98
Exercise 7
sample is dried because variable occlusion of water in different minerals and the
volatilization of certain organic compounds can occur at relatively low temperatures
(American Public Health Association et al. 1989). Generally 105°C or 180°C is used to
dry the samples.
Procedures
1. Combust porcelain evaporating dishes of 150- to 200-ml capacity in a furnace at
550°C for 1 h. Cool and obtain an accurate tare weight.
2. Filter samples of water through glass fiber filters (Whatman GFIF, 0.6- to 0.7-llm
pore size).
3. Measure a volume of the sample filtrate, sufficient to yield between 100 and 250 mg
of residues, into the tared evaporating dishes.
4. Dry the samples to a constant weight at either 105°C or 180°C. While still warm,
place the dishes into a desiccator to cool.
5. Weigh the samples as soon as they have cooled on an analytical balance accurate to
at least 0.5 mg.
6. Report data as total "dissolved" residue on drying at ~_oC in mgjl to the nearest
whole mg:
T 1 "d' 1 d"
'd ( II) (mg filterable residue)(lOOO)
ota
ISS0 ve reSl ue mg =
1
1
m samp e
7. Repeat the analyses on unfiltered samples. Compare these values for total residues
with the results of total dissolved residues from the filtered samples.
AUTOMATED ANALYSES
Many of the standard procedures discussed above have been adapted for automated
analysis. In some cases new methods have been developed to facilitate automation.
Here some of the more common approaches to automated analyses will be described
briefly. The instruments required for these analyses are very expensive but, if available,
would allow samples to be analyzed more rapidly and would reduce random errors
associated with contamination, measurement of volumes, and reaction times.
Atomic Absorption and Flame Emission Spectroscopy
Flame Emission Spectroscopy. When a metal atom is subjected to a source of energy
such as a flame, electrons in orbit about the nucleus are raised to a higher energy level.
As the electron returns to its former conditions, energy is given off in the form oflight at
a specific wavelength.
To analyze for a particular metal in solution using this method, the solution is
aspirated into a high temperature flame. The energy of the flame raises some of the
metal atoms to the excited condition; on their return to the ground (neutral) state, the
light emitted is resolved by a monochromator and isolated at a specific wavelength. The
increase in intensity at this specific wavelength is proportional to the original
concentration of metal ion in solution.
Atomic Absorption Spectroscopy. Atomic absorption spectroscopy is an extremely
sensitive method for the analysis of metals in solution, based on the capability of atoms
Exercise 7
sample is dried because variable occlusion of water in different minerals and the
volatilization of certain organic compounds can occur at relatively low temperatures
(American Public Health Association et al. 1989). Generally 105°C or 180°C is used to
dry the samples.
Procedures
1. Combust porcelain evaporating dishes of 150- to 200-ml capacity in a furnace at
550°C for 1 h. Cool and obtain an accurate tare weight.
2. Filter samples of water through glass fiber filters (Whatman GFIF, 0.6- to 0.7-llm
pore size).
3. Measure a volume of the sample filtrate, sufficient to yield between 100 and 250 mg
of residues, into the tared evaporating dishes.
4. Dry the samples to a constant weight at either 105°C or 180°C. While still warm,
place the dishes into a desiccator to cool.
5. Weigh the samples as soon as they have cooled on an analytical balance accurate to
at least 0.5 mg.
6. Report data as total "dissolved" residue on drying at ~_oC in mgjl to the nearest
whole mg:
T 1 "d' 1 d"
'd ( II) (mg filterable residue)(lOOO)
ota
ISS0 ve reSl ue mg =
1
1
m samp e
7. Repeat the analyses on unfiltered samples. Compare these values for total residues
with the results of total dissolved residues from the filtered samples.
AUTOMATED ANALYSES
Many of the standard procedures discussed above have been adapted for automated
analysis. In some cases new methods have been developed to facilitate automation.
Here some of the more common approaches to automated analyses will be described
briefly. The instruments required for these analyses are very expensive but, if available,
would allow samples to be analyzed more rapidly and would reduce random errors
associated with contamination, measurement of volumes, and reaction times.
Atomic Absorption and Flame Emission Spectroscopy
Flame Emission Spectroscopy. When a metal atom is subjected to a source of energy
such as a flame, electrons in orbit about the nucleus are raised to a higher energy level.
As the electron returns to its former conditions, energy is given off in the form oflight at
a specific wavelength.
To analyze for a particular metal in solution using this method, the solution is
aspirated into a high temperature flame. The energy of the flame raises some of the
metal atoms to the excited condition; on their return to the ground (neutral) state, the
light emitted is resolved by a monochromator and isolated at a specific wavelength. The
increase in intensity at this specific wavelength is proportional to the original
concentration of metal ion in solution.
Atomic Absorption Spectroscopy. Atomic absorption spectroscopy is an extremely
sensitive method for the analysis of metals in solution, based on the capability of atoms