Testing Paper for VFA's

[joehem]

Hello,

Totally new to using GC! We are looking to use GC with FID to test paper for volatile fatty acids, mainly butyric. I did some internet research and couldn't find much for how to test the dry paper. I found I can buy some butyric in a standard and calibrate to this... but it is not clear how I prep the paper to be able to us GC to measure butyric acid. Thank you for sharing your knowledge

[rb6banjo]

Welcome to the wonderful world of GC. What is your equipment? Can you sample using headspace or do you have to extract the paper and perform a liquid injection?

The more information you can give about what is possible for you, the better we can help you.

[AICMM]

There are several options for derivatization but need more information.

Best regards,

AICMM

[joehem]

Welcome to the wonderful world of GC. What is your equipment? Can you sample using headspace or do you have to extract the paper and perform a liquid injection?

The more information you can give about what is possible for you, the better we can help you.

Sorry for delay - I found responses in my spam folder! No headspace capability... we will need to extract the paper and perform a liquid injection. Thank you!!

The equipment is a GC-FID from Lucidity

[rb6banjo]

What concentration of butyric acid do you expect to find in the paper samples you analyze? What detection limit do you need?

Does your industry have standard methods for this sort of thing or is everyone able to do whatever they want?

[joehem]

What concentration of butyric acid do you expect to find in the paper samples you analyze? What detection limit do you need?

Does your industry have standard methods for this sort of thing or is everyone able to do whatever they want?

We see now 900 to 1600 ppm.. We would like to improve and get down to 250 ppm maximum. I have looked, but I can't find any industry standard test methods. Thanks

[rb6banjo]

At those concentrations, a simple solvent extraction of the paper followed by a direct injection into your GC should do the trick. When analyzing short-chained carboxylic acids, you probably want to use a wax column of some sort.

Go to restek.com, choose the "resources hub". Search the chromatograms for butyric acid and you will find app notes that show their Stabilwax DA could be what you want. Agilent.com is a good place to find columns and application notes as well.

Water extractions might not be what you want as the thermal expansion of water is enormous and injection of 1 µL in standard split/splitless inlets will overfill it. Precision problems are likely to abound. Other solvents like methylene chloride or even methanol are better from a thermal expansion perspective. Methylene chloride has it's problems from an environmental perspective.

You have a bit of an advantage from that standpoint in that with those types of concentrations, you can likely run at a pretty high split ratio. You're not trying to find a needle in a haystack.

It's tough to "get somethin' for nothin'" in this game. Good luck.

BTW, yesterday I took some cardboard from some secondary packaging I had here in the lab. I cut some 4 cm2 pieces and placed them in 2 separate 21 mL headspace vials. I had previously determined that it took 150 mg of MeOH to saturate the 4 cm2 piece of cardboard. To one vial I added 200 µL of MeOH, sealed vial. To another I added 200 µL of MeOH:BF3 reagent (Sigma-Aldrich), sealed the vial. I heated those in an oven at 60 °C for 1 hour then cooled them to RT. I opened the vials and added 5 mL of water then resealed them. Then I analyzed the water/cardboard mixtures by headspace GCMS (solid-phase microextraction sampling). Compared to the blank prepared using MeOH:BF3 and water (200 µL reagent, no cardboard) there was a "bunch-o-fatty-acid-methyl-esters" in there. Not so much butyric acid but C6 and heavier for sure.

[AICMM]

joehem,

rb6banzo has a very good point about SPME. I have seen volatile fatty acids done with SPME and derivitization.

Best regards,

AICMM

[joehem]

At those concentrations, a simple solvent extraction of the paper followed by a direct injection into your GC should do the trick. When analyzing short-chained carboxylic acids, you probably want to use a wax column of some sort.

Go to restek.com, choose the "resources hub". Search the chromatograms for butyric acid and you will find app notes that show their Stabilwax DA could be what you want. Agilent.com is a good place to find columns and application notes as well.

Water extractions might not be what you want as the thermal expansion of water is enormous and injection of 1 µL in standard split/splitless inlets will overfill it. Precision problems are likely to abound. Other solvents like methylene chloride or even methanol are better from a thermal expansion perspective. Methylene chloride has it's problems from an environmental perspective.

You have a bit of an advantage from that standpoint in that with those types of concentrations, you can likely run at a pretty high split ratio. You're not trying to find a needle in a haystack.

It's tough to "get somethin' for nothin'" in this game. Good luck.

