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

0.02

0.03

0.04

0.05

0.06

0.07

0.08

0.09

0.10

Abso

rban

ce

1000 1500 2000 2500 3000 3500 4000 TFS

-0.02

0.00

0.02

0.04

0.06

0.08

0.10

0.12

0.14

0.16

0.18

0.20

Abso

rban

ce

1000 1500 2000 2500 3000 3500 4000

-0.04

-0.02

0.00

0.02

0.04

0.06

0.08

0.10

0.12

0.14

0.16

0.18

0.20

0.22

0.24

0.26

0.28

0.30

0.32

0.34

0.36

0.38

Abso

rban

ce

1000 1500 2000 2500 3000 3500 4000

-0.02

0.00

0.02

0.04

0.06

0.08

0.10

0.12

0.14

0.16

0.18

0.20

0.22

0.24

0.26

0.28

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