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Collected Applications
Thermal Analysis
EVOLVED GAS ANALYSIS
Preface
Over the past decades, the development and characterization of materials has become increasingly
specialized due to the ever-increasing demands placed on quality. In addition, the widespread use of
products such as blends, composites, new stabilizers and additives has resulted in relatively complex
chemical systems. The great interest in material sciences has created a need for specific analytical tools to
characterize the constituent inorganic and organic molecules. One particularly important development has
been to combine well-established separation and identification techniques into one instrument system.
This drastically increases the amount of specific information that can be obtained and shortens analysis
times.
This booklet provides an insight into two such so-called hyphenated techniques, TGA-FTIR and TGAMS. The first part of the booklet focuses on basic principles and describes the techniques. It also includes
a practical section and an introduction to the interpretation of spectra. The second part discusses some 15
different applications performed in our applications laboratory using TGA-MS and/or TGA-FTIR. Two
additional applications illustrate the use of the rather unusual combination of TMA with MS.
I would like to thank the Materials Characterization Section of the Market Support Group in
Schwerzenbach, Switzerland for their helpful discussions, Mrs. Helga Judex for preparing the layout and
Dudley May for checking the text.
Schwerzenbach, October 2001
Cyril Darribère
This application booklet presents selected application examples. The experiments were conducted with
the utmost care using the instruments specified in the description of each application. The results were
evaluated according to the current state of our knowledge.
This does not however absolve you from personally testing the suitability of the examples for your own
methods, instruments and purposes. Since the transfer and use of an application is beyond our control,
we cannot of course accept any responsibility.
When chemicals, solvents and gases are used, general safety rules and the instructions given by
the manufacturer or supplier must be observed.
® TM
All names of commercial products can be registered trademarks, even if they are not denoted
as such.
METTLER-TOLEDO Collected Applications
EVOLVED GAS ANALYSIS
Page 1
Contents
Preface ......................................................................................................................................................1
Content......................................................................................................................................................2
Abbreviations and Acronyms ...................................................................................................................3
Introduction to TGA-EGA........................................................................................................................4
TGA-MS ...................................................................................................................................................5
TGA-FTIR ..............................................................................................................................................11
Introduction to the Applications .............................................................................................................20
Applications List.....................................................................................................................................21
1
Decomposition of Acetylsalicylic Acid....................................................................................22
2
Thermal Degradation of BHET ................................................................................................24
3
Influence of the Heating Rate on MS Response.......................................................................27
4
Decomposition of Technical Lauryl Alcohol ...........................................................................30
5
Detection of Residual Solvents in a Pharmaceutical Substance...............................................33
6
Decomposition of Calcium Oxalate Monohydrate (Tutorial) ..................................................35
7
Influence of Sample Weight on MS Sensitivity .......................................................................37
8
Decomposition of Copper Sulfate Pentahydrate (Tutorial)......................................................39
9
Desorption of a Zeolite Filled with Organic Matter .................................................................41
10
Pyrolysis of PVC Powder .........................................................................................................43
11
Investigation of Fluorinated Cable Wires.................................................................................46
12
Detection of Methyl Salicylate in a Sample of Rubber. ...........................................................49
13
Degradation of a Silicone Polymer...........................................................................................51
14
Curing and Decomposition of an Amino Resin........................................................................54
15
Identification of BR and NR Rubbers. Study of Thermal Transitions and Decomposition.....57
16
Delamination of Printed Circuit Boards ...................................................................................61
17
Expansion and Decomposition of the Polymer Used to Encapsulate a Blowing Agent ..........63
Index .......................................................................................................................................................66
Notes .......................................................................................................................................................68
Page 2
EVOLVED GAS ANALYSIS
METTLER-TOLEDO Collected Applications
2
Thermal Degradation of BHET
Purpose
The aim of the experiment was to demonstrate how the evolved gas profile and
evolved group profile techniques can be used to identify degradation products.
Sample
BHET (bis-hydroxylethyl terephthalate). A common industrial synthetic route
involves the esterification of terephthalic acid (TPA) with ethylene glycol (EG).
BHET is usually polymerized to polyethylene terephthalate (PET).
