Portable XRF analyzer for low atomic number elements

A portable XRF analyzer includes a pressure measurement device disposed to measure the ambient air pressure and a processing subsystem responsive to a detector subsystem and the pressure measurement device. The processing subsystem is configured to calculate the concentration of at least one low atomic number element in the sample based on the intensity of the x-rays detected by the detector subsystem at an energy level corresponding to the element. The intensity value is corrected based on the ambient air pressure. An XRF method is also disclosed wherein the concentration of an element is determined automatically by taking into account the barometric pressure.