F. Desantis et al., DEVELOPMENT OF A PASSIVE SAMPLING TECHNIQUE FOR THE DETERMINATION OF NITROGEN-DIOXIDE AND SULFUR-DIOXIDE IN AMBIENT AIR, Analytica chimica acta, 346(1), 1997, pp. 127-134
Since conventional badge-type samplers depend entirely on an empirical
calibration against gas mixtures and use of the constant determined f
or calculations, a system based on the use of two badge-type passive s
amplers of different lengths has been studied for the determination of
NO2 or SO2. The samplers make use of a filter membrane barrier to dam
p out eddy motions and promote molecular diffusion from the ambient ai
r to the trapping medium. The badges have a large ratio of cross-secti
onal area to length of diffusion in order to increase sensitivity. Dif
fusion theory applied to this configuration shows that the concentrati
on results are independent of wind-flow velocity. The samplers have be
en evaluated at different levels of relative humidity ranging from 0%
to 90%. Batches of samplers were exposed for 48 h side-by-side with sa
mplers exposed for consecutive periods of 24 h over the same interval.
The results, expressed as a ratio (R) between the 48 h and the consec
utive 24 h periods showed that the analytes collected (nitrite and sul
phate) are stable (R=0.98+/-0.05 for nitrite and R=1.08+/-0.09 for sul
phate). The detection limit attained (5 ppb of NO2 and 10 ppb of SO2 f
or a 24 h sampling) is adequate for the determination in urban and rur
al areas. The accuracy of the proposed method, expressed as percent re
lative error, when compared to a standard denuder technique for NO2 an
d SO2, was found to be better than about +/-10% with coefficient of va
riation of 5.5% and 6.5%, respectively.