Detection of Nickel, Copper and Lead in Food Using Portable XRF

Introduction:  Heavy metal contamination of food is a significant health concern across the world, particularly in developing nations. To allow for testing in regions where traditional laboratory analysis is expensive, time consuming or unavailable, a simple, inexpensive, and portable method is needed for the rapid onsite analysis of food to prevent chronic and acute heavy metal poisoning.

Purpose:  The purpose of this research was to evaluate a portable X-ray fluorescence (XRF) analyzer for the analysis of nickel, copper, and lead in food, and to develop simple sample preparation procedures and test methodologies that yield reliable results.

Methods:  Samples were prepared using two methods. First, samples of lettuce, strawberry, and ground chicken were homogenized in a stomacher and spiked with known concentrations of the analytes. Using this procedure, concentrations of 0 to 90 ppm were tested. In the second procedure the samples were stomached, oven dried at 90°C and then crushed. The second procedure was used to concentrate the analyte to increase sensitivity.

Results:  Lettuce, strawberry, and chicken samples prepared by stomaching exhibited detection limits of 20 ppm for nickel and copper and five ppm for lead. Regression plots of predicted concentration versus actual concentration had R² values ranging from 0.9449 to 0.9982. The samples prepared by drying and crushing had detection limits for lead of 0.5, 1, and 1 ppm for lettuce, strawberry, and chicken, respectively.

Significance:  The results demonstrated that the XRF has the potential to predict heavy metal concentrations in the low ppm level, by stomaching. Additionally, drying and crushing of samples facilitates the detection of high ppb heavy metal concentrations in media with high water content.