Appen dix B: Gra vimetric An alysis Proc edure
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71
package.
4.
O-Rings, Nuclepore, Stock No. 490402, 10 per package.
5.
Quick disconnect air line fittings--Foster No. 11-3 male, attached to the
filter holders.
6.
Plastic caps for protecting filters--60 mm ID.
7.
Drain discs--Nuclepore 47 mm Stock No. 231100.
8.
Plastic Sandwich Bags to protect loaded filters.
9.
Petrislides--Millipore Corporation, 47mm, stock no. PD15 047 00.
B.
Filter Handling and Weighing
1.
Set up and calibrate balance as detailed in Section III. Record relative
humidity, temperature, and time in weighing book.
2.
Carefully we igh the first three filters (control filters:
C
1,2,3
)of each new lot
as controls, then set aside in slotted petri dishes. These filters are to be
weighed at the beginning (con trol filter masses:
C
1ca,2ca,3ca
) and end
(control filter masses:
C
1cb,2cb,3cb
) of each weigh ing session for any filters
from the same lo t. The ave rage differe nce betw een their o riginal we ights
and current weights is used to adjust the tare for the group weighed at the
time.
Chang es in the w eight of the control filters o ver time a re most re adily
explained by assuming that water adsorbs on the surface of the filter
substrate. Attached (Figure B.1) is a time plot of the relative humidity of
the filter weighing roo m and the c hanges in w eights of three control filters
(Whatman 47mm QM-A lot #99165, multiplied by 500). The fact that the
changes in filter masses follows the changes in relative humidity is most
evident.
Airmetrics MiniVol Users Guide
72
Airmetrics
Figure B.1.
Relative Humidity Effects on Quartz Filters
