5.2 Quantitation
Outlook
In addition to identification, the process of quantitation is a main task of
analytical work. Here, the principal procedures for chromatographic based
quantitative determination are presented.
Beside identification, the quantitative determination of individual analytes is the
second major issue of analytical work. Identification is mainly based on detection
methods such as mass spectrometry or IR spectroscopy, but for quantitation the
chromatography is the key method. In Organic Geochemistry dominantly GC/MS
and LC/MS analyses are used for quantitation, since the measurement of individual
organic molecules are needed. This is in contrast to most inorganic analyses, where
the determination of the elemental composition is the main task.
A basic precondition for quantitative determination is a defined relation between
the measured signal in a detector and the corresponding amount of analyte. Nearly
all quantitation in Organic Geochemistry are using a linear correlation, hence the
area of linearity of a detector is an important parameter for achieving a wider range
of determinable concentrations or amounts (see Fig. 5.17). These ranges of linearity
vary between enormously e.g. 10
3 to >10
6 (see Fig. 4.9 in Sect. 4.1). However, as an
important analytical task prior to any determination procedure, it has to be checked
whether the expected concentration levels match the range of linearity of the selected
detector system.
However, a single signal (e.g. the sum of ions of a mass spectrum) is not sufficient
for quantitation. The clue of quantitative determination in organic analyses is related
to the chromatographic peaks. Chromatographic peaks represent a time resolved
measurement of signals. As an important consequence, also the peaks (equivalent to
individual signals) exhibit the same correlation to a measured concentration or
concentration
y
t
i
s
n
e
t
n
i
l
a
n
g
i
s
d
e
r
u
s
a
e
m
b0 A
signal intensity
b1
calibration range
0
linearity range of detection
Fig. 5.17 The linearity
range of a detector which
represents also the
calibration range
120
5 GC/MS Data Evaluation
Outlook
In addition to identification, the process of quantitation is a main task of
analytical work. Here, the principal procedures for chromatographic based
quantitative determination are presented.
Beside identification, the quantitative determination of individual analytes is the
second major issue of analytical work. Identification is mainly based on detection
methods such as mass spectrometry or IR spectroscopy, but for quantitation the
chromatography is the key method. In Organic Geochemistry dominantly GC/MS
and LC/MS analyses are used for quantitation, since the measurement of individual
organic molecules are needed. This is in contrast to most inorganic analyses, where
the determination of the elemental composition is the main task.
A basic precondition for quantitative determination is a defined relation between
the measured signal in a detector and the corresponding amount of analyte. Nearly
all quantitation in Organic Geochemistry are using a linear correlation, hence the
area of linearity of a detector is an important parameter for achieving a wider range
of determinable concentrations or amounts (see Fig. 5.17). These ranges of linearity
vary between enormously e.g. 10
3 to >10
6 (see Fig. 4.9 in Sect. 4.1). However, as an
important analytical task prior to any determination procedure, it has to be checked
whether the expected concentration levels match the range of linearity of the selected
detector system.
However, a single signal (e.g. the sum of ions of a mass spectrum) is not sufficient
for quantitation. The clue of quantitative determination in organic analyses is related
to the chromatographic peaks. Chromatographic peaks represent a time resolved
measurement of signals. As an important consequence, also the peaks (equivalent to
individual signals) exhibit the same correlation to a measured concentration or
concentration
y
t
i
s
n
e
t
n
i
l
a
n
g
i
s
d
e
r
u
s
a
e
m
b0 A
signal intensity
b1
calibration range
0
linearity range of detection
Fig. 5.17 The linearity
range of a detector which
represents also the
calibration range
120
5 GC/MS Data Evaluation