Limitations of ZAF Correction Factors in the Determination of Calcium/Phosphorus Ratios: Important Forensic Science Considerations Relevant to the Analysis of Bone Fragments Using Scanning Electron Microscopy and Energy-Dispersive X-Ray Microanalysis
Payne, CM
Research professor, Department of Pathology, College of Medicine, University of Arizona,Tucson, AZ.

Cromey, DW
Senior medical technologist, Electron Microscopy Laboratory, University Medical Center, Universityof Arizona, Tucson, AZ.


Abstract
A series of calcium phosphate standards having calcium/phosphorus (Ca/P) molar ratios of 0.50, 1.00, 1.34, 1.50, and 1.67, respectively, was prepared for bulk specimen analysis using scanning electron microscopy (SEM) and energy-dispersive X-ray microanalysis (EDXA). The standards were mounted on carbon planchettes as either pure crystals or crystals embedded in epoxy resin. Ten different samples of each embedded and non-embedded standard were analyzed in a JEOL 100 CX electron microscope interfaced with a Kevex 8000 EDXA system using a lithium-drifted silicon detector and a multichannel analyzer. The Ca/P ratios were determined by calculating both net peak intensities without matrix corrections and atomic k-ratios using the MAGIC V computer program with ZAP correction factors for quantitative analysis. There was such extensive absorption of phosphorus X-rays in standards embedded in an epoxy matrix that the observed Ca/P ratio were statistically compatible with four different standards ranging in theoretical Ca/P ratios from 1.0 to 1.67. Although the non-embedded crystals showed a greater separation in the Ca/P ratios, both methods of preparation produced serious flaws in analysis. Direct application of the discovery of this caveat to the identification of suspected bone fragments for forensic science purposes is discussed.

Keywords:
forensic science, microscopy, X-ray analysis

Paper ID: JFS353900560

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Author Payne CM, Cromey DW Title Limitations of ZAF Correction Factors in the Determination of Calcium/Phosphorus Ratios: Important Forensic Science Considerations Relevant to the Analysis of Bone Fragments Using Scanning Electron Microscopy and Energy-Dispersive X-Ray Microanalysis Symposium , Committee on