Appen dix B: Gra vimetric An alysis Proc edure
Airmetrics
67
B GRAVIMETRIC ANALYSIS PROCEDURE
Introduction
The low loadings of particulate matter caught on the filter medium by the MiniVol
sampler necessitate special handling and weighing techniques. The preparation of
the filters for sampling and the handling after return from the field have become so
closely geared to the gravimetric operations involved in mass determination that the
procedure is bes t considered as a sin gle topic. Thus the s ections to follow are
divided by variations in samplers or filter types rather than by operation.
Apparatus and Supplies
Listed here are the general equipment and space requirements for filter handling
and mass determination.
1.
Weighing table should be desk height, sturdy and vibration free, with a
smooth, easily-c leaned surface; an d equipped w ith a comfortable c hair,
preferably adjustable in height, with swivel and rollers. This working area
must be in an environment that is away from air currents and experiences
minimal temperature and humidity changes, and is substantially free of dust or
other contaminants.
2.
Micro balance . We us e a Cah n Mo del C-32 Electroba lance w hich has a capaci-
ty of 1.5g, and sensitivity of 0.1µg.
3.
A class S 200 mg weight certified by the State Metrology Lab, and thus
traceable to National Institute for Standards and Technology (NIST), is used as
a primary calibrating standard.
4.
Weight handling forceps with sm ooth plastic tips.
5.
Hygrometer, Abbeon wall mounting dial-type, accurate to ±3%.
6.
Thermometer. Celsius, with resolution to 0.5 degrees and range over normal
room temperatures.
Airmetrics MiniVol Users Guide
68
Airmetrics
7.
Staticmaster ionizing units. One is centered in balance chamber, another
mounted c onveniently on stand near balan ce.
8.
Filter handling forceps and spatula both should be of non-magnetic stainless
steel with rounded edges and smo oth surfaces.
9.
Tackle boxes modified to contain a base platform fitted with quick disconnect
(female) fittings to transport sampling materials.
10. Field data sheets.
11. Petrislides, Millipore®, 47mm.
Filters and supplies for each type of sampling are listed in the appropriate section
to follow.
General Instructions for Microbalance
A. The balance must be turned on and allowed to warm up for a minimum of 30
minutes. Six hours warm up is recommended by the manufacturer for
maxim um stab ility. Since w e use the b alance d aily, it is conv enient to lea ve it
on continuously.
B.
Handle Class S weights with care and store each in its individually-marked
box. They should be handled only with plastic or bone-tipped forceps, since
steel will scratch the surfaces. The forceps should not be used for any other
purpose. Particular care must be exercised to prevent contamination by dirt or
anything which could cause oxidation, since the weights can change
significantly without apparent deterioration.
C.
Adhere to a cleaning schedule. The bench top and working surfaces should be
dusted daily. All equipment and supplies in the working area should be
removed, and they and the chamber interior cleaned weekly at minimum.
NOTE : Do not use freon-type pressure dusters in or around the chamb er.
D. The following procedure is followed to set up the balance for each filter
weighing session:
1.
Set the balance to operate in the 250 mg range. 47mm quartz or Teflon®
