Hi,

could anyone told me how to calculate the LD based on areas ( % in areas)?

It's usually calculated by peak height cause it's easiest to determine noise in terms of height.

However you can determine noise by area by preparing three low concentration samples (from the lowest quarter of the linear range, around presumed LOD and LOQ). Inject each solution six times, calculate mean and SD of areas of each solution and average SD from the individual SD's. Plot calibration graph (mean area vs. concentration) and determine the slope of the graph. Noise would be 'average SD' divided by the slope. Three times noise would be LOD and ten times noise would be LOQ.

Reference: Harry G. Brittain, Validation of analytical methodology; a detailed look at how to assure the quality of your data, Journal of Validation technology, Special edition, analytical method validation.