PSII-25 - Use of energy dispersive X-ray fluorescence for determination of indigestible markers in digesta samples

Abstract: Titanium dioxide and chromium ethylenediaminetetraacetic acid are commonly used as indigestible markers for determining passage rates of diets to aid in determination of digestibility. However, commonly used methodology involving acid digestions and utilizing inductively coupled plasma spectroscopy and atomic absorption spectroscopy for both Ti and Cr analysis involves hazardous chemicals, destruction of samples, and low sample throughput. The objective of this experiment was to develop and validate an accurate and precise method for measuring both Ti and Cr using energy dispersive X-ray fluorescence (ED-XRF). Energy dispersive X-ray fluorescence is an analytical technique used for analyzing elements in various sample types. The samples are added to the ED-XRF machine and irradiated with X-rays and the intensity of the X-rays emitted (termed fluorescent X-rays) are used for calculation of the concentration of the element. The method for Ti was constructed using fecal samples from cattle consuming three different diet types (finishing diet, dairy lactation diet, and grazing native range pasture). The Cr method was developed for rumen fluid analysis. To determine accuracy and precision of the method, samples were spiked with various amounts of Ti or Cr and measured for their respective compounds with percent recovery and inter- and intra-assay CV calculated thereafter. Additionally, a regression was performed using PROC REG in SAS 9.4 (SAS Institute Inc., Cary, NC) to determine the relationship between grams of Ti added and grams of Ti recovered for each diet type. The average recovery for Ti across all diet types was 100.3%, and the recovery for Cr in rumen fluid was 95.7%. The average inter – and inter-assay CV for Ti, across all diet types, were 9.70 and 2.16%, respectively. For Cr, the average inter – and inter-assay CV were 5.41 and 8.45%, respectively. Across diet type, the regression for grams of Ti added versus grams of Ti recovered indicated the recovery was not altered by the amount added (P ≤ 0.062). The ED-XRF method requires minimal additional chemicals, is cost-effective, and allows for sample preservation as well as a high throughput of samples. Our results indicate utilization of ED-XRF is an accurate and precise method for determination of Ti in feces and Cr in rumen fluid.