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ANALYTICAL CHEMISTRY, VOL. 51, NO. 2, FEBRUARY 1979
Exchange of Comments: Particle Size Effects in the Determination of Respirable &-Quartz by X-ray Diffraction Sir. Edmonds, Henslee, and Guerra ( I ) appear to have misinterpreted their experimental results relating t o orientation. T h e authors appear t o assume (Discussion, Orientation) t h a t t h e relative intensity of diffraction lines of a randomly oriented phase will be the same for both bulk and thin-layer preparations. This is not a valid assumption, I feel. Whereas the intensity of a diffraction line for an “infinitely” thick sample is independent of B,J and directly proportional t o the quantitation constant of the diffraction line k i J , the intensity/ weight of a thin-layer sample (relatively free of absorption effects) is proportional to k,,,-cosec H,, (2. 3 ) . For a diffractometer with a 8 compensating slit, both statements would need t o include another BIJ term but, considering bulk sample relative to thin-layer, the previous sentence would remain valid. Thus, from the authors‘ Table 111, if t h e determined relative intensities of a bulk sample of randomly oriented Minusil 15 was 100:101:110:112 = 15:100:9:1i, then t h e expected relative intensities for the same randomly oriented sample as a thin-layer would be 19:100:7:9. This is reasonably close to what the authors found in their Table I11 for air filtered Minusil 15 as a thin-layer. My laboratory is active in the field of quantitative thin-layer X-ray powder diffractometry. In such work, diffraction intensity is assessed by integrated peak area, a constant divergence slit is used, and standards are prepared by filtration Table I.
of respirable dust (
