An Overview of Basic Principles of Analytical Methods - Field Sampling: Principles and Practices in Environmental Analysis - page 260

and are called thermograms. Each point of change in the thermograph corresponds to a
particular reaction of the sample; therefore the thermograph can be unique for a particular
sample and thus used as a form of identification.
Anything done to a sample—during sampling in the field, transportation, or storage—
that affects potentially volatile components can change the sample, leading to
misidentification (e.g., leaving a sample in a sun-heated vehicle could lead to the loss of
organic compounds, which could lead to this type of error when a thermal analysis is
carried out) [5].
10.7.2. Titrimetry
In titrimetry, compounds or groups of compounds are quantified by measuring the
volume of a reagent solution of known concentration—termed the titrimetric solution or
titrant—that is required for a defined, complete chemical conversion of the compounds to
be determined. Titrant is added until an end point is indicated, and the whole procedure is
termed a titration. Chemical conditions required for a titrimetric determination are a
defined course of the reaction between the sample and the titrant and the ability to
recognize the equivalence point (the titration end point). The type of titration is specified
on the basis of the type of reaction occurring [e.g., acidmetry (titrations with acids),
alkalimetry (titration with bases), redox titration (transfer of electrons), precipitation
titrations (also a form of gravimetry), and complexometric titrations, which are the
formation of complexes between the sample and the titrant]. End points are found by a
change in an indicator, usually a color change; by measuring pH or changes in pH using a
pH meter; or by measuring some other electrical characteristic of the solution being
titrated.
10.7.3. Instrumental
As the name implies, instrumental methods require special analytical instrumentation
techniques and knowledge beyond the use of balances, burettes, and other glassware.
Instrumental analysis consists of a number of steps in two phases: the extraction or
sample preparation phase and the analytical or quantitative phase, which is where the
sample extract is characterized. The last step is to relate these results back to the original
sample and field.
Instrumental methods can be divided into three main groups based on the principle
involved. The first group is based on the emission or absorption of electromagnetic
radiation (light). Interactions among atoms, molecules, ions, and electromagnetic fields
and radiation are used to produce analytical data. These methods are often grouped
together as either atomic or molecular spectroscopy, both of which can be either emission
or absorption in nature. Atomic spectrometric methods, used for analyzing metals,
include atomic absorption spectrometry (AA), atomic emission spectrometry, flame
emission photometry, and X-ray fluorescence. Molecular spectroscopic methods, used
mostly for organic compounds, include ultraviolet and visible (UV-Vis), infrared (IR),
mass (MS), and nuclear magnetic resonance spectrometry (NMR). Mass spectrometry is
most often used in combination with a separation method, such as gas chromatography