Environmental Engineering Reference
In-Depth Information
components with a very high sensitivity (it is possible to detect ppm and even ppb)
and needs a very small amount of matter (around 1 mg). Unfortunately, the stone
must be put into a solution; this is therefore a destructive technique. The samples
cannot be re-used for other analyses.
All chromatography methods rely on the principle of differential displacement of
the components of a mobile phase in an immobile one. They differ by: the substrate
where the separation occurs (column or plate), the nature of stationary (solid or
liquid) and mobile phases (liquid or gaseous), and the mechanism of separation
(gravity, pressure, adsorption, ion exchange, etc. [CER 96]). Adapted detectors put
at the exit of the column or plate create a chromatogram that allows qualitative and
quantitative analyses of the mixture [ROU 92].
In this kind of analysis, we usually aim to very accurately quantify one
component rather than detecting all of them. It is therefore suitable to select the
detector that is the most adapted to the detection of these component [CER 96, ROU
92].
Within the numerous chromatography methods used, the main ones are high-
performance liquid chromatography (which covers almost all applications of
gaseous chromatography) and ionic chromatography, which allows us to separate
ions in solution whatever they are inorganic or organic. Ionic chromatography
provides a good match to quantification of the salts forming cations and anions in
stones and rain waters (Na
+
, K
+
, Ca
2+
, Mg
2+
, NH
4+
, Cl
-
, SO
3-
, NO
3-
, CO
3-
, etc.) [FAS
93a, KLE 96, MIL 93, MOR 93] and in the treatment products used in former
restorations [REI 96]. Liquid chromatography will mainly be used to characterize
historical organic treatments and sometimes the biological colonization of stones.
10.1.1.6
. Spectroscopic analyses
These methods are based on interaction mechanisms between electromagnetic
radiation and matter. Absorption and diffusion of radiation by matter is typical of the
elements that constitute it. In the same way, excited matter (due to irradiation, a flux
of particles or increase in temperature) emits rays that are characteristic of its
compounds.
Emitted spectra are different whether they result from interaction of the ray with
atoms, molecules, groups of molecules or ions. These spectra are due to
modifications of the energy states of atoms, molecules and ions between a
fundamental state of lower energy and excited states. Allowed energetic states have
a discontinuous distribution. They are typical for each atom and accurately known
by quantum physics.
