Three procedural steps are required prior to analysis. First, a spectral scan helps to set various calibration parameters. Next build the calibration. Almost all of the time the instrument is in use, it is dedicated to analyzing production samples. Typically, spectral scans are performed on representative standards to identify the occurrence of elemental peaks of interest in the spectrum, as shown in Figure 11.1.
Figure 11.1 Spectral scan of silicone coating on supercalendered kraft paper
Table 11.1 Typical Results for Silicone Calibration on Paper
Scanning is a qualitative tool and will reveal the presence of any potential interface elements. For example, a Fe-55 source will excite elements on the following periodic scales: aluminum to vanadium and zirconium to cerium. With the right combination of sources, it is theoretically possible to measure from aluminum to uranium. Calibration can be established once any interference has been identified through spectral scanning. Prepare samples by cutting discs and placing them on nickel-plated paper holders. The holder ensures that the sample remains as flat as possible, as uneven surfaces introduce reproducibility errors, caused by scattering and voids at the incident surface. Table 11.1 gives typical calibrations for silicon coating weights.
Once the calibration is established, select two samples that support the operating range of the sample being tested. These samples will be used to correct for changes in instrument performance over time. The measurement of both standards and the background correction of uncoated samples is a push-button procedure. Terminology restandardization is performed once per shift. Analysis can then be performed: the operator simply cuts the sample to be analyzed, inserts it into the instrument, and begins the measurement. Within 23 minutes, the instrument will determine the concentration of the element of interest and print and display the results.
