#(i)# #"AAS is sensitive......."# And in fact AAS is good at #"ppm"# levels, that's #"parts per million"#, i.e. #mg*L^-1#.
#(ii)# #"AAS is atom specific......."# Given appropriate sample preparation, AAS may be made PARTICULAR to a particular element.
#(iii)# #"AAS is fairly routine......."# There are vast data on sample preparation and measurement. Given a required analysis it is fairly easy to develop an experimental protocol - and these are developed in house by the operator (as of course they should be).
Note that as in all analysis, a calibration curve is usually the first assignment. That is we analyze the response of known concentrations of analyte, and a calibration curve is constructed, which is linear to a first approx. The unknown sample is then matched to the curve.