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ISOGEOCHEM  July 2019

ISOGEOCHEM July 2019

Subject:

Re: Excessive reactor product on TC/EA cracking ceramic tubes

From:

"Wolfram Meier-Augenstein (pals)" <[log in to unmask]>

Reply-To:

Stable Isotope Geochemistry <[log in to unmask]>

Date:

Wed, 24 Jul 2019 16:36:07 +0000

Content-Type:

text/plain

Parts/Attachments:

Parts/Attachments

text/plain (145 lines)

Hi Matt,

I can only second Jon’s and Gerry’s suggestions.

We have run 1,000s of water samples (by direct injection) and never seen any of the problems you describe. That being said, yes, the gc chips get dull with use but most of them can be “rejuvenated” by rubbing with lapping paper and a quick swim in an ultrasonic bath. Any deposits on the outside of the gc tube should come off easily after a few days exposed to air. What cannot be tapped off is removed with fine emerald paper.

To avoid loosing time and through-put, we had several complete reactors on the go, so we could swap the reactor taken out for cleaning with a refurbished one thst was ready to go.

We didn’t have the reverse He flow setup but we always run our helium (99.999%) through a Supelco High Capacity Gas Purifier first, followed by Supelco OMI gas purifier tube second (see  Table II.A.2 in the 2nd edition of Stable Isotope Forensics; cough, cough). ;-)

Carrier gas pressure required to achieve a sensible flow rate very much depends on reactor packing we found, so we sieved gc chips to achieve more reproducible packings and conditions.

We ran the reactor at 1420C. To avoid a large dead volume inside the reactor resulting in peak broadening (and excessive tailing), we packed the gc tube almost all the way to the top with gc chips. The gap between top of the gc tube and top of the ceramic tube was bridged with a stainless steel insert. For manual (!) injection (of 100-120 nL) we used SGE syringes (1 uL barrel) with a 26 gauge needle, 70 mm in length. This way the needle reached all the way through the insert and the tip of the needle ended up just above the gc chips. This way the water vapour cloud resulting from depressing the plunger could only expand into a small volume, ultimately yielding “sharp” H2 peaks.


Best,

Wolfram

******************************************************
Prof. Dr W Meier-Augenstein, CChem, FRSC
Stable Isotope Forensics & Analytical Sciences

Robert Gordon University
School of Pharmacy and Life Sciences
The Ian Wood Building
Garthdee Road
Aberdeen
AB10 7GJ

E-mail:   [log in to unmask]

https://onlinelibrary.wiley.com/doi/book/10.1002/9781119080190
________________________________
From: Stable Isotope Geochemistry <[log in to unmask]> on behalf of Jonathan Karr, Ph.D. <[log in to unmask]>
Sent: 24 July 2019 17:06:16
To: [log in to unmask]
Subject: Re: [ISOGEOCHEM] Excessive reactor product on TC/EA cracking ceramic tubes


Matt,

I use 5 degrees C per minute (300 per hour), so it doesn't take but a few hours. I use 1450C  because I get too much tailing at lower temps. I also use 85C on the GC and ~1 bar carrier pressure. I have the high temp purifier and oxygen trap after, and the reactor and trap last me several years with UHP He (99.999)

Jon


Jonathan D. Karr, PhD
Technical Director
Duke EnVironmental stable Isotope Lab (DEVIL)
NEW SHIPPING ADDRESS FOR UPS/FEDEX:
Levine Science Research Center
Room A129
308 Research Drive
Durham, NC 27708-0328

for US mail you MUST include:
Campus Box 90328 or it will not be delivered and may be lost
This is a Campus Box, NOT a PO Box

http://nicholas.duke.edu/devil/
919-698-2504 (cell)
919-660-7418 (voicemail)
________________________________
From: Stable Isotope Geochemistry <[log in to unmask]> on behalf of Matthew Lachniet <[log in to unmask]>
Sent: Wednesday, July 24, 2019 11:54:06 AM
To: [log in to unmask] <[log in to unmask]>
Subject: Re: [ISOGEOCHEM] Excessive reactor product on TC/EA cracking ceramic tubes

Thanks Jon,

What temperature ramp rates have you used for the frequent ramp up and down?

