practical concerns in ega
TRANSCRIPT
Practical Concerns
in EGA
Kevin P Menard, Ph.D. MBASept 29, 2015
Internal usage only
The problem with TGA
Anything we say now about the weight losses is an educated guess
Temperature
Weight
0
m1
m2
T1 T2
Internal usage only
A brief history of solutions
1960s – Use of TGA with MS - Limitations imposed by the vacuum TGA could hold - Gas were collected and manually transferred initially
1970s – Development of better systems- Transfers lines improved, alterative direct TGMS system tried- Other techniques still used “gas bomb”
1980s – Wendlandt listed TCD, GC and MS as coupled to TGA- Development of FTIRs lead to TG-IR
1990s – Provder et al “Hyphenated Techniques in Thermal Analysis”- Collected work to date
2000s – Groenewund and other summarized the status- TG-IR the most popular technique.- GCMS difficult to do
Internal usage only
The problem of EGA
The approach started out simply.- Hook a tube up to your TGA exhaust and see what's there.
This has some problems- You have multiple instruments – each with their own eccentric requirements- You have a gas to transport- What you see in the TGA may not be the whole storySmall or slow weigh lossCompositional changes in a weight loss not separated.
- Or be detected in DTG
Internal usage only
The error comes the parts
What is optimal for TGA may not be for FTIR, MS, or GC- All techniques do not allow tracking with time- Sensitivity vary- Components have to be transported or stored
All EGA methods represent compromises
TGAFurnaceBalance
Gas Control All or part
Transfer LineHeater
Capillary or tubeGas control
EGACell
Sampling loopTemperature control
Etc.
Internal usage only
The TGA
Sample weight- Enough to detect by EGA- Larger than instrument min weight
Gas Flow- Component concentration in sample
is not what we actually detect- It is diluted by the gas flow- All gas flows add to the dilution
effect- Gas flow must be turbulent to allow
mixing - Dead zones must be eliminated- Thermal expansion of gases
Heating- Eliminate cold spots- Vary rate as needed
Internal usage only
Min Weight Concept and application to EGA
Min Weight- The amount of weight you can
detect reproducibly under specific conditions
- Important to understand for TGA or balance performance
Applied to EGA- How much do we need to see,
with reasonable reproducibility, in the chosen EGA technique
- Depending on the technique, this might be less than the min weight.
If we have 200 ppm of X, what sample size is need when the gas is
diluted by 80cc/min flow?
Internal usage only
Transfer lines
Temperature- Overall - Cold spots where things condense- Hot spots where things degrade
Volume- Flow rate- Time Lag
What makes it flow?- Pressure differential- Vacuum pumps- Pushed from TGA
How laminar is the flow?
Flow meters, valves, filters? TGA
Internal usage only
So what goes on the other end?
GC/MS
MS
FTIR
ICP MS
Internal usage only
Comparison of techniques- why what?
Gaseous products
are "known"
Gaseous products
are unknown
Masses < 300 am
uFTIR GC/MS
Storage MS GC/MS
Internal usage only
IR
• Path length is important in dilute samples like gases. Desire as long a path length as possible
• BUT need to keep volume low enough that eluted components don't mix.
• How long do you need to purge to remove CO2 and H20?
• Cell needs a relative fast turnover to track changes from the TGA
• Designed to prevent condensation and build-up on walls.
• Do windows need to be water resistant?
• How long do I need to purge between runs?
• Does your software support automation?
