several times (usually 4–5 times). Each step of standard addition creates a peak area
difference that is correlated with the added concentration. Based on this correlation,
a response factor can be calculated that can be applied to the peak area of the target
analyte in the untreated extract (see Fig. 5.23).
Based on the three calibration methods, the concentration in an extract or sample
can be determined but this value does not represent the concentration or amount in a
natural sample (e.g. a river water or coal sample). To complete a quantitation, the
extract concentration must be converted to the absolute amount of analyte by
multiplication with the extract volume and, secondly, this resulting amount needs
to be normalized to the total sample amount used for extraction. This procedure
converts e.g. an extract concentration of several ng/μL to a water sample concentration of some ng/L or a soil contamination of some ng/g.
General Note
Quantitative analyses in Organic Geochemistry dominantly use chromatography. Quantitation follows on two steps, a peak integration and a calibration for
converting the detected peak area to a concentration.
In Organic Geochemistry of fossil matter often biomarker analyses are
performed. Here, a distinct determination of absolute quantitative data is not necessary, since ratios of chemically similar compounds are target parameters. For
calculating such ratios, the peak areas can directly be used. However, two
k
a
e
p
area
concentration c
5
4
3
2
1
Calibration function
=
+
measured peak area
of unknown sample
Corresponding
concentration of unknown
sample
Fig. 5.21 Scheme of an external calibration procedure
124
5 GC/MS Data Evaluation
difference that is correlated with the added concentration. Based on this correlation,
a response factor can be calculated that can be applied to the peak area of the target
analyte in the untreated extract (see Fig. 5.23).
Based on the three calibration methods, the concentration in an extract or sample
can be determined but this value does not represent the concentration or amount in a
natural sample (e.g. a river water or coal sample). To complete a quantitation, the
extract concentration must be converted to the absolute amount of analyte by
multiplication with the extract volume and, secondly, this resulting amount needs
to be normalized to the total sample amount used for extraction. This procedure
converts e.g. an extract concentration of several ng/μL to a water sample concentration of some ng/L or a soil contamination of some ng/g.
General Note
Quantitative analyses in Organic Geochemistry dominantly use chromatography. Quantitation follows on two steps, a peak integration and a calibration for
converting the detected peak area to a concentration.
In Organic Geochemistry of fossil matter often biomarker analyses are
performed. Here, a distinct determination of absolute quantitative data is not necessary, since ratios of chemically similar compounds are target parameters. For
calculating such ratios, the peak areas can directly be used. However, two
k
a
e
p
area
concentration c
5
4
3
2
1
Calibration function
=
+
measured peak area
of unknown sample
Corresponding
concentration of unknown
sample
Fig. 5.21 Scheme of an external calibration procedure
124
5 GC/MS Data Evaluation