Matt

On Wed, Jul 24, 2019 at 8:21 AM Jonathan Karr, Ph.D. <[log in to unmask]<mailto:[log in to unmask]>> wrote:

Matt,

My experience is that the buildup is faster with higher temps, but you have to use what gives you the best peak shapes and reproducibility. I never run more than about 48 hours continuously without bringing the reactor down and cleaning everything. I use ultra-fine sandpaper, say at least 400-600 grit, to lightly go over the carbon tube to remove the loose stuff, but you have to go easy or you can quickly start necking-down the carbon tube. Then I use diamond files to work on the harder hump that forms right at the hotspot. If you can file this bulge down as close as possible to original diameter without removing much carbon, this will greatly extend the life. I also check the ceramic tube against a light for any cracks and roll it on a table to see if it is starting to warp. I usually go through 2 ceramic tubes for every carbon tube, and I can get between 1000-2000 injections per carbon tube. I also replace any carbon chips that have dulled to charcoal appearance and rub them over a metal sieve while checking them.

Jon


Jonathan D. Karr, PhD
Technical Director
Duke EnVironmental stable Isotope Lab (DEVIL)
NEW SHIPPING ADDRESS FOR UPS/FEDEX:
Levine Science Research Center
Room A129
308 Research Drive
Durham, NC 27708-0328

for US mail you MUST include:
Campus Box 90328 or it will not be delivered and may be lost
This is a Campus Box, NOT a PO Box

http://nicholas.duke.edu/devil/
919-698-2504 (cell)
919-660-7418 (voicemail)
________________________________
From: Stable Isotope Geochemistry <[log in to unmask]<mailto:[log in to unmask]>> on behalf of Matthew Lachniet <[log in to unmask]<mailto:[log in to unmask]>>
Sent: Wednesday, July 24, 2019 11:06:26 AM
To: [log in to unmask]<mailto:[log in to unmask]> <[log in to unmask]<mailto:[log in to unmask]>>
Subject: [ISOGEOCHEM] Excessive reactor product on TC/EA cracking ceramic tubes

Hi all,

I'm looking for ideas to help with a problem I had last year while running waters on my TC/EA (ConFlo III to Delta V Plus).

Over the course of around 2-5 weeks while running water samples, the reaction product builds up on the outside of the glassy carbon tube to such a degree that it periodically fuses to the ceramic tube, ending up cracking both and resulting in rapid failure and an expensive replacement and downtime.

Considering the high cost of He and glassy carbon tubes, I want to have a plan to solve this before running TC/EA again.

I have the reverse flow modification on the TC/EA.

I leak tested every part of the system I can think of using soap bubbles and never found a leak. I use Ultra High Purity Helium (grade 5, 99.999%).

I never had this problem in the past until I switched gas suppliers so I did wonder if that was the reason. I could go to Research Grade He (99.9999%) but that is a much higher cost and haven't tried it yet.

Reactor temperature was on the low side (1350 degrees C) because this is what was giving the lowest m/z 28 signal. Reaction at 1400 C or higher gave too much m/z 28 to get a good precision, so I wondered if the low reaction temperature could be a culprit.

I don't know how accurate the thermocouple reading is.

GC temp was around 85 degrees C.

I always use super slow ramp rates on the Jumo controller to change temperature (usually over 12 hours or more to go from room temperature to 1350 C and vice versa).

I also tried using the high purity ceramic tubes but that didn't solve it either.

Any advice for how to handle this? Anything else I should look at?

Thanks in advance,

Matt

________________________________

Robert Gordon University has been awarded a TEF Gold award for the quality of its undergraduate teaching and learning, placing it in the top 20% of Universities in the UK


Robert Gordon University, a Scottish charity registered under charity number SC 013781.

This e-mail and any attachment is for authorised use by the intended recipient(s) only. It may contain proprietary material, confidential information and/or be subject to legal privilege. It should not be copied, disclosed to, retained or used by, any other party. If you are not an intended recipient then please promptly delete this e-mail and any attachment and all copies and inform the sender. Please note that any views or opinions presented in this email are solely those of the author and do not necessarily represent those of Robert Gordon University. Thank you.

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