Comparison of ICP-OES and XRF Performance for Pb and As Analysis in Environmental Soil Samples from Chihuahua City, Mexico

Lead (Pb) and arsenic (As) levels on PM10 were measured for indoor and outdoor atmospheres and soil samples in Chihuahua City (Chihuahua, Mexico). The concentration of both Pb and As in the soil samples was determined and compared using two instrumental techniques, Inductively coupled-plasma optical emission spectroscopy (ICP-OES) and X-ray fluorescence (XRF). Statistical analyses were performed to determine if significant differences existed between the instrumental techniques, which included F-test for variances evaluation and t-test for mean comparison. The statistical analysis demonstrated that no statistically significant differences were observed for the As concentrations; however, for the Pb concentrations, significant differences did exist between the instrumental techniques. In addition, two microwave assisted digestion techniques were also tested to determine if the difference in the Pb concentrations were due to the extraction technique rather than instrumental method. The first digestion technique used nitric acid (HNO3), which commonly is used for the extraction of soluble materials within a sample. The second digestion technique used a 1:4 mixture (1 part of concentrated HNO3: 4 parts of concentrated HCl) which generally extracts more refractory elements but destroys more of the sample matrix than HNO3. Similar statistical tests (F-test and t-test) were applied to the data from both digestion types, which showed no significant difference between the extraction techniques.