Application NoteRESIDUAL GAS ANALYSIS

Monitoring Decomposition of Thermally Sensitive Materials
During Pharmaceutical Freeze-Drying
Freeze-drying is a technique commonly used in the pharmaceutical industry to stabilize sensitive drug and biological products
prior to long-term storage. In a typical cycle, the product is first dispensed into vials and loaded into the freeze-dryer. Thematerial is then frozen on cooled shelves to separate the solvent from the solute. Once solidified, a vacuum system lowers theambient pressure surrounding the product to induce sublimation. These conditions are held until all frozen solvent is removed.
The product is then sealed in vacuum before the system returns to atmospheric pressure. The shelf life of freeze-dried products
ranges from months to years, depending on storage conditions and material properties. Ongoing innovation in the pharmaceuticalsector has led to the introduction of highly complex systems, many of which exhibit high thermal sensitivity. In some cases,
freeze-drying these materials too aggressively can lead to decomposition of the active pharmaceutical ingredient or other criticalcomponents in the formulation. Residual Gas Analysis (RGA) is an effective process analytical technology that can mitigate thisbehavior while simultaneously providing a means to optimize the freeze-drying process.

Experimental
The Transpector® CPM 3 compact process monitor is aquadrupole RGA integrated with a research and development
freeze-dryer (REVO® by Millrock Technologies Inc.) to monitor
the gas composition inside of the process chamber during thefreeze-drying process. Transpector CPM 3 contains a seriesof dosing orifices to permit sampling of high-pressure gases
up to 1 Torr. An image of the setup is shown in Figure 1. The
tested formulations consisted of sucrose and ammonium
bicarbonate of varying concentration dispensed into 20R typeI glass tubing vials. The RGA monitored gas composition in thefreeze-dryer from 0.5-200 amu with a resolution of 0.1 amu.
Mass spectra for compounds typically found in freeze-drying
are shown in Table 1.

Mass Spectra of Species CommonlyFound in Freeze-Drying
Compound

Mass

Relative
Abundance

N2281410.138

H 2O

181716
1920

1
0.212
0.009
0.005
0.003

CO244
28
16124510.098
0.096
0.087
0.012

NH3171615141810.801
0.075
0.022
0.004

32
1640
20

10.21810.146

O2Ar

Figure 1: INFICON Transpector CPM 3 installed on Millrock
REVO lyophilizer in the LyoHub Demonstration Facility atPurdue University.

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Table 1: Mass Spectra of Species Commonly Found inFreeze-Drying

Monitoring Decomposition During Pharmaceutical Freeze-Drying |    Application Note

Results: Model API Documentation with
Bulking Agent
An aqueous formulation of ammonium bicarbonate (0.5%w/v) and sucrose (5% w/v) was freeze-dried to simulate
decomposition of a thermally sensitive active pharmaceuticalingredient (API).
The process data from the freeze-dryer and corresponding
signals from the RGA are shown in Figures 2a and 2b,respectively. The formulation was initially frozen to -40°C
near atmospheric pressure. Once solidified, the pressure wasreduced to 70 mTorr and the shelf temperature was raised
to -20°C. This sequence of steps induces sublimation of
the water ice and marks the beginning of the primary drying
phase. According to Figure 2b, the primary constituent in theprocess gas during this period is water vapor (m/z=18). Tracenitrogen (m/z=28) was also present. Nitrogen ballast gas is
introduced by freeze-drying systems to maintain a constantpressure as the sublimation rate varies throughout the cycle.
After an elapsed time of around 18 hours, the water vapor
signal began to decrease as the water ice was fully consumed.

at the end of primary drying is removed by increasing the shelftemperature in a process known as secondary drying. Typicaltemperature for this process range between room temperatureand 40°C. Secondary drying occurred at an elapsed time of 33
hours and let to a simultaneous increase in water vapor anddecrease in nitrogen as the system attempted to maintain aconstant pressure. Following the peak, water and ammonia
traces then decayed towards the baseline. Close examinationof the water vapor (m/z=188 and m/z=17), carbon dioxide(m/z=44), and ammonia (m/z=15) traces indicate subtle
differences in desorption rates. The consequences of thisbehavior were not investigated but could provide useful data
to formulation development and process optimization.

