Principles of Quantitative Analysis
This document is based on the report by N. Hirashita and T. Uchiyama published in Bunseki Kagaku (Analytical Chemistry), 43, 757 (1994).
The quantification of desorbed gases can be performed directly from the thermal desorption spectrum measured using a Thermal Desorption Spectroscopy (TDS) analyzer.
When the pumping speed of the measurement chamber is sufficiently high compared to the pressure change within the chamber caused by the desorbed gas,
the variation in the partial pressure of the desorbed gas component is directly proportional to the desorbed amount per unit time (desorption rate).
In a mass spectrometer, since the ion current is proportional to the partial pressure, the ion current inherently becomes proportional to the desorption rate.
Consequently, the total desorbed volume can be calculated from the area intensity obtained by integrating the ion current over time.
By pre-determining the proportionality factor between the area intensity and the desorbed volume using a standard silicon specimen ion-implanted with a known amount
of H+, the absolute hydrogen desorption volume can be determined for a wide variety of specimens from the integrated area intensity of the m/z=2 signal.
Furthermore, for molecular species other than hydrogen, the corresponding proportionality factor can be accurately calculated using parameters such as the relative ionization efficiency,
fragmentation factor, and transmission efficiency between hydrogen and the target molecule.
Utilizing this calculated proportionality factor enables the precise quantitative analysis of various gas species other than hydrogen.
