Dumb Cheesewedge project edition

Time to figure out how this this shimadzu GC-14A gas chromatograph works.

Except for the keypad the unit seems in pretty good physical condition, and the damage to the keypad seems to be superficial only so that's good.

Turning on the power switch the unit springs to live. The large fan circulating chamber air is definitely louder than expected but is tolerable with the door shut.

With the heaters turned on the unit quickly stabilises to a chamber temp of around 25C (7C above ambient) and holds it. This is good as I don't want to heat the column too much, as it is likely filled with air and might be damaged if heated without purging first, but shows that at least the heating section is fully functional.

The control unit also seems to operate as expected, with the VFD seven segment display still being nice and bright and seemingly all buttons working and it displaying chamber temperature. It will take a few more hours with the manual tho until I can actually understand how to operate it.

This unit was bought untested for little money, so that is fantastic news, I was half expecting to find a dead lump of metal.

Here are some initial pictures:

#analyticalChemistry #chemistry #gasChromatography #shimadzu

Jan 20, 2023 at 10:32pmWeb
Show threadDumb Cheesewedge project editionJan 21, 2023

I managed to get a mostly complete scan of the manual here:
http://www.quimica.uns.edu.ar/images/stories/descargas/Manuales%20LIUC/Shimadtzu%20CG.pdf

Shimadzu seems to only sell the paper version for 65€ so this will have to do for now.

The unit is equipped with the following options:

TCD thermal conductivity detector
This seems to come standard with all shimadzu GCs, at least these old ones. In the diagrams it seems to only be used with packed columns, and requires a second, flow-rate matched stream of carrier gas for a comparative thermal conductivity measurement. As I only have the capillary column and FID is superior in most applications I don't think I will be using it, but I guess it is nice to have?
As a TCD does not destroy the sample it would be neat to first run it through the TCD and then the FID, but that would probably negatively affect separation, I don't think I've ever seen it done.

FID flame ionisation detector
FID seems to be the most common detector even on more modern units, so that is what I will probably be working with the most. It works by burning the sample in a hydrogen flame, this creates charged ions if certain atoms, like carbon, are present and these charged ions are captured and their current is measured. As these are extremely small currents modern detectors probably have a much higher sensitivity than this one.
It also requires more process gasses, where TCD only need the carrier gas FID also needs hydrogen and compressed air to work.

SPL Split/Splitless injector
This injector is used for the capillary column and resembles injectors common on more modern GCs. The sample is injected through the rubber septum into a glas tube called the liner where it evaporates. Carrier gas is decided into three ports. A small amount is flowed upwards as a septum purge, preventing contaminates and air from getting in if the septa develops a small leak. The main gas flow is directed through the vaporised sample and into the column and split line. The split line acts to dilute the sample in order not to overload the column. The ratio of gas going into the column to gas exiting through the split line can be controlled between 1/20 and 1/200, or splitting can be completely disabled. There is also a solenoid on the split line to save on carrier gas when no sample is currently being injected as the split flow is much higher than the purge flow and the column flow.
Note that this device does not measure split flow so you need to use an external flow meter to set your split flow rate, or just set it to something and never touch it I guess?

2 Port injector
These injectors are mainly used with packed columns, which I do not have. They are very simple with just a carrier gas line pushing all of the sample into the column.
Honestly I don't yet quite understand what the purpose of having two ports is, maybe it is just to increase capacity by running two columns at once?

Show threadDumb Cheesewedge project editionJan 21, 2023

Time to take apart the split / splitless injector and see what condition it is in. Make sure you are wearing gloves for this step, as any volatile contaminants will end up in your sample!

Luckily the instructions are very detailed on not only how to swap septum and liner, but also on how to clean them.
Nowadays most GCs use disposable parts, to minimise downtime and to ensure a lower, more reliable baseline even with very sensitive detectors.

These replacement parts can get pretty pricy tho, especially for hobby use so I am very glad this is possible. I will probably have to get more septa at some point, as they do have a limited lifespan but that's a problem for another day.

I wasn't able to capture it, but the liner is pretty filthy with burned bits stuck all over it, so cleaning it will definitely be a thing I do at some point.

The manual also seems to mention a different type of liner with what looks like a hole in the side. I am worried that that might be required for split injection, and I can only use this one for splitless operation, but I am not sure about that.

Liners are not that expensive at 25€ a piece but I only found them in a 5 pack so I'll probably pass on that for now

Show threadDumb Cheesewedge project editionJan 21, 2023

AliExpress had some shimadzu compatible septa, guess I’ll find out in a few weeks how good they are.

Also ordered some GC syringes, no clue what typical injection volumes are, so I just got a 10uL and a 100uL one wich should cover most ranges

Show threadDumb Cheesewedge project editionJan 21, 2023

Guess the next step is to get a gas supply hooked up, as I can't really test the detectors without it.

The big question is, helium or hydrogen?
From what I have gathered here helium is preferred for safety reasons, but hydrogen is actually the better carrier gas as it can run at twice the linear velocity with the same resolution.