It should be noted that indications of this endpoint are alsoprovided by the Pirani vacuum gauge in Figure 2a. The Pirani
gauge is a gas-dependent pressure sensor that is typicallycalibrated in nitrogen. Referencing this device to the absolutepressure (provided by a capacitance manometer) provides
an indication of water vapor composition. However, although
the Pirani method is a useful, low cost, and straightforward
technique, it is unable to distinguish between different gases in
non-binary systems. The nitrogen signal in Figure 2b increased
sharply at the end of the primary drying as the machine
introduced additional ballast gas to maintain pressure. The
argon principal peak (m/z=40) increased proportionally during
this event. The nitrogen gas is boiled off from a liquid source
and is known to contain condensed argon. This observation
was therefore reasonable and expected. The increasing
product temperature after 18 hours was also met with aproportional increase in m/z=15.
Figure 2: Freeze drying process (a) and RGA (b) data for amodel pharmaceutical system containing thermally sensitive
active pharmaceutical ingredient and bulking agent1.

aial47a1

This is believed to be a fragment of ammonia vapor andindicates mild decomposition of the dried solid. Note thatammonia has a principal peak at m/z=17. This is also an isotopeof water vapor, so the ammonia contribution is likely obscured
by its strong signal. Any remaining water bound to the dry solid

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Due to our continuing program of product improvements, specifications are subject to change without notice.

Monitoring Decomposition During Pharmaceutical Freeze-Drying |    Application Note

Model API Decomposition

Conclusion

An identical experiment was conducted using pure aqueous
ammonium bicarbonate to investigate the decomposition
process in more detail. These results are summarized in
Figure 3. Similar to the previous formulation, the majority ofthe vapor composition throughout primary drying is watervapor. However, near the end of this phase, the increasein product temperature led to a sharp increase in m/z=44
and m/z=15. The response from these masses confirms that
thermal decomposition of the ammonia salt is occurring invacuum. It also highlights the utility of monitoring off-principal
peaks when investigating compounds that have strongly
overlapping spectra. A second sharp response was also seen
during secondary drying followed by a decay to a constantvalue. In this case, all ammonium bicarbonate had sublimed,
and product vials were empty at the conclusion of the cycle.

Historically, quadrupole mass spectrometry has been used in
the pharmaceutical freeze-drying industry for detecting leaks
and evaluating cycle endpoint. Recently, this technique has
provided a useful tool for cycle development and optimizationof sensitive formulations. This note applied the INFICON
Transpector CPM 3 to investigate the decomposition ofammonia salts during the freeze-drying process. Ammonia
and water vapor have tightly overlapped spectra, especiallynear the principal peak region. This characteristic makes
identification of the individual species difficult. The highsensitivity and performance of the INFICON Transpector RGA
allows off-principal and unique m/z traces to be monitoredwith high precision. This capability provides significant value
to formulation development scientists looking to dry lifesaving drugs and biologics with the highest speed possible,
while also preserving stability and efficacy.

For more information    inficon.com
1Strongrich, A. D., Tobyn, M., Iyer, L. K., Park, Y., Hong, J., & Alexeenko, A. A. (2023).
In-Process Vapor Composition Monitoring in Application to Lyophilization of Ammonium
Salt Formulations. Journal of Pharmaceutical Sciences, 112(1), 264-271.

Liechty, E.T., Strongrich, A.D., Moussa, E.M. et al. In-Situ Molecular Vapor
Composition Measurements During Lyophilization. Pharm Res 35, 115 (2018). https://doi.org/10.1007/s11095-018-2395-4.
2Ganguly, A., Stewart, J., Rhoden, A., Volny, M., & Saad, N. (2018). Mass spectrometry
in freeze-drying: Motivations for using a bespoke PAT for laboratory and production
environment. European Journal of Pharmaceutics and Biopharmaceutics, 127, 298-308.
3

aial47a1

Figure 3: Freeze drying process (a) and RGA (b) data for amodel thermally sensitive active pharmaceutical ingredient1.

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Due to our continuing program of product improvements, specifications are subject to change without notice.