Abstract: A method of calibrating an analytical instrument, for example an atomic absorption spectrophotometer, comprises measuring the absorbance of a plurality of standards of known concentration (100) and plotting the measured absorbance against concentration (101). A straight line is fitted to the plotted points (102) and a quality co-efficient calculated (103). If the quality co-efficient is acceptable (104) the calibration line is used for measurement of samples (105). If not, then the slope of the line joining each point to the origin is determined and if the slopes are random (107) then a robust regression technique is used to fit the calibration line (108). If outliers are then detected (109) it is determined which points are outliers (110) and appropriate action taken, for example to restrict the range if the last point(s) is/are outliers (111).

Abstract: An analytical instrument, for example an atomic absorption spectrophotometer, comprises means for measuring the absorbance of a plurality of standards of known concentration (100) and plotting the measured absorbance against concentration (101). A straight line is fitted to the plotted points (102) and a quality co-efficient calculated (103). If the quality co-efficient is acceptable (104) the calibration line is used for measurement of samples (105). If not, then the slope of the line joining each point to the origin is determined and if the slopes are random (107) then a robust regression technique is used to fit the calibration line (108). If outliers are then detected (109) it is determined which points are outliers (110) and appropriate action taken, for example to restrict the range if the last point(s) is/are outliers (111).