes.
Table 1. Measurement condition used for the analysis of Pb content in paint
Calibration using Stratos
For this study, only one bulk sample - one of PANalytical’s Omnian setup standards - was used to set up a calibration for Pb. In order to quantify the mass per unit area of Pb in paint, the Pb Lα fluorescent line was used as proposed by the Virtual Analyst.
Sample description and preparation
Three NIST lead in paint CRM standards were measured as unknown samples for validating the method. The samples are Pb-containing paint films on a polyester supporting sheet. With the large sample mode in the Epsilon software, these samples can be analyzed directly without any additional sample preparation, or they can be cut into smaller pieces to fit into a standard Epsilon 4 sample holder with a diameter of 42 mm. For this study the samples were cut into small pieces and placed into a standard sample holder.
Results and discussion
Figure 1 shows spectra obtained for two standards containing different amounts of Pb. Table 2 presents the Stratos results obtained for the three NIST samples in comparison with the certified values. Data for these samples fell within the 2 standard deviations of the certified uncertainty, indicating excellent agreement, without the need for Pb in paint layered calibration standards.
In order to evaluate the repeatability of this method, sample ‘SRM 2569 Level 2’ was measured 10 times consecutively. Figure 2 shows these ten single measurements of Pb content (in mass per unit area) with the mean value and standard deviation illustrating the very good repeatability of the method. Furthermore, the repeatability is more than 5 times lower than the uncertainty of the certified concentration of the NIST standard, confirming the excellent instrument performance.
Figure 1. Spectra obtained for SRM 2569 Level 2 (blue color) and SRM 2569 Level 3 (purple)
Figure 2. Results of 10 repeated measurements for sample SRM 2569 Level 2
Table 2. Analysis results for the mass of Pb per unit area
This application note demonstrates that Epsilon 4 in combination with the Stratos software module is capable of performing accurate analysis of Pb in paint films. This was achieved in just 2 minutes and calibrated using only one bulk standard.