In FPXRF analysis, the standard deviation (SD) from the counting statistics of an individual measurement is defined as the square root of the gross counts for the target analyte peak. On the data printout from most FPXRF instruments, the SD of the measurement will be given. Most manufacturers state that, if the measured value is less than three times its counting statistics SD, the value should not be reported. It is possible that an analyte measurement would be more than three times its SD, but less than the MDL, calculated from the replicate measurements. It is advisable in such a case to code the data "J" as estimated. |