O
O
OH +
2
HO
O
OH
HO
O
HO
+ 2HO
2
O
O
TPA
Conditions
OH
BHET
EG
Measuring cells:
TGA/SDTA851e coupled to a Nicolet Nexus FTIR
Pan:
Alumina 70 µl, no lid
Sample preparation: As received, no preparation. 18.122 mg
TGA measurement: Heating from 50 °C to 900 °C at 10 K/min, blank curve
corrected
Atmosphere:
Nitrogen, 80 ml/min
Degradati on of BHET (A)
%
TGA curve
Step -36.6665 %
-6.6447 mg
Step -54.8433 %
-9.9387 mg
50
0
%min^-1
10.09.2001 13:47:28
DTG curve
-5
-10
-15
0.10
0.05
Gram-Schmidt curve
0.00
-0.05
100
Interpretation
Page 24
200
300
400
500
600
700
°C
The two-step degradation of BHET results in maxima in the DTG curve at about
300 °C and 450 °C. Theses peaks correspond to the maxima in the GramSchmidt curve.
EVOLVED GAS ANALYSIS
METTLER-TOLEDO Collected Applications
Evolved gas profile
Interpretation
Functional group
profile
The evolved gas profile method (see chapter on interpretation procedures of
TGA-FTIR measurements) was used to identify the cause of the first weight loss
step (DTG maximum at 300 °C). Direct comparison of the FTIR spectrum at
300 °C with database spectra characterizes the first component evolved as pure
ethylene glycol. The doublet between 2340 and 2360 cm-1 (A) is due to residual
carbon dioxide in system. Absorption bands in the range 4000-3500 cm-1 and
2000-1200 cm-1 (B) are attributed to water (background moisture).
Degradati on of BHET (B)
10.09.2001 13:47:37
%min^-1
DTG curve
-10
-20
3000-2850 cm-1
Alkane
-30
1280-970 cm-1
Alcohol
1800-1600 cm-1
Carboxylic acid
20
1790-1650 cm-1
Ester
200
METTLER-TOLEDO Collected Applications
400
600
EVOLVED GAS ANALYSIS
°C
Page 25
Interpretation
Evaluation
Conclusion
Page 26
Direct comparison of the spectrum at 450 °C with the database did not identify
any one particular decomposition product. The functional group profiles of
possible decomposition products are displayed above. As expected, the maxima
correspond to the maxima of the DTG curve. The identification of the
degradation products is based on the measurement of the absorption bands
corresponding to different chemical groups, for example the characteristic
absorption bands of C-O for alcohols, carboxylic acids and esters. The profiles
for aromatic ring and ketones were measured but no significant signals were
detected. In fact the side chains of BHET are cleaved at temperatures above
400 °C with the formation of hydroxy formic acid ester (CH-CO-O-(CH2)2-OH).
Step, %
Peak temperature DTG, °C
Possible products
36.7
298.5
ethylene glycol
54.8
446.1
hydroxy formic acid ester
The two closely lying weight loss steps cannot be interpreted with TGA alone.
The use of a TGA-FTIR combination allows a qualitative characterization of the
decomposition process. Based on an analysis of the spectrum at 300 °C, we
concluded that the first decomposition step is due to the loss of ethylene glycol.
The second step was assumed to be due to the cleavage of the side chains of the
aromatic group, i.e. the elimination of hydroxy formic acid ester. This study
illustrates the application of the evolved gas profile and the functional group
profile methods described in the introduction. The two techniques provide
complementary information.
EVOLVED GAS ANALYSIS
METTLER-TOLEDO Collected Applications
3
Influence of the Heating Rate on MS Response
Purpose
The aim of the experiment was to investigate the influence of different
heating rates on the response of the mass spectrometer.
Sample
Malonic acid (COOH-CH2-COOH).
Conditions
Measuring cells:
TGA/SDTA851e coupled to a Balzers Thermostar©
mass spectrometer
Pan:
Aluminum 40 µl, no lid
Sample preparation: The crystals were ground in a mortar. Sample
weights of approx. 10 mg were used.
