Sample thickness considerations for quantitative X-ray fluorescence analysis of the soft and skeletal tissues of the human body - theoretical evaluation and experimental validation

摘要

A good estimation of the matrix composition and the areal mass of the sample is critical for quantitative X-ray fluorescence (XRF) analysis. Integrated aspects of the XRF quantitative analysis of various human body organs are presented. Special emphasis is placed on the determination of the sample thicknesses at which the specimen can be regarded as thin, thick, or intermediate thickness depending on the element under consideration. Moreover, a method for a fully quantitative analysis allowing the determination of the masses per unit area of chemical elements in thin, thick, and intermediate thickness samples is discussed. It was found that for an incident beam of 17keV energy, a 15 μm thick sample is of intermediate thickness for all elements between P and Ca and becomes thin from Fe for most human body tissues in a natural form. Dried samples of soft tissues excluding these of low water content can be regarded as thin for all elements from phosphorus to strontium. The use of thin sample approach in quantification of intermediate thickness specimen may result in about 30-45% discrepancy in areal mass (weight fraction) of phosphorus, 20-35% of sulfur, 15-25% of chlorine, 8-15% of potassium, and 5-10% of calcium. Theoretical evaluations presented in the work are verified experimentally. The analysis of human brain samples (white and gray matter) and bovine liver (National Institute of Standards and Technology standard reference materials 1577b) confirms high accuracy of the XRF quantification on the basis of the described procedures.