This new apparatus (International patent Caprai-CNR pending no. PCT/IB2005/001568)
for use in the analysis of gas mixtures can be fitted on one or more gas
chromatographers working in parallel or at different times, and used to adjust the
internal pressure of the gas to the value most convenient for introducing the
sample into the analyzer. It can also be used for only one or two points of
calibration of a pure gas standard (no preparation of a particular external
standard is necessary). No detector overloading of any kind will occur.
It can be applied to any kind of gas analysis, but is particularly suited to
environmental and geochemical investigations.
1. Where a number of runs are required, there is no need to take different
samples of gas from the flask.
2. We have a continual knowledge of the internal pressure of the flasks.
3. We achieve similar conditions for standards and samples.
4. We simplify the standardization procedure.
5. We can increase pressure so as to introduce more absolute small quantities
of a given component.
The advantages of this system include:
1. Analytical error is minimized because pressure is completely under control.
2. One quantity of sample only can be analyzed several times in different gas
3. The pressure inside the flasks is legible.
4. Both sample and standard can be introduced at the same pressure.
5. Excellent standardization can be achieved with two calibration points.
6. Errors in preparation of standards can be avoided.
7. The pressure of low-pressure samples can be increased.
Application at Pozzuoli Solfatara
Caprai A., Calvi E., Doveri M., Leone G. and Mussi M.
In 2001, a team from the Institute of Geosciences and Earth Resources working in
the Phlegrean Fields area began a new survey consisting of the systematic sampling
of the fluids emerging from the Pozzuoli Solfatara, and particularly from the
fumarole known as Bocca Grande; the same team had carried out a similar survey from
1982 to 1985, while Cioni (CNR-IGG) and his co-workers monitored the same
parameters in the area from 1982 to1997 and Martini (Università di Firenze – DST)
from 1994 to 2000. The results of chemical analyses of the most reactive gases,
such as H2, CH4, and H2S, from 2001 until now, have revealed a trend that is shown
in the triangular diagram. The main feature of this trend is the temporal evolution
of the chemical composition of the above gases in Pozzuoli Solfatara during the
period 2001-2005, which indicates a gradual return to the same compositions
measured during the period 1983-1985, with a significant increase in bradyseism.
The chemical composition of these gases reached values very similar to the current
values in coincidence with the maximum displacement of bradyseism recorded at the
end of 1984.
A similar trend in gas chemical composition can also be observed for the period
1989-1997 and 1998-2000. Comparison of triangular diagrams H2, CH4, H2S with the
plot of altitude variations available up to 2003 reveals a correspondence between
the evolution of relative gas concentrations and the trend of bradyseism. On the
basis of the data available, we can observe a typical trend characterized by a
relative increase of H2S and decrease of CH4 during the phase of changing tendency
in bradyseism . These observations should be verified by a careful comparison with
renewed measurements of ground movement.
Further evidence of an apparent correspondence between temporal evolution of gas
chemical composition and the trend in bradyseism would confirm the important role
of geochemical monitoring of these parameters in the prediction of bradyseismic