TGA measurement: Heating from 50 °C to 640 °C at 5, 10, 20, 30, 40
and 50 K/min, blank curve corrected
Atmosphere:
Nitrogen, 50 ml/min
^exo
Influence Heati ng Rate on MS (A)
%
10.09.2001 13:49:49
5
10
20
30
40
50
TGA curves
50
K/min
K/min
K/min
K/min
K/min
K/min
0
°C
SDTA curves
-5
-10
-15
80
Interpretation
100
120
140
160
180
200
220
240
260
280 °C
Samples of malonic acid were measured with TGA at heating rates
between 5 and 50 K/min and the corresponding TGA signals recorded.
The thermal decomposition of malonic acid exhibits a single weight loss
step that shifts toward higher temperatures with increasing heating rates.
The SDTA curves indicate that the sample begins to melt at approximately
134 °C (onset temperature), and that this is independent of the heating rate.
The decomposition process in the liquid phase depends on the heating rate;
higher heating rates shift the onset of decomposition and the
decomposition range to higher temperatures.
METTLER-TOLEDO Collected Applications
EVOLVED GAS ANALYSIS
Page 27
Influence Heati ng Rate on MS (B)
10.09.2001 13:49:59
m/z 60
Heating
rate
Integral
50
2326.99 nsA
Integral
40
50
nA
2287.02 nsA
Integral
30
2273.32 nsA
Integral
2213.86 nsA
20
10
5
0
Interpretation
Evaluation
Page 28
10
20
Integral
2185.62 nsA
Integral
2154.70 nsA
30
min
The decomposition of malonic acid results in the elimination of acetic
acid, which was confirmed by the m/z 60 ion curve (see MS spectrum of
acetic acid in Application 1). The m/z 60 ion curve was measured at each
different TGA heating rate and the corresponding peak areas calculated.
The results are summarized in the above diagram. The TGA curve showed
that the weight losses were the same for each sample, i.e. the amount of
acetic acid evolved was independent of the heating rate. Constant peaks
areas for the m/z 60 curves were therefore also expected. In fact the
calculated peak area shows a slight increase at higher heating rates.
Heating rate,
K/min
Onset / peak temperatures
SDTA, °C
MS peak area
(m/z 60), nsA
Melting
Decomposition
5
134.2
173.6
2154
10
134.1
182.9
2185
20
134.1
188.7
2213
30
134.0
194.3
2273
40
134.0
191.5
2287
50
134.0
203.7
2326
EVOLVED GAS ANALYSIS
METTLER-TOLEDO Collected Applications
Peak area m/z 60 [nsA]
3000
2000
1000
0
10
20
30
40
50
60
Heating rate [K/min]
Conclusion
The weight loss step due to the decomposition of malonic acid to acetic
acid is independent of the heating rate. The m/z 60 peak area depends to a
slight extent on the heating rate, although similar quantities of material are
transported to the mass spectrometer. This effect might be due to the fact
that because the heating rates are different, the concentration of acetic acid
in the evolved gases is in each case very different.
METTLER-TOLEDO Collected Applications
EVOLVED GAS ANALYSIS
Page 29
4
Decomposition of Technical Lauryl Alcohol
Purpose
The aim of the experiment was to investigate the possible decomposition
products of lauryl alcohol.
Sample
Technical 1-dodecanol; CH3(CH2)11OH, lauryl alcohol.
Conditions
Measuring cells:
TGA/SDTA851e coupled to a Nicolet Nexus FTIR
Pan:
Aluminum 40 µl, pierced lid (diameter: 50 µm)
Sample preparation: The waxy material was melted in a water bath at
50 °C. The homogeneous liquid was then filled
directly into the crucible and cooled to room
temperature before measurement
TGA measurement: Heating from 30 °C to 600 °C at 5 K/min, blank
curve corrected
Atmosphere:
Nitrogen, 50 ml/min
Decomposition of Lauryl Al cohol
%
TGA curve
50
0
%°C^-1
DTG curve
10.09.2001 13:47:14
Step -57.2342 %
-18.6028 mg
Step -9.0136 %
-2.9297 mg
Step -32.2443 %
-10.4804 mg
-1
-2
Gram-Schmidt curve
0.05
0.00
100
Interpretation
200
300
400
500
°C
The measurements were performed in crucibles sealed with pierced lids to
improve the separation of the two weight loss steps in the TGA curve
compared with measurements in an open crucible.