BTW, yesterday I took some cardboard from some secondary packaging I had here in the lab. I cut some 4 cm2 pieces and placed them in 2 separate 21 mL headspace vials. I had previously determined that it took 150 mg of MeOH to saturate the 4 cm2 piece of cardboard. To one vial I added 200 µL of MeOH, sealed vial. To another I added 200 µL of MeOH:BF3 reagent (Sigma-Aldrich), sealed the vial. I heated those in an oven at 60 °C for 1 hour then cooled them to RT. I opened the vials and added 5 mL of water then resealed them. Then I analyzed the water/cardboard mixtures by headspace GCMS (solid-phase microextraction sampling). Compared to the blank prepared using MeOH:BF3 and water (200 µL reagent, no cardboard) there was a "bunch-o-fatty-acid-methyl-esters" in there. Not so much butyric acid but C6 and heavier for sure.

This is fantastic! I really appreciate you sharing your knowledge

[rb6banjo]

You are welcome. Actually, thinking about this problem made me remember something similar from back in the day. Someone asked if I could tell if damaged cardboard packaging was tainted with a particular beverage. Had I thought of this approach, it might have helped answer that question. I got it a different way.

So, I took a little time and roughed out something. With SPME, you will be able to reach your low limit of detection. This is just a rough method. Precision could be improved by adding an internal standard, etc. But, it's certainly good enough as is to tell you if the BA concentration in the paper is less than 900 ppm.

https://i.postimg.cc/Sx5dFfcx/Me-OH-BF3 ... c-Acid.jpg

[joehem]

You are welcome. Actually, thinking about this problem made me remember something similar from back in the day. Someone asked if I could tell if damaged cardboard packaging was tainted with a particular beverage. Had I thought of this approach, it might have helped answer that question. I got it a different way.

So, I took a little time and roughed out something. With SPME, you will be able to reach your low limit of detection. This is just a rough method. Precision could be improved by adding an internal standard, etc. But, it's certainly good enough as is to tell you if the BA concentration in the paper is less than 900 ppm.

https://i.postimg.cc/Sx5dFfcx/Me-OH-BF3 ... c-Acid.jpg

This is excellent! Out of curiosity... what type of profession are you in? We only have GC with FID... no SPME... With the GC I just need to be able to test paper board that is considered "Good" vs "Bad" (stinky) it doesnt matter so much on ppm or concentration values

[rb6banjo]

Happy to share. I have a Ph.D. in Analytical Chemistry. I work for a large food company. I've worked in all areas of the company from starting materials through the process all the way to finished goods - including packaging. So I know a little about cardboard, plastic, coatings, etc. My background is pretty diverse. I've been at it for more years than I care to recall.

You can convert your direct-inject GC to SPME very easily by simply changing the inlet liner to a 0.75 mm id, low-volume inlet (for SPME). Then, you just need the manual holder and some fibers. For what I did here, I used a carboxen/pdms/divinylbenzene fiber. That's all the equipment you need. After that, just read up on how people use it and you're off and running. With the large concentrations you're detecting, you can probably run split injections. For more trace concentrations, you might have to run splitless. That's no big deal. It's a setting in your inlet parameters in your GC method. You can get everything you need from Sigma-Aldrich.

[joehem]

Excellent!

Quick side question... we are trying to figure out how to measure fiberglass content in water. Our water has paper fibers, and a lot of calcium carbonate.... so we run up to 1080C in our lab oven ... everything burns off and a white powder is left. From what I read the calcium carbonate converts to calcium oxide above 825C. Working with our GC supplier they said since it wont burn the equipment can't measure concentrations. So we are trying to figure out if we can separate the calcium oxide from the fiberglass somehow. We have a very accurate lab scale that could measure the weight differences.

[DR]

When you have a hammer, everything looks like a nail.

CaO determination sounds more like a titration to me...
If that option is too cost effective, there's AA.

[rb6banjo]

Google Gemini tells me that fiberglass is generally more complicated that just CaCO3 as the filler. But, if you're just after the calcium content to relate it to CaCO3, then the way to do it is to dissolve the solid that remains in acid and analyze for Ca2+ using flame atomic absorption (AA) spectroscopy.

Is the GC the only thing you have in your lab? GC is only good for organic molecules that are volatile to some degree. If you're stuck with the weight loss procedure, everything in that white solid you recover will have to be counted as the same thing (CaO, SiO2, etc.).