Page 282 - Modern Analytical Chemistry

1400-CH08 9/9/99 2:18 PM Page 265

Chapter 8 Gravimetric Methods of Analysis 265

EXAMPLE 8.8
A 200.0-mL sample of water was filtered through a preweighed glass fiber filter.
After drying to constant weight at 105 °C, the filter was found to have increased
in mass by 48.2 mg. Determine the total suspended solids for the sample in
parts per million.
SOLUTION
Parts per million is the same as milligrams of analyte per liter of solution; thus,
the total suspended solids for the sample is
48 2. mg
= 241 ppm
0.2000 L

8D.3 Evaluating Particulate Gravimetry
The scale of operation and detection limit for particulate gravimetry can be ex-
tended beyond that of other gravimetric methods by increasing the size of the
sample taken for analysis. This is usually impossible for other gravimetric meth-
ods because of the difficulty of manipulating a larger sample through the indi-
vidual steps of the analysis. With particulate gravimetry, however, the part of
the sample that is not analyte is removed when filtering or extracting. Conse-
quently, particulate gravimetry is easily extended to the analysis of trace-level
analytes.
Except for methods relying on a quartz crystal microbalance, particulate
gravimetry uses the same balances as other gravimetric methods and is capable
of achieving similar levels of accuracy and precision. Since particulate gravime-
try is defined in terms of the mass of the particle itself, the sensitivity of the
analysis is given by the balance’s sensitivity. Selectivity, on the other hand, is de-
termined by either the filter’s pore size or the properties of the extracting phase.
Particulate gravimetric methods based on filtration are generally less time-,
labor-, and capital-intensive than other gravimetric methods since they require
only a filtration step.

8E KEY TERMS

adsorbate (p. 239) inclusion (p. 238) relative supersaturation (p. 241)
coagulation (p. 242) occlusion (p. 239) supernatant (p. 244)
digestion (p. 239) particulate gravimetry (p. 234) thermogram (p. 256)
electrogravimetry (p. 234) peptization (p. 245) thermogravimetry (p. 255)
gravimetry (p. 233) precipitant (p. 235) volatilization gravimetry (p. 234)
homogeneous precipitation (p. 241) precipitation gravimetry (p. 234)