The Gram-Schmidt curve shows two peaks that correspond to the weight
loss steps at 207 °C and 395 °C (maxima of the DTG curve).
Page 30
EVOLVED GAS ANALYSIS
METTLER-TOLEDO Collected Applications
Interpretation
The FTIR spectrum measured at about 207 °C was very similar to that of
1-decanol in the spectrum database (e.g. stretching and bending vibrations
of the alkane part at 2970, 2930, 2860, 1460 and 1380 cm-1 and the
primary alcohol at 3670, 1350 and 1050 cm-1). A detailed comparison of
the measured spectrum and the reference spectrum of dodecanol in the
range 1500-900 cm-1 confirms that no dodecanol evaporates.
A distinct shoulder can be observed on the high-temperature side of the
peaks in both the DTG and GS curves of the first weight loss step. Spectra
recorded in this shoulder however showed no new absorption bands.
Possible explanations for this could be presence of other dodecanol
isomers in the original sample, i.e. isomers with a higher boiling point, or
polymerization. This would have to be checked with TGA-MS
measurements.
METTLER-TOLEDO Collected Applications
EVOLVED GAS ANALYSIS
Page 31
Interpretation
Evaluation
Conclusion
Page 32
Some additional peaks were observed in the spectrum at 395 °C. Besides
the characteristic bands for alkanes and alcohols, the absorption bands at
3085 cm-1 (C-H stretching), 1640 cm-1 (C=C stretching) and 990/910 cm-1
(out-of-plane C-H bending) indicate the presence of a vinyl group. The
second weight loss step could result from the decomposition of a
polymerized compound.
Step, %
Peak temperature
DTG, °C
Possible products
57.2
206.9
1-decanol
9.0
237.7
isomerization /
polymerization
product
32.2
395.1
alkyl chain with a
vinyl and alcohol
group
The main functional groups such as alkane, alcohol and alkene were
identified by FTIR measurements. The cleavage of the dodecanol chain
results mainly in a shorter aliphatic alcohol (first step) and an alkene (third
step). An isomerization or polymerization reaction is proposed to explain
the degradation products of the second weight loss step.
EVOLVED GAS ANALYSIS
METTLER-TOLEDO Collected Applications
5
Detection of Residual Solvents in a Pharmaceutical Substance
Purpose
The aim of the experiment was to identify residues of solvents left in a
pharmaceutical substance after recrystallization in a solvent mixture.
Sample
Pharmaceutically active substance.
Conditions
Measuring cells:
TGA/SDTA851e coupled to a Balzers Thermostar©
mass spectrometer
Pan:
Alumina 70 µl, without lid
Sample preparation: As received, no preparation. 1.3640 mg
TGA measurement: Heating from 30 °C to 350 °C at 10 K/min, blank
curve corrected
Atmosphere:
Nitrogen, 20 ml/min
Detecti on of Resi dual Sol vents
%
TGA curve
10.09.2001 13:48:21
Step -2.2889 %
-31.2205e-03 mg
95
Step -4.6543 %
-63.4850e-03 mg
90
85
lg(nA)
m/z 43
-2
MS curves
m/z 31
-3
-4
50
Interpretation
100
150
200
250
300
°C
The TGA curve shows a number of weight loss steps in temperature range
measured. The initial weight loss below 60 °C is probably due to the
gradual evaporation of adsorbed moisture or solvent(s) while the final step
(above 250 °C) no doubt arises from the decomposition of the product.
The change in the intensities of the m/z 31 (methanol) and m/z 43
(acetone) fragment ions measured by TG-MS in the MID mode correspond
to the weight loss steps in the range 70-190 °C and 190-225 °C
respectively. The MS spectra of methanol and acetone are shown in the
following diagrams. While methanol is evolved over a wide temperature
range, the acetone (m/z 43) peak is appreciably sharper. The higher
temperature indicates that acetone is more firmly bound in the substance in
the form of a solvate.
