Table 2. Comparison of results from one particular experiment (Roter et al., 2026 ▸) (with from Section 3.5) against calculated values for mass concentrations and detected number of fluorescent photons per pixel, along with the number of incident photons  per pixel. As noted in Section 3.5, we did not have a direct measure of the air gap distance d_g of equation (21); therefore, we show the ratio of experimental to theoretical incident photons for the sample d_sdp = 0.98 cm from the detector plane, as well as for a revised value of d_sdp = 4.5 cm (see Section S4 of the supporting information).

Element	(µg cm−2)	(photons per pixel)	[equation (8)] (photons per pixel) (dsdp = 0.98 cm)(dg = 0.58 cm)	(dsdp = 0.98 cm) (dg = 0.58 cm)	(dsdp = 4.5 cm) (dg = 4.1 cm)
P	9.893	3.64	2.9 × 106	132.5	1.44
S	1.853	5.08	1.1 × 107	35.0	0.79
Ca	0.073	3.54	3.5 × 107	10.9	0.70
Fe	0.025	4.11	2.9 × 107	13.2	1.18
Ni	0.010	2.83	3.4 × 107	11.5	1.05