Besides being blended with a powdered sample, binders can also be used in unblended form as a sample support. A typical XRF disc made with a SPEX SamplePrep Sleeve-and-Plunger Set consists of a thin layer of powder supported by a binder matrix. Since most of the X-ray fluorescence emission measured by an XRF spectrometer comes from within a few microns of the surface, the technique is successful with small quantities of sample, often a gram or less. Other advantages are that the disc is quite strong and stable without a Spec-Cap, is easy to remove from the die, and will not scratch the bore of the die. The sample is also presented to the spectrometer in nearly undiluted form, as the binder penetrates the pore space between particles rather than separating them. (Binders have a much lower specific gravity than most sample materials. Even though samples are typically blended with 10% binder by weight, the disc may have a much higher proportion of binder by volume, diluting the sample and diminishing its XRF emissions.)

When SPEX SamplePrep Sleeve-and-Plunger Set is used to make XRF sample discs, this is the technique. First the barrel and base are assembled, and the lower polished pellet placed in the bore of the die. Then the sleeve is inserted in the bore. The sample is poured onto that part of the polished pellet left exposed, and the plunger inserted in the sleeve to even out the sample powder and tamp it down. Now the plunger is carefully withdrawn followed by the sleeve. This leaves a thin layer of formed sample in the die, onto and around which the binder is poured. Finally the upper polished pellet is inserted in the bore, followed by the die plunger, and the assembled die is transferred to the press and put through a pressing cycle. The finished disc consists of solid binder with a uniform sample layer “bull’s-eye” in the target area of the disc.

Sleeve-and-Plunger Sets are available for SPEX SamplePrep 31 mm, 35 mm, and 40 mm size dies.