METTLER-TOLEDO Collected Applications
EVOLVED GAS ANALYSIS
Page 33
MS spectrum of
methanol
100
Rel. Abundance
80
60
40
20
0
10
20
30
40
50
60
40
50
60
m/z
MS spectrum of
acetone
100
Rel. Abundance
80
60
40
20
0
10
20
30
m/z
Evaluation
Conclusion
Page 34
Evaluation range, °C
Step, %
Possible products
70-190
2.3
methanol
190-225
4.7
methanol, acetone
From the TG-MS results, it was possible to identify the solvents used to
recrystallize the active ingredient. In this case (and in general), it is
possible to distinguish between residual solvent that is merely adsorbed
and solvent molecules that are more strongly bound in the form of
solvates.
EVOLVED GAS ANALYSIS
METTLER-TOLEDO Collected Applications
6
Purpose
Sample
Conditions
Decomposition of Calcium Oxalate Monohydrate (Tutorial)
Calcium oxalate monohydrate is used as a tutorial sample to demonstrate
the decomposition reaction and stoichiometry. Calcium oxalate
monohydrate decomposes in three reaction steps given by the following
equations:
(1)
CaC2O4.H2O
Ö
CaC2O4 + H2O
(2)
CaC2O4
Ö
CaCO3 + CO
(3)
CaCO3
Ö
CaO + CO2
Calcium oxalate monohydrate (CaC2O4.H2O).
Measuring cells:
TGA/SDTA851e coupled to a Balzers Thermostar©
mass spectrometer
Pan:
Alumina 70 µl, no lid
Sample preparation: As received, no preparation. 26.465 mg
TGA measurement: Heating from 70 °C to 950 °C at 30 K/min, blank
curve corrected
Argon (50 ml/min) was used instead of nitrogen in
order to be able to detect CO since CO and N2 ions
appear at the same m/z ratio
Atmosphere:
Decomposition of CaC2O4 (A)
%
10.09.2001 13:46:48
TGA curve
100
Step -12.4872 %
-3.3049 mg
Step -18.8643 %
-4.9926 mg
80
60
Step -30.2613 %
-8.0089 mg
Residue
38.3819 %
10.1581 mg
40
100
Interpretation
200
300
400
500
600
700
800
°C
The TGA curve shows three weight loss steps in agreement with the threestep reaction scheme given above. The loss of water of crystallization and
the two decomposition steps yielded weight losses of 12.5%, 18.9% and
30.3% respectively. This is in good agreement with the theoretical
stoichiometric values based on the fact that one mole of CaC2O4⋅H2O
gives rise to one mole each of H2O, CO and CO2.
METTLER-TOLEDO Collected Applications
EVOLVED GAS ANALYSIS
Page 35
^exo
Decomposition of CaC2O4 (B)
mgmin^-1
10.09.2001 13:46:56
DTG curve
-1
-2
MS: H2O
MS: CO
MS: CO2
5
nA
100
Interpretation
Evaluation
Conclusion
Page 36
200
300
400
500
600
700
800
900
°C
From the above reaction scheme, one would expect H2O, CO and CO2 to
be evolved in turn at each step. The TG-MS ion curves showed this is in
fact the case. However, in contrast to the reaction scheme, a small CO2
peak was observed during the decomposition of the anhydrous oxalate in
the second weight loss step. This is due to the disproportionation of CO to
CO2 (2CO → CO2 + C).
Stoichiometric step
%
Measured
step
%
Peak
temperatures
DTG, °C
Possible
products
12.3
12.5
221.3
water of
crystallization
19.2
18.9
528.5
CO, CO2
30.1
30.3
847.6
CO2
According to the above reaction scheme, calcium oxalate monohydrate is
expected to decompose in well-defined steps with the release of H2O, CO
and CO2. It seems that this process is more complicated as slight
differences were observed between the measured and theoretical weight
loss steps. The TG-MS results help clarify the matter by showing that CO2
is also formed during the second reaction step. This was concluded as
arising from the disproportionation reaction 2CO → CO2 + C.
EVOLVED GAS ANALYSIS
METTLER-TOLEDO Collected Applications