Calibration curves of the spiked standards were obtained from unweighted least-squares linear regression analysis of the data. The slope and intercept of the calibration graphs were determined through linear regression of the peak areas vs concentration plot. Individual peak areas were then interpolated on the calibration graphs to determine the found (back calculated) concentrations. The quality of fit was determined using back-calculated-to-nominal concentrations and the Fischer test used confirmed the linearity of the method. Within-day (repeatability) and between-day (intermediate precision) and accuracy were determined by carrying out replicate analyses of the spiked leaf calibration standards. Repeatability was determined by preparing and analysing all five spiked leaf standards five times within a single day, and the intermediate precision was determined by carrying out the same operations for five days over a 10-day period. The precision was given by mean relative standard deviation of the back-calculated concentrations, and the accuracy of the method was