Internal usage only
D
C
B
A
x
x
x
x
Sample 2, 69.2380 mgHeating rate 10 K/minUnder nitrogen
Gram-Schmidt curve
0.2
TGA curve%
30
40
50
60
70
80
90
100
°C100 200 300 400 500 600 700 800 900
D
C
B
A
X
X
X
X
DTG curve
1/°C0.005
9265 sample2 TG-DTG-GS 07.06.2004 17:07:00
SW 8.10eRTASDEMO Version
Internal usage only
Chemigrams
m/m
0 ;
[-]
Temperature0
TG
DTG
1
COHCL
Internal usage only
In 3-D
-0.01
0.00
0.01
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0.10
Abso
rban
ce
1000 1500 2000 2500 3000 3500 4000 TFS
-0.02
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Abso
rban
ce
1000 1500 2000 2500 3000 3500 4000
-0.04
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rban
ce
1000 1500 2000 2500 3000 3500 4000
-0.02
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Abso
rban
ce
1000 1500 2000 2500 3000 3500 4000
Data from Veritas Testing & Consulting, Dallas, Texas
Internal usage only
MS
"Analysis by smacking things with a hammer and looking at the pieces"
Stability of the filament
Mechanism of fragmentation and ionization
- EI - CI- Cold ionization
Highest AMU- Limited by what your system
can transport
Fragmentation patterns and libraries
- How complex is the degradation
Pump
Gas from CapillaryMass Filter Ionisation
TurbomolecularPump
Detector
10-6 mbar 10-4 mbar
5 mbar
Time
Cur
rent
m/e = xm/e = y
Internal usage only
Data similarities
Or if you know what you are looking for, you can track specific AMU
Internal usage only
Either way, you can end
Internal usage only
Both good and bad…
Internal usage only
GCMS
GC requires a greater level of sophistication than other EGA techniques
More options but more ways to mess up- Choices of detectors besides MS- Choices of type of MS – type, mass range, resolution, detection limit- Choice of filament for Ionization- Choice of column- Temperature program
Internal usage only
Sampling options Trapping
- Collection on an medium such as a tube or the head of a column- Pros
Concentrates all the components Allows for faster runs
- Cons Need to know what is coming off Loss of temperature information
Storage - Collection and storage of 250 µL of evolved gas at defined time (temperature). Up to 16 fraction (loops) of evolved gas can
be stored and analyzed.- The GC-MS sequence is automatically started once all loops have been collected- Pros
Separation of evolved gas at specific decomposition temperature Compound profile according to the TGA curve
- Cons Relatively long analysis time
Multi-injection- Only one loop is used- The IST collects for e.g. 30 s the evolved gas from TGA and injects every e.g. 30 s to the GC one injection every minute- Isothermal column temperature such as e.g. 250 °C- Pros
Short analysis duration (same as TGA experiment) Good for solvent detection and compound profile from specific ion
- Cons No real GC separation Injection to the GC may create baseline artifacts on the heatflow curve
Internal usage only
Example – SBR concentration
4.00 6.00 8.00 10.0012.0014.0016.0018.0020.00200000400000600000800000
1000000120000014000001600000
Time-->
Abundance 7.5% SBR in NR/SBRTIC of loop 12 (400 °C)
4.00 6.00 8.0010.0012.0014.0016.0018.0020.0022.0024.00
100000
200000
300000
400000
Time-->
Abundance 100% SBR
TIC: loop 12 (400 °C)
4.00 6.008.0010.0012.0014.0016.0018.0020.0022.0024.00500000
1000000150000020000002500000300000035000004000000
Time-->
Abundance
100% NR TIC: loop 10 (370 °C)
Internal usage only
Quantification calculation
The content of SBR is individually calculated using loop 9 to loop 15
22
SBR content at different temperatures
360 °C 370 °C 380 °C 400 °C 420 °C 440°C 460°C
2.5% SBR in NR/SBR 2.27% 2.47% 2.76% 2.51% 2.21% 2.08% 1.64%
5.5% SBR in NR/SBR 5.74% 5.90% 5.89% 6.06% 5.30% 4.97% 4.28%
7.5% SBR in NR/SBR 6.30% 6.94% 7.18% 7.66% 5.91% 5.97% 5.55%
SBR content average Formulation
2.28% ± 0.36% 2.5%
5.45% ± 0.64% 5.5%
6.50% ± 0.77% 7.5%
Internal usage only
Summary
Technique Advantages Limitations Typical applications MS
Pfeiffer Vacuum Thermostar GSD
320 T
- Online technique, typical resolution1 2°C
- High dynamic range (> 5 decades) high sensitivity
- Quantitative evaluation is possible
- Maximum mass 300 amu - Interpretation requires some
knowledge about the expected evolved gases
- Gas inlet may clog with large molecules (Condensation)
- Detection of small molecules (COx, NOx, SOx, H2O, HCl etc.) inorganic materials
- Residual solvents in API's
FTIR
Thermo Scientific Thermo Nicolet
iS10 / iS50,
- Online technique, typical resolution2 2 °C
- Can also be used for the analysis of solids (requires an add-on for ATR-spectroscopy (iS50 only)
- Delivers also information about the molecular structure of the evolved gases
- Dynamic range around 3 decades (DTGS detector)
- Quantitative evaluation is difficult
- Spectrum interpretation requires a lot of experience and some knowledge about the expected evolved gases
- less sensitive than MS and GC/MS
- Detection of complex organic as well as simple molecules
- Pharmaceuticals - Polymers
GC/MS
SRA IST16 Agilent 7590 GC Agilent 5975 MS
- Mixture of unknown gases can be easily analyzed (GC separation, MS identification)
- Quantitative evaluation is possible (based on the chromatogram)
- Can be operated stand alone for analysis of liquids
- Storage mode: maximum of 16 gas samples during one TGA scan; time consuming
- Multiinjection mode: poor separation (GC is bypassed)
- Maximum mass 1050 amu
No restrictions