The Pb in the filters was analyzed by graphite
furnace absorption spectrometry, using the procedure
described by Manes et al. (1991).
Filters were introduced in Pyrex tubes (40 ml)
fitted with a Teflon-lined screw stopper. Determinations
were carried out with a Perkin-Elmer
Atomic Absorption Spectrophotometer (Model
2380), equipped with a deuterium lamp for background
correction, a Perkin-Elmer HGA400
graphite furnace and an Intensitron lead hollow
cathode lamp. Argon was used as the purge gas.
The wavelength used was 283.3 nm. The furnace
programme settings are given in Table 1. Injected
volume was 10 ~1 and integration time 5 s. The
data obtained were corrected by blank values,
which were usually very low. All the samples were
analyzed three times.