The Chairman of Princeton Testing Laboratory, Bill Pickup, developed the first commercially available solder analysis program in 1967. At that time the technique used for determining impurity levels  was emission spectroscopy and Bill was co-author of the ASTM method. We still have the capability of emission spectroscopy and use it when required. However the Direct Reading Spectrograph takes care of impurities very efficiently and permits us to give even faster service. many times results are available the day following receipt of sample and always within two to three days. 

Tin is always done by iodimetric titration following ASTM:E-46.