I already need hydrogen for the FID, and getting a bottle of helium seems to be prohibitively expensive at like 500€ a filling plus a few hundred for bottle, regulator and tubing so for now I will use hydrogen carrier and be extra careful for leaks.

I should get a hydrogen detector.

The main gas coming through the column will get burned in the FID, but the septa purge, split injector, and (if I use it) TCD vent will just get released into the room as it is set up now. I need to calculate the exact volume if it is enough to be dangerous, I guess it's around 10L/h so maybe having a window open might be enough? Could always run the exhaust outside.

Buying even just the hydrogen is fun, local gas shop wants 0.65€ a day for just the bottle in rent, so that's pretty pricey, actually buying the bottle with gas is like 400-500€.

There is a used scientific hydrogen generator available for 600€ so that might be a good deal, but I am worried It'll only add needless complexity

Show threadDumb Cheesewedge project editionJan 21, 2023
Time to learn more about gas fitting than I ever wanted to know.
What are all these? What is a swageloc and why does it cost like 50$? What do you mean I can't reuse the ferrule ?
Show threadDumb Cheesewedge project editionJan 29, 2023

Slow progress, hydrogen bottle came, very fun to play with.
The old system seems to have used copper tubing for all gas supplies and I want to continue that trend, probably to not introduce any contamination from plastic hoses.
I however was not able to find a G3/8 LH gas fitting to 3mm swagelok adapter so I made one by soldering two pieces together. Feels sketchy but I'm pressure testing it overnight to see if it holds, so far it's looking pretty good.

I guess the proper way is to get the regulator by swagelok but that probably costs $$$.
I can barely afford the parts I need second-hand surplus, they won't even show you prices unless you register and give them your firstborn so I don't expect that to be any lower than high three digits.

When the swagelok ferrules show up tho I'm pretty much set to power on the FID, well after figuring out how to connect my air compressor but that should be doable.

Air filters will take a few more weeks but since air won't be going through the column I'm fine using dirty air for now

Show threadDumb Cheesewedge project editionJan 30, 2023

The diy solution held overnight so I call that leak free enough!

I actually found the a swagelok regulator for sale second hand, I am debating if I should get it.
It would be the "proper" way to go, but it still costs around 85€ and I am pretty sure it is for inert gases so wrong thread *shrug*

The nerd in me wants to get the proper equipment but what I have is enough so I guess I will pass on this. Still a massive coincidence that I ran across the parts I thought I would never find in an unrelated search just a few hours later

Still waiting on the ferrules!

Show threadDumb Cheesewedge project editionFeb 6, 2023

It's been a busy weekend!
The swagelok ferrules came, and I disconnected the regulators to get a look inside, which did not result in many insights. As expected the 5 lines coming from the regulators are FID Air, FID Hydrogen, SPL injector carrier, dual injector carrier 1, and dual injector carrier 2.

To avoid leaks I have left the dual injector unconnected, connected hydrogen to the FID and SPL, and air to the FID air supply. Right now the air supply is just directly connected to my oilless air compressor, as the 4 stage air filter has not arrived yet, however baseline seems to be pretty stable for just running on regular air, but more on that later...

Pic 1:
Connections as the unit arrived. The lower unit controls the FID and the SPL injector, the upper unit the dual injector. Curiously the upper unit is different from the lower one, supposedly having a mass flow controller for carrier gas. I am not yet sure how that is used

Pic 2:
Tracing the lines and adding labels...

Pic 3:
Reinstalling the lower regulator and connecting the lines again, leaving off the upper regulator and the dual injector tubes unconnected (covered in foil to avoid contamination), with a y splitter for FID Hydrogen and SPL carrier, and a cursed looking soldered 1/2" compressed air quick connect fitting.

Show threadDumb Cheesewedge project editionFeb 6, 2023

Figuring out the FID was a fun challenge, but also the part I was most scared of. I half expected it to just be a brick but so far I think it is fully working now, sort of.

After having plumbed air and hydrogen the first challenge came, lighting it. From looking at instructions for other machines I thought the FID would ignite on it's own, using a wire inside that would be heated to red hot, so I spent quite some time stumbling around the user interface to no avail. Reading the manual I was surprised that the FID is to be lit with a lighter.

Next step is testing if it actually works, the FID output is directly connected to the detector controller, outputting an analog voltage from -1.5V to 1.5V.
Initially, like most very sensitive pieces of lab equipment currently on fire, it did not work, however this turned out to simply be oxidised contacts on the connector.

After a few hours of chasing my own tail I figured that out, having gotten very close to tearing the while thing apart. I connected my Scope to the output and was met with a surprisingly stable baseline, given I was using unfiltered air directly from my (oilless) compressor.

I figured out how to control the sensitivity from the keypad, and dropping in a small drop of isopropanol into the FID outlet created a large spike.

Problem now is nothing seems to be coming through the column...