a method and apparatus for determining the concentration of an element in a sample with a fluorescent x - ray qualitative analytical procedure is provided . an x - ray tube radiates a sample with primary x - rays to create fluorescent x - rays from elements in the sample . the computer system can have preset conditions for a measurement of a predetermined concentration amount of an element at a predetermined probability of accuracy . the x - rays coming from the sample are detected , and calculations are performed to determine both the concentration of the element and the predetermined probability of accuracy . these values can be compared automatically with the predetermined values and , when the comparison indicates that the calculated concentration of the element meets the predetermined amount or is greater within the predetermined probability of accuracy , the measurement cycle can be stopped , thereby avoiding unnecessary measurement time .