Page:NIOSH Manual of Analytical Methods - 7505.pdf/6

LEAD SULFIDE: METHOD 7505, Issue 2, dated 15 August 1994-Page 6 of 7 METHOD WRITTEN BY:

J. Palassis, NIOSH/DTMD, M. T. Abell, D. D. Dollberg, Ph.D. and M. Hawkins, NIOSH/DPSE.

APPENDIX:

INTERFERENCES

If interferences are present, use a different lead sulfide peak. Lead oxide (PbO yellow-form), lead sulfate (anglesite) and copper iron sulfide (CuFeS 2chalcopyrite) interfere with the primary lead sulfide peak, using copper K α X-ray radiation. Lead oxide (Pb 3O4 orange-form) and lead sulfate (anglesite) also interfere with the secondary lead sulfide peak. The oxides of lead do not occur naturally in appreciable amounts in galena mining but are formed when lead sulfide is heated at high temperatures (i.e., in smelting and roasting operations) [7]. Dolomite, zinc sulfide (ZnS sphalerite) and chalcopyrite that are normally found in galena mining do not interfere with the secondary lead sulfide peak; for this reason the secondary lead sulfide peak was chosen as the analytical peak. The tertiary lead sulfide peak interferes with the secondary silver peak.

When peak overlaps are not severe, a smaller receiving slit or chromium X-radiation may be used; however, a new calibration curve will be necessary.

The presence of some elements in the sample (iron, in particular) can result in appreciable X-ray fluorescence, leading to increased background intensity. This can be minimized by a diffracted beam monochromator.

The interfering effects of X-ray absorption by the sample result in attenuation of the diffracted beam and correction must be made (step 12 and Table 1). NIOSH Manual of Analytical Methods (NMAM), Fourth Edition